How many solar panels would be needed to power the USA?

The planet needs to move away from fossil fuels and adopt renewable energy. Let's say you only used solar power. What would that look like?

Photo of a large solar panel installation

From the start, let’s make it clear that there are no serious proposals to power the planet using only solar energy.

The renewable energy technologies available today - solar, wind, geothermal, tidal, hydro, along with energy storage - are complementary. Each technology has strengths and weaknesses, but when we use all them in concert, it’s possible to power the entire planet with clean energy.

Even so, it’s an interesting thought to consider how many solar panels we would need if that was the only power source available. Let’s think about what that might look like for the United States.

How much electricity does the United States use?

According to the US Energy Information Administration (EIA), the United States generated about 4 trillion kilowatt hours (kWh) of electricity last year. That’s a lot! For comparison, the average household uses about 11,000 kWh each year.

Only about 20% of that currently comes from renewable sources, a majority of which is hydroelectricity from dams. Still, solar and wind energy are growing rapidly: Bloomberg New Energy Finance predicts that wind and solar together will provide 56% of the country’s electricity generation by 2050.

That means we’ll need a lot of solar panels!

How much electricity can one solar panel generate?

To figure out how many solar panels we’d need to generate 4 billion kWh, let’s start with the basic unit: how much electricity can you generate with just one solar panel?

The answer to that depends on a couple things:

  • How efficient is your solar panel?
  • How sunny is it where you’ve installed your panel?

Efficiency refers to how much sunlight is converted into electricity. High efficiency is desirable because you can generate more electricity with fewer square inches.

At the moment, one of the highest efficiency solar panels is the SunPower X-Series, which reaches 22.2% efficiency.

But that’s what the panel could generate under ideal conditions, which are rarely experienced in the real world. A more realistic expectation is that this SunPower panel could hit 17.8% efficiency, which is the NOTC rating listed on the manufacturer’s datasheet. (For more about this, read our article on solar panel specifications.)

Where are you going to put your solar panels?

Another key factor is how much sunlight is available. If you plan to power an entire country with only solar panels, you ideally want to place them in the sunniest location available.

In the United States, that means the Southwest, and Palm Springs is one of the sunniest cities in the country. According to the National Renewable Energy Laboratory, Palm Springs has a global horizontal irradiance (GHI) of 5.8 kWh of solar energy per square meter per day (kWh/m²/day).

On the other hand, maybe you’re not lucky enough to live somewhere so sunny. Maybe you live in Seattle - a really nice city that is known for rain and clouds. It has a GHI of only 3.4 - 58% as much sunlight as Palm Springs.

How much would one solar panel generate?

GHI is the amount of solar energy that hits a horizontal surface. If you have a solar panel flat on the ground, GHI would tell you how much sunlight it receives.

So, if one square meter of land in Palm Springs receives an average of 5.8 kWh of energy per day, how much electricity does that translate to?

If we’re using the SunPower panel mentioned above, we can realistically expect the panel to convert 17.8% of that sunlight into electricity, or about 1.03 kWh/m²/day.

However, a solar panel isn’t one square meter in area. This X-Series panel is 1.05 meters wide by 1.56 meters long.

That’s 1.64 m² of area, which means that one panel will generate 1.69 kWh of electricity per day, or 50.6 kWh per month, or 617 kWh per year.

What if your solar panel is in Seattle instead, where the GHI is only 3.8? Your one solar panel would generate only 0.99 kWh every day, or 362 kWh per year.

How many solar panels would you need to power the United States?

Remember that we need to generate 4 trillion kWh of electricity every year to supply the United States. (That’s 4,000 terawatt-hours.) If we obtained enough land near Palm Springs, how many solar panels would we need?

It turns out that you would need 6.5 billion high efficiency solar panels to power the entire country. That’s a lot!

What if all of your solar panels were instead located near Seattle? Because of the lower amount