Solar panels are made up of photovoltaic (PV) cells made of silicon. When the sun’s rays hit them, these cells convert sunlight to electricity. Individual cells are wired together to form a solar panel. Panels are typically three feet by five feet. They are coated in tempered glass, which allows them to withstand harsh weather.

The electricity produced by a single solar panel is not enough to power a home or business, so multiple solar panels are needed. The number of panels varies by installation, but every solar system (also called an “array”) will include a series of panels mounted and wired together. This array may be installed on a roof (“rooftop solar”) or on the ground-level (“ground-mounted solar”).

The electricity generated by solar panels takes the form of direct current (DC). However, most appliances and electricity-consuming objects (called “electric load”) require alternating current (AC). To convert the solar electricity from DC to AC, an inverter is needed. You will need to choose between two types of inverters: a central inverter and microinverters. While both perform the task of converting electricity from DC to AC, they differ in critical ways.

A central inverter receives all of the electrical output of your entire solar system and converts it from DC to AC at a single, central location. A single central inverter is required for a solar system. It is often mounted on the side of your home or building next to your electric meter. Central inverters are steadfast and affordable, but they are susceptible to variations in panel performance. If one panel is shaded and produces less electricity than the others, the total electrical output will drop.

If shading is of concern, microinverters or DC optimizers can help maximize production. Unlike central inverters, microinverters and DC optimizers individually mount to the backside of each individual solar panel.  They capture the electricity that flows off of each panel. DC optimizers work with a central inverter that converts DC to AC. Microinverters convert DC immediately to AC right under the panel. With either DC optimizers or microinverters, if one panel is shaded, it will not affect the output of the whole array. By design, both DC optimizers and microinverters help maximize the conversion of electricity and are useful in situations with variable shading. What’s more, because they allow each panel to operate independently of one another, both make it easy to add more panels to a solar array in the future.

Once electricity is produced by the solar panels and converted from DC to AC by the inverter(s), it will flow through your electric meter and into your home or building. It will be used on site the moment it is created. Any excess will flow back out through your electric meter and onto the local grid.

Think of your solar array as a 25-year investment. Solar panels will produce electricity for at least 25 years. (See “Do systems come with warranties?” question for information on the warranties you’ll receive with your system) Panels will continue to generate electricity after 25 years, but at a decreasing rate. While microinverters will likely last for the duration of the PV system, you may need to replace central inverters after 15 years.

The size of your optimal solar array will be influenced by many variables. Before analyzing those variables, you should understand how solar is sized and measured.  The electrical capacity of solar panels is measured in watts (W). The typical solar panel is rated at 250-300 W. To get the total power (in watts) of your solar array, add together the wattages of each panel. Let’s say you had 10 300 W panels installed. The total wattage of your system would equal 3,000 W. 1,000 W is equal to 1 kilowatt (kW), so another way to describe the size of that system would be 3 kW. The average size of a solar array is 5 kW.

Your installer will estimate how many panels can fit on your roof given its footprint and shade susceptibility to determine the ideal size of your system. If the size of your roof is limited (meaning fewer panels can be installed), installers can compensate by offering high-efficiency panels. These panels will have a higher power rating (typically 300-350 W), and therefore will produce more electricity per panel. Installers will also use geospatial data to determine the optimal system size for your property, as roof orientation and climate factors will affect how much electricity your system produces. The final factor that will influence the size of your solar array is your project budget. Installers work closely with clients to maximize the amount of solar they install for the customer’s budget.

While sizing your solar array, installers will consider how much the solar electrical output will offset your electricity needs. While the power capacity of solar panels is measured in watts (or kilowatts), the amount of electricity produced by the panels is measured in watt-hours (or kilowatt-hours).

You may recognize the term kilowatt-hour (kWh) from your electric bill. Utilities charge their customers based on how many kWh of electricity they consume each month. If you look at your utility bill from any billing cycle, you’ll be able to see exactly how many kWh of electricity your home or building consumed that month.  Each kW of solar you install will produce a certain number of kWh, which will directly offset your utility electricity consumption. The kW-to-kWh relationship varies with latitude and climate. Your installer will be able to accurately predict how many kWh of electricity your solar panels will produce each year.

To estimate how much solar you can install on your roof (and how much electricity it will produce each year), we recommend using the PV Watts tool. To get a sense of how much your solar will offset your electricity needs, divide the annual kWh production estimate by your annual kWh consumption of utility electricity (the sum of 12 monthly bills). View tutorial.

You will earn credit for the solar electricity you generate through a policy called net metering. Net metering allows you to offset your utility electricity consumption with the solar electricity your array produces. When your system generates electricity, that electricity flows into your home or building and is consumed on-site. When your solar panels produce more electricity than your home or building needs, the excess electricity is sent out to the local grid, where it is consumed by your neighbors. Through net metering, you receive full credit for the excess electricity you feed onto the grid. Once you install solar, your monthly electric bill will be calculated to reflect: the total amount of electricity you consumed minus the total amount of electricity you produced (i.e., the solar electricity you fed onto the grid).

It is common for solar arrays to produce surplus electricity during certain times of the day, months, or seasons. Consider, for example, a sunny summer day. Your panels will produce a high volume of solar electricity during the day, but you are likely away from home and not consuming any of that electricity. In that case, the solar surplus will flow back out to the grid. Net metering enables you to receive credit for these seasonal or daily surpluses. Your utility will then apply those credits to your monthly bill, covering the electricity you purchase at night or during periods of low solar production. Should you have excess credit at the end of a billing cycle, you’ll be able to roll it over to the next month.

By allowing you to offset your utility electricity consumption with your solar electricity production, net metering helps you reap the full financial value of your solar array. Most states have passed laws enabling net metering.  If you live in a state with net metering legislation, you are guaranteed the right to net metering, regardless of where you live or who your utility company is. Learn more about state-specific net metering laws.