HomeMy WebLinkAboutInformation Only 012626AGENDA
INFORMATION UPDATE
January 26, 2026
4:00 PM,
I.Information Update
I.A Information Only - Grant Update - Microgrids for Community Resilience
I.B Work Session Follow Up Memo - Community Picnic
Info Only - MicroGrid For Community Resilince Grant.docx
Final Report_Aspen_MicrogridEnergyAnalysis.pdf
2026_Follow-Up_worksession_January_12.docx
1
1
INFORMATION ONLY REPORT
TO: Aspen City Council
FROM: Andy Rossello, Senior Project Manager, Utilities
THROUGH: Erin Loughlin, Utilities Director
Tyler Christoff, Deputy City Manager
MEETING DATE: January 27th, 2026
SUBJECT: Grant Update - Microgrids for Community Resilience
INTENDED OUTCOME & SUMMARY:
This memorandum is for informational purposes only. This memo is to inform Council on the
completion of a planning report associated with a U.S. Department of Energy (DOE)
Microgrids for Community Resilience Grant Program awarded by the Colorado
Department of Local Affairs (DOLA). Council accepted the grant through Resolution #104
Series of 2024 to explore planning, feasibility, and preliminary design of a microgrid within
the City of Aspen Electric Service territory.
DISCUSSION:
A microgrid facility supports continued operations in the event of loss of electric service
regionally or locally. The microgrid planning project contemplated the use of 100%
renewable energy sources to improve grid resilience for selected City-owned facilities in
the event of extended power outages affecting the entire Aspen area.
City staff selected consultant engineer City Light and Power Engineering (CLPE) through
a competitive Request For Proposals (RFP) process to develop a planning and feasibility
proposal. Within the attached report (Attachment A) the consultant engineer provided an
analysis on the following items:
Designated City owned facilities to be powered in the event of prolonged power
outages.
Microgrid load analysis.
Investigated proposed generation and storage locations for feasibility,
constructability, interconnections, operations and maintenance, and other potential
challenges.
Multiple alternatives for microgrid generating resources and switching
configurations, and estimated planning-level costs for each alternative.
2
High-level scope of work and budgetary estimates for the design, procurement,
construction, and commissioning of the proposed microgrid.
Outlined what City of Aspen staffing and technology would be required for
implementation of the analyzed microgrid.
The report suggests system-wide improvements for a simultaneous installation
approach for a microgrid for 4,12, 24, and 72-hour durations. Site constraints and
current renewable generation limitations within the City are analyzed for the preliminary
design. If the City were to install these improvements simultaneously for a 72-hour
power outage, costs were estimated to be approximately 48 million dollars for the
defined city-owned facilities. Those funds are not currently planned within the electric
utility’s long-range budgets. Staff intend to monitor developments in renewable
generation and switching technologies identified in the planning study as necessary for
implementation. Staff also intend to incrementally plan for the installation of equipment
that meets current electrical needs and may be used to facilitate implementing a
microgrid in the future.
NEXT STEPS:
No action is requested of Council.
Council has prioritized the replacement of aging electrical distribution circuits citywide.
The Utilities Department is currently in year five of a 15-year planned circuit
replacement project. Staff have begun including new switching equipment with
automation and remote sensory capabilities as part of the planned circuit replacements,
which are an integral part of future smart grid capabilities. Staff will continue to install
equipment to modernize and maintain safe, reliable, and resilient operation of the City’s
electric system.
ATTACHMENTS:
Attachment A – City of Aspen Microgrid Planning Study
CITY MANAGER NOTES:
3
CITY OF ASPEN
MICROGRID PLANNING STUDY
ASPEN, CO
J.O./W.O. NO.: 63034
CLP ENGINEERING, LLC
6312 SOUTH FIDDLERS GREEN CIRCLE, SUITE 200-E
NOVEMBER 17, 2025
4
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary i
REVISION HISTORY
Revision Date Description Author Approval
A 08/20/2025 DRAFT FOR REVIEW EPR APS
B 10/24/2025 BACKCHECK REVIEW EPR APS
C 11/17/2025 FINAL REPORT EPR APS
TABLE OF CONTENTS
ABBREVIATIONS AND ACRONYMS ........................................................................................... ii
SECTION 1.0 EXECUTIVE SUMMARY ................................................................................... 1
1.1 MICROGRID KEY COMPONENTS ................................................................................. 1
1.2 MICROGRID SOLUTIONS ............................................................................................. 2
1.3 RECOMMENDED NEXT STEPS ..................................................................................... 4
SECTION 2.0 COLORADO DOLA MCR PROGRAM.................................................................. 6
2.1 MICROGRIDS FOR COMMUNITY RESILIENCY .............................................................. 6
SECTION 3.0 CITY OF ASPEN ELECTRICITY SYSTEM ............................................................... 8
3.1 ASPEN MUNICIPAL ELECTRIC DISTRIBUTION SYSTEM................................................. 8
3.2 ASPEN RENEWABLE ENERGY GENERATION AND PURCHASES .................................... 8
3.3 ASPEN DISTRIBUTION LOCATION RELATIVE TO TRANSMISSION SYSTEMS ................. 8
SECTION 4.0 ASPEN MICROGRID OVERVIEW ....................................................................... 9
4.1 ASPEN MICROGRID KEY CHALLENGES AND IMPACTS ................................................. 9
SECTION 5.0 ASPEN MUNICIPAL FACILITIES ENERGY ANALYSIS .............................................. 12
5.1 CITY OF ASPEN ELECTRIC RATE STRUCTURE ............................................................. 16
5.2 “BLUE SKY” BENEFITS ................................................................................................ 16
5.3 FIRMING RENEWABLE ENERGY THROUGH STORAGE ............................................... 17
SECTION 6.0 MICROGRID SWITCHING AND ISOLATION ...................................................... 20
6.1 SCADA OPERATION OF MICROGRID DISTRIBUTION SYSTEM .................................... 20
6.2 MICROGRID SWITCHING STRATEGY .......................................................................... 20
SECTION 7.0 MICROGRID GENERATION AND STORAGE SIZING .......................................... 24
7.1 FACILITIES ELECTRIFICATION ESTIMATED IMPACT .................................................... 24
7.2 SOLAR NET ZERO ELECTRIC SYSTEM SIZING AND AREA REQUIREMENTS ................. 25
7.3 PEAK DEMAND MODELING TO SUPPORT STORAGE SIZING ..................................... 29
7.4 MICROGRID GENERATION AND ENERGY STORAGE TECHNOLOGIES AND COSTS ..... 30
SECTION 8.0 MICROGRID DESIGN FRAMEWORK AND NEXT STEPS ..................................... 36
8.1 ASPEN DISTRIBUTION SYSTEM AND MICROGRID ELECTRICAL TOPOLOGY .............. 36
8.2 ASPEN MICROGRID LOADING ................................................................................... 37
8.3 MICROGRID ISLANDING, RESTORATION, AND OPERATING MODES ......................... 37
8.4 DISTRIBUTED ENERGY RESOURCES CAPACITY AND OPERATION .............................. 37
APPENDIX A – GENERATION AND STORAGE TECHNOLOGY REVIEW .................................. A-1
A.1 KICKOFF MEETING .......................................................................................................... A-2
A.2 TECHNOLOGY BRAINSTORMING .................................................................................... A-3
5
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary ii
A.3 TECHNOLOGY FOCUS AREAS .......................................................................................... A-4
A.4 TECHNOLOGY SURVEY DISCUSSION ............................................................................... A-4
APPENDIX B – MICROGRID FUNCTIONAL REQUIREMENTS ............................................... B-1
B.1 SUMMARY ...................................................................................................................... B-2
B.2 DISTRIBUTION SYSTEM UPGRADES ................................................................................ B-2
B.3 MICROGRID ELECTRICAL TOPOLOGY .............................................................................. B-3
B.4 MICROGRID ISLANDING, RESTORATION, AND OPERATING MODES ............................... B-4
B.5 DISTRIBUTED ENERGY RESOURCES CAPACITY AND OPERATION .................................... B-7
B.6 MICROGRIDS LOADS TIER PROFILE ................................................................................. B-8
B.7 CONTROL SYSTEM OPERATION....................................................................................... B-8
B.8 CYBERSECURITY ............................................................................................................ B-10
ABBREVIATIONS AND ACRONYMS
ARC Aspen Recreation Center
BESS battery energy storage system
CLPE CLP Engineering
DC direct current
DER distributed energy resources
DOLA Colorado Department of Local Affairs
EUI energy use intensity
HCE Holy Cross Energy
HMI human machine interface
hr. hour
kVA kilovolt-ampere
kW kilowatt
kWh kilowatt-hour
LDES long duration energy storage
LF load factor
MBtu thousand British thermal units
MMBtu million British thermal units
MCR microgrids for community resilience
MEAN Municipal Energy Agency of Nebraska
MW megawatt
ORC Organic Rankine Cycle
PRV pressure-reducing valve
PV photovoltaic
SCADA supervisory control and data acquisition
SF square feet
SPP Southwest Power Pool
VFI vacuum fault interrupter
WTP water treatment plant
6
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary iii
yr. year
7
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 1
SECTION 1.0 EXECUTIVE SUMMARY
Colorado Department of Local Affairs (DOLA) awarded the City of Aspen a grant under the
Microgrids for Community Resilience (MCR) program. The DOLA MCR Program supports electric
cooperatives and municipal utilities in evaluating microgrid resources for placement within
communities at significant risk of service interruption from severe weather or natural disaster
events. In 2018, the Lake Christine Fire nearly destroyed electric transmission lines serving the
Aspen area, prompting evaluation of microgrid technologies.
CLP Engineering (CLPE) was awarded the microgrid planning project to investigate microgrid
options for the City of Aspen. As part of this planning process CLPE worked closely with the City
of Aspen electric utility technical team to evaluate on-site generation options, energy storage
requirements, switching configurations and microgrid implementation strategies.
1.1 MICROGRID KEY COMPONENTS
Seven (7) City of Aspen municipal buildings are identified as the primary Aspen Microgrid
facilities. The Aspen Microgrid supports community resiliency by providing power to these
buildings during extended regional grid outages.
The City of Aspen Municipal Electric Utility has initiatives underway to improve automation of the
electric distribution system. The microgrid switching strategy has been configured to allow
electricity isolation of these seven (7) municipal facilities. This microgrid builds upon ongoing
automation efforts so timing of future distribution system investments may need to be configured
to coincide with microgrid infrastructure investments. The microgrid system includes multiple
existing components including transformers, controls, wiring, and switches or isolation
equipment.
Key considerations for microgrid implementation include:
• Electric grid modernization, in particular switching point isolation needed to separate the
microgrid from the remainder of the de-energized City of Aspen system.
• Installation of communications connecting isolation and control points.
• Procurement, configuration, and installation of a microgrid control system.
• Installation of a combination of new generation and/or storage to meet the expected
power and energy demand of the microgrid. Generation and storage sizing includes
multiple scenarios as listed below:
o 4-, 12-, 24-, and 72-hour (hr.) outage intervals
o Summer wildfire season vs year-round (including winter peak) outages
o Inclusion of non-critical loads within the microgrid switching boundary
8
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 2
The City of Aspen needs to interconnect new generation and storage technology directly to the
electric distribution system. Technology used in these facilities also should be consistent with
Aspen’s sustainability and climate objectives.
