Tech

Cleaner, greener, cheaper: How solar panels work

Residential solar technology is helping the planet and your wallet

January 18, 2020
Photovoltaic solar panels on the roof of a home. By 2024, 2.5 percent of all U.S. homes will have solar panels, according to solar energy advocacy organization Solar Energy Industries Association (SEIA). [Credit: skeeze/Pixabay | CC]
Photovoltaic solar panels on the roof of a home. By 2024, 2.5% of all U.S. homes will have solar panels, according to solar energy advocacy organization Solar Energy Industries Association (SEIA).  [Credit: Pixabay free license]

The solar energy industry is booming. There are now over 2 million residential, commercial and utility-scale solar photovoltaic (PV) installations in the United States, enough to power the equivalent of 13.5 million homes, according to the Solar Energy Industries Association (SEIA).

If you’ve got solar panel envy and would like to join the crowd, here are some questions and answers that may help.

What are solar panels, anyway?

At the most basic level, solar panels are devices that convert sunlight to electrical energy. The technical name for a solar panel is a photovoltaic module or PV module. The “photo” refers to sunlight and “voltaic” to electricity.

What’s in a panel?

A PV solar panel consists of solar cells, sandwiched between glass and plastic layers and a frame that secures it all. There’s also an electrical box for connecting multiple panels. The transparent plastic sheets allow light to pass through and enter the solar cells and protect the cells from weather damage, says Mowafak Al-Jassim, a materials scientist at the National Renewable Energy Laboratory in Colorado.

Solar cells are the meat of this sandwich and play the most important role — turning sunlight into energy.

How do solar cells turn sunlight into usable energy?

When sunlight hits a solar panel, the sun’s photons are absorbed by the solar cells. Each photon that is absorbed generates an electron inside the solar cell’s silicon material, explains Randall Ellingson, a materials scientist studying photovoltaics at the University of Toledo. Excited electrons within the silicon shuttle from one side of the solar cell to the other, a movement that creates electricity. This electrical current flows to an inverter that transforms this direct current electricity into alternating current that can be used by consumers to power everything from lighting to microwave ovens.

How much power does a solar panel produce?

A typical solar panel installed in a residential home contains about 60 solar cells and is roughly the size of a 5.5-foot-tall person. Each cell is usually a 4 inch by 4 inch or 5 inch by 5 inch silicon square. Sixty cells are enough to produce 300 to 350 watts of power, which can light more than five 60-watt bulbs.

So, how are solar panels saving the environment?

If you’re in a location that receives a lot of sun, solar panels will not only reduce your electric bill, but also carbon emissions. Most electricity is generated by burning coal or natural gases, which emits carbon, says Garth Heutel, an energy economist at Georgia State University.

“You’re getting electricity production [from solar panels] with almost no carbon emissions or no any emissions of any sort, which is an advantage over burning coal or burning natural gas to generate electricity,” says Heutel.

Are all solar panels the same?

Not quite. Most photovoltaic solar cells on the market are made from silicon. Manufacturers melt raw silicon in order to make silicon solar cells. A seed crystal is added to a silicon melt to grow a large silicon crystal. Once complete, this big silicon crystal is called an ingot, explains Michael Heben, managing director of the Wright Center for Photovoltaics Innovation and Commercialization at the University of Toledo. A silicon ingot is a salami-shaped bar of silicon, according to PC Magazine.

Silicon ingots are manufactured into either monocrystalline or polycrystalline solar cells. These two kinds of solar cells are made into two kinds of solar panels — monocrystalline and polycrystalline — that make up more than 95% of the solar market, according to Sarah Kurtz, a materials scientist at the University of California, Merced.

The monocrystalline panels contain solar cells made up of slices of single crystals, says Heben, and these single crystals have a repeating, orderly pattern of crystal atoms. The perfect order of crystals within monocrystalline panels allow these panels to convert light to electricity more efficiently and have few defects. Polycrystalline panels, on the other hand, are made of different sizes of crystals, and can have lower performance efficiency.

One example of this is a tennis ball analogy, says Kurtz. You can take a box and fill it with tennis balls. If you start putting the balls in the box in an orderly array it will look perfectly lined up. If you just toss the tennis balls in a box, some of them will align nicely and others won’t. So wherever there is an irregularity in the structure, like the polycrystalline, that’s called a defect, says Kurtz.

