723 Spring Str

1. 723 Spring Street
– Solar System Case Study
Scott Phillips
October 8, 1012
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2. Summary
• The SunPower 8.64 kW system generated
10,429 kWhs and provided 55% of the of
the annual energy usage
• Based on BTU’s per square
foot, 723
Spring Street uses 50% of similarly
sized homes.
• The net cost of the system after utility
rebate & federal tax credit was $29,276
or $3.39/watt.
• Year 1 Savings were $2,367 including an 11 cent/kwh renewable
energy credit, first year total utility cost was $0, the simple
payback was 12.5 years and the annual ROI equals 8%.
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3. Home Construction & Design
• 723 Spring Street was Ann Arbor’s first
LEED Platinum house, constructed in
2007 by Meadowlark Builders.
• The envelope of the home consists of ICF
walls, SIP panel roofs and the home has
geothermal heating & cooling.
• Other efficiency factors include an energy
recovery ventilator, recirculating hot
water system, low flow water fixtures and
solar powered window blinds.
• 723 Spring Street scored a HERS Rating
of 40, using approximately 60% less
energy than a Code built home
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4. SOLAR SYSTEM DETAILS
• 8.64 kW system comprised of 36 SunPower
E19/240 solar panels at 240 watts and 19.3%
efficiency - Enphase Energy Micro-inverters.
• The panels were mounted with UNIRAC
SolarMount rail systems. RoofGrip Easy Feet
mounts attach the rail system to the SIP roof.
• The system also includes an Envoy
Communications Gateway and web-based
Enlighten monitoring website.
• The system was installed in August of 2011 by
Mechanical Energy Systems
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5. SOLAR SYSTEM PERFORMANCE
• Based on system design, the projected KWh production for was 10,301.
• The actual production was 12,380 kWh or 120% of projection.
• Peak daily generation was 53.7 kWh.
• This chart displays monthly kWh actual production Vs. estimated.
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6. ENERGY USAGE
• Total energy usage for this twelve
month period was 23,319 kWh.
• The PV system provided 55% of
annual electrical energy usage
and 41% of total energy usage.
• At 105M British Thermal Units
(Btus) of annual energy
usage, 723 Spring uses 65% of the
energy of similar sq. ft. homes.
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7. COSTS, REBATES & CREDITS
• The gross invoice cost of the systems was
$57,375 or $6.64/watt.
• The DTE Solar Currents Program provided
an up-front rebate of 2.40 per DC watt
which totaled $15,552 and an on-going
production incentive 0.11 per kWh.
• Less the federal tax credit of $12,547
($41,823 X 30%), the net cost was $57,375 –
15,552 - $12,547 = $29,276 or $3.39/watt.
• This charts compares 723 Spring Street’s
utility cost per sq. ft. for new
construction, single family homes & similarly
sized homes.
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8. PAYBACK / ROI / REAL ESTATE VALUATION
• Based on net cost of $29,276, generation of 10,761 kWh and savings
of $2,367, the payback is 11.3 years & ROI is approximately 9%.
• The annual savings of $2,582 is comprised of $1,398 in energy
purchase reductions & $1,184 in renewable energy credits.
• Based on research from Clean Power Research, this ROI & payback
is slightly better than the U.S. annual average of similar homes.
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