As long as the sun is shining, solar cells are absorbing the sun’s energy. Solar panels are designed to convert electromagnetic radiation from the sun into usable direct-current energy. Solar panel system installation also includes electrical equipment, inverters and control circuitry that produce alternating-current power. With a net metering or a solar battery, you can store electricity for later to power your systems and devices like normal.
What are solar panels?
The easy definition of a solar panel is a grid of silicon, glass and wires that converts sunlight into electrical energy.
Photovoltaic (PV) cells make up the most basic component of solar panels. A panel is made from a group of interconnected PV cells. A collection of panels, also called modules, make up a solar array.
A PV cell is approximately 6 inches long by 6 inches wide and squarish and looks like a small reflective window. The number of photovoltaic cells needed for an array depends on the size of the module. For example, a 12-volt module has 36 cells connected in a grid, while a 24-volt module has 72 cells.
Each cell contains layers of oppositely charged semiconductive materials. Traditional solar cells are made from silicon — the second-most abundant element on Earth, after oxygen.
Solar electric technology employs crystalline silicon as a semiconducting material. In residential solar panels, this material is most typically monocrystalline or polycrystalline silicon. Monocrystalline panels are made from single-crystal silicon and have a uniform dark appearance with rounded edges. Polycrystalline panels are made from multicrystalline silicon and have a speckled blue look with square edges.
A solar panel’s efficiency is largely determined by the purity of silicon in its cells. Monocrystalline is more pure, so it can generate more solar power with less space than polycrystalline cells. There are different types of solar modules, such as those with amorphous silicon or thin-film solar cells, but they're not generally considered suitable for home installation.
How do solar panels work?
The sun is like a natural nuclear reactor, always releasing energy in the form of tiny particles of electromagnetic radiation called photons. Solar panels generate power through the photovoltaic effect, a physical and chemical phenomenon that converts energy from the sun into usable electricity. When sunlight comes in contact with a module, the solar cells absorb light energy (photons).
Put simply, solar panels work by converting solar energy into a direct current, which is converted into the alternating current that powers your home.
- Solar cells absorb photons: Think of photons as tiny particles of light from the sun. A photon knocks an electron loose and creates a “hole” in the solar cell. The negatively charged electron and the location of the positively charged hole are now free to move around.
Thin metal “fingers” at the top of the cell help catch loose electrons. When a photon hits a solar cell, it triggers a pair of positive and negative charges that results in voltage and electrical current. In silicon cells, atoms quickly separate as electrons join the flow of a current.
- Solar panels generate current: Solar cells convert photons into a direct current (DC). Each solar cell consists of crystalline silicon sandwiched between a positive and negative conductive layer. The negative layer has extra electrons, while the positive layer has extra space for holes. Electrons are free to wander across the junction where the two layers meet, which leaves a positive charge on one side and a negative charge on the other.
Each cell only puts out about half a volt, which is why they must be strung together in modules to power a house. For reference, it takes 12 photovoltaic cells to charge a cell phone and several modules (dozens or even hundreds of individual cells) to power an entire house.
Solar panels generate currents more efficiently with an expanded range of convertible wavelengths. New solar power technology advances could lift the ceiling on maximum silicon solar cell efficiencies, according to Chemical & Engineering News.
- Inverter changes DC to AC: Solar cells are not capable of powering a home on their own — an inverter is required to convert the currents they produce into usable electricity. The power that comes out of the panel is a direct current (DC). An inverter transforms DC electricity into alternating current (AC) energy, during which a small amount of power is lost.
Solar power systems typically have a single inverter for the entire system or a microinverter connected to each panel. Either way, the purpose of the inverter is to convert DC power to AC power.
- Converted electricity is available: From the inverter, AC electricity flows to an external circuit and, eventually, through your home. You can use the solar-generated electricity to power light switches, appliances, televisions and the rest of your home electrical systems. Sometimes, solar panels produce more power than you and your family need. When this happens, electricity can be stored in a battery bank or sold back to the grid.
- Sell or store extra energy: You can store excess energy with a solar battery or sell it back to your local utility company through a net metering program. If you prefer that your system be off the grid, you should consider investing in a solar storage battery. This gives you 24/7 access to power, even on cloudy days when solar panels generate electricity less efficiently. If the initial installation cost isn’t an issue, storage batteries are probably a better choice.