1.1.1 WILDFIRE SEASON SCENARIO MICROGRID NEEDS
Summer and winter loads in Aspen differ considerably so separate scenarios have been developed
for wildfire season in the summer and fall versus overall year-round peak, which reflects winter
peak loads. Summer loads tend to be much lower than winter loads when electric space heating
and tourism are at their peak.
Wildfire season tends to occur in the summer and early fall so sizing the microgrid energy system
for this time of year supports the primary objective. As another benefit of the summer scenario,
solar photovoltaic (PV) supports Aspen Microgrid operation in those months. For longer outage
intervals, the solar energy production results in less energy storage being necessary to meet
projected load requirements.
1.1.2 YEAR-ROUND SCENARIO MICROGRID NEEDS
Aspen’s electric distribution system is winter-peaking, often coinciding with the week between
Christmas and New Years as increased tourism and heating occurs.
Although Aspen receives significant solar during many winter days, there are also extended
periods when solar generation is not likely to contribute significantly to microgrid operation.
Shorter days combined with snowfall events can reduce or eliminate electricity generation. As
storms move on and the sun returns, snow often covers solar panels preventing generation. Since
solar PV generation varies from week to week in the winter, solar does not reduce battery energy
storage system (BESS) requirements as solar would do in the summer.
1.2 MICROGRID SOLUTIONS
Numerous microgrid configurations are possible but only a small subset meets Aspen’s
requirements. Key factors arising in the evaluation of potential solutions include the following:
• Compatibility of generation and storage with sustainability and greenhouse gas goals.
• Ongoing purchases of 100% renewable energy electricity.
• Ability to physically interconnect generation or storage technology with municipal electric
distribution system.
• Potential for co-locating generation or storage technology at existing municipal facilities.
• Commercially available technologies that meet limited land and space availability.
• Options that support outage planning durations from 4- to 72-hours.
9
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 3
The criteria removes fossil fuel-based sources commonly used to provide backup power and
energy to microgrids. The desire for proven, commercially-available options removes pre-
commercial or emerging technologies such as Long Duration Energy Storage (LDES), hydrogen-
based technologies, and geothermal-based electricity generation using Organic Rankine Cycle
(ORC) technology.
• Localized energy storage charged by the grid and owned by City of Aspen appears to be
the technology that is most compatible with microgrid operation for Aspen. The Aspen-
owned storage would primarily be charged and discharged by grid-based renewable
energy during times of excess supply and during times of minimum grid congestion.
Aspen’s customers are not presently allowed to use the grid to charge energy storage.
• New or additional hydropower capacity. The City of Aspen meets 45% of renewable
energy needs directly and much of this is from hydropower that does not directly
interconnect with the City of Aspen electric system. If distribution lines can be extended
to existing or new generation then baseline generation could be provided by hydropower,
possibly coupled with battery energy storage system (BESS) or LDES technologies.
Additional discussion on technologies is provided within the report, in particular in Section 7.4.
Table 1 summarizes energy storage and generation capacity investment requirements assuming
lithium ion BESS, possibly coupled with solar. The year-round peak occurs in the winter and is
represented by Scenario 1. System loading tends to be lower during the wildfire season, when
solar can supplement storage needs. The wildfire season, represented by Scenario 2, is a time of
year with increased risk to power transmission and distribution system. The bottom of the table
provides costs for conventional fossil fuel microgrid components. It is assumed that this type of
generation does not align with Aspen’s climate objectives. However, the data is provided as a
point of comparison or for consideration as a third tier of resiliency.
10
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 4
Hours of Storage Capacity
4 12 24 72
Scenario Microgrid Requirement
1. Year-Round Peak BESS Sizing
(kWh) 7,100 10,700 21,300 63,900
Installed Cost ($/kWh) $1,300 $1,300 $1,000 $750
Scenario 1 Budgetary Cost ($) $9,230,000 $13,910,000 $21,300,000 $47,925,000
2a. Wildfire Season BESS Sizing
(kWh) 3,800 9,200 14,700 14,700
2b. Solar Sizing (kW) 0 0 0 3,000
BESS Installed Cost Assumption
($/kWh) $1,500 $1,300 $1,200 $1,200
Solar Installed Cost Assumption
($/kW) N/A N/A N/A $5,000
Scenario 2 Budgetary Cost ($) $5,700,000 $11,960,000 $17,640,000 $32,640,000
Additional Costs
Electric Grid Automation and
Communication
$5,000,000 with the following assumptions:
Some Investments in Automation Are Ongoing
as Part of Direct Bury Electric Distribution
Replacements. Additional switches,
automation, and grid control system
modifications (not including microgrid
controller): $2,000,000
• Assuming approximately $100 per linear foot
for directional drilling in Aspen and nearly
30,000 linear feet to interconnect each of the
switches / reclosers in the microgrid: $3,000,000
Microgrid Controller $1,000,000
Fossil Fuel Generation (Assumed to Not Meet Aspen’s Requirements)
Fossil Fuel Engines ($/kW) $4,000
Wildfire Season Modeling (1,500
kW) $6,000,000
Year -Round Peak Modeling (2,500
kW) $10,000,000
Table 1: Aspen Microgrid Sizing and Cost Parameters
1.3 RECOMMENDED NEXT STEPS
This microgrid planning study provides multiple options for Aspen Electric Utility and City Council
consideration. The following list outlines the key decisions to support the next steps of planning,
design, and construction activities:
11
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 5
• Is the microgrid’s intended use mostly applicable for summer/wildfire season or do we
need to consider all year around resilience, which includes the winter peak?
• If all year around resilience is required, should provisions be made for electrification
including converting heating use from natural gas to electricity?
• How many hours of backup capability should be used (this study considered 4-, 12-, 24-,
and 72-hours)?
• Where are the preferred location(s) of storage / generation technologies:
o Is use of rooftops allowed?
o Is use of carports allowed?
o What is the allowed proximity of BESS to existing buildings?
o Is use of undeveloped City of Aspen-owned land allowed?
• Types of storage/generation technologies allowed to be included or excluded from
consideration such as the following:
o Lithium-Ion BESS?
o Solar PV?
o Imported liquid green hydrogen? (Please see discussion in Section 7.4.4 for
additional discussion)
o Onsite creation of hydrogen using grid power?
o Commercialized vs demonstration/emerging technologies?
o Fossil fuel technologies?
• Date of desired system operation?
o Inclusion of additional distribution system automation as part of microgrid or
separately funded?
• Are there budget or cost effectiveness criteria applicable to the microgrid?
• Contracting approach for next steps including:
o Concept planning and major equipment scopes of work package development
o Design-build package solicitation
o Full design solicitation followed by construction package solicitation
Following Aspen Electric Utility and City Council decision-making and budget approvals, the
microgrid design could proceed per the selected contracting approach.
12
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 6
SECTION 2.0 COLORADO DOLA MCR PROGRAM
DOLA awarded the City of Aspen an MCR grant in support of this planning study. The DOLA MCR
Program supports rural electric cooperatives and municipal utilities in establishing microgrid
resources that serve rural communities at significant risk of service interruption from severe
weather or natural disaster events.
In 2018, the Lake Christine Fire nearly destroyed electric transmission lines serving Aspen. Aspen’s
municipal facilities provide a variety of services including water treatment, maintenance,
recreation, education, and civic functions that are important to maintain during long-duration
grid outage. The intent of this microgrid planning effort is to support resilience in a manner
consistent with Aspen’s decarbonization, electrification, renewable energy, and grid resilience
goals.
2.1 MICROGRIDS FOR COMMUNITY RESILIENCY
The vision for Aspen’s microgrid includes resiliency for community-supporting facilities when the
regional electric transmission system is not available. These less common but higher impact
extended grid outages can coincide with events such as wildfires. A combination of the following
is necessary to allow Aspen’s municipal facilities to continue to operate as part of a microgrid
during an extended transmission outage:
• Distribution and communication system modifications
• Energy storage system and/or onsite generation
• Microgrid control system
Microgrid benefits can include:
• Localized energy sources
• Reduced carbon emissions
• Grid resilience for municipal operations in support of the public during emergencies
• Potential for blue sky benefits such as demand response
A microgrid is an integrated energy system consisting of loads, generation, storage, and controls
capable of operating as a coherent unit, either in parallel with or islanded from the power grid,
with a primary purpose to support critical loads during severe contingencies.
Typically, power system operating condition categories include:
1. Normal: no emergency conditions
2. Typical emergency: abnormal conditions/outages that are typical, localized, short
duration, and low impact
13
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 7
3. Abnormal emergency: high impact/low frequency events that can cause widespread and
long-term outages
If an extended transmission service outage occurs, the present configuration of the City of Aspen
distribution system would not allow for islanded operation due to the absence of a system
aggregating isolation, distribution automation, controls, storage, and generation.
Upon completion of the project, the microgrid will be able to sustain the loads within its boundary
for as long as on-site generation or stored energy is available. This project requires upgrades to
existing medium voltage infrastructure, construction of energy storage and on-site generation,
and integration of microgrid controls. This type of advanced infrastructure requires the addition
of communications lines such as fiber optic cables across the City of Aspen electric system to
interconnect the resources necessary for communications, coordination, and control.
14
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 8
SECTION 3.0 CITY OF ASPEN ELECTRICITY SYSTEM
The City of Aspen owns and operates an electricity distribution system. Holy Cross Energy (HCE)
transmits electricity to the City of Aspen municipal electric system. HCE also serves customers
near Aspen that are not served by Aspen’s municipal electric utility.
3.1 ASPEN MUNICIPAL ELECTRIC DISTRIBUTION SYSTEM
The City of Aspen Municipal Electric system includes 265 transformers, 34 miles of primary cable,
and approximately 600 streetlights while serving approximately 4 square miles and 3,100
customers in and around historic Aspen. The City of Aspen Electric System was fully
undergrounded between 1976 and 1986. Aspen is presently undertaking the replacement of
those direct bury lines within the congested downtown area.
Supervisory Control and Data Acquisition (SCADA) infrastructure exist within the Aspen electric
system, but the system is relatively new with few connected devices. As a result, the
implementation of this microgrid effort requires SCADA expansion.
3.2 ASPEN RENEWABLE ENERGY GENERATION AND PURCHASES
The City of Aspen electricity portfolio is entirely renewable due to a combination of self-owned
hydropower and purchases of renewable energy. Aspen owns and/or purchases power generated
by the local Ruedi, Maroon Creek, and Ridgway hydroelectric facilities. This carbon-free electricity
is generated nearby yet these facilities are not directly connected to the City of Aspen electricity
system and must be wheeled through the transmission system of others. Aspen owns and/or
purchases the generation from these sources, which meet 45% of electricity needs. Power needs
not met directly occur through the City’s wholesale energy provider, Municipal Energy Agency of
Nebraska (MEAN), which wheels power through multiple transmission systems to reach the City
of Aspen. For purposes of microgrid planning, it is assumed these renewable energy sources are
offline along with the transmission system during regional outages.
3.3 ASPEN DISTRIBUTION LOCATION RELATIVE TO TRANSMISSION SYSTEMS
The City of Aspen electric distribution system physically exists at the end of a transmission line
routed through narrow canyons vulnerable to wildfires and outages. Without alternative delivery
points, the distribution system could experience extended down time from a failure in the
transmission system. HCE’s transmission system delivers electricity to the municipal electric
system.
