How Do Solar Panels Work

Solar panels capture the sun's energy and convert it to electricity for your home. Photovoltaic (PV) cells are chained together to form the solar panels you see on rooftops. As the sun shines on the solar panel, each photovoltaic cell absorbs photons from the sunlight, producing an electrical current across the solar panel layers. Solar panels can be used individually, or you can link several together into a solar array, depending on your energy needs.

A solar panel is made up of numerous photovoltaic cells linked together. The panel is encased in glass with an anti-reflective coating that ensures that the solar panels get the most sun exposure possible. Under the glass, there is insulation that protects the components from humidity and regulates the temperature inside the panel to keep it operating efficiently.

Photovoltaic cells are made of two layers of silicone. The top layer is treated with phosphorus to create a negative charge, while the bottom layer is treated with boron to create a positive charge. When the two layers are placed together, an electric field is created in the space between the positive and negative layers.

Light strikes the panel, causing energy to be transferred to the semi-conductor material which releases electrons.

The electric field in the cell forces the electrons to flow in one direction, creating an electrical current. Thin metal plates on the sides of each cell collect the energy and transfers it to wiring which feeds the DC current into a power inverter.

There are three types of solar cells: monocrystalline, polycrystalline or amorphous.

• Monocrystalline cells are comprised of a uniform silicone crystal. They’re made from a large silicon block cut into wafers and attached to panels. These are higher-efficiency panels, but require the most labor to produce, making them expensive to manufacture—and buy.
• Polycrystalline cells are made up of different silicone fragments, made by melting silicon crystals and fusing them together into the panels. They are also less efficient than monocrystalline cells and work best in climates with a lot of sun, but come at a significantly lower cost. Amorphous cells are made from thin, light flexible sheets of photovoltaic film. In a panel, these cells can be combined to increase their power output. A budget-friendly option, polycrystalline solar panels are not as efficient as monocrystalline panels, but they’re more efficient than amorphous silicon.
• Amorphous solar panels are lighter and easier to work with and perform better in areas that get less direct sunlight. They are the most versatile solar cell, making them ideal for thin film solar panels. These cells are made by applying a thin layer of amorphous silicon on a substrate of glass, plastic or metal foil, which is then deposited onto a flexible surface. This method of construction makes amorphous silicon solar panels the most cost-effective. While the technology is advancing rapidly, currently they are more expensive than mono- and polycrystalline solar cells and are less durable than either.

A residential solar array requires a solar power inverter to convert the DC electricity (direct current) produced by the solar energy from the panels into AC electricity (alternating current) used by the electrical grid. The two different types of solar inverters for a residential solar energy system are string and microinverters.

• String inverters are a cost-effective option because multiple panels are strung together into one solar inverter. The drawback is if one PV panel in your system is damaged, it will negatively affect the electrical output of the whole system.
• Microinverters are a larger investment than string inverters because they are placed on every PV panel in a solar panel system. Damage to one panel does not affect the total electrical output of the whole solar array.

Many variables affect how much solar energy your solar panel system collects and uses each day. Temperature, light wavelength and reflection all affect the ability of a photovoltaic cell to absorb solar energy. If your solar panel system is not producing as much solar energy as your home is using, a solar battery will make up the difference.

If you tie your system to the local utility grid, then the local utility acts as your solar PV system battery storage. But even those who are connected to the local grid may choose to use batteries, too. Here are some of the most common reasons homeowners want a solar battery bank:

• There's no local utility grid to tie into. If you live in a location with no access to a public utility, a solar battery bank will be your backup power source, so it should be large enough to store several days’ worth of solar energy.
• Greater energy independence. Even if you tie into a public utility, having a solar battery backup gives you greater independence from the grid—and a safety net for an emergency.
• Compensation for power outages. If you need a consistent and dependable supply of power that you can't get from the public utility because of frequent power outages, a solar battery will keep your power on even if the grid is out.
• Battery power during peak times. During peak times, local utilities charge a higher rate for energy. With a solar battery, you can use your stored solar energy during those times and save money.

Many people question how solar panels work at night, since they obviously no longer have light to generate power. In reality, solar panels don't work at night. In order to work at night, they must utilize solar batteries to store energy. Or, if your home is tied into the local utility electrical grid, you'll use that energy to power your home when the sun sets.

