Wednesday, October 29, 2014

Doing the Numbers on Solarizing: Guest Post by Dr. Robert Hargraves

Dr. Robert Hargraves
I attended Solarize Hanover at the high school Thursday evening, an event put on by many well-intended neighbors. To fight global warming from CO2 emissions they recommend rooftop PV solar panels for electricity that our utility company, Liberty, would otherwise generate from natural gas. An investment of $20,000 for a 5 kilowatt-peak-power PV system would “net" 6000 kilowatt-hours per year of electricity. At about 15 cents/kWh otherwise paid to Liberty this saves the homeowner $900. Solarize Hanover claims an investment payback of 7-12 years. This is only possible through extensive subsidies. Almost half of the $20,000 is recovered by tax credits, placing that cost on other citizen taxpayers.

Other Liberty utility customers also provide a subsidy because of “net” metering. On sunny days the PV solar panels indeed generate 5 kW of power for a few mid-day hours, but the average household consumption is only about 1 kW, so roughly 4 kW of the power (80%) is sent back to Liberty, which is required to buy it at the 15 cents/kWh rate. This raises Liberty’s costs, because it would normally buy cheaper electricity from hydro, nuclear, or natural gas generators at about 5 cents/kWh. This raises rates Liberty must charge other customers. This other-customer subsidy is roughly 80% x (15-5) cents/kWh x 6000 kWh = $480 per year.

CO2 emissions saved by avoiding burning natural gas for electricity are 333 grams/kWh, so each such Solarize Hanover home reduces emissions by 6000 x 333 grams = 2 tonnes of CO2 per year. World CO2 emissions from coal-fired generation of electricity are 10 billion tonnes/year and are expected to double as developing nations prosper.


Dr. Robert Hargraves is the author of Thorium, Energy Cheaper than Coal and an occasional guest blogger on this blog.  I have always been particularly fond of his humorous post: Vernon, New Hampshire?  He is also the author of many more scholarly works, and I recommend his website on radiation safety limits. Exposure limits for radiation should be set a lot higher than they are currently set.

This post appeared as a letter to the editor in the Valley News, October 28. However, the Valley News edited out the sentence on the calculation of other-customer subsidies.  This is the complete letter.

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