15
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 9
SECTION 4.0 ASPEN MICROGRID OVERVIEW
The City of Aspen microgrid supports renewable energy and resiliency in municipal buildings
providing community benefits in time of emergency. The level of investment determines the
number of hours of outage and under what conditions the microgrid can be expected to be
available to provide community support.
4.1 ASPEN MICROGRID KEY CHALLENGES AND IMPACTS
Unique challenges for the City of Aspen microgrid include the following:
Challenge: The City of Aspen is seeking to lower its carbon footprint. The electricity grid is already
100% renewable.
Impact: Fewer types of generation and storage technologies are compatible with a system
that is already 100% renewable and seeking to further reduce carbon emissions. Although
convenient for providing resiliency, the use of diesel or natural gas as part of the microgrid
would adversely impact efforts to increase use of renewables and would increase
municipal building carbon footprints.
Challenge: The City of Aspen is seeking to lower its carbon footprint. The microgrid should not
use diesel. Use of natural gas may be a potential option but is likely not desired, even during
emergencies.
Impact: Fewer types of generation and storage technologies are compatible with a system
where fossil fuels cannot provide emergency backup.
Impact: Electrification efforts displace the use of natural gas for heating but will increase
peak electric winter demand at municipal facilities.
Challenge: The City of Aspen contracts electricity through MEAN. Aspen goes from 45% self-
owned renewable electricity to 100% renewable electricity through 55% electricity procured from
MEAN’s Green Power Pool. MEAN has placed restrictions on Aspen’s use of new renewable
energy. The present limit involves a relatively complex equation that factors in Aspen’s electricity
purchases from MEAN. MEAN indicates 27 units with a cumulative capacity of 230.84 kW
presently exist. Systems less than 25 kW can contribute to MEAN’s limit, but MEAN requires their
involvement for systems over 25 kW.
Impact: Without adequate onsite generation to meet microgrid needs, onsite electric
energy storage recharged by renewable electricity becomes the focus for the microgrid
masterplan. The storage must meet the full duration of outages with minimal anticipated
contribution from onsite generation.
16
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 10
Caveat: MEAN may allow onsite renewables exceeding their limit if MEAN is the PPA
provider.
Challenge: The City of Aspen has crews performing snow removal at municipal facilities
throughout the winter. Concern exists regarding impact on operations and maintenance
personnel regarding installation of solar.
Impact: For solar production at existing facilities, options include roof and carport solar.
For rooftop solar, spacing needs to exist from roof edges and mechanical equipment if
roof is flat. For many municipal buildings, the roof slope reduces snow accumulation but
also reduces solar output for north-facing roof sections. Carport solar is likely not a viable
option for Aspen due to the impact on snow removal operations.
Challenge: Open spaces are highly valued across Aspen. Land available for development tends to
be very expensive. As a result, land available for placing solar power is highly limited. Aspen’s
electric distribution system spans the Aspen valley floor. The City of Aspen electric system does
not extend to local mountain ridges. The ridgelines tend to be the preferred location for
renewable energy such as wind. Areas such as the City of Aspen water treatment plant are located
on north-facing slopes, which reduces potential output from solar systems in the winter.
Impact: The impact of geography is that onsite renewable energy options are limited.
Options were discussed during the initial brainstorming found in APPENDIX A –
GENERATION AND STORAGE TECHNOLOGY REVIEW.
Impact: The approximate area necessary to attain net zero electricity over the course of a
year was reviewed. The Aspen Water Treatment campus may represent one of the more
attractive areas, however, with the north facing terrain, production would be limited in
the winter, and the installation size would exceed MEAN’s limit. The snow could remain
throughout the winter months and portions of spring and fall, thereby preventing solar
production.
Challenge: Aspen’s municipal buildings are distributed across the community. Only one or two
facilities are located within a sectionalized circuit. The electric one-line indicates additional
switching and automation will be necessary to isolate intended loads (municipal buildings
supporting a resiliency function) from other community loads.
Impact: The need for additional switching and automation creates a cost tradeoff
between centralized microgrid generation and storage versus distributed generation and
storage.
Challenge: This planning study evaluated resiliency for 4-, 12-, 24-, and 72-hr operating periods
for the microgrid loads.
17
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 11
Impact: Market participants install commercial storage today to provide 1 to 4 hours for
market participation, resiliency, or solar firming. LDES recharged with renewable grid
electricity encompasses an emerging solution set for each time interval from 4 to 72
hours. LDES is less commercially mature than BESS.
o The study includes consideration during the winter months when peak demand
for the City of Aspen occurs.
o The study also includes consideration during the summer months, when wildfires
are a more likely resiliency concern.
This microgrid evaluation builds upon past progress made by the City of Aspen. Although
microgrids represent a new solution set in many respects, traditional microgrid approaches
involving some combination of solar, wind, natural gas, and diesel generation are not viable for
resiliency during Aspen’s peak demand week in the winter.
This City of Aspen Microgrid Planning Study examined multiple innovative solution sets for
consideration. If commercialized proven solutions are desired, technologies such as geothermal
to electricity using ORC, hydrogen-based technologies, and LDES are not likely to be viable.
Potential solution sets following elimination of non-viable alternatives includes the following:
• Install solar PV systems to the degree allowed by practicality and policy.
• Install hydropower at existing water distribution pressure reducing valves (PRVs), run-of-
river locations, and existing water retention features.
• Leverage geoexchange heating and cooling systems to decrease electrification impact on
the grid.
• Explore range of energy storage, including BESS and LDES, powered by renewable
electricity and used to support microgrid and grid operations.
18
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 12
SECTION 5.0 ASPEN MUNICIPAL FACILITIES ENERGY ANALYSIS
The microgrid includes the seven (7) facilities listed in Table 2. These seven (7) facilities are
identified by Site number using callouts in Figure 1.
Site
# Address Name
Square
Feet Property Type
1 861 Maroon Creek
Aspen Recreation
Center (ARC) 81,828 Fitness Center/Health Club/Gym
2 500 Doolittle Water Treatment Plant 20,318
Drinking Water Treatment &
Distribution
3 1080 Power Plant Streets Department 22,339
Repair Services (Vehicle, Shoe,
Locksmith, etc.)
4 215 N Garmisch Yellow Brick 25,413 Pre-school/Daycare
5 110 E Hallam Red Brick 28,535 Other
6
219 Puppy Smith
Rd Puppy Smith Electric 2,000 Energy/Power Station
7
427, 437, 455, 470
Rio Grande City Hall 172,600 Office, Parking, Performing Arts
Table 2: Aspen Microgrid Municipal Facilities
The facilities listed above represent more than 350,000 square feet of municipal facilities. The
sites are not collocated and are spread throughout the community.
19
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 13
Figure 1: Aspen Municipal Electric Distribution System and Locations of Microgrid Facilities
Figure 1 contains an overview of Aspen’s electric system along with proposed microgrid facilities. Located to the west of downtown Aspen, Site 1 (the Aspen Recreation Center), and Site 2 (the Aspen Water Treatment Plant)
and Site 3 (the Old Power Plant which, presently used by the Aspen streets department). Site 4 (Yellow Brick pre-school and day-care facility) along with Site 5 (Red Brick Center for the Arts and Recreation Center), and Site 6
(Puppy Smith Electric Office and Switching Station) are in the center of Aspen’s downtown. Site 7, City Hall, is located near the eastern or central portion of downtown.
20
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 14
(Please Consider the Environment Before Printing - Page Intentionally Left Blank)
21
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 15
Table 3 contains the energy use intensity (EUI), electricity and natural gas consumption, and
energy audit status for each of the facilities targeted for inclusion in the microgrid. EUI is
calculated by summing electricity and natural gas energy consumption and dividing by the total
square feet of the facility. The units for EUI are thousand Btu per square foot (MBtu/SF), electricity
is kilowatt hours per year (kWh/yr), and natural gas is million Btu per year (MMBtu/yr).
# Nickname
2022 EUI
(MBtu/SF)
Electricity, 2022
(kWh/yr)
Natural Gas, 2022
(MMBtu/yr)
1 Aspen Recreation Center (ARC) 260.0 2,347,297 13,263
2 Water Treatment Plant 115.4 308,363 1,293
3 Streets Department 145.0 159,859 2,694
4 Yellow Brick 50.3 83,995 992
5 Red Brick 73.8 174,245 1,510
6 Puppy Smith Electric 132.7 77,786 -
7 City Hall 26.5 1,220,478 409
Table 3: Microgrid Municipal Building Energy Profile
Greenhouse gas inventories tend to focus on controllable emissions, in particular Scope 1 and
Scope 2 emissions. Scope 1 emissions include direct, onsite combustion of fuels such as natural
gas, propane, and fuel oil. Scope 2 emissions include indirect emissions resulting from onsite
consumption of electricity. The Scope 2 carbon emissions are released at the coal or natural gas
power plant generating the electricity consumed onsite but reducing consumption of electricity
reduces such emissions. In Aspen, the carbon footprint associated with Scope 2 electricity
consumption is close to zero since City of Aspen Electric Utility owns or purchases 100%
renewable energy. With minimal Scope 2 emissions, Aspen targets onsite natural gas use to
reduce facility-related greenhouse gas emissions.
The peak demands listed in Table 4 are estimated using an assumed energy load factor of 30% for
annual peak demand and 35% for summer peak demand. Transformer capacity is in units of
kilovolt-ampere (kVA) and peak demand is units of kilowatt (kW).
# Address Nickname
Transformer
(kVA)
Summer Peak
Demand, Est
(kW)
Peak
Demand, Est
(kW)
1 861 Maroon Creek ARC – Main 750 698 700
2 500 Doolittle WTP - Main Meter 500 & 75 32 107
3 1080 Power Plant Streets Department 150 30 55
4 215 N Garmisch Yellow Brick 150 30 38
5 110 E Hallam Red Brick 150 53 65
6 219 Puppy Smith Rd Puppy Smith Electric 75 9 25
7 427 Rio Grande City Hall 750 & 750 178 464
Sum 3,350 1,030 1,454
Table 4: Present Estimated Peak Demand and Transformer Sizing
22
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 16
5.1 CITY OF ASPEN ELECTRIC RATE STRUCTURE
The City of Aspen charges customers based on service size (in amps) and consumption for
residential while commercial and three-phase residential bills also have a demand component.
The residential rate structure encourages conservation by increasing costs per kWh as total usage
increases. There is an alternate rate structure that encourages residential electrification by
allowing more kWh to be consumed before the next higher tier of cost per kWh. This type of
billing structure emphasizes reduction in consumption versus timing of consumption.
5.2 “BLUE SKY” BENEFITS
There are not presently demand response incentives or similar “Blue-Sky” benefits expected to
provide significant financial benefit to support microgrid operation. Electricity markets in
Colorado and across much of the West are evolving. The expansion of the Southwest Power Pool
(SPP) into Colorado, in particular the SPP Markets+ expansion as shown in Figure 2 could create
monetary incentives for dispatchable generation and storage that do not presently exist.
Figure 2: SPP Expansion into Colorado (Source: https://www.spp.org/western-services/ Date Captured: Mar 11, 2025)
23
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 17
5.3 FIRMING RENEWABLE ENERGY THROUGH STORAGE
Figure 3 below demonstrates a typical modeled day in the non-peak months. Although the system peak in the winter months is
modeled as 1,700 kW, the peak on this modeled typical day is less than 400 kW. The solar system assumed in the graph below is
approximately 1,000 kW, well below consumption on this modeled typical day.
