Determining how many solar panels a house needs

A typical home needs 18-26 solar panels to cover 100% of its electricity usage. While there are many elements you can analyze to determine the ideal size of your future system, these four are most worth your time.

• Your household energy consumption
• Peak sun hours for your area
• Output of each solar panel
• Your solar goals

Here's a deeper look at each of these elements.

Energy consumption

When people begin thinking about home solar, the questions they ask are often similar:

• " How much energy does a solar panel produce?"
• “How many solar panels can I fit on my roof?"
• "How large of a solar system do I need?"
• "How many panels are needed to power a house?"

When determining the number of panels you need, it boils down to one factor: The amount of energy you use (or plan to use) in your home.

To figure out the right number of solar panels for your house, you should first determine how much electricity you use during an average month. Start with your last 12 monthly electric bills, add up your total usage in kilowatt-hours (kWhs) and divide by 12.

Peak sunlight hours

Solar panels rely on direct sunlight to generate electricity. Peak sun hours, a measure of the intensity and duration of sunlight a location receives, tells you how much sun they receive.

Where you live is a factor in how much energy your solar panels will produce in a day. For example, the American southwest regularly receives well over six peak sun hours a day, while the American northwest gets closer to four.

The best way to learn the amount of sustained sunlight your area receives is to speak with a solar energy system expert, like the ones at Palmetto. You can also consult the U.S. State Solar Resource Map from the National Renewable Energy Laboratory.

Credit: NREL

Solar panel output

Different solar panels have different electricity generation capabilities. Their output might vary depending on their efficiency or the number of solar cells they contain.

Your solar goals

People switch to solar for different reasons. Some want to save money on electricity bills, others want security through power outages, and others want to minimize their carbon footprint and use clean, renewable energy. Those are all good considerations to help you determine the number of panels to achieve your desired power output.

Let’s consider three common options:

• Depending on your utility’s net metering, the number of solar panels that maximize your savings may vary.
• If avoiding power outages is your goal, a good solar battery storage system will ensure you store enough electricity to use when needed.
• If you want to use solar to help the planet, you will need enough solar panels to produce 100% of your electricity needs.

How can I calculate the number of solar panels I need?

Palmetto has a solar savings calculator to help customers estimate the size of the solar energy system they need and their potential energy savings.

Alternatively, you can use a formula to determine the system size you need to power your house:

(Monthly electricity usage / Monthly peak sun hours) x 1,000 / Solar panel wattage = Number of solar panels

Determine your energy consumption

Total the last 12 months of usage from your electricity bills and divide by 12 to get your home's monthly average. We’ll use 1,200 kWh per month as an example.

Determine how much sunlight you receive in your area

You need to know the peak sun hours your area receives. Keep in mind, average daily peak sun hours aren’t merely the hours when the sun is in the sky. They’re a measure of sunlight intensity over time.

Plug consumption and peak sun hours into the formula

1,200 kWh / (7.42 × 30) = 5.4 kW solar system

Convert kW to total watts

Since 1 kW equals 1,000 watts, we will multiply 5.4 kW by 1,000:

5.4 × 1,000 = 5,400 watts

Determine the generation capacity of your potential solar panels

Different solar panel designs have different power generation capacities. 400 W panels are a common size installed by Palmetto

Divide the total watts above by the wattage output of a single solar panel to determine how many solar panels you will need:

5,400 / 400 = 13.5 solar panels needed to cover total electricity usage.

The number of solar panels you need depends on you

Besides the raw number of panels that will cover your electricity consumption, there are other factors that might affect the number of solar panels you can actually install.

How many solar panels do I need for my roof design?

The design of your roof determines how the solar panels will be installed, and how much sunlight they will get. If your roof is well-angled and features enough usable roof space, it can accommodate more panels. If there is only a small available area, you’ll be limited to a smaller number of panels.

How many solar panels do I need for home appliances?

Credit: US EIA

To track the energy usage for individual appliances, you can install a home energy monitor or smart plug between the outlet and the appliance. Leave the usage monitor on for a week.

How many solar panels do I need if I have a lot of trees?

Like anything that blocks the sun from your panels, the beautiful trees around your home can impact how much solar energy your solar panels generate.

How many solar panels do I need for my future energy plans?

Is your electricity consumption likely to increase in the coming years? When assessing your solar panel requirements, think about any big changes in your electricity usage that might develop.

Frequently asked questions

How many solar panels do I need to power my home?

This answer starts with knowing your current and projected electricity usage.

How many solar panels can I put on my roof?

You can put as many solar panels on your roof as will fit. This means having the right size while meeting your budget and your family’s needs.