Solar battery backups allow you to use solar energy even at night. The solar batteries charge during peak solar times, when the sun is at its highest. Once the sun sets, the electricity in the battery storage will power your home until the sun rises and you can draw electricity from the solar panels again.

The home electrical panel is fed by the energy converted by the inverter. However, neither the solar panels nor the inverter have an inherent means of storage. This is why it is necessary to utilize high-capacity, deep-cycle solar batteries as a part of an effective solar energy system.

Deep-cycle batteries are used to store power from the solar panels. During the day, any extra power produced is used to charge the solar battery. Most solar batteries have their own inverters and can store the DC power as AC.
At night, the battery sends the stored energy back into your electrical system to power the home electrical panel while the solar panels are not generating energy.

The type of battery you need for your home solar system depends on a wide range of factors, including how much you want to invest, how much electricity you need to store, how important green factors are to you, and how much space you have to store the batteries. The five most common types of batteries for residential solar panels are:

• Flooded lead-acid batteries: These are best for medium to high off-grid use. Similar in size to a car's battery, a full bank may take up a large amount of space. The charging time is slow—it can take a day or more to get a full charge. Flooded batteries are budget-friendly solar batteries that last from four to eight years. They require significant maintenance and safety precautions for safe handling.
• Gelled electrolyte sealed lead-acid batteries last about five years and are maintenance-free. Charge time is several hours instead of days, and the cost is only slightly more than flooded batteries.
• Sealed absorbed glass mat lead-acid batteries charge up to five times faster than flooded batteries and last four to seven years. They are less expensive than gel cells and maintenance-free. Use caution when handling any lead-acid battery, since they’re toxic.
• Lithium-ion is the most common battery for solar energy storage today. Its larger initial investment is offset by long-term savings. Lithium-ion batteries are smaller than the other types—a home lithium battery storage system is the size of a washing machine. Lithium-ion batteries charge in about three hours, last up to ten years, are maintenance-free, and some are made with organic, toxin-free materials.
• Flow batteries are ideal for storing large amounts of solar energy. They’re the most environmentally friendly option, and advances in technology may lower the cost in the future. The lifespan of flow batteries is around 25 years, and they’re safe to handle and require little maintenance.

It’s no surprise that the long-term savings of a solar panel system outweighs the initial cost. How much you enjoy in solar savings may vary from $10,000 to $30,000 over 20 years. Some of the most important factors that determine how much you’ll save include:

• Where you live: The amount of direct sunlight your solar array receives during the day makes a big difference—as does the size and slope of your roof.
• Cost of utility electricity: The cost of electricity from the utility grid varies greatly from state to state, but there is a consistent annual increase of about two percent in electrical utility cost.
• How much electricity you use: One reason many people invest in solar energy is to get credit on their electricity bill. If your solar array produces more energy than you use, the excess solar electricity is transferred to your local utility grid. This is called net metering. The utility may even pay you for your electricity if the net metering shows you produce significantly more of it than you use.

A solar-powered home is usually still connected to the municipal power grid. Net meters send any excess energy that your solar panels produce – after your solar batteries are fully charged – back into the municipal electrical system. The power company then issues you credit on your electric bill. In effect, they are paying you for the extra power your solar panels generate. In times of low production from your solar panels – night time or extended periods of inclement weather – you can use energy from the municipal grid; your credits offset your energy costs.

When you invest in a solar panel system, money isn't the only thing you’ll save. According to a study by the University of California at Berkeley, a residential solar system can power an entire home with a carbon emission that’s about 80 percent lower than that of fossil fuels.

Using a renewable energy source like solar power reduces your greenhouse gas emissions, significantly reducing your carbon footprint. A small residential solar system can reduce carbon emissions by about 4.7 metric tons—the equivalent of taking a car off the road for a year.

If you think it’s time to take the next step and invest in renewable energy for stellar solar savings, schedule a consultation for solar panel installation with the experts at Home Depot. We have everything you need to start powering your home with renewable energy, from solar panel kits to solar power accessories—and we deliver all online orders for free, where and when you need them.