Figure 3: Municipal Building Cumulative Electric Load Profile in Summer / Shoulder Season
Figure 4 demonstrates the need to export at times, however, the assumption is that the microgrid cannot export so instead curtailment
is required. By coupling solar with energy storage, the microgrid can store excess solar during the day that is used to offset overnight
loads.
24
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 18
Figure 4: Municipal Building Cumulative Electric Load Profile in Summer / Shoulder Season with Solar and without Storage
25
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 19
The demand curve for energy storage is asymptotic as shown in Figure 5. At lower percentages of
load being met with solar, the excess daytime production is consumed overnight. At higher
percentages, some of the storage is needed to shift production across weeks or seasons.
Figure 5: BESS Requirements with Increased Use of Solar
Figure 5 is not specific to the City of Aspen Microgrid. However, the asymptotic nature of the
curve applies to Aspen.
Considerable benefits arise for distribution systems, in particular load shifting from day to night
solar renewable energy production, with a four-hour BESS. However, multi-day events and
extended outages remain a vulnerability without LDES. The 12-, 24-, and 72-hour resiliency
desired as part of the City of Aspen Microgrid are each viewed by the U.S. Department of Energy
as LDES energy storage intervals.
Since the City of Aspen has 100% renewable, low-carbon electricity, the City of Aspen as a utility
could recharge local energy storage with renewable electricity, which results in consumption of
renewable energy instead of diesel or natural gas during outages.
26
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 20
SECTION 6.0 MICROGRID SWITCHING AND ISOLATION
The Aspen electric distribution has evolved over time to meet the needs of residents. The system
was converted from an overhead system to an underground system to improve uptime. Aspen’s
electric distribution infrastructure includes switches that are arranged to provide normal
electricity feed in one direction but that can feed in different directions during planned or
unplanned outages. This configuration further supports resiliency although it is largely manually
operated by line crews within Aspen.
6.1 SCADA OPERATION OF MICROGRID DISTRIBUTION SYSTEM
An alternative to manual switching changing operations is to automate the systems, through near
real-time use of SCADA. SCADA systems can be used for monitoring or for monitoring and control.
Often SCADA resides on and leverages dedicated communication pathways such as fiber. Aspen’s
SCADA is newer with limited capability accompanied with long-term planning to increase
connection to devices over time as distribution system infrastructure upgrades are made. As a
result, microgrid operation requires upgrades to isolation points at the microgrid boundary. The
new communication connectivity would need to be accompanied by upgrades to SCADA to add
the devices along with installation of new intelligent isolation devices.
6.2 MICROGRID SWITCHING STRATEGY
In the Figure 6 oneline, areas within the microgrid are indicated by darker line weight. The lighter
line weight represents loads not included in the microgrid. Location Notes 1 through 7 identify
the municipal facilities included in the microgrid as presented in Figure 1. Key Notes A [Upgrade
to Vacuum Fault Interrupter (VFI)], B (Install Pad-Mounted Recloser), C (Move Existing Open Point
to New Location), and D (Existing VFI Requires Field Verification) represent locations where new
SCADA fiber and accompanying automation are necessary to isolate the microgrid.
27
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 21
Figure 6: City of Aspen Microgrid Electric Distribution Isolation Points and Required Upgrades
28
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 22
(Please Consider the Environment Before Printing - Page Intentionally Left Blank)
29
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 23
As shown in Figure 6, the bold electric distribution line segments include transformers for
facilities other than those serving the City of Aspen facilities. These additional loads will be
included in the microgrid operation unless additional isolation devices are added. As shown in
Table 5, the number of additional loads are relatively minimal and concentrated near Aspen’s Red
Brick and Puppy Smith Electric facilities. However, these transformers are large and projected to
add 20-25% to the microgrid loads operated by the City of Aspen.
Passive
XMFRs Location Description
Transformer
(kVA)
Peak
Demand,
Estimated
(kW)
Annual Use,
Estimated
(kWh)
1 Post Office 300 109 285,555
2 B-Phase Between Post Office and Red Brick 75 27 71,389
3 Between Red Brick and Red Brick PMH-9 300 109 285,555
4 MOLLIE Aspen Hotel 225 81 214,166
Table 5: Passive Transformers Included in Microgrid
30
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 24
SECTION 7.0 MICROGRID GENERATION AND STORAGE SIZING
Microgrid generation and storage sizing varies based on multiple criteria. The City of Aspen is
considering 4-, 12-, 24-, and 72-hr microgrid resiliency goals. Other factors include non-intended
loads within the microgrid, load growth, vehicle electrification, and facilities electrification.
Locally-connect renewable energy generation sources are limited. Grid electricity in City of Aspen
is 100% renewable so storage-only options represent an important consideration. Energy storage
has the added benefit of supporting grid-wide sustainability efforts. As additional renewable
energy generation are added, storage systems off-take excess production thus preventing
curtailment and supporting renewable energy adoption.
The City of Aspen electric system experiences peak demand in the winter. Microgrid sizing could
be based on winter operation, when solar renewable generation will not be available for extended
periods. The microgrid could also be sized based on summer operation when loads are lower,
wildfires are more likely, and solar generation is more consistently available.
7.1 FACILITIES ELECTRIFICATION ESTIMATED IMPACT
The City of Aspen has aggressive carbon reduction goals, as outlined in the City of Aspen 2023
Aspen Sustainability Action Plan. The 2023 City of Aspen Municipal Greenhouse Gas Inventory
Report identifies sources of Aspen’s emissions. The Scope 1 inventory includes direct emissions
such as the use of natural gas for heating. The Scope 2 inventory emissions are indirect such as
the purchase of electricity, which is relatively low due to 100% renewable energy purchases.
In 2024, the City of Aspen released a solicitation targeting electrification and carbon reduction in
facilities. The results of this study were not available during the analysis portion of this microgrid
planning study, so estimates are used based on natural gas consumption conversion to air source
electric heat pumps with supplemental electric resistance heating for the coldest days. The
analysis indicates electric demand is likely to double for these facilities.
Demand increases on the coldest days of the year. Newer technologies including cold weather
heat pumps have a positive ratio of energy input to output, however the benefit decreases as the
temperature decreases. Designers tend to size heat pump capacity for typical use and couple the
heat pump with supplemental electric resistance heating for use on the coldest days. Even in
combination with geothermal heat pumps, designers may use electric resistance to address the
added envelope load on the coldest days rather than oversize the geothermal well field and heat
pump capacity.
The Puppy Smith Electric switching facility does not consume natural gas, and the newly
constructed City Hall has reduced reliance on natural gas heating as well.
31
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 25
As part of the microgrid assessment, CLPE has estimated the potential impact of electrification
on each microgrid facility. Table 6 contains present energy consumption and estimated peak
demand as well as projected impact of electrification on energy consumption and peak demand.
Site
# Address
Electricity
Use
(kWh/yr)
Summer
Peak
(kW)
Winter
Peak
(kW)
Facility
Electric
Heat
Impact
(kW)
Total
Peak
w/
Electric
Heat
(kW)
Electric
Facility
Heating
Impact
(kWh/yr)
Electric
Facility Total
Electric
Consumption
(kWh/yr)
1
861
Maroon
Creek 2,347,297 698 700 1,319 2,019 1,554,863 3,902,161
2
500
Doolittle 308,363 32 107 129 210 151,526 459,889
3
1080
Power
Plant 159,859 30 55 268 323 315,826 475,685
4
215 N
Garmisch 83,995 30 38 99 137 116,302 200,297
5
110 E
Hallam 174,245 53 65 150 215 177,046 351,291
6
219
Puppy
Smith Rd 77,786 9 25 - 25 - 77,786
7
427 Rio
Grande 1,220,478 178 464 41 505 47,916 1,268,394
Total 4,372,024 1,030 1,454 2,005 3,434 2,363,479 6,735,503
Table 6: Present Use Versus Electrification - Consumption and Peak Demand
Electrification has the potential to more than double electric peak demand while increasing
electric energy consumption by just over 50%.
7.2 SOLAR NET ZERO ELECTRIC SYSTEM SIZING AND AREA REQUIREMENTS
As shown in Table 6, the present electric consumption of the municipal facilities is approximately
4.4 million kWh per year. Fully electrified facility consumption is expected to increase to 6.7
million kWh per year. Since the electricity in Aspen is already 100% renewable, there is less of a
driver to achieve net zero electricity through use of onsite solar PV systems.
However, sizing a solar system to meet facilities’ needs provides insight and can provide a basis
for comparing costs of other generation and storage technologies. For the seven (7) municipal
facilities, approximately 2.8 MW of solar is necessary to present electricity needs. Approximately
4.4 MW of solar is necessary to meet electrified facility energy needs.
32
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 26
To generate 2.8 MW of solar, approximately 620,000 square feet of area is necessary. For 4.4 MW
of solar, nearly 1 million square feet of arrays would be necessary as shown in Table 7. However,
in evaluating the potential for solar on these rooftops, only 300 kW is likely to be available.
Site
Present Electric
Use: Net Zero
PV Sizing
(kW DC)
Electrified
System Electric
Use: Net Zero
PV Sizing
(kW DC)
Present
PV Area
Needs
(Square
Feet)
Electrified
System PV
Area Needs
(Square
Feet)
Preliminary
Rooftop
Generation
Potential (kW
DC)
1. ARC 1,524 2,534 331,975 551,877 92
2. WTP 200 299 43,611 65,041 23
3. Streets Department 104 309 22,609 67,275 23
4. Yellow Brick 55 130 11,879 28,328 55
5. Red Brick 113 228 24,643 49,683 83
6. Puppy Smith Electric 51 51 11,001 11,001 0
7. City Hall 793 824 172,611 179,387 0
Sum 2,839 4,374 618,329 952,593 275
Table 7: Present Use Versus Electrification – Net Zero Solar PV Sizing and PV Area Requirements
33
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 27
To provide perspective, Figure 7 contains an area hatched in purple that represents approximately 1 million square feet. This is the approximate cumulative area necessary to attain net zero electricity using solar PV arrays.
The location presented is near the Aspen Water Treatment Plant, although that area faces the north and is not a favorable candidate location for a large array.
Figure 7: City of Aspen Electric Distribution System and Locations of Microgrid Facilities
34
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 28
(Please Consider the Environment Before Printing - Page Intentionally Left Blank)
35
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 29
7.3 PEAK DEMAND MODELING TO SUPPORT STORAGE SIZING
To support decision-making, multiple durations of microgrid resiliency are presented. The desired
timeframes include 4-, 12-, 24-, and 72-hr resiliency microgrid operation. This duration could be
met through energy generation, storage, or combinations of generation and storage.
7.3.1 YEAR-ROUND PEAK STORAGE REQUIREMENTS
Table 8 contains the estimated storage duration required for microgrid operation prior to
considering the impact of electrification. Table 8 assumes full peak demand across the 4-hr.
duration. For the other three durations, Table 8 assumes greater load variability will exist with a
50% load factor (LF) over the duration for the 12-, 24-, and 72-hr scenarios.
