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Proposed Business Case: Public-Private Partnership
Community Solar for CTA Heavy Maintenance Facility & Rail Yard
System Owner: Developer
Installation Type: Rooftop/Carport
Subscriber Model: Panel Lease
Host Site Owner: Public Sector
System Size: 1,900 kW
Subscribers 175
September, 2017
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 2
Contents Case Study ..................................................................................................................................................................3
Overview .................................................................................................................................................................3
Business Case Assumptions ....................................................................................................................................3
Site Assessment ..........................................................................................................................................................3
Shading Analysis .....................................................................................................................................................3
Structural Assessment ............................................................................................................................................4
Mounting Stuctures ................................................................................................................................................4
Permitting ...............................................................................................................................................................4
Interconnection ......................................................................................................................................................5
System Design ............................................................................................................................................................5
Panel Layout & Design Considerations ...................................................................................................................5
System Components and Costs ..............................................................................................................................5
System Performance ..............................................................................................................................................6
Operations and Maintenance .................................................................................................................................6
Business Model ...........................................................................................................................................................7
Ownership Structure ..............................................................................................................................................7
Subscriber Model....................................................................................................................................................7
Financial Model ..........................................................................................................................................................7
Inputs & Assumptions ............................................................................................................................................7
Subscriber Metrics ..................................................................................................................................................8
Host Site Metrics ....................................................................................................................................................8
System Owner Metrics ...........................................................................................................................................8
Subscriber Management ............................................................................................................................................9
Customer Acquisition .............................................................................................................................................9
Subscriber Management ........................................................................................................................................9
Marketing & Outreach ................................................................................................................................................9
The Cook County Community Solar Project ............................................................................................................ 10
About the SunShot Initiative ................................................................................................................................... 11
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 3
Case Study Overview
The Chicago Transit Authority Heavy Maintenance Facility & Rail Yard in Skokie houses multiple shops on more
than 30 acres. Rail lines connecting the site to the CTA system limit the possibility of ground mounted PV.
However, the building has more than 400,000 sf of roof space and significant parking lots. The proposed
community solar system installation would utilize nearly the entire roof to host 1,128 kW of rooftop solar and
772 kW in solar parking canopies to be installed over the north and south lots. This proposed business case is a
developer-owned model, with the CTA as an anchor subscriber, and the remainder of subscribers coming from
households and businesses from the surrounding community.
Business Case Assumptions
The intent of this proposed business case is to provide a high-level assessment of installing solar at this location
and providing a rationale and proposed model for operating a community solar program. While system designs,
assumptions and costs are provided in this report, they are not intended to serve as construction ready drawings
or designs, financial pro forma or commitments. It is assumed that each site, stakeholder or solar developer will
pursue design, engineering, interconnection and business planning separately and specifically. Neither Cook
County nor any person acting on their behalf (a) makes any warranty, express or implied, with respect to the use
of any information or methods disclosed in this report or (b) assumes any liability with respect to the use of any
information or methods disclosed in this report.
Site Assessment The initial assessment looked at ground mount solar over undeveloped land at the south end of the property.
Research indicated that the land assessed actually was not owned by the CTA. The engineering team then
looked at the roofs and potentially carports at this site. The multiple buildings on this campus represent more
than 400,000 sf of roof space across at least 10 roof segments/buildings. These roofs vary in age and structure. A
number of the roofs are currently in fair condition and would be replaced prior to solar installation. The initial
assessment indicates that the flat roofs are suitable for the addition of solar arrays, while the sawtooth roof may
require reinforcements. Parking lots are suitable for solar canopies if the minimum height can accommodate the
heavy equipment and trucks that are present at the campus.
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 4
Shading Analysis
A shading analysis was conducted to
determine the impact of shading on the kWh
output of the proposed PV system. The
HelioScope software program was used to
determine the amount of shading and
corresponding reduction in kWh output. The
results of the analysis indicate that overall
rooftop and carport annual rated kwh
output will be reduced by 1.4%. This system
loss due to shading is incorporated into the
system performance calculated by PVsyst
and informs the overall design.
