How Many Solar Panels Do You Need? | Comprehensive Solar Calculator

Most homeowners need between 15 and 19 solar panels to cover their power needs. But how do you calculate the number of panels necessary to run your specific home? Solar expert Ben Zientara breaks down the calculations in the video below, or you can read on to find out how to estimate the amount of solar panels that are right for you. 

Step-by-step guide: how to calculate how many solar panels you need

Let’s take a closer look at where you can find this information and how to use it to determine what solar system size is right for you in four easy steps!

Step 1: Find out how much electricity you use

Check your most recent power bill to see your monthly electricity consumption. The total amount of electricity used is usually shown at the bottom of the bill in kilowatt-hours (kWh).

Your electricity usage is the biggest deciding factor in how many solar panels you need. If you use a lot of electricity, you’ll need more panels to cover the costs!

According to the U.S. Energy Information Administration, an average home in America uses about 886 kWh of electricity each month. That’s a monthly electric bill of about $135.

Remember that electricity usage can vary widely depending on your home, your habits, and where you live, so it’s essential to check your electricity bills to get the most accurate estimate possible!

Step 2: See how much sunlight your home gets

The amount of sunshine that hits your roof also plays a vital role in how many solar panels you need. Solar energy production is higher in sunnier states, meaning you’ll need to install fewer solar panels than those in overcast states.

How much sunlight an area gets is measured in peak sun hours. Sunny states like Arizona can get up to 210 peak sun hours monthly, while somewhere with more cloudy days, like Alaska, will only get 90 peak sun hours a month. The following map outlines the estimated monthly peak sun hours each state receives.

Step 3: Determine what solar panel system size you need

Now that you know your electricity usage and sun exposure, you can calculate the size of the solar system you need in kilowatts (kW). Simply divide your household electricity consumption by the monthly peak sun hours to find the right system size for your home.

Step 4: Calculate how many solar panels you need

Finally, you can divide the system size by the power output of a solar panel to find out how many solar panels you need. The higher a solar panel’s power output, the fewer panels you need to install.

Most solar panels produce about 2 kWh of energy per day and have a wattage of around 400 watts (0.4 kW).

If you’re interested in a specific solar panel model, you can find its wattage on its datasheet, where it will usually be labeled as maximum power, rated power, nominal power, or “Pmax”.

Remember, for this calculation, you need to convert a panel’s power rating from watts to kilowatts by dividing the wattage by 1,000.

Factors that determine how many solar panels you need

Many things can impact the right number of solar panels for you, from your energy habits and roof characteristics to environmental factors and your personal solar goals and budget.

Electricity usage

How much electricity you use has the biggest impact on how many solar panels you need. If you use a lot of electricity, you’ll need a lot of solar panels!

There are plenty of factors that impact your energy use. Energy consumption can vary with the size of your family, how energy-efficient your home is, the appliances you use, and the state you live in.

For example, a home with an electric stove, water heater, and clothes dryer will have a higher electricity bill than a home with gas appliances! Homes that utilize smart thermostats or have energy-efficient appliances may use less energy. 

Solar panel wattage

Higher-wattage solar panels can produce more energy than lower-wattage solar panels. So, if you opt for a high-wattage panel, you can install fewer!  The following table outlines how many solar panels you would need to cover an average household’s electricity usage, depending on the wattage of the panel:

Sun exposure and climate

Solar panels need sunlight to generate electricity. If you live somewhere with lots of sunshine, you can install fewer solar panels to cover your electricity bills. 

For example, one 400-watt solar panel in Arizona can produce almost 90 kWh of electricity in one month. That same panel could only generate 36 kWh in Alaska.

Shading

If your panels get shaded at any point of the day, they will produce less electricity. Depending on the design of your solar system, shading one panel could impact an entire string of them!

So, you may need to install a few more panels on a shady roof or cut down overhanging trees to ensure your solar panel system can produce the most electricity possible.

Roof angle and direction

Solar panels operate best on south-facing roofs at an angle between 30 and 45 degrees. This orientation maximizes the amount of sun exposure panels can get.  

If your roof faces north, you can still install solar, but the panels will generate less energy. Solar panels on north-facing roofs produce about 30% less electricity than those installed on south-facing roofs. So, if you install solar on the north side of your roof, you’ll probably need to install more panels.

Roof size

The size of your roof may limit how many solar panels you can install. A typical solar installation will need a minimum of 335 square feet of suitable roof space. For reference, an average roof is 1,700 square feet. 

If your roof can’t fit all the solar panels you need - that’s okay! You can install fewer panels that do fit on your roof, but the system will only cover a portion of your electricity needs. Those with smaller roofs, like a tiny home with solar panels, for example, should also consider high-efficiency solar panels, which can generate more electricity in a smaller space.

The following table outlines how much roof space is needed for different amounts of solar panels:

*Assumes 400-watt panels

Roof characteristics 

Some roofs have obstructions, such as chimneys, vents, dormers, or skylights, that can limit the number of solar panels that can be installed. If you have any of these features on your roof, it may complicate your solar system design and reduce the number of panels that can be installed.  

Solar panel cost and budget considerations

A typical solar panel system costs about $20,000 before any incentives are considered. Once the solar tax credit is taken into account, the cost of solar drops to $14,000. The upfront cost of solar panels might not be in your budget, but there are some options if you need a cheaper solar panel system. 

One option is to install fewer solar panels and only cover a portion of your electricity bills. While you won’t eliminate all of your energy bills, you can cut down a decent chunk. There may also be solar incentives and rebates in your area that bring solar panel prices down!

You can also finance solar panels, which eliminates the burden of upfront costs, and instead allows you to pay for solar through monthly payments that better suit your lifestyle. 

Utility rules and regulations

Powering your home with solar panels requires working with your utility company to ensure that the panels are working safely and that you are getting compensated for the energy you use. 

Every utility company bills solar customers differently, which can impact the number of solar panels you should install. 

For instance, some companies may not provide full credit for excess solar power produced beyond your monthly energy consumption. In such cases, it's best to install just enough panels to cover your monthly energy usage to avoid overpaying for a larger installation that won't be fully compensated.

Many utilities have restrictions on the size of a solar panel system. In some areas, the size of solar installations may be limited based on the grid infrastructure, while in others, utilities may restrict oversizing the system beyond a certain percentage of typical energy usage.

Personal solar energy goals

What you want out of going solar can also affect the number of panels you need to install. 

Is your goal to reduce your carbon footprint? Then you’ll want to install as much solar as possible and consider pairing the system with solar battery storage to use the most clean energy possible. Maybe you want to maximize your electricity bill savings. If that’s the case, you’ll want a system that produces as much energy as possible to lower your utility costs. 

You could also want to get the best return on your solar investment. Then, you’ll have to weigh the upfront cost of solar and compare it to the savings you can get with the net metering policies available to you, which might not mean installing as many solar panels as you can. 

No matter your goals, a reputable solar professional can help you get the system that’s just right for you.