Site
4-hr (at peak,
present needs),
kWh
12-hr (50% LF, at
peak, present
needs), kWh
24-hr (50%
LF, at peak,
present
needs), kWh
72-hr (50% LF,
at peak,
present
needs), kWh
1. ARC 2,800 4,200 8,400 25,200
2. WTP 527 791 1,582 4,747
3. Streets Department 220 330 660 1,981
4. Yellow Brick 152 228 457 1,370
5. Red Brick 261 391 782 2,346
6. Puppy Smith Electric 99 149 298 894
7. City Hall 1,858 2,786 5,573 16,719
Sum 5,917 8,876 17,752 53,527
Table 8: Energy Storage Sizing Requirements Based on Peak Demand Modeling
Table 8 assumes that local generation resources are not available to support microgrid operation.
The sun cannot be counted on during the peak week to provide generation support and Aspen-
owned hydrogeneration is not physically connected to the City of Aspen distribution system.
7.3.2 WILDFIRE SEASON STORAGE REQUIREMENTS
In the winter peaking scenario, adequate generation is necessary to provide resiliency
throughout the outage. During the summer, localized production of solar electricity is more likely
to be available. During the month of August, the model assumes approximately 310,000 kWh of
electricity will be consumed by the seven (7) City of Aspen municipal facilities. Approximately 2.4
MW DC of photovoltaic solar energy is necessary to produce a similar amount of energy. The
model indicates that with a 12,000-kWh storage system, the electricity needs of these facilities
could be met 90% of the time. If the solar system was upgraded to 3.0 MW DC, the same 12,000
kWh of storage would meets modeled needs each hour of August.
36
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 30
7.3.3 YEAR-ROUND VS WILDFIRE SEASON STORAGE REQUIREMENTS
Modeling of system operation offers insight into potential storage needs across the range of
storage durations sought by the City of Aspen. Table 9 includes estimated storage needs for
Aspen’s municipal facilities included within the microgrid under both annual peak and wildfire
season modeling.
Hours of Storage Capacity
4 12 24 72
Energy Storage Sizing Scenario Storage Capacity (kWh)
1. Year-Round Peak Demand Modeling 5,917 8,826 17,752 53,257
2. Wildfire Season Hourly System Modeling
(Assuming 3 MW Solar System) 3,060 7,500 12,000
Table 9: Energy Storage Capacity Necessary to Meet Duration of Resiliency
As shown in Table 9, the range of energy storage could vary from 5,000 kWh to 60,000 kWh for
municipal buildings alone prior to inclusion of non-municipal buildings within a particular
distribution scheme.
7.3.4 IMPACT OF NON-MUNICIPAL LOADS WITHIN SAME CIRCUIT
As described in Section 6, the microgrid isolation approach has removed most loads not intended
to be included in the microgrid. There remain some transformers not intended to be included.
These passive transformers could be replaced with active transformers or isolated using a switch.
If the loads remain in the microgrid, the following table can support in planning for costs. As
shown in Table 10, the range of energy storage could vary from 7,000 kWh to 65,000 kWh for
municipal buildings plus inclusion of non-municipal buildings.
Hours of Storage Capacity
4 12 24 72
Energy Storage Sizing Scenario Storage Capacity (Rounded kWh)
1. Year-Round Peak Demand Modeling 7,100 10,700 21,300 63,900
2. Wildfire Season Hourly System Modeling
(Assuming 3 MW Solar System) 3,800 9,200 14,700
Table 10: Energy Storage Capacity with Passive Transformers Included
7.4 MICROGRID GENERATION AND ENERGY STORAGE TECHNOLOGIES AND COSTS
Multiple options exist for energy generation and storage but local factors lead to lithium-ion BESS,
possibly paired with solar for shorter duration periods. For longer outages, technologies involving
37
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 31
LDES may also be applicable and lithium-ion BESS pricing can be used as a point of comparison
for LDES technologies.
7.4.1 MICROGRID CONTROL SYSTEM AND ELECTRIC DISTRIBUTION SYSTEM
AUTOMATION COSTS
The Aspen electric distribution system includes automation at key locations such as
interconnection points with HCE. The proposed microgrid isolation points require new
communication and automation capabilities. Additional Aspen distribution system automation is
being phased in as components are replaced over time.
In addition, a microgrid control system comprised of microgrid controller, communication
interfaces, human machine interface (HMI), and power supply systems will be required for
controls and operations of the system. For budgetary purposes, a microgrid control system may
cost close to a million dollars for the proposed size and complexity of the microgrid for Aspen.
7.4.2 SOLAR COMBINED WITH BATTERY ENERGY STORAGE SYSTEM PARAMETRIC COSTS
This planning study includes evaluation of four (4) energy storage durations. Some benefits of
scale are assumed for longer storage durations.
Table 11 presents budgetary costs of storage for lithium-ion BESS.
Hours of Storage Capacity
4 12 24 72
Energy Storage Sizing
Scenario Storage Capacity (kWh)
1. Year-Round Peak Demand
Modeling 7,100 10,700 21,300 63,900
Installed Cost Assumption
($/kWh) $1,300 $1,300 $1,000 $750
Budgetary Cost ($) $9,230,000 $13,910,000 $21,300,000 $47,925,000
2. Wildfire Season Hourly
System Modeling 3,800 9,200 14,700 14,700
2b. Solar (kW) 0 0 0 3,000
BESS Installed Cost
Assumption ($/kWh) $1,500 $1,300 $1,200 $1,200
Solar Installed Cost
Assumption ($/kW) N/A N/A N/A $5,000
Budgetary Cost ($) $5,700,000 $11,960,000 $17,640,000 $32,640,000
Table 11: Cost of Energy Storage Using Lithium-Ion BESS Technology
38
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 32
The Aspen Microgrid is assumed to be charged from the grid. This is not permitted for Aspen’s
customers but is assumed to be an option for the municipal electricity due to grid benefits. The
City of Aspen requires its customers to charge energy storage only from behind-the-meter solar.
Charging from utility-supplied power is specifically prohibited. In addition, BESS discharge ratings
are not to exceed 150% of the size of the installed solar system and onsite consumption by
customers is required (discharge to the City of Aspen electric distribution system is prohibited).
7.4.3 LONG DURATION ENERGY STORAGE
For energy storage durations longer than eight (8) hours, LDES reflects a variety of technologies
to consider. The Department of Energy ’s LDES Consortium includes a variety of technology
developers and industry representatives seeking to fill the need for cost-effective storage that can
last greater than ten (10) hours. CLPE has been an active participant in the LDES Consortium over
the past two years. Technology development companies have envisioned many solutions, but few
are ready for pilot demonstrations, much less widely commercially available.
Since LDES tends to encompass a broad group of emerging technologies, costs tend to be vendor
and technology specific. Commercially available lithium-ion BESS costs provide a point of
comparison for longer duration LDES technologies. The costs found in Table 11 for 12-, 24-, and
72-hour lithium-ion BESS represent a conceptual budget that LDES vendors would try to match or
improve upon.
As a conceptual example of LDES goals, one vendor for LDES is targeting $20 per kWh of storage
and is targeting to be able to provide systems in the next couple of years. However, the minimum
investment is $40 million for 2.2 million kWh of storage in a 100-hour energy storage system
supplying 20 MW of power. The 2.2 million kWh of storage contrasts with the 60,000 kWh of
storage using lithium-ion BESS presented in Table 11, resulting in much greater storage per dollar
of investment.
7.4.4 FUEL-BASED GENERATION AS STORAGE
Fuel-based generation is an umbrella term for the use of fuel stored or obtained locally in
quantities sufficient to generate electricity. Examples include standby diesel electricity generation
found commonly at site-specific backup generators. The City of Aspen has converted backup
generation from diesel to natural gas. Similarly, it would be possible to use natural gas generation
to provide direct or backup support to the Aspen Microgrid. However, there is a strong desire to
avoid use of fossil fuels, including natural gas, as part of this microgrid initiative.
To meet present load requirements, 2-3 MW of natural gas-fed electricity generation would be
necessary. The units themselves have a budgetary cost of $1 million per MW with a budgetary
site development cost of $2 million per MW. The total cost for 3 MW of generation might be $3
39
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 33
million per MW in most locations or $4 million per MW to accommodate Aspen construction
costs. The full budgetary cost might be $12 million for 3 MW or $4 million for 1 MW. The cost to
operate a 3 MW engine for 72 hours using natural gas would be approximately $20,000.
Traditional fossil fuel-based generation configured to support a microgrid might have a similar
capital cost budget to a 4-hour BESS but a much lower capital cost compared with longer
durations.
Hydrogen is another emerging option for fuel-based microgrid localized energy storage. Vendors
are pursuing multiple approaches using hydrogen for onsite, on-demand, energy storage.
• Since the City of Aspen electricity system is already 100% renewable, localized generation
of compressed hydrogen is an option. Although space availability would need to be
confirmed along with verification of staffing, operation, and maintenance impacts, a
facility such as the Aspen Water Treatment Plant may be viable to consider since industrial
operations are already occurring at the site. Hydrogen generation and compression would
occur during off-peak periods. A firm out of Boulder, CO, is offering this type of system.
• Another option includes import of liquified hydrogen created at a facility powered by
renewable energy. Pacific Gas and Electric recently implemented this type of system in
Calistoga, CA. Prior to use of hydrogen, the utility rented diesel generators each fire season
and operated the generators through extended grid outages. The replacement system
includes a combination of BESS electricity storage for fast response and liquid hydrogen
fed into fuel cells for LDES. Each shipment of liquid hydrogen delivers 50 MWh of energy
with a cost from $0.50 to $1.00 per kWh of input energy. Once the hydrogen is converted
to electricity, the fuel cost increases to $1.00 to $3.00 per kWh. These prices are an order
magnitude higher than the cost of electricity during normal grid operations so liquified
hydrogen would likely only be used as a backup fuel source. The green hydrogen presently
originates in Georgia, however, there are efforts underway to source across additional
locations. The system releases hydrogen slowly due to the thermal difference between
the liquid hydrogen and ambient temperature. The plant uses vaporized hydrogen to
continuously power standby systems.
7.4.5 GEOTHERMAL ELECTRICITY GENERATION, DIRECT USE, AND INDIRECT USE
In 2011, a 1,500-foot test well was drilled in Aspen to support use of geothermal energy. The test
well did not have favorable results for technology as of that time. A 2015 report summarized the
findings from the 2011 test well. Three attempts were made before drilling successfully reaching
the target Leadville formation:
• The first bore hole encountered a variety of challenges.
40
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 34
• The second well attempted to reuse the first bore hole but also was not successful in
reaching the Leadville formation.
• The third well was successful in reaching the Leadville formation. However, the high-angle
Sawatch shear zone was encountered because of a previously unmapped fault. This
formation resulted in a large amount of cold water producing from the test well, which
affected results. The cold water is believed to originate from snowmelt injection near
Smuggler Mountain. The first bore hole located 30 feet away on the surface did not
encounter the same high-angle Sawatch shear zone.
The analysis indicates the second well location could be close to ideal for water intended for
consumption by the City of Aspen due to the flow rate and type of zone. The 2015 report also
suggested direction drilling from Rio Grande Park and Wagner Park north towards Red Mountain
could reduce the depth of drilling and the temperature of hot water produced. Thermal quality
within the earth is expected to be up to 140-degree Fahrenheit, which may be too cool for
conventional building heating systems but warm enough for modified building heating systems
or snow melt systems. The 2015 paper envisions injecting water produced at Rio Grande Park and
Wagner Park into the Molly Gibson mine as one option since that mine appears to already be
connected to the Leadville formation.