Mounting Structures
The solar panel roof mounting approach used in this proposed design consists of both direct attachment rails
and ballasted systems. The direct attachment system is proposed for the sawtooth portion of the roof. Special
roof attachment hardware is directly attached onto the underlying roof framing and sealed with flashing and
sealants to maintain a weatherproof building envelope. These attachment points will allow a bracket and rail
system to be used to install the panels flush on the sawtooth portion of the roof.
The approach used for the remainder of the flat roofs is a ballasted system, which precludes the need to pierce
through the roof membrane. Instead the PV panels are attached to trays with ballast weights to secure the
modules and negate the wind uplift effects. Wind deflectors can also be attached to the modules to decrease
the required ballast weight resulting in a system with a total uniform load of less than 6 pounds per square foot
(psf). Applications of the ballasted system are limited to low slope roofs with pitch less than 10 degrees, which
works for this site.
Structural Assessment
Typically, we assume a uniform dead load of 15 psf for steel framing to account for the weight of the roof
framing and roofing material. The additional weight due to typical solar panels and the associated mounting
hardware is in the order of 6 psf. Based on a design roof live load of 32 psf as indicated on the existing building
drawings, structural reinforcements would not be required to support the proposed ballasted system on the flat
roofs of the existing buildings. It is however likely that some secondary steel reinforcement would be required
to attach the PV panels flush on the sawtooth portions of the roof. These reinforcements have been accounted
for in our design and site preparation budget.
Permitting All panels are proposed to be roof or carport mounted for this site. Thus, only building permits are anticipated
to be required.
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 5
Interconnection
The CTA site is currently fed from a 3-phase 12kV line supplying power underground to pad-mount transformers
on the property. The interconnection will require the installation of a power transformer, fused disconnect,
relaying, and metering equipment at the point of interconnection. The ComEd distribution system may require
a relay upgrade for the feeder based on the interconnection pre-screen report provided by ComEd. The costs
associated with these upgrades have been included in our design and financial model. However, a full
interconnection analysis will need to be conducted to confirm required upgrades and costs.
The Utility Side of the Meter On the utility side of the meter, a 2,000 KVA power transformer
will be required to step-up the PV solar system voltage to 12kV, as
well as a potential transformer (PT) for voltage monitoring of the
relay. These are both installed on the ComEd side of the meter,
with upfront costs incurred by the utility. The system owner pays
for associated construction and engineering costs, as well as a
monthly fee via the Rider NS agreement, which is typically $200-
$400 per month.
The Customer Side of the Meter The interconnection costs incurred by the system owner include
the relay, fuse switch, distribution panel and the cable/conduit to
connect the PV system to the grid. While the costs for transformers
are incurred by the utility and paid for monthly by the system
owner, the engineering and construction costs are paid for upfront
by the customer. Total interconnection costs are less than the
industry average of $.09 per installed watt.
Customer Side Materials Costs
Relay for DER Protection $1,000
Fused Disconnect Switch $5,000
Distribution Panelboard $15,000
2” Sch. 40 PVC $300
Misc. Bends / Couplers $240
Cable $7,500
TOTAL $26,040
Utility Side Materials Costs
Potential Transformer $400*
2,000 kVA Power Transformer $60,000*
Meter $300*
TOTAL $60,700*
*Rider NS, Not in upfront total
Total Customer Interconnection Costs
Engineering $20,000
Materials $26,040
Construction $120,000
Interconnection Application $2,100
Total $148,140
System Design Panel Layout & Design Considerations
The proposed design incorporates roof-mounted arrays
along with parking lot canopies. The proposed system
uses nearly 6,000 panels in a layout that takes
advantage of most of the available flat roof space in a
non-penetrating, ballasted racking system, as well as
fixed penetrating mounts for the sawtooth roof over the
main garage. The design also uses parking canopies in
small enough proportion to ensure overall costs remain
as close to $2 per installed watt as possible. Costs based
on this design are anticipated to be $2.06 per installed
watt overall. This maximizes output and maintains a
competitive cost.
