The Working Waterfront

For Maine, here comes the sun

Residential solar power can help state hit goals

Meghan Grabill
Posted 2021-12-08
Last Modified 2021-12-08

Maine’s climate goals are to decrease greenhouse gas emissions by 45 percent by 2030 and 80 percent by 2050. The residential sector accounts for the second-highest source of emissions in Maine (after transportation), making up almost 20 percent of the state’s carbon pollution.

Solar power is one of many options for reducing emissions of our homes. Depending on the details, rooftop solar can break even around year eight—with federal tax credits—and can provide mostly free electricity for many years beyond.

“Maine has seen substantial growth in solar at all scales as policy changes in the past few years opened up the market,” Ethan Tremblay, energy policy analyst with the Governor’s Energy Office reports. “In fact, we’re among the top ten fastest growing markets in the country, according to national industry rankings.”

“We’re among the top ten fastest growing markets in the country…”

Solar panels are installed in a place that maximizes sun exposure, which on homes usually means south-facing rooftops. These panels absorb the sun’s energy to generate direct current, or DC electricity. An inverter then converts the energy from DC to alternating current, or AC power because residential houses are wired for AC.

Solar panel output is measured in wattage, with the listed wattage determined based on ideal conditions. With current technology, a single rooftop solar panel of roughly 5 feet by 3 feet produces between 250-400 watts, but this varies based on shading, orientation, location, time of year, and temperature.

A single solar panel could potentially power a 15-cubic foot freezer, or 20-30 LED light bulbs. Many panels are needed to power an entire house, but many homes in Maine have only enough suitable roof area to cover part of their electricity needs.

To get a rough idea of the number of panels necessary to meet household demand, I can use my household as an example. We consume about 9,000 kilowatt hours (kwh) each year. In Maine, it is expected that 1 kw (or 1,000 watts) of south-facing rooftop solar panels will produce 1,200 kwh per year. I’d therefore need a 7.5 kw solar array. Assuming each panel is rated for 375 watts, I would need 20 panels.

If you are fortunate, like me, to have a south-facing roof with no architectural details and limited obstructions of the sun, like trees, there is a good chance you have more space than necessary to produce more energy than you consume. There are also ground-mounted options if the roof space is inadequate.

Currently, most residential solar installations send power to the main grid. Remaining connected to the grid allows you to have a steady electricity supply. Legislation for “net metering” allows residents to get credit on their energy bill for the solar power they send to the grid.

Living here in Maine you may be thinking, “Great, I can keep my lights on when the grid goes out from a storm, since I’m generating my own electricity.” But wait, no. With standard residential solar installations that is not exactly accurate. For the safety of utility workers, all power distribution must be shut down during an outage, so even power generated on your rooftop will not be delivered to your home.

If you’re looking for backup power, one option is to couple your solar generation with an energy storage system—a battery. This allows homeowners to store the energy they produce and remain connected to the grid with safety controls to disconnect during grid outages. There is also the completely off-grid option.

When it is bright and sunny and the house is using lower amounts of power, the solar production can generate more than is used and put extra energy into storage. At night, when it is cloudy, or during a high demand time, the house can call on the stored energy. The battery can also be used to store power from the grid.

The biggest drawback is the cost. Solar and storage technology have recently improved greatly, but batteries are still expensive.

Homeowner-based solar generation has many benefits.

“Along with providing some of the most cost-effective electricity available, solar is central to making our communities resilient to the effects of climate change and creates good-paying clean energy jobs for Maine people,” says Tremblay.
With so many positive benefits, it may be time to contact a solar installer to get a system for your house to help Maine reach its climate goals and save some money on your electric bill. I know I am considering it.

Meghan Grabill is a senior community development officer with the Island Institute, publisher of The Working Waterfront. She leads the Institute’s community data team.