There has been renewed interest recently in geothermal, in particular the use of ORC heat engines
in combination with geothermal wells. Horizontal drilling techniques are being used to improve
cost efficiencies associated with geothermal but challenges with cost-effective ORC heat engines
remain.
With today’s commercially available technologies, 140-degree water remains too cool for use in
an ORC heat engine. In Aspen, it may be that relatively cold water from the Sawatch shear zone
or from overnight average air temperatures are sufficient to create the difference in hot and cold
temperatures necessary for successful ORC heat engine operation sometime in the future.
Assuming a low-side temperature of 40-50 degrees Fahrenheit and a high side temperature from
120 to 130 degrees Fahrenheit at the ORC heat engine, it may be possible to generate electricity
with an upper theoretical limit of 12-15% Carnot cycle thermal efficiency. As part of the research
for this microgrid effort, geothermal heat pump firms that could make use of Aspen geothermal
resources were not identified.
The 2015 Geothermal Test Well paper suggests 1,000 to 5,000 gallons per minute could be
produced from each well site. Assuming a 12% Carnot Cycle efficiency, 2 to 2.5 MW of electricity
could be generated from two wells. The fluid leaving then ORC heat engine might still be at
sufficient temperature to be used for heating or snowmelt purposes. ORC heat engines
traditionally have been difficult to implement. However, for an application such as this where
fossil fuels are not an option and the cost to generate electricity can be compared with storage
41
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 35
technologies such as lithium-ion BESS, there may be increased potential for such a project to be
viable once ORC technology improves.
42
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 36
SECTION 8.0 MICROGRID DESIGN FRAMEWORK AND NEXT STEPS
The microgrid’s focus includes providing backup power to city facilities during a transmission
outage. City facilities within the microgrid include the water treatment plant, public works
facilities, office buildings, and community-focused amenities. The microgrid consists of loads and
distributed energy resources (DERs) operating as a coherent unit, either in parallel with or
islanded from the primary power grid, whose main purpose is to support critical loads during
severe contingencies.
The DERs may also participate in various load management and demand response programs to
generate revenue or provide stability during normal (“blue sky”) grid operating conditions. For
Aspen microgrid DERs, the primary objective is islanded operation during utility outages or grid
constraints, with normal operation of demand management and system stability as the secondary
function. The implementation of a microgrid would provide backup power and system resiliency
in the event of a transmission line outage. The Aspen microgrid is aimed at providing resilience
of the system during abnormal emergencies.
The following are the microgrid functional requirements:
• Upon loss of power from the utility, the microgrid controls shall be capable of forming an
island that transitions from the grid to the proposed energy generation systems.
• The microgrid controls shall be capable of dispatching and controlling DER’s within the
proposed boundary to support microgrid loads.
• The microgrid controls will be able to differentiate between DER availability and
coordinate system reenergization through voltage ramping by the BESS or step loading
when rotational generation is available to support inrush currents.
• The microgrid controls shall be capable of load shedding during an issue with a DER or if
the operators determine that there is a need/capability for rolling brownouts due to load
demand, DER availability, or duration of the outage.
See APPENDIX B – MICROGRID FUNCTIONAL REQUIREMENTS for detailed microgrid functional
requirements.
8.1 ASPEN DISTRIBUTION SYSTEM AND MICROGRID ELECTRICAL TOPOLOGY
The microgrid primary isolation points from HCE are the Puppy Smith Switching Station and Golf
Course PMH. There are an additional six isolation points within the Aspen distribution system.
These points are used to isolate most of the distribution system from the microgrid. VFIs, Pad
Mounted Reclosers, and normally open points will be used as the isolation methods for the
microgrid. The Microgrid Controller, VFIs and Reclosers coordinate and control the microgrid
isolation from the normal utility transmission source during normal and abnormal conditions. The
43
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 37
microgrid controller also coordinates the operation of DERs within the microgrid and monitor for
abnormal conditions. Presently no switching devices are capable of automation to allow isolation
of the proposed microgrid area; therefore, the scope includes the installation of electronic
automatable reclosers and switches including communication infrastructure.
8.2 ASPEN MICROGRID LOADING
The Aspen distribution system services city facilities whose uninterrupted operation would
benefit the community in times of emergency. The SCADA is new but limited in the number of
devices presently visible. Additional system metering and monitoring is required for accurate
control and operation of the microgrid by a centralized controller, which can be achieved through
the implementation of electronic reclosers or circuit breakers equipped with digital protective
relays.
8.3 MICROGRID ISLANDING, RESTORATION, AND OPERATING MODES
The microgrid shall be manually controlled and formed through the HMI and microgrid controller
when deemed necessary by Aspen Electrical Department personnel. The microgrid controller will
also be capable of optional manual, semi-automated, or automated responses to utility outages
to form the microgrid. During island operations the microgrid controller monitors, controls, and
notifies operators of any changes within the microgrid boundaries. When the transmission utility
is restored, the microgrid controls must support the transition of the system back to grid
connected mode.
8.4 DISTRIBUTED ENERGY RESOURCES CAPACITY AND OPERATION
Microgrid DERs include generation and storage sizing and technologies to be determined in the
future by the City of Aspen. The DERs shall be configured for parallel operation with the grid,
including providing peak shaving, demand response, or primary source load relief to the City of
Aspen and the transmission utility. With uncertainty regarding the impact of Colorado’s transition
to SPP / SPP+, there may be economic opportunities in the future to dispatch permitted
generation sources.
Following Aspen Electric Utility and City Council decision-making and budget approvals, the
microgrid would proceed per the selected contracting approach.
If minimization of the initial investment were prioritized, the first phase of the microgrid might
involve site design, Aspen major material procurement, and construction contractor install of a 4-
hour BESS sized using the wildfire / summer season pre-electrification scenario for BESS sizing.
Since grid-provided electricity is already 100% renewable, the BESS would be charged by the grid
44
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary 38
to support peak demand management in the winter and to provide resiliency during the summer.
No solar photovoltaic systems are assumed in the initial roll-out. Although Aspen’s customers
need to pair BESS with renewable energy generation, it is assumed that the City of Aspen will be
able to install a stand-alone BESS operated by the utility to support grid operation. Subsequent
phases would take advantage of LDES as solutions become more commercially available.
45
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-1
APPENDIX A – GENERATION AND STORAGE TECHNOLOGY REVIEW
The following storage and generation brainstorming outline and general discussion regarding key
objectives and technologies for the City of Aspen Microgrid evaluation.
46
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-2
A.1 KICKOFF MEETING
During the kickoff meeting, representatives from CLPE and the City of Aspen discussed objectives
and technologies of interest. Key objectives of the planning effort include the following:
• Provide continuity of service for municipal facilities.
• Improve resiliency of municipal buildings.
• Reduce climate impact versus fossil fuel-based electricity generation.
• Serve as a reference guide on constraints and capabilities of existing systems and
microgrids.
As part of this study, there needs to be a clear Summary for review by Aspen Electric Utility, City
Council, and stakeholders containing realistic costs for certain ranges of resiliency and hours of
backup power. The report should reflect present technology and not aspirations for future pricing.
The intent should not be to oversell, and findings need to be realistic, actionable, and achievable.
The microgrid should not include new diesel or natural gas but existing investments in assets such
as natural gas generators may be viable if necessary to improve financial viability of the microgrid.
The City of Aspen confirmed during the kickoff hydropower in general would be good to include
in the microgrid. PRV-based generation is unlikely to provide significant support to the microgrid
but a 2010 study detailed quantity of energy at Aspen’s PRVs that could be generated.
The City of Aspen contains minimal available land. Undeveloped land is embraced as open space,
regardless of ownership. Certain areas such as the Aspen Recreation Center or Aspen Water
Treatment Plant could represent viable locations for generation and sto rage. Mountains surround
the City of Aspen, but adjacent mountaintops are beyond the City of Aspen’s electric territory.
Geothermal via new wells or old mine shafts are intriguing options for non-conventional energy
generation and storage. Old mine shafts may also be an option for gravity energy storage.
Small modular reactors are unlikely to be a good fit for Aspen.
Biofuels could be an option but the microgrid study should document constraints including factors
such as fuel fouling, transportation emissions, and adverse impact to Aspen Valley air quality.
The City of Aspen municipal government does not operate wastewater treatment facilities but
does include a water treatment facility where land may be available to support energy storage
for the microgrid. The existing SCADA system includes a handful of devices. The AMI and SCADA
systems are distinct and do not communicate with each other, nor would that be desirable.
In addition to limited available land, MEAN as the energy wholesaler to the City of Aspen limits
cumulative localized solar production.
47
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-3
A key takeaway from this discussion was the desire to maintain a practical, yet blank slate for
fossil fuel-free generation and storage technologies. A broad, brainstorming-level generation and
storage technology meeting followed the kickoff meeting.
A.2 TECHNOLOGY BRAINSTORMING
On 06 January 2025, CLPE presented a broad list of technologies, as found in Appendix A.4 to
review and discuss opportunities and limitations of microgrid-related generation and storage
technologies within the City of Aspen. Aspen is already 100% renewable, so the use of fossil fuel-
based electricity represents a step backwards for Aspen.
A summary of technologies considered and reviewed includes the following:
• Solar: Use of open space is not a viable option. The planning study should consider
maintenance and snow clearing impact of solar. The City of Aspen’s electricity contract
with MEAN allows some solar, but project-specific circumstances limit the total
percentage. The City of Aspen could consider solar on rooftops, parking lot canopies, or
locations consistent with existing operations.
• Hydropower: hydropower represents most of Aspen’s 45% self-owned or directly
contracted renewable energy. Additional hydropower is allowed by the City of Aspen’s
contract with MEAN. Extending the Aspen distribution system to potential generation
locations is the primary barrier for this technology. Water rights issues impede
consideration of pumped hydro.
• Wind: Aspen’s partner in renewable energy, MEAN, provides approximately 55% of
Aspen’s renewable electricity largely from utility-scale wind turbines located elsewhere
such as the central plains. The City of Aspen is in a valley with lower wind speeds and less
output than would be true of nearby ridgelines. Smaller wind turbines tend to be much
less cost effective than larger utility-scale turbines. Aspen does not expect wind to be a
viable technology to support the microgrid.
• Geothermal and Geoexchange: Geothermal may have potential for reducing electricity
needs. However, n o large local commercial geothermal power production facilities exist
in Aspen, and a sample well drilled in Aspen did not result in adequate temperatures to
justify development. Geoexchange through use of ground source heat pumps exists as an
option to use electricity more efficiently than air source heat pumps.
• Lithium-Ion Storage: BESS tend to provide power commercially in the 1 to 4-hour range.
However, adding BESS to achieve longer durations of storage can be a method for
evaluating cost competitiveness of LDES technologies.
48
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-4
• LDES Storage
o Flow Battery: The microgrid study can consider new and emerging forms of
storage.
o Gravity Storage: For storage, the use of gravity storage is intriguing with the
potential to locate within older mine shafts or elsewhere in the community.
o Hydrogen Storage: As part of any project development using hydrogen, the project
team would need to document and review hazards with fire authorities.
