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Will Your Roof Make Your Electricty?

Topher Belknap

This picture shows the solar potential of downtown Damariscotta and Newcastle. All of the colored roofs will produce electricity at a lower cost than the price we pay to Central Maine Power (CMP). The red colored roofs are flat, which means that the panels need to be tilted in order to best intercept the sun's rays, so fewer panels can be placed such that they don't shade each other. The green roofs are oriented and tilted in such a way as to make electricity they produce cost between 9 and 10¢ per kiloWatt-hour (kWh). The blue roofs produce eletricity costing between 10 and 11¢ per kWh. The purple costing more than 11¢, but still less than the retail price from CMP.

Solar Potential of Downtown Damariscotta / Newcastle
photo credit: Topher Belknap

The Solarize Central Lincoln County (Solarize CLC) campaign is endeavoring to put up as many solar roofs in this area as possible before the end of the 30% tax rebate at the end of 2016. By buying in bulk, economies of scale reduce the price that everyone has to pay. Basically for every 10 houses we get solarized, the price for each house drops $600.

Each roof on the map has two numbers associated with it. The first is the yearly electricity production that can be expected if the entire colored area is covered with solar panels. This number is given in MegaWatt-hours (MWh), that is, thousands of kWh. This number should be compared to your yearly electricity usage, to see what percentage of your electric bill can be offset with solar electricity. You will see your last 13 months of usage at the bottom of your CMP bill, add up 12 of those to find your yearly usage. Divide by 1000 to see your MegaWatt-hour usage; if your bill is less than the number on your roof, you can offset your entire bill with solar.

The second number gives the expected price that you will pay per kWh for this replacement electricity. It is calculated assuming the base price for a solar installation (i.e. before any group buy discounts), and includes the tax rebate, and the cost of borrowing the entire cost at 2.99% interest for 20 years, and a presumed (guaranteed) lifespan of 25 years for the panels). Other assumptions will, of course, give other results, but the upshot is that for any unshaded, uncomplicated roof, the cost of electricity with solar will be cheaper, from the very first day, then what you are currently paying CMP. And that price will never go up. After 20 years, that price will vanish and you will pay only the minimum connection fee (currently around $11).

If your roof is not shown, you can contact me, Topher Belknap at topher@greenfret.com to find out your personal numbers. For more information see: