Solar in Snow
March 09, 2015
With the season’s snowfall now well past the 100-inch mark, no one needs to be reminded of how rough a winter it’s been for Bostonians. Ice dams are everywhere, gutters are straining to the breaking point, and leaks have become the prime topic of water cooler conversation. Yet amidst it all, residential solar power systems have soldiered on.
To be sure, there have been many days when the latest dump of snow has blocked the wintry sun from reaching the 23 solar panels mounted on the roof of our home and adjacent garage. But surprisingly quickly, the snow has slipped off our panels’ slick glass surfaces even as it has clung to the surrounding asphalt shingles. Soon enough our solar panels have resumed their work, generating a healthy flow of electrons.
Take Winter Storm Juno as an example. Even though it dropped two feet of snow on Boston in late January, this first big storm is now a distant memory. (After all, we’ve since endured later storms running through Octavia, Pandora, Quantum, Remus, Sparta, and Thor.) But, for me, Juno revealed just how resilient our 5.86-kilowatt photovoltaic (PV) system can be. Just a few hours after the last flakes had fallen in the early morning hours of January 28, most of our panels had shed their snow.
Here’s how things looked by the middle of that day:
Luckily PV panels draw their power from the sun’s light rather than its heat. They actually function more efficiently in colder weather, so on that frigid but sunny January day, when the thermostat topped out at 25⁰F, our PV panels were performing better than in the mid-summer sun. (Of course, winter days are much shorter so the overall daily output of a PV array in January is likely to be much less than in July.)
One of the many appealing features of our PV system is the accurate performance readout I can get on my smartphone or while sitting in the comfort of my home office. Our Enphase Energy monitoring screen shows each individual panel’s electric output in real time, allowing me to see which panels are partially or fully covered by snow without ever having to venture outdoors.
Over the course of that day, our solar panels generated about 10 kilowatt-hours of electricity, which is enough to keep more than a hundred 60-watt-equivalent LED bulbs glowing for eight-plus hours—obviously much more than we would ever need to light our home. Those same kilowatt-hours would also be enough to wash fifty loads of dirty laundry. (I’m not including clothes drying—the biggest power consumer in most New England households aside from summertime air conditioning or electric heating, for those who have it. We’ve sworn off using our dryer, instead hanging clothes on indoor racks in the winter and on lines off our back porch in the summer.)
On a year-round basis, solar energy now supplies about three-quarters of our household electric needs. This includes the daily charging of our Ford C-Max Energi—a hybrid electric car that averages about 150 miles per gallon as it takes my wife, an architect, to her office and job sites in and around Boston. Since our solar system began producing power in April 2013, we have generated enough electricity to offset nearly eight tons of carbon emissions.
From a financial standpoint, our PV system looks equally appealing. The nominal price of the system was about $27,000, but a federal investment tax credit and state rebate, combined with a discount from our installer, brought the actual cost down to about $17,000. Through reduced electric bills and the Solar Renewable Energy Certificates (SRECs) that we earn on every megawatt our solar panels produce, we expect to recoup our full investment in about seven years. Any investment adviser will tell you that’s a very respectable rate of return.
While we chose to purchase our solar system outright, about two-thirds of all US residential solar arrays installed in 2014 involve third-party arrangements where homeowners either lease their solar systems or enter what’s known as a “power purchase agreement,” or PPA. In states that allow third-party ownership of solar arrays, a company like SolarCity—the best known of many residential solar developers—installs a PV system on a home or other building at no upfront cost. The property owner, in turn, commits to buy the output of that system at an agreed-upon rate that is competitive with retail electricity over a fixed period, usually 20 to 25 years. These third-party arrangements have brought solar within easy reach of millions of American homeowners who might otherwise rule out solar energy as beyond their budget.
As the spring thaw approaches, we look forward to the first of this year’s “shoulder seasons”—those months in the spring and fall when the days are longer but air conditioning isn’t needed. If last year is a predictor, we will become net-positive power producers by April: The electricity generated by our solar panels will exceed our total power use that month. By year’s end we will likely have at least three other net-positive months thanks to the sun.
Meanwhile we’re just hoping that Winter Storm Zelus never arrives.
Philip Warburg, an environmental lawyer, is the author of Harness the Sun: America’s Quest for a Solar-Powered Future, to be released by Beacon Press in September. His previous book, Harvest the Wind: America’s Journey to Jobs, Energy Independence, and Climate Stability, was published by Beacon in 2012. Connect with him on his website and Twitter.