A.3 TECHNOLOGY FOCUS AREAS
In both the kickoff and brainstorming sessions, hydrocarbon-based fuels, in particular diesel, were
emphasized as not desirable for powering the microgrid. Although natural gas generators exist in
municipal facilities that could be called upon at the facilities where they exist, the intent of the
microgrid is to seek out low carbon resiliency during emergency situations.
The electricity provided to the City of Aspen is presently 100% renewable so consumption of
electricity to power or regenerate storage resources is consistent with the microgrid objectives.
A.4 TECHNOLOGY SURVEY DISCUSSION
In December 2024 and January 2025, two separate technology discussions were held with
Aspen personnel. The discussion approached technologies from a brainstorming level where a
broad range of technologies could be considered with dialog on each followed by review for
applicability as part of the Microgrid Planning Study.
Solar Energy Technologies
Established Technologies
• Rooftop Solar PV: Ideal for public spaces, schools, and municipal buildings to reduce reliance
on external energy sources.
• Ground-Mounted Solar PV: Scalable for utility-scale projects in available land areas.
• Covered Parking Solar PV: Combines solar generation with shading for parking
infrastructure.
• PV ESS Hybrid systems in distributed and central formats
Geothermal Energy Technologies
Established Technologies
• Geothermal Heat Pumps: Provide heating and cooling for residential and commercial
buildings with high efficiency.
Emerging Technologies
49
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-5
• Geothermal Power Plants: Utilize thermal recovery wells for clean, baseload electricity.
• Enhanced Geothermal Systems: Advanced techniques to utilize fractured wells, expanding
geothermal potential in areas without traditional reservoirs.
Wind Energy Technologies
Established Technologies
• Utility-Scale Wind Turbines: utility generation technology typically connected as power
producer. Some cases of installation behind-the-meter.
Emerging Technologies
• Small Wind Turbines: Suitable for energy needs in remote off-grid settings.
• Vertical Axis Wind Turbines: Compact, efficient, ideal in urban and constrained
environments.
Thermal Generation (Fuel Based)
Established Technologies
• Microturbines: Compact combined heat and power for small-scale distributed generation.
• Gas Turbines: Flexible fuel options for efficient operation in larger applications such as utility
power.
• Natural Gas Reciprocating Engines: Highly efficient in distributed generation and peak
shaving applications.
• Diesel Generators: Reliable backup power for critical infrastructure.
Emerging Technologies
• Renewable and Blended Fuels: Options including biodiesel and renewable natural gas to
reduce carbon intensity.
• Linear Generators: Advanced modular power generation with low emissions and high
efficiency, suitable for various fuel types.
• Hydrogen Combustion Systems: Clean fuel alternatives for conventional turbine
technologies.
Fuel Cells
Established Technologies
• Fuel Cells: often fueled with natural gas through a reformer, can also be configured to
directly use stored hydrogen.
Energy Storage Technologies
Established Technologies
• Lithium-Ion Batteries: Widely deployed for grid stabilization and backup power.
Emerging Technologies
• Thermal Energy Storage: integration of solar and CHP systems
• Gravity Storage: Innovative solutions using potential energy for grid-scale storage.
50
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-6
• Flow Batteries: Long-duration storage suitable for renewable integration.
• Sodium-Sulfur and Solid-State Batteries: Emerging alternatives for safer and more durable
storage solutions.
• Flywheel Energy Storage: Provides high-speed response for grid frequency regulation.
• Compressed Air Energy Storage: Scalable for large-scale grid storage.
• Supercapacitors: Suitable for rapid charge and discharge cycles in concert with ski lifts
• Zinc-Air Batteries: Promising cost-effective, long-duration energy storage.
Regenerative Energy Applications
Emerging Technologies
• Regenerative Power from Ski Lifts: Harness energy from braking systems in ski lifts for local
energy use or storage.
Small Modular Reactors
Emerging Technologies
• Nuclear Small Modular Reactors: A reliable baseload energy source with lower upfront costs
and scalable deployment potential.
Hydro Technologies
Established Technologies
Hydropower: use of existing dams to generate power.
Emerging Technologies
• Conventional and Run-of-River Hydropower: Reliable and renewable electricity generation.
• Pumped Hydro Storage: Highly efficient for energy storage and grid balancing.
• Micro-Hydro Systems: Ideal for small-scale, community-based renewable energy projects.
Fuel Options for Resiliency
Established Technologies
• Diesel, Natural Gas, and Propane: Reliable bridge fuels with established infrastructure.
Renewable and Emerging Fuels
• Hydrogen: Versatile for fuel cells, combustion, and industrial applications.
• Synthetic Fuels: Carbon-neutral alternatives for traditional fossil fuels.
• Biofuels: Derived from organic matter for diverse applications.
Additional Resiliency-Related Technologies
Established Technologies
• UPS Systems
• Docking stations for portable assets
Emerging Technologies
51
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary A-7
• Flywheels
52
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-1
APPENDIX B – MICROGRID FUNCTIONAL REQUIREMENTS
The following is the detailed analysis of the functional requirements for the City of Aspen
microgrid.
53
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-2
B.1 SUMMARY
Typical power system operating conditions can be characterized as:
• Normal: no emergency conditions
• Typical emergency: abnormal conditions/outages that are typical, localized, short
duration, and low impact
• Abnormal emergency: high impact/low frequency events that can cause widespread and
long-term outages
The Aspen microgrid provides resilience during abnormal emergencies across the desired
duration.
The following microgrid functional requirements relate to site characterization:
• Upon loss of power from the utility, the microgrid controls shall be capable of forming an
island that transitions from the grid to the proposed energy generation systems.
• The microgrid controls shall be capable of dispatching and controlling DER’s within the
proposed boundary to support microgrid loads.
• The microgrid controls will be able to differentiate between DER availability and
coordinate system reenergization through voltage ramping by the BESS or step loading
when rotational generation is available to support inrush currents.
• The microgrid controls shall be capable of load shedding during an issue with a DER or if
the operators determine that there is a need/capability for rolling brownouts due to load
demand, DER availability, or duration of the outage.
B.2 DISTRIBUTION SYSTEM UPGRADES
The microgrid primary isolation points from HCE are the Puppy Smith Switching Station and Golf
Course PMH. There are an additional six isolation points within the Aspen distribution system.
VFIs, Pad Mounted Reclosers, and normally open points will be used as the isolation methods for
the microgrid. The VFIs and Reclosers coordinate and control the microgrid isolation from the
normal utility transmission source during normal and abnormal conditions.
Some SCADA and communications fiber is owned by the City of Aspen Municipal Electric Utility.
However, most of the isolation points do not have fiber. Aspen needs to add communications
infrastructure to each of the generation, storage, and isolation points to allow safe operation of
the microgrid area.
54
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-3
Presently no communication backbone and no switching devices are capable of automation to
allow isolation of the proposed microgrid area, therefore the microgrid requires the installation
of electronic automatable reclosers and switches including communication infrastructure.
B.3 MICROGRID ELECTRICAL TOPOLOGY
The following list outlines the electrical topology of the proposed microgrid system:
• The existing medium voltage distribution system infrastructure within the microgrid
boundary is underground.
• The boundary points of the proposed microgrid are the isolation points.
• Aspen will install storage and/or generation at locations appropriate to the selected
technologies. Since the City of Aspen procures 100% renewable electricity, storage
technologies are higher priority versus local generation.
• Aspen should configure the step-up transformers to be protected on the primary side via
relay, and by the corresponding equipment low voltage breaker on the secondary side.
• Aspen should install the microgrid controller at a facility with knowledgeable electric or
maintenance personnel, which makes Puppy Smith Electric or the Water Treatment Plant
the preferred locations.
• Aspen will upgrade four existing PMHs with VFIs for metering, communications, and
controls capability requirements.
• Aspen will verify two existing PMHs with VFIs are compatible with metering,
communications, and controls capability requirements.
• Aspen will install one Pad Mounted Recloser with electronic vacuum bottle reclosers
equipped with digital relays to accommodate metering, communications, and controls
requirements of the microgrid controller.
• Aspen will verify the communications backbone and SCADA at each of the isolation points,
microgrid control station, and generation and storage resources used to power the
microgrid.
The following are the microgrid functional requirements related to the electrical topology:
1. Integrate, control, and dispatch the new and existing DERs to maintain power quality
factors such as frequency, voltage, and VAR support in accordance with industry
standards.
2. The microgrid controller shall be capable of and configured to communicate with DERs to
curtail production based on demand within the microgrid and the grid forming inverters’
minimum output setpoints.
3. The microgrid shall have its own control and SCADA system. Output from the system shall
be visible via the operator workstation co-located with the microgrid controller.
55
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-4
4. The microgrid controller, in conjunction with the DERs’ individual controllers, will monitor
and ensure the microgrid voltage profile is within Aspen’s acceptable operational limits
(+/- 5%). The microgrid hardware will be capable of handling any load imbalance.
5. Maintain adequate system protection settings, metering, monitoring, and controls for the
switching points that are equipped with digital protective relays and controls for both
islanded and grid connected operations. Different protective relay settings may be
required during islanded operations due to lower available fault current levels.
6. Provide adequate protection for generation assets from abnormal conditions such as
overcurrent, overvoltage, underfrequency, etc.
7. Comply with all applicable local, state, and federal codes, standards, and regulations.
8. Integrate and accommodate changes (additions or removals) to microgrid
boundaries/switching points, DERs, and loads if the storage and generation capabilities
are maintained to support the loads.
B.4 MICROGRID ISLANDING, RESTORATION, AND OPERATING MODES
For manual operation, formation occurs through the human machine interface (HMI) and
microgrid controller when deemed necessary by Aspen Electrical Department personnel. The
microgrid controller will also be capable of optional manual, semi-automated, or automated
responses to utility outages to form the microgrid within a programmable period. The microgrid
operates on a break-then-make concept. The microgrid controller will monitor grid status and will
include sufficient delay to allow Aspen’s reclosers and switching to restore power using grid
resources. If the grid remains out, the microgrid controller will call for isolation point to open,
verify, they are open, and commence microgrid operations.
When the transmission utility is restored, the microgrid controls support the transition of the
system back to grid connected mode. For the proposed Aspen Microgrid, there are several custom
operating modes that the microgrid needs to be capable of accommodating.
The following are the microgrid functional requirements related to islanding, restoration, and
operating modes:
1. Transitions between grid-connected and islanded operation will be open transitions. This
means the microgrid controller will isolate and de-energize all assets within the microgrid
boundaries prior to deploying DERs in grid-forming mode or reconnecting back to the grid
once the utility has been restored.
2. The microgrid controller and automated switching devices will be powered by dedicated
auxiliary power supplies such as 48V or 125V DC battery packs and chargers to remain
operational during the open transitions.
56
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-5
3. Once the microgrid is isolated and de-energized, the microgrid controller will dispatch
generation to form a grid by energizing the lines, transformers, and loads. The microgrid
controller will be capable of identifying DERs and coordinating remote commands for
generation dispatch once the microgrid has been isolated from all external sources. The
microgrid controller will coordinate step loading/shedding and dispatching of the DERs to
supply the loads while in microgrid mode.
4. The microgrid shall be formed either manually by an operator-initiated command or
capable of semi-automatic or automatic restoration mode if the utility is lost for a pre-
determined length of time.
5. If the operator manually initiates a microgrid formation command (even if the normal
utility source is not lost), the microgrid controller will perform automated switching steps
to isolate the microgrid from the utility supply to create an island and open all step loading
switching devices to prepare the system for islanded operation.