Monocrystalline panels are usually more energy-efficient than polycrystalline because they are formed from one crystal, but some polycrystalline panels outperform monocrystalline modules made by a different manufacturer, says Kurtz. The differences between these two types of crystals matter less to the consumer than the design packaging of the solar cells and the quality of the manufacturing, she adds. Both type panels are “very reliable” if the purchase is from a high-quality manufacturer and will last many decades on a roof, says Joseph Burdick, founder of Burdick Technologies Unlimited, a solar installation company in Colorado.

A key consideration, says Ellingson, is whether to spend more on energy efficient panels. The best residential panels, he says, are about 20% efficient, which means that 20% of the sunshine that hits the panel is converted into electricity. The average efficiency for a solar panel is between 15 and 18%, according to Solar.com. The solar panel manufacturer SunPower has the highest efficiency solar panel at 22.8%.

I want to install solar panels, what do I do now?

The first step is to consult with a few local solar installation companies. To find a reputable company look on SolarReviews, contact your town’s conservation committee or clean energy center if you have one, or check the Better Business Bureau, says Garrett Colvin, director of residential sales at SolarFlair, a solar energy industry in Ashland, Mass.

Installers will look at your home to see if your roof is suitable and to assess how much power your house uses. Their quote for installation should also include various financing options.

What about installation?

Roughly 7,000 to 8,000 watts are needed to power an average home size on New York’s Long Island, says Bryan Spodek, vice president of Wood Kingdom West, a solar panel installation company in Farmingdale, NY. He says a typical 1- or 2-day installation costs about $23,000.

Installation usually takes 3-4 days, says Burdick. His installation projects in Colorado are usually between 3,000 and 8,000 watts — or 10 to 30 solar panels. The cost for a project of that size in Colorado can run anywhere between $10,000 and $50,000, he says.

Every solar panel installation also replaces your conventional electric meter with a net meter. A net meter records how much solar energy your solar panels are generating, as well as how much power you draw from the grid. When you use more energy than you produce from solar panels, says Burdick, the meter will turn forward. But when you produce more energy than you use, this excess energy turns the meter backward. This excess energy goes back to the grid and is bought by your utility company, says Burdick, however, some utility companies will pay you a lower rate when you’re selling energy back to them. The more energy you produce, the less you’ll end up paying to your regional electric company at the end of the month.

“The whole point of solar is to turn that meter backwards so that you pay a lower bill,” says Burdick.

So, will I really save money?

This depends on where you live, how much energy your home uses, the local cost electricity, and how large and efficient your solar panel system is. A person in an apartment might save $20 or $30 a month, but someone in a bigger home could save as much as $300 a month, say Burdick and Colvin.

A significant factor is the payback period, which is the amount of time that passes before a solar panel system saves enough energy to cover the costs of the initial installation. Payback periods can vary widely, but a typical period for a residential home is 7-10 years, according to Long Island’s Spodek. In Massachusetts, Colvin says it is typically 5-7 years.

The amount you save as well as the length of your payback period also depends on the federal tax incentive, your state’s incentives, solar renewable energy certificates, and how you manage your finances, says Colvin.

Should every home have solar panels?

It’s up to you and where you live.

States in the South and Southwest, such as New Mexico and California, are usually best for solar energy, but going solar can make sense in other regions of the U.S., too, says Burdick. You can find out your home’s sun exposure through the NREL’s online system, or ask a solar installation company to tell you.

Georgia State University’s Heutel says most people do not install solar in their homes because they do not live in a sunny location, there is a large upfront investment, and a slow gradual payback period.

“There’s thousands and thousands of people who are putting solar panels on their home in the United States, so they seem to think it’s a good idea, but yet there’s still millions and millions of people like me who don’t have solar panels,” says Heutel.

About the Author

Taylor is a science journalist who likes writing about health and technology. During her undergrad, she worked in labs that ranged from horseshoe crabs to studying breast cancer but later realized she enjoyed communicating science more than actually doing it. Her work has been published in Dana-Farber Cancer Institute and NOVA WGBH.

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