With net metering, a utility company pays you for generating electricity. Depending on your local utility company’s program, you might get bill credits for the surplus power your panels send into the grid. Power production credits help save on bills, but you won’t get cash for supplying electricity to the grid.
How solar panels are made
The main ingredient in solar panels is silicon, which comes from sand. Once the sand is extracted from quarries, it must be processed and purified. To separate the pure silicon crystals, the sand is heated to more than 3,600 degrees Fahrenheit.
Because silicon is not a good natural conductor, a process called “doping” intentionally adds impurities — usually boron, which bonds with the silicon to create a positive charge, and phosphorus, which combines to create a negative charge. The crystalline silicon is then melted into ingots and thinly sliced into panel-sized sheets called wafers.
Silicon is naturally shiny, so it must be treated with an anti-reflective coating to minimize energy waste. An anti-reflective coating, such as titanium dioxide, is painted on and baked into place. High-tech computers then spray a layer of semi-liquid metal onto the panels, which helps get the energy from the panel to your plugs and into the appliances you need to power.
This manufacturing process is used for more than making silicon solar cells. Silicon wafers are also used to fabricate integrated circuits and make computer microchips. While photovoltaic cell panels are a smart option for environmentally conscious homeowners, the process to make them is not entirely green since they require fossil fuels to manufacture.
Some solar cells include a perovskite compound, such as a hybrid organic-inorganic lead, instead of silicon as the light-harvesting active layer. According to research from the Solar Energy Technologies Office, perovskite cells are more efficient, cheaper to produce and easier to manufacture.
Solar cells on space satellites use thin-film technologies with cadmium telluride and amorphous silicon. It’s the grouping of these cells into a grid that makes up a panel with the ability to absorb sunlight and facilitate renewable energy production.
How long do solar panels last?
Solar panels are surprisingly durable — they can last up to 25 years or more with little to no maintenance. Electrons are the only moving part in a solar cell, and they all go back where they came from. In order to maintain optimum output, though, you’ll want to regularly clean your solar panels and have any damaged panels replaced.
Most solar panel manufacturers predict a degradation rate of about 0.8% every year. After 20 years, solar energy production should be around 84% of the efficiency standard. Typically, residential panels come with a performance warranty that lasts between 10 and 25 years, which may not cover the full life span of your system.
Some crystalline panels have been known to function at relatively high efficiency for 40 years. Panels can even withstand wind speeds of up to 140 miles per hour, according to EnergySage. Coverage for solar panels is also included in most homeowners insurance policies to protect against damages.
Solar PV inverters and batteries don’t last as long. It’s likely that you will have to replace both within your system’s life span. Solar PV inverters can last anywhere from 10 to 15 years. You can expect a good solar battery to last between eight and 15 years.
Like panels, battery and inverter performance can also decline over time. As you compare solar equipment, look for brands that include a warranty and performance guarantee.
Solar panel questions
- Do solar panels save money?
- Yes, solar panels save money. Most Americans who install PV panels save between $1,000 and $2,000 per year on electric bills. To figure out how much money solar panels can save you, you need to consider your average monthly utility bill and the total cost of equipping your home to run on solar energy.
EnergySage projects the average 20-year savings for a home in Washington (a state with above-average cloud cover) at around $10,000, while savings for California homes are closer to $30,000.
PV panel installation typically pays for itself within five to 10 years. The National Renewable Energy Laboratory expects solar panel costs to continue decreasing through 2030, thanks to market maturation, product innovation, business model integration and economies of scale.
- Can you build your own solar panels?
- No, most people can’t build their own solar panels. The technology and manufacturing process are too complicated.
- Why is DC current produced from solar panels?
- Solar panels produce direct-current (DC) electricity when photons from the sun knock loose electronics in the silicon PV cell. Like regular household batteries, each solar cell has a positive layer and a negative layer. This creates a DC electric field, meaning the flow in the circuit moves in one direction. Since most homes are wired for AC electricity, an inverter is needed to convert a DC current into usable power.
- Do solar panels work at night?
- Solar modules require sunlight to generate electricity, but your system can still provide power while it’s dark. With a storage battery, excess energy during the day is stored for later use, so you can still run on solar energy when your panels aren’t producing electricity. If your rooftop solar panels aren’t producing enough power to meet your electricity needs, you can still source power from the grid too.
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