Trying to calculate which solar panel you need for a solar power system can be an intimidating process, starting with the amount of power you'll receive from each panel. No homeowner wants to invest time and money in a solar array and not get the electrical power they thought they were going to get.

What sizes do solar panels come in?

A typical silicon photovoltaic panel used in rooftop arrays is about 5.4 feet by 3.25 feet, or 95 inches tall by 39 inches wide. There may be a slight variation in size depending on manufacturer, but the differences are negligible. Custom panels and those manufactured for larger, commercial installations typically produce panels that are about 6 feet in length.

Most standard residential solar panels contain 60 square solar photovoltaic (PV) cells, each of which is a standard 6 square inches (156 square millimeters). No matter how large your array is, all the solar cells will be linked to each other by wires, which carry the electricity from the cells to a junction box and then on to an inverter. The more cells, and there for the more panels, working in tandem, the more energy they produce.

When choosing solar panels, it's important to compare reviews from fellow consumers and examine the best solar options for your area and your needs.

How many solar panels do I need for a 2,000 square foot home?

The average home in the United States is about 2,000 square feet in size. The average home will use about 800 kWh of power per month or 9,600 kWh per year.

The amount of solar panels needed to cover this amount of electricity use varies by the state and city because solar irradiance varies with geography. Our solar calculator shows how many solar panels you need to power the average home in each state of America.

A home that size would require between 14 and 18 panels to provide about 80 percent of your electrical needs. Of course, an estimate on the number of panels you'd need for your own home depends on another, entirely different formula:

  • The number of kilowatt-hours (kWh) used every month.

  • The amount of electrical power you want to offset with solar power.

  • The state you live in determines the hours of sunshine you receive.

There are two solar panel calculators available that will make the process of determining the number of panels you need much easier. Many solar consumers find it helpful to start out with some basic information before allowing the calculators do all the work.

How much power can I expect to get from a 300-watt solar panel?

The amount of electricity produced by a solar panel depends on the size of the panel, the amount of sunlight the panel gets, and the efficiency of the solar cells inside the panel. For example, if a 300-watt (0.3kW) solar panel in full sunshine actively generates power for one hour, it will have generated 300 watt-hours (0.3kWh) of electricity. That same 300-watt panel produces 240 volts, which equals 1.25 Amps.

Unfortunately, solar panels don't generate a steady stream of electricity all day. They generate less power when the sun is low in the sky (mornings and evenings) or when clouds are moving across the rooftop. Wattages are assigned according to each panel's peak capacity for generating energy - usually during afternoon hours of direct sunlight under perfect weather conditions. This capacity level is also referred to as watts peak (Wp).

The best way to determine the correct amount of energy a panel or system will deliver on an average day is to take advantage of the professionals in your area and the online tools such as calculators that are available to you.

What factors influence a solar panel's output?

Taking note of these elements will help you to make smart decisions when choosing a panel. The type of panel you choose will affect efficiency. Monocrystalline, polycrystalline, and thin-film solar panels all provide different levels of efficiency.

  • Shade of any type, from cloudy days to overhanging tree branches, can wreak havoc with the output of solar panels. Because the cells are linked together, shade on one cell can affect the efficiency of all the others.

  • In this country, all non-tracking solar systems should face true south for the best exposure to sunlight. And the angle or pitch of the rack holding the panels should be calibrated according to the latitude of your location.

  • The high temperatures normally found on rooftops can adversely affect the output of a solar panel. The best way to combat that is to choose photovoltaic panels designed for your climate and install a mounting system that sits several inches above the roof.

Most residential solar panels on the market feature output ratings ranging up to 400 watts, which makes a 300-watt solar panel close to the top range, power wise. If 300-watts is the solar panel you have your eye on, do some in-depth research, talk to the experts, and enjoy your new solar power system.