Calculate how many solar panels you need on your home

Calculate how many solar panels you need on your home

Calculating how many solar panels you need to power your home?

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One of the first things you will want to work out when considering a solar panel installation for your home is how many solar panels it will take to power your home.

If your utility offers net metering (utilities in approximately 35 States offer net metering or a similar feed in tariff scheme) it is relatively easy to calculate how many solar panels you need to run your home because you can aim to install a size solar array that will give you energy production matching your energy usage over 12 months.


net metering

Why does net metering make it easy to calculate how many solar panels you need to power your home?

Net metering allows you to ignore the fact that the kWh per month produced by solar panels will vary over the year and that you will need to use kilowatt hours of utility power at night when your solar panels aren't working. Net metering provides a full "one for one" credit for excess solar power produced and exported to the utility grid at any time making it easy to design a solar system. You just have to make sure that you design a system size that produces the same total number of kilowatt hours of power as what you use each year.

You can get your total annual kilowatt hours (kWh) of usage from your power bills. Alternatively solar panel kWh production calculators like the one on this site can also estimate your annual usage from your address and the cost of your last month's power bill because they have a database of the electric rates charged by your utility company and can reverse engineer the kilowatt hours of usage from the amount you paid.

Most solar panel cost and savings calculators will assume that you want to install a system that will produce the same amount of power as what you use. Some solar panels calculators default to assume that you want to eliminate your electricity bill completely rather than to cover just your usage. In practice the difference shouldn't be large.

How does your roof affect how many solar panels can be installed?

The number of solar panels installed will be limited by the square footage of available roof space. If you have limited suitable roof space then this might be a reason to look at more efficient panels. A more efficient solar panel can have a higher panel wattage in a smaller physical space.

how roof affects number of solar panels
map marker los angeles

How does your location affect the number of solar panels needed to power a home?

The reason we need to know your location is that solar panels produce different amounts of power depending on the location where they are installed. The electricity produced by solar panels is measured in kilowatt hours per day or per year. This figure is usually quoted as the number of kilowatt hours produced daily or annually per 1 kW of DC peak solar power capacity installed.

This figure varies from a low of 3 kWh per day per 1 kW of peak DC solar panels in some areas of the North East and around the Great Lakes up to highs of 4.7 kWh per day in parts of Southern California, Arizona, Utah, New Mexico and Nevada. To annualize these numbers we get a range between 1095 kWh per year per 1 kW of solar panels up to a high of 1715 kWh per year per kilowatt in areas with the greatest solar irradiation. This obviously makes a big difference to the amount of solar panels you need to produce a specific amount of electricity and this is why we need to know your location to do these calculations.

How does your utility company affect the number of solar panels required?

It is important that we know which utility you are with because we have the residential electricity rates for each of the utility companies in our database and this means if you tell us your average monthly bill we can work out how many kilowatt hours of power you need your solar panels to produce.

utility power lines

What size solar system do I need for my home?