Thanks to improved technology and increased competition, the cost of residential solar panels has plummeted — and installations have soared across the country. So what do Mainers need to consider if they want to harness solar energy to power their homes? We asked Phil Coupe, a managing partner at ReVision Energy in Portland and Liberty, to fill us in on everything under the — you know the rest.

Maine is famous for its long, dark winters. Does a solar-powered home really make sense here?

If there’s not enough sunshine, why bother trying to harvest it, right? But Maine actually has a rather powerful solar resource. A solar array installed here will produce the same amount of electricity on an annual basis as one installed in Houston, Texas, because solar electric panels actually prefer a cool, dry climate like ours to a hot and humid one like Houston’s. Maine also gets 30 percent more sunshine than Germany, which is the world leader in renewable energy adoption, because we’re situated at better latitude. In fact, Maine’s latitude is identical to that of Marseille on the Mediterranean Sea in France. We don’t have a year-round Riviera climate because of the way the Gulf Stream pulls weather patterns through our region, but the point is, we’re at a very sunny latitude.

How do you determine if your roof is suitable for solar electric panels?

There are a couple rules of thumb. First, the best roof pitch approximates your latitude. In Maine, we’re at 43 degrees north latitude, so solar panels on a roof pitch between 30 and 45 degrees  — which encompasses the majority of Capes, Colonials, and farmhouses here — are going to give really good production. Even a shallow-pitch ranch roof is good for solar because it will optimize summer solar production and reduce winter production, when the sun is less available. This is called “seasonal performance trading,” whereby you accept an increase at one time of year for a decrease at a different time. While 30 to 45 degrees is ideal, we actually install on roofs as low as 10 degrees depending on site conditions.

The second rule of thumb is your orientation — and here’s where we get into geek speak! South on the compass is technically 180 degrees, but to arrive at solar south, you factor in your declination. Declination in Maine is 16 degrees west, so you add 16 degrees to 180 to get the ideal orientation: that’s 196 degrees magnetic on your compass. Actually, anywhere from about 150 degrees to the southeast to 240 degrees to the southwest is viable.

What if your roof isn’t a good candidate? Do you have any options?

We start looking at placing them on the ground on your property. Ground mounts are about 10 to 15 percent more expensive because we have to build the mounting structure and securely affix it to the ground with an anchoring system. That said, we always get maximum output from a ground mount because we’re able to install at the ideal compass orientation and angle.

How about a community solar farm, like the ones you’ve built in South Paris, Edgecomb, and other towns, where homeowners share a single large array?

Unfortunately, Maine currently limits community solar farms to nine members, which makes it impossible to build at scale and gain efficiency. We have had to put on hold the construction of any more community solar farms in the state because they’re not cost effective. But there’s a lot of demand out there, and we strongly believe that after the elections we’re going to be able to change that policy in 2019.

Will a rooftop or ground-mounted solar array meet all of a homeowner’s electricity needs?

It varies. Solar typically offsets between 70 and 95 percent of total household electricity consumption, depending on the size of the system and the homeowner’s goals. For starters, solar electricity can power your lights, refrigerator, television, computer, and all the other appliances in your home. Because the cost of solar electric panels has dropped about 80 percent over the past 10 years, they’ve also become dominant in the renewable energy field, and they can power other increasingly popular appliances, like heat pumps, which deliver heat at the cost equivalent of $1.80 a gallon for oil and air conditioning at twice the efficiency of the best window units on the market. And you can use solar electricity to charge the battery in an electric car and thereby eliminate the need to purchase gasoline.

What about power outages? They’re a fact of life in Maine in winter.

You can get battery storage for homes, which is like having a backup generator. It enables people to keep the power on without burning fossil fuels when the utility grid goes down.

And the inevitable question: How much does it cost to go solar?

The average home system is between $15,000 and $20,000. But there’s a 30 percent federal tax credit for residential arrays that brings the cost down quite a bit.

Are there incremental steps you can take to converting to solar as your budget allows?

If you’re building new, you can put in conduit from the attic to the basement and run the wires at some future time, but 90 percent or more of our work is retrofits, and with those, we typically have to do everything at once. Sometimes people do heat pumps first and add solar later. Efficiency Maine offers a $500 cash rebate for a heat pump and another $250 for a second unit. If you do a heat-pump water heater, it’s a $750 rebate straight up.

How long do solar panels last and when can you expect them to pay for themselves in energy savings?

Most come with a 25-year warranty and a 40-year expected useful lifespan. The typical payback is about 10 years.

Explain how that works with regard to your energy bill.

First, you consume all the energy you’re generating — your household demand is satisfied, whether you’re powering your refrigerator or charging your car. Then, any excess you’re generating gets exported to the grid, and you get a credit from your utility for what you export. That’s called net metering.

Bring us up to date on what’s happening with net metering in Maine.

In years past, the credit was a full retail one to one: If you exported a kilowatt hour to the grid, then you got a kilowatt hour credit allocated from the utility. In 2017, after intense lobbying by Governor Paul LePage, the Maine Public Utilities Commission passed an anti-net-metering rule, which gradually steps down the credit. People who install a system in 2018 get 100 percent of the credit for the wholesale electricity part of their bill and 90 percent of the credit for their transmission and distribution charge. People who install in 2019 get 100 percent of the credit for wholesale electricity and 80 percent for transmission and distribution. And so on for the next nine years until you’re down to just the wholesale electricity credit. However, the Conservation Law Foundation is contesting this rule in the Maine Supreme Court. We’re also cautiously optimistic that a new governor in 2019 will help unwind or step down the anti-net-metering rule.