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 6
System Components and Costs The design uses (3,458) 325-watt modules for
rooftop arrays and (2,376) 325-watt modules for
carport arrays. A total of 5,831 modules are used, as
well as 28 small inverters for cost effectiveness and
to minimize the effect of inverter down time. With a
number of small inverters, only a small part of the
system will be taken out of service if there is a
failure. Utilizing 1,000VDC strings allows a larger
number of PV modules per string and reduces cost.
Using 480AC three-phase for power distribution is
recommended to minimize voltage drop.
System Performance PVsyst V6.41 software was used to analyze the anticipated power generation performance of the system based
on the design. PVWatts uses solar irradiance data from the closest possible set of typical meteorological data
(TMY). In this case, the nearest set of TMY for this site is from Midway Airport. Based on this analysis, the system
is anticipated to generate more than 2,378 megawatt hours of energy per year, enough to power about 300
average Cook County homes.
Operations and Maintenance A robust maintenance plan can ensure optimal system performance. The
U.S. Dept. of Energy suggests that an optimal operations and
maintenance (O&M) plan for solar arrays can increase typical
performance from 91% to 95%. The components of O&M include site
maintenance, electrical inspections and panel maintenance. The single
biggest expense for maintaining arrays is inverter maintenance and
replacement. Most inverters have a planned mechanical life of about 10
years, which this model assumes.
Component Costs per Watt Ground Carport Combined
PV Modules: $0.45 $0.45 $0.46
Inverters: $0.13 $0.13 $0.13
Racking: $0.15 $1.00 $0.48
Balance of System: $0.10 $0.10 $0.10
Engineering and Design: $0.02 $0.02 $0.02
Permitting and Interconnection: $0.10 $0.10 $0.04
Installation Labor: $0.40 $0.40 $0.41
Equipment Rental and Freight: $0.03 $0.03 $0.03
Development Overhead: $0.40 $0.40 $0.40
Total Installed Cost $1.78 $2.63 $2.06
O&M Costs $/kW
General Site Maintenance $1.40
Electrical Inspection $2.49
Panel Washing $0.82
Inverter Maintenance $4.08
Inverter Replacement $6.22
Total $15.00
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 7
Business Model Ownership Structure
Developer-owned, host-owned and equity investor models were analyzed. The equity-investor model produced
an Internal Rate of Return of just 7.8% before taxes. The host-owned system produced a better overall Net
Benefit over the life of the system, But the IRR was just 3.3%. The developer-owned system produced the best
overall return for both developer with an Internal Rate of Return of 9.9%. The earnings for the host were very
good, as well, and it allowed no upfront investment or risk. The Return On Investment (ROI) for the Developer
for this proposed model is anticipated to be 25.6% and the host site average annual return over was more than
$19,000 annually over the life of the system.
Subscriber Model
The proposed subscriber model is a panel lease model, with the Chicago Transit Authority as an anchor
subscriber. Households and businesses from the surrounding community will take the remaining shares. The CTA
will subscribe to 40% of the system output, or approximately 950,000 kWh annually. They will lease panels for
$1.11 per month, which represents a 10% savings on their electricity rate the first year. Residential subscribers
will lease panels for $1.56 per month each, which also represents a 10% savings. Our model assumes subscribers
lease an average of 20 panels each, requiring about 175 subscribers to reach full subscription. Savings are
anticipated to increase over time as energy prices increase.
Financial Model Inputs & Assumptions
Financial models were developed using the Community Solar Business Case Tool developed by the Cook County
Community Solar project team. Inputs were based on findings from the engineering assessment conducted by
Primera, LLC on behalf of Cook County, solar design outputs from Elevate Energy and Microgrid Energy using
Helioscope and PVSyst, interconnection pre-screening reports from ComEd, as well as industry data for some
inputs identified in cooperation with the National Renewable Energy Laboratory1 and Lawrence Berkeley
National Laboratory2. The Community Solar Business Case Tool version used to develop these financial models is
the Illinois specific tool, which is based on an energy-only residential bill credit rate of $0.0587 per kWh and
average commercial and industrial bill credit rate of $0.035 per kWh. SREC values used were $45.00 per MWh,
based on our assumption of increasing blocks for system size ranges.