6. If the utility is lost and all the other supervisory parameters are satisfied, the microgrid
controller shall detect the loss of the utility and initiate a programmable countdown timer.
If the utility is still down after the predetermined delay duration has passed, perform semi-
automated or automated switching to the island by opening or verifying the open status
of isolation point equipment.
7. All timers should be programmable by the operator.
8. If the utility returns within the predetermined delay duration (e.g. 1 minute), the
microgrid controller will do nothing. This delay will allow ride through of any transient
issues, voltage sags, or reclosing actions during temporary faults.
9. If a permanent fault is detected on the Aspen system when islanding would normally be
implemented, the microgrid controller will do nothing because the fault is within the
microgrid boundary and forming a microgrid can cause feeding into an existing fault.
10. Black start the microgrid utilizing the lead BESS within a programmable period (e.g. 2
minutes) from the time the microgrid island is isolated. Synchronize any additional DER’s
with the BESS. All non-lead sources will be grid-following but may require curtailment or
isolation during startup or load shedding.
11. Detect return of utility and start timer for a programmable period (e.g. 5 minutes). If the
utility remains stable (voltage and frequency) for the duration of the timer, transition the
microgrid to grid-connected mode by de-energizing DERs and then closing normally
closed reclosers.
12. Provide fully manual microgrid operation mode. When this mode is enabled:
57
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-6
a. The microgrid controller detects the loss of the utility and informs the operator,
but does not perform any automatic islanding, switching, or dispatching.
b. The operator has complete manual control of each control function.
c. The operator can manually create the microgrid island by opening the reclosers
and breakers. However, they cannot black start the system before all the switching
is complete and an island is established.
d. Once an island is confirmed, the operator can manually start the lead BESS and
black start the microgrid.
e. The operator has manual control of synchronization and dispatch capabilities of
the DERs.
f. There shall be safeguards and supervisory procedures in place so that operators
cannot operate the equipment in an improper sequence and cause power quality
issues, an outage, or damage to the grid or DERs.
13. Provide semi-automatic microgrid mode. When this mode is enabled:
a. The microgrid controller identifies specific control actions (isolation switching,
dispatch, etc.) that are then presented to the operator in pre-programmable
switching orders for approval.
b. Once the operator approves each step, the microgrid controller executes the
action.
14. Provide automatic control mode. When this mode is enabled the microgrid controller will
automatically perform the following in order:
a. Identify and confirm the loss of the transmission utility and wait a
programmable pre-determined amount of time before initiating system
switching for isolation.
b. Upon successful isolation from the transmission utility, implement pre-
programmed switching to open all switching devices to prepare the system for
load stepping.
c. Verify availability and status of DERs. Black start the system with the BESS and
reenergize the system within the microgrid boundaries.
d. Initiate load stepping through the switching devices until all loads are online or
maximum loading to DERs output capabilities is achieved.
e. Control deployment of the DERs maintaining a stable, synchronized, and
controlled system.
f. Monitor and maintain stable island operation for a minimum of 4-hours.
g. During islanded operation the microgrid controller will automatically perform
the following:
58
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-7
i. Alert operators if loading exceeds DERs capabilities for potential
implementation of programmable rolling brown/black out scenarios.
ii. Maintain real time stable load to generation by managing the DER parallel
operations, with capabilities for management of future generation assets.
iii. Alert operators when energy reserves of the energy storage system reach
less than one hour of remaining operability.
iv. Perform controlled load shedding and shutdown of the DERs when less
than the pre-programmable amount of energy storage remains.
h. Monitor for return of the normal transmission utility. When a stable normal
transmission source is detected for a programmable set amount of time load
shed the microgrid and prepare for return to normal source.
i. Shut down and isolate DERs from the system within the microgrid boundaries.
j. Perform pre-programed switching to return the system to normal operating
state.
B.5 DISTRIBUTED ENERGY RESOURCES CAPACITY AND OPERATION
The Phase I microgrid DERs includes generation and storage sizing and technologies based on
future funding and decision-making by the City of Aspen.
The City of Aspen is in a unique situation because of ongoing 100% renewable energy purchases.
As a result, the City of Aspen could have a renewable energy microgrid without any new
generation.
The DERs shall be configured with the capability for parallel operation with the grid, including
providing peak shaving, demand response, or primary source load relief to the City of Aspen and
the transmission utility. With uncertainty regarding the impact of Colorado’s transition to SPP /
SPP+, there may be economic opportunities in the future to dispatch permitted generation
sources.
The following are the microgrid functional requirements related to DER capacity and operations:
1. Allow for inclusion of future energy storage and generation systems.
2. Dispatch and control/coordinate DER (present and future) outputs during microgrid
operations.
3. Protection schemes will be developed for both islanded and paralleled operations to
ensure safe, reliable, and coordinated operation of protective devices under all
operational scenarios.
4. The DER system shall be capable of forming a grid from a black start condition, which
requires specification of which storage and generation assets are grid-forming versus grid-
following. If multiple grid-forming assets are included in the system, the microgrid
59
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-8
controller will specify the lead grid-forming asset. The DER operating alone will be capable
of voltage ramping to reenergize the microgrid. The microgrid controller will prevent
overloading of the DER by only allowing a combination of loads up to load step capacity
of the resource.
5. When an inverter-based DER (BESS, microturbine, etc.) is operating in parallel with non-
inverter-based (engine, etc.) generation assets the combination of DERs will be capable of
picking up the entire load of all switching steps through any combination of step loading
of the system.
6. The present and future DERs shall be capable of supporting the distribution transformer
inrush and cable/line charging inrush from a cold-load pickup. If required during detailed
design, additional switching isolation points may be added at strategic locations to the
feeders to reduce the line charging and equipment inrush currents.
7. The present and future DER controls shall be equipped with all necessary protections,
controls, metering, monitoring, and annunciation systems to ensure safe and stable
operation.
B.6 MICROGRIDS LOADS TIER PROFILE
For the concept phase of this design, loads are not specifically tiered, but the microgrid controller
will be capable of closing or opening any generation protective device as well as feeder recloser
devices to better control stability of generation assets with consideration to real time system
loading. The microgrid controller will include capabilities for tracking up to the most recent 7-day
load profiles for the distribution feeders to ensure black start loading remains within acceptable
operational parameters. The following are the key functional requirements regarding potential
future microgrid load tiering:
1. The microgrid controller and communications systems shall be capable of integrating
future load-shedding provisions and if desired by the operator and control them in a tiered
structure.
2. A tiered loading structure may require the microgrid controller to add or remove certain
feeders with all their corresponding loads during microgrid operation based on their
priorities.
3. The user/operator shall have the option to assign priorities to each curtailable load and
update them at any time as load priorities may change based on time of day, events, and
other factors.
B.7 CONTROL SYSTEM OPERATION
The microgrid will have the following control points:
60
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-9
• Six (6) 25kV VFI Switchgears
• One (1) 25kV pad mounted recloser
• One (1) Normally open point
• Storage and Generation DERs
In the future, the microgrid may expand and include more distribution grid isolation points,
energy storage, additional solar PV, and load shedding points.
The following are the key functional requirements for the control system:
1. Control and visibility shall be provided to Aspen personnel. Communications will be fiber
based to ensure reliability and status/command signal speed.
2. Each of the locations mentioned above (and future additions) shall be equipped with
smart control, metering, monitoring, and communication capabilities.
3. The field control devices shall have a local user interface for local controls and access of
device status, settings, metering, and monitoring data points.
4. The microgrid shall have reliable communications to each of the switching and DER control
points and execute control, metering, and monitoring functions as necessary to maintain
safe and stable operation of the system during grid-connected or islanded operations.
5. If communication is lost between the microgrid controller and one or more of the control
devices during microgrid operation, the control device shall maintain its tasks and actions
locally to allow continuous and safe islanding and operation of the microgrid.
6. If one or more control devices fail during microgrid operations (due or loss of power
supply or hardware failure), the microgrid controller shall notify operators and maintain
safe and stable operation of the microgrid until the operator has a chance to take manual
control.
7. If the microgrid controller fails during microgrid operation (due to power supply loss or
hardware failure), the field control devices shall take local control and maintain safe and
stable microgrid operation until the operator has a chance to take manual control.
8. The microgrid controller shall include a user-friendly human-machine-interface (HMI) for
manual controls, semi-automatic controls, metering, monitoring, alarms, and user input
interface.
9. The microgrid controller shall provide seamless integration of microgrid-specific control
devices and the necessary metering and monitoring data points. Aspen personnel shall
have full access to the controls, metering, and monitoring of all the control points.
10. Control of microgrid control devices should be supervised, managed, monitored, and
processed by the microgrid controller to prevent any inadvertent operations that may
compromise safe and stable operation of the microgrid.
61
Revision: C City of Aspen E-EDS-001
Date: 11/17/2025 Microgrid Planning Study
Proprietary B-10
11. The microgrid controller will supervise energy storage system charging against system
capabilities and control throttling of charge rates in relation to system load to ensure
system equipment will not be overloaded.
B.8 CYBERSECURITY
The microgrid system will rely heavily on a reliable communication network between the
microgrid controller and various field control points for its operation. The communication
network must be secured and controlled to prevent unauthorized access that may compromise
microgrid control settings, logic, and operations whether they are intentional or unintentional.
The following are the key functional cybersecurity requirements:
1. The microgrid controller, communication network, and field devices shall be fully
compliant with Aspen’s cybersecurity standards, policies, and procedures.
2. Communications between the microgrid controller and field control points shall be
secured and controlled.
3. All communication ports at the field control points and microgrid controller location must
be secured and locked so that no unauthorized personnel can access them virtually or
physically.
4. The microgrid controller shall be capable of providing access control, account
management, and time stamped event logging.
62
FOLLOW-UP REPORT
ORIGINAL MEETING DATE: January 20, 2026
FOLLOW-UP REPORT DATE: January 27, 2026
SUBJECT: Community Events | Community Picnic
PRESENTED BY: Wesy Armour-Cook & Nancy Lesley
COUNCIL MEMBERS PRESENT: Mayor Richards, Councilmembers Doyle,
Guth, Benedetti and Rose
______________________________________________________________________
WORK SESSION DISCUSSION SUMMARY:
There was full Council support to re-invigorate the Community Picnic. A majority of
Council are happy to serve food, and were also supportive of kids and family friendly
activities. The following comments were received and noted by staff.
Happy to serve food
Place in the shoulder season
Not attached to the history of the event and supportive of moving it out of the
heart of the summer
Would be OK with splitting into 2 events; one at the beginning and one at the end
of summer
Moving the event locations has possibly hurt the event with the inconsistency
School calendar changed, please make sure to check it out and keep in mind
Bring in a competition element that includes the businesses
More “fun” elements like a photo booth that gives a “takeaway” that can live in
the house/on the fridge and bring up great memories
If the kids like it the families come!
Please ensure the dates don’t conflict with Council obligations
Include non-profits and interactives (ie fire truck/hose and smoke house)
NEXT STEPS:
Staff is taking a deep dive into the various calendars; the events calendar as a whole,
the school calendar with its earlier summer release and the City Council calendar. In
63
addition to brainstorming the appropriate comments and ideas to incorporate Council
feedback into a re-envisioned community picnic for this coming year.
CITY MANAGER NOTES:
64