When my wife and I built our retirement house in eastern coastal Maine, we powered it with 6.2 kW of mono-crystalline silicon solar cells manufactured by SunPower. We chose to connect to the grid, because while the summer days are very long in Maine, the winter days are very short. With net-metering, we wanted to be able to bank enough credits with our local power company during the summer to carry us through the winter, without the expense of having a big battery pack in the basement. All this cost about $47000, including some site excavation and installation by Revision Energy. With the 30% Federal tax credit for installed solar, our net cost was slightly more than $33000. Unfortunately, the state of Maine provides no tax credit or rebate.
Are we happy? In 2015 we generated 7460 kW-hr of electricity which more than covered our needs for electric heating, hot water, refrigeration and other appliances in a 1600-square-foot house with exceptional insulation. (All the lighting in the house uses LED bulbs, which draw only small amounts of power.) Normally, our electricity would have cost $ 1100. We pay a small connection fee each month, amounting to about $100/year, so our savings is about $1000/year.
We will amortize our investment over 33 years—not a great decision for a business, but fine for a couple of folks who want to do their best for the environment. I prefer to think of our investment as a $33000 bond that pays about 3% interest ($1000) each year. Your experience with solar will vary depending upon tax credits and the rate your power company charges for electricity.
The cost of solar panels has dropped precipitously during the past decade and the efficiency of the available models has gone up dramatically. Our panels are advertised to convert 21.5% of the Sun’s radiation into electricity. Various thin-film panels do even better. And just over the horizon, stacked-panels and panels based on perovskite may regularly convert more than 25% of the Sun’s radiant energy into electricity.
While solar generates only about 0.5% of electricity in the United States. With widespread adoption in Europe and China, wind and solar power now generate more than 9% of the world’s electricity. Some of this power is generated by local users, like us, and some is generated in large solar farms, especially in California and the desert Southwest. Utility-scale solar is not without its own set of environmental impacts, but rooftop solar is benign. We can expect these percentages to rise as the U.S. complies with the protocols signed in Paris a few weeks ago.
You can join the movement now, or wait until the panels are even more efficient and cheaper in just a few years. Either way, you will want renewable energy in your future.
Peng, J., L. Lu and H. Yang. 2013. Review on the life cycle assessment of energy payback and greenhouse gas emission of solar photovoltaic systems. Renewable and Sustainable Energy Reviews 19: 255-274.
Sessolo, M. and H.J. Bolink. 2015. Perovskite solar cells join the major league. Science 350: 917.
Warburg, P. 2015. Harness the Sun: America’s quest for a solar powered future. Beacon Press.
 Net metering is an agreement between homeowners and the local power company that credits the homeowners with any extra power that is delivered to the grid, and charges the homeowners during those periods when they draw from the grid. Essentially, your electric meter runs forwards and backwards, and you pay only for the net amount used in any year. In some states, what you get paid for delivering to the grid is less than what you get charged when you draw on the grid, and some states allow the power company to charge a connection fee that helps pay for the grid itself.