1 U.S. Solar PV System Cost Benchmark: http://www.nrel.gov/docs/fy16osti/66532.pdf 2 Tracking the Sun quarterly solar price report: https://emp.lbl.gov/publications/tracking-sun-ix-installed-price
Business Case Tool Version: The tool version used is a customized version of v1.21. All macros were removed and separate rate inputs
were added for C&I/anchor subscribers. The PVWatts rate generator is disabled in this version. To adjust generation rate outputs,
download the latest version here: https://www.elevateenergy.org/community-solar/communitysolarbusinesscasetool/
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 8
Subscriber Metrics Subscribers gain value by leasing panels for $1.56 per month and
receiving credits on their electricity bill at an effectively higher rate.
The proposed subscriber model assumes a 10% savings for subscribers
on their electricity rate. While the average number of panels leased is
estimated to be 20, subscribers can lease more or less to
accommodate their electrical load. Subscribers leasing 20 panels will
save $37 their first year and an average of $170 annually over the life
of the system.
Subscribers from households of 80% or less Area Median Income
(AMI) may qualify for an incentive from Illinois Solar For All that we
have estimated to be 50% of the cost of their subscription. These
subscribers will save on average $224 the first year.
Host Site Metrics
As the host site, the Chicago Transit Authority earns value in two ways: first by leasing their land to the system
owner, which we have assumed to be $5,000 per year. They also receive value by subscribing to an anchor share
of 40% of the system and saving money on their energy. In our proposed model, we have assumed no upfront
costs and an immediate net positive experience. Their first year savings is estimated to be $8,078 and their
average annual savings over the life of the system is $19,096.
System Owner Metrics
The proposed business case allows for a developer to build, own and maintain the system, taking advantage of
SRECs at $45 per megawatt hour produced, the federal Investment Tax Credit at 30%, the Modified Accelerated
Cost Recovery System (MACRS) at 35% over six years, as well as the $250 per kW capacity rebate from the
utility. Allowing for a 10% energy savings for subscribers, the system owner sees an Internal rate of Return (IRR)
of 9.9%, a Return On Investment of 25.6% and an overall Net Benefits of nearly $1.4 million.
Unsubsidized Subscriber Metrics
25-Year Costs: (9,360)
25-Year Revenues: 13,604
25-Year Net Benefits: 4,244
Upfront costs $0
Year 1 Bill Savings: $37
Subsidized Subscriber Metrics
25-Year Costs: (9,360)
25-Year Revenues: 18,284
25-Year Net Benefits: 8,924
Upfront costs $0
Year 1 Bill Savings: $224
Key Performance Indicator Subscriber
25-Year Costs: (778,708)
25-Year Revenues: 1,256,103
25-Year Net Benefits: 477,395
Upfront costs $0
Payback Period: 0
First year savings $8,078
Average Annual earnings over 25 years: $19,096
System Owner Metrics
25-Year Costs: (5,436,598)
25-Year Revenues: 6,826,652
25-Year Net Benefits: 1,390,054
25-Year Net Present Value (NPV): 180,194
Return on Investment (ROI): 25.6%
Payback Period: 4.2
Internal Rate of Return (IRR) 9.9%
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 9
Subscriber Management Customer Acquisition The proposed business case calls for approximately
175 subscribers leasing an average of 20 panels
each. It is anticipated that the customer acquisition
effort is moderate for this project and that full
subscription will be reached within one year. The
average cost for customer acquisition is $431 per
subscriber during the first year.
The turnover rate of subscribers is estimated to be 1.5% per year. This turnover represents subscribers that
move out of the utility territory or cancel their subscription. Customer acquisition for these subscribers is then
required to bring the project back to full subscription.
Subscriber Management
The management of billing is the largest ongoing subscriber management
function anticipated. This will consist largely of managing share percentages
monthly and providing breakdowns for the utility in a timely manner.
Reconciling billing discrepancies can be an issue in the early stages of any
community solar project. This, together with customer service and general
program questions makes up the biggest share of subscriber management
costs in the first two years after customer acquisition. After the second year,
subscriber management costs lessen and the tasks become routine.
Marketing & Outreach The Village of Skokie has a population of 64,270. However,
the number of households within 5 miles of the facility is
more than 290,000. This represents a densely populated
suburban area. Because the subscriber model and terms are
very positive and because the Chicago Transit Authority can
easily support the marketing, outreach and subscriber
acquisition efforts through its ridership, the acquisition for
the 175 needed subscribers should be a fairly simple task.
We have anticipated reaching full subscription within a year.
There are a number of innovative approaches the CTA can
take to support the customer acquisition for this developer,
including outreach and co-marketing on buses and trains, as
well as internal to employees.
Total Upfront Administrative Costs Total ($) $/Subscriber
Marketing & Communications $27,323 $156
Customer Acquisition Setup $9,900 $56
Outreach Setup $2,400 $14
Admin Setup $1,400 $8
Year 1 Subscriber Management Costs $34,642 $198
TOTAL UPFRONT COSTS $75,665 $431
Lifetime Subscriber Mgt. Costs
Outreach $4,860
Sales $895
Sign-up Transaction $639
Customer Service $5,935
Billing Admin $358,676
TOTAL COSTS $371,005
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 10
The Cook County Community Solar Project Project Background
The Cook County Community Solar Project was launched in early 2015 with a grant from the Department of
Energy’s Solar Market Pathways Program. This two year project began on the premise that community solar was
not only possible in our region, but has the potential to bring access and equity in renewables to the 80% of our
population currently left out because of technical, structural or financial barriers. Community solar also has the
potential to bring significant economic development to the region, with more than 600 MW of community solar
development projected in Illinois through 2030 after the launch of the Future Energy Jobs Act in June of 2017.
Project Partners, including Cook County, Elevate Energy, the Environmental Law & Policy Center, The City of
Chicago, ComEd and West Monroe Partners, have produced a series of reports, analyses and tools that are
aimed at supporting stakeholders to grow the emerging community solar market in our region. Project
deliverables include an opportunity assessment, policy analysis, best practices, value and impact analysis and a
series of 15 site-specific project case studies, in which this document is one. More on the project and
deliverables can be found here: https://www.cookcountyil.gov/service/solar-energy
Key Project Contacts Deborah Stone Project Sponsor Chief Sustainability Officer and Director Cook County Department of Environmental Control [email protected]
Vito Greco Project Lead Solar Program Manager Elevate Energy [email protected]
Laura Oakleaf Project Manager Legislative Coordinator Cook County Department of Environmental Control [email protected]
CS060 Prairie State College Case Study Cook County Community Solar Project
©Elevate Energy 2016 11
About the SunShot Initiative The U.S. Department of Energy SunShot Initiative is a collaborative national effort that aggressively drives
innovation to make solar energy fully cost-competitive with traditional energy sources before the end of the
decade. Through SunShot, the Energy Department supports efforts by private companies, universities, and
national laboratories to drive down the cost of solar electricity to $0.06 per kilowatt-hour. Learn more at
energy.gov/sunshot.
This material is based upon work supported by the U.S. Department of Energy under Award Number DE-
EE0006916.
This report was prepared as an account of work sponsored by an agency of the United States Government.
Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty,
express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness
of any information, apparatus, product, or process disclosed, or represents that its use would not infringe
privately owned rights. Reference herein to any specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement,
recommendation, or favoring by the United States Government or any agency thereof. The views and opinions
of authors expressed herein do not necessarily state or reflect those of the United States Government or any
agency thereof.
All photos courtesy of the National Renewable Energy Laboratory’s Image Gallery