PhotoVoltaics
Let's look at the economics of putting a 2.3 kWe solar PV
system on the roof of a home. With a big splash roof top solar PV homes are
now being sold as of January 20,2007 in Roseville California
Nation's largest solar community to debut. The advertisement in the newspaper says
the owner can sell the excess electricity back to the utility and also reap benefits of
having their own electricity . After you read what I have written below you will see that
the advertisements are completely false. There will be no excess. But so what, there
are no guarantees that the solar systems will generate anything.
The Table below presents the lifetime financial duration of the PV system for 30 years
of cost data. The state rebate is $2.50 per Watt. The loan term is 30 years. The system
capital cost is $20,000 and the Federal tax credit of 30% is limited to a tax credit of
$2,000. The state rebate is thus $2.50 per watt times 2,300 watts = $5,750
The total amount financed by the owner is:$20,000 - $5,750 - $2,000 = $12,250.
The home owner can finance the $12,250 for 30 years at 6.2% or 4.10% effective
mortgage rate after deduction for interest. This assumes the homeowner is in the 34%
combined federal and state income tax bracket. The annual cost of the mortgage is
$710, the annual amount of electrical energy generated is 3,022 kWh, the current cost
of electrical energy to the homeowner is $0.0798 and I assumes that it escalates 3% per
year. The saving in electrical energy payments the first year is thus 3,022 kWh x 0.0798
per kWh = $241. But the first year's net cash flow to the home owner is minus $469.
PG&E tells me that the annual usage of electrical energy varies, but 10,000 kWh is a
good number for residential homes with a 2.3 kWe solar PV system on their roof top.
Thus the solar PV system would supply about 3,022 kWe/10,000 = 30% of the
homeowners electric energy.
Financial data over 30 years of a 2.3 kWh capacity solar PV system installed on a
residential home
Year Annual Savings Net Cost Cost of Energy
Payments per Year per Year 3% Escalation
per Year
2007 $710 $241 ($469) $0.0798
2008 $710 $248 ($494) $0.0822
2009 $710 $256 ($480) $0.0847
2010 $710 $264 ($465) $0.0872
2011 $710 $271 ($450) $0.0898
2012 $710 $280 ($435) $0.0925
2013 $710 $288 ($419) $0.0953
2014 $710 $297 ($402) $0.0981
2015 $710 $306 ($385) $0.1011
2016 $710 $315 ($368) $0.1041
2017 $710 $324 ($350) $0.1072
2018 $710 $334 ($331) $0.1105
2019 $710 $344 ($312) $0.1138
2020 $710 $354 ($293) $0.1172
2021 $710 $365 ($272) $0.1207
2022 $710 $376 ($251) $0.1243
2023 $710 $387 ($230) $0.1281
2024 $710 $399 ($208) $0.1319
2025 $710 $411 ($185) $0.1359
2026 $710 $423 ($162) $0.1399
2027 $710 $436 ($137) $0.1441
2028 $710 $449 ($112) $0.1485
2029 $710 $462 ($87) $0.1529
2030 $710 $476 ($60) $0.1575
2031 $710 $490 ($33) $0.1622
2032 $710 $505 ($5) $0.1671
2033 $710 $520 $24 $0.1721
2034 $710 $536 $54 $0.1773
2035 $710 $552 $84 $0.1826
2036 $710 $568 $116 $0.1881
Summatio $21,300 $11,474 ($7,117)
Conclusions: Notice that for 32 years the homeowner has a
negative cash flow. The home owner has only four years out of
thirty where there is a positive cash flow.
The final sum over thirty year was a loss of $7,117
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