This is an Ignite Style presentation (five minute max presentations with slides that automatically advance every 15 seconds) that was a part of the 2014 Solar Symposium Innovation Showcase. Jon Hillis, Vice President, Prospect Solar Combining Solar with Green Roofs: Find out how Green Roof Integrated PV in urban areas like DC can take advantage of the symbiotic relationship between solar panels and green roof plants, alleviate competition for roof space, and address energy concerns and storm water drainage issues that are prevalent in larger cities.

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2.  District of Columbia has installed over 2
million square feet of green roofing.
 1st among US cities when compared to
available roof space.
 Additional 2 million square by 2018.
 Grants and other funding available for
green roof installations.

3.  30% Federal ITC, SREC market, and new
legislation regarding property tax and
community solar, make DC an excellent
solar market.
 Sustainable DC plan includes 20% of
renewable energy by 2023, 2.5% coming
from solar.
 Potential for 19% of electricity generated
from rooftop solar PV systems in DC.
 Competition for roof space between green
roofing and solar.

4.  Green roof is integrated with solar.
 Solar racking system is integral with the
drainage/retention layer of the green roofing.
Solar installed over green roofing Solar Garden Roof

5. Solar over green roofing
 Uses penetrating racking system which is more expensive
(about $0.35/Watt).
 Reduced life span of roof system compared to ballasted
racking system.
 Solar panels receive minimal benefit from the micro-climate
the plants create at the roof level.

6. Solar Garden Roof
 Soil ballasts the water retention/racking system without
penetrations.
 Hot rubberized asphalt roof membrane is utilized with life
span 2-3 times that of conventional roofing.
 Creates a cooler surrounding micro-climate. Modules
operate up to 10% more efficiently.

7. 1. Remove insulation and inspect/repair and install HDPE root barrier.
2. Reinstall insulation.
3. Install moisture retention mat and air layer.
4. Install water retention and PV racking modules.
5. Install system filter fabric.
6. Install soil and gravel drainage.
7. Install plants.

8.  Meet the goals of the Renewable Portfolio Standard.
 Increase low-income resident ownership of solar.
 Majority of low-income residents in DC are not in
living situations where they can own solar at their
premises.
 Storm water retention requirements creates
competition for rooftop space.

9.  Renewable portfolio standard and Solar Renewable
Energy Credits (SRECs) market.
 Stormwater Retention Credit Trading Program (SRCs)
through DDOE.
 Community Renewable Energy Act (CREA).
 Property Assessed Clean Energy (PACE).

10.  Solar Garden Roof systems installed on…
Multi-family dwellings
Non-profit organizations
Universities and institutions
Office buildings
Government buildings

11. SRECs
SRCs
PACE
Third party ownership and Power Purchase
Agreements (PPAs)

12. …to provide solar ownership for low-income
residents through the Community Renewable
Energy Act or Community Solar.

13.  Roof area
 Solar capacity
 Energy production
 Unit cost for green roof components ($/SF)
 Unit cost for solar ($/watt)
 Value of SRECs generated
 Value of SRCs generated
 Grants available
 Financing costs
 Date of installation – SREC pricing will vary

14.  Roof condition and existing warranty
 Structural capacity of existing roof deck
 Wind uplift
 Shading and orientation for solar array(s)
 Potential future use of roof area
 Storm water retention capacity created
 Financing capacity created

17.  Roof area – 10,000 SF
 Solar capacity – 51,740 watts
 Energy production – 63,438 kWh/year
 Unit cost for green roof components - $20.00/SF
 Unit cost for solar ($/watt) - $2.80/watt
 Grants available - $0
 Interest rate – 5%
 Amount to finance - $344,872
 Date of installation – 1/01/15
 SRC value - $2.27 per SRC (1 SRC/SF/Year estimated to
be generated)
 Owner is for-profit commercial property

19.  Net cash flow after 25 years does not take into account
energy production after year 25.
 $2.27 price per SRC is very speculative as the market is
new.
 Analysis provided is for a for-profit commercial
property owner.
 Additional savings if racking system and soil are
included in the cost basis to determine federal tax
credit.
 DDOE/AWS Green Roof Rebate program considerations.

20.  Solar Garden Roofs should be considered on new
development projects in DC.
 Should be considered on re-roofing projects as well.
 Installation of a Solar Garden Roof after completion of
the green roofing greatly increases cost.
 These retrofits can be cost prohibitive.
 These systems, funded through SRECs, SRCs, and
PACE, provide an excellent method to bring
community solar to low-income residents in the
District of Columbia.
Thank you!