How many solar panels do I need for my home?

Written by Vikram Aggarwal

We estimate that a typical home needs between 17 and 21 solar panels to cover 100 percent of its electricity usage. To determine how many solar panels you need, you’ll need to know: your annual electricity consumption, the wattage of the solar panels you’re considering, and the estimated production ratio of your solar system. You can calculate the number of solar panels you’ll need by dividing the system size by the production ratio, and again by the panel wattage. 

The actual number of panels you’ll need to install depends on factors including your geographic location, panel efficiency, panel rated power, and your personal energy consumption habits. Importantly, the number of solar panels you need for your home directly impacts the price you pay for solar. While the answer isn’t always simple, we’ve put together some example cases to help you understand, at a high level, how many solar panels you need to install an effective home solar array.

What do you need to know to calculate how many solar panels you need?

Before you start to calculate the number of solar panels you need, there are several considerations to keep in mind: 

1. Your annual electricity usage
2. The wattage of the solar panels you’re considering
3. The estimated production ratio of your solar power system

How to calculate how many solar panels you need

You can calculate how many solar panels you need by dividing your yearly electricity usage by your area’s production ratio, and then dividing that number by the power output of your solar panels. Let’s break that down a bit:

Calculating how many solar panels you’ll need to meet all of your energy needs depends on several factors. The easiest way to find out how many panels you’ll need is to use our Solar Calculator. When you put in your address and estimated monthly power bill, we’ll do all of the math for you so that you can make an informed decision. If you’d like to do those calculations for yourself, we’ve explained our formula below to help.

The formula we used to estimate the number of solar panels you need to power your home depends on these key factors. Here are the assumptions we made, and how we did our math:

Annual electricity usage

Your annual electricity usage is the amount of energy you use in your home over a full year. Measured in kilowatt-hours (kWh), this number is influenced by the appliances in your home that use electricity and how often you use them. Refrigerators, air conditioning units, small kitchen appliances, lights, chargers, and more all use electricity.

According to the U.S. Energy Information Administration (EIA), the average American household uses 10,632 kWh of electricity per year (or 886 kWh per month), so we’ll use that number as the ideal solar panel system or solar array size, which would mean you could offset 100 percent of your electricity usage and utility bill with solar panels (in practice, it’s not this neat, but bear with us here). If you’re interested in getting a more exact number based on how much energy you use, check last year’s electric bills to find out your average electricity consumption. Once you have that number, feel free to plug it into the equations below.

Solar panel wattage

Also known as a solar panel’s power rating, panel wattage is the electricity output of a specific solar panel under ideal conditions. Wattage is measured in watts (W), and most solar panels fall in the range of 300 – 400+ W of power. We’ll use 390 watt panels in these calculations because 390-400 W is the most quoted capacity range on the EnergySage Marketplace according to our latest Intel Report.

Production ratios

A solar panel system’s production ratio is the ratio of its estimated energy output over time (in kWh) to its actual system size (in W). These numbers are almost never 1:1 – depending on how many hours of sunlight your system will get (which is primarily based on your geographic location), your production ratio will change accordingly. 

For example, a 10 kW system that produces 14 kWh of electricity in a year has a production ratio of 1.4 (14/10 = 1.4) – this is an entirely realistic production ratio to see out in the real world. In the U.S., production ratios are usually between 1.3 and 1.6, so we’ll use those two numbers as the high and low estimates for our calculation.

Now, let’s work out the math

We have our three main assumptions (energy use, solar panel wattage, and production ratios) – so how do those numbers translate to an estimated number of solar panels for your home? The formula looks like this:

Number of panels = system size / production ratio / panel wattage

Plugging our numbers in from above, we get:

Number of panels = 10,632 kWh / 1.3 or 1.6 / 390 W

…which gives us between 17 and 21 panels in a solar array, depending on which production ratio we use (17 for a 1.6 ratio, and 21 for a 1.3 ratio). So, 17 panels at 390 W each result in a total system size of about 6.6 kW!

Solar panel cost 

There is consideration for how many solar panels to buy without including cost as a factor. Solar panels cost $2.86/W on average. The total average cost of an installation is $20,020 for a 10 kW system (after accounting for the 30 percent federal solar tax credit). This varies widely depending on location, installation cost, and incentives with warmer climates being cheaper but needing more panels and vice versa for colder climates.

Main considerations to determine how much solar you need

Calculating how many solar panels you need can be done with the three inputs above, but digging deeper, there are many more factors at play in determining your ideal solar panel system size. Understanding production ratios, the relationship between system size and the number of panels, and the impact of home size can all be important when you’re designing your ideal solar panel setup.

How much solar power can your panels produce? 

The amount of power (kWh) your solar energy system can produce depends on how much sunlight exposure your roof receives, which in turn creates your production ratio. The amount of sunlight you get in a year depends on both where you are in the country, and the time of year. For instance, California has more sunny days annually than New England. But in either location, you’ll be able to produce enough power to cover your energy needs and say goodbye to your utility bills – if you live in an area that gets less peak sunlight hours, you’ll just need to have a larger solar array system installed at your home. Thus, production ratios differ according to geographic location and a lower production ratio (because of less sunlight) means you’ll need more solar panels to get the amount of energy production you need.

Here’s an example: two comparably sized households in California and Massachusetts consume the average amount of electricity for an American household, which is 10,632 kWh annually as mentioned above. The California household needs about a 6.6 kW system to cover 100 percent of their electricity needs. By comparison, the comparable household in Massachusetts needs about an 8.2 kW system to cover their electricity needs. Solar panel systems in California are smaller than solar panel systems in Massachusetts but are able to produce the same amount of power because they’re exposed to more peak sunlight hours each year. Homeowners in less sunny areas, like Massachusetts, can make up for this disparity by simply using more efficient panels or increasing the size of their solar energy system, resulting in slightly more solar panels on their rooftop.

How many solar panels do you need for specific system sizes?

In our long example at the beginning of this piece, we determined that a 6.6 kW system would probably cover the average energy use for an American household if you live in an area with a production ratio of 1.6, which might be a realistic number for homes in most parts of California. 

Let’s extend that a little further, and look at a few more examples. In the table below, we’ve compiled some solar panel number estimates for common solar system sizes seen on the EnergySage Marketplace. Again, the big caveat here is that we’re using 1.6 as the production ratio of choice. For California shoppers, this might actually be realistic, but for folks in the Northeast or areas with less sun, these estimates might be a bit high on the production end and low on the number of panels needed.

Number of solar panels needed for specific system sizes

The table above again assumes that you’re using 390 solar panels and your production ratio is 1.6 – however, the number of panels you need to power your home and the amount of space that your system will take up on your roof will change if you’re using lower-efficiency panels or high-efficiency panels (which generally correlates to low and high power rating, respectively).

Perhaps one of the most difficult aspects of sizing a solar panel array is estimating the annual amount of energy usage for your household. A number of larger consumer products or add-ons can significantly change your annual kWh requirements and greatly impact how many panels you will need. For example, if you’re running central air conditioning or powering a heated swimming pool in your backyard, the size of your solar panel array could be drastically altered. To get a feel for the size you’ll need, you should evaluate the energy impact of various products you own or are considering for your home.

How much roof space do you have?

Ultimately, you’ll only be able to install as many panels as you can fit on your roof. Below is a table that will give you a sense of how many square feet your system will take up on your roof, depending on the power output of the solar panels you select.

Square footage of different size solar panel systems

If your home is small or has an unusually shaped roof, the size of solar panels can be very important to consider. While those who have a large roof may be able to sacrifice some efficiency and buy larger panels to achieve the ideal energy output, homeowners with a smaller roof must be able to use fewer small high-efficiency panels – like those from SunPower, LG, or REC – to get optimal output. For those atypical roofs, you might end up getting a system design like this:

How does your home size affect the number of solar panels you need?

While solar panel dimensions have more or less remained steady over the past several years, the power output within the same area has dramatically increased. In fact, many manufacturers like SunPower have reduced the size of gaps between panels and use invisible framing and mounting hardware to keep the panels tight, efficient, and aesthetically pleasing. Check out the table below for a ballpark estimate of how many solar panels your home would need based on its square footage (assuming 390 W solar panels and a production ratio of 1.6).

Home square footage compared to the number of solar panels needed

How many solar panels do you need for common appliances?

By reviewing the various kWh requirements for everyday household appliances and products, one thing is clear: certain add-ons will dramatically change monthly energy use and can have an outsized impact on the size of the solar panel system you should install. For example, pairing your electric vehicle with solar panels is a great way to reduce carbon emissions and improve energy efficiency; however, it should be planned accordingly, considering it could potentially double the size of your solar energy system. 

Though it’s certainly possible to install a solar system and then have a solar installer add more panels later to accommodate increased energy needs, the most pragmatic option is to size your system as accurately as possible based on your expected purchases – such as an electric vehicle, swimming pool or central air system. Asking yourself, “how many solar panels will I need for my refrigerator, my hot tub, etc.” is a great habit for any new solar homeowner.

Solar panel requirements for individual appliances

Frequently asked questions

Do you still have an electricity bill with solar panels?

Once you install solar panels, you’ll still receive a monthly electricity bill. However, it should be lower, close to zero, or even negative! If you’re still experiencing high utility bills after installing solar panels, you may need to reconsider the size of your system. Especially if you have added electricity loads since your solar installation (like an electric car), your current system size just might not cut it anymore.

The only situation in which you won’t have an electricity bill is if you choose to go off-grid by installing a solar battery – but in most cases, it’s better to keep your solar energy system grid-tied, even if you do add battery storage.

Are there disadvantages to powering a home with solar panels?

The two main disadvantages of solar energy are the high upfront costs and intermittency, meaning that solar energy isn’t available 24/7 because the sun doesn’t shine at night. Luckily, that problem can be partially sorted with battery storage. Check out our article about the advantages and disadvantages of renewable energy to learn more.

Are solar panels worth it?

Depending on your electricity prices, how much electricity you consume, your desire to be eco-friendly, and your home’s geographic location, solar panels are definitely worth installing. While the initial investment in solar panels is high, they do pay off over time by cutting down your electricity bills. On average, EnergySage solar shoppers “break even” on their solar investment in about eight to nine years. And, as solar deployment continues to grow (reducing cost) and inflation rates rise further, solar will likely become even more worth it.

How can you calculate how many solar panels you need?

You can find how many solar panels you need by dividing your yearly electricity usage by your area’s production ratio, and then dividing that number by the power output of your solar panels.

Start your solar shopping on the EnergySage Marketplace

There are multiple variables to consider when seeking out the best solar panels on the market. While certain panels will have higher efficiency ratings than others, investing in top-of-the-line solar equipment doesn’t always result in higher savings on your utility bills. The only way to find your property’s “sweet spot” is to evaluate quotes with varying equipment and financing offers. If you want quotes from local contractors today, check out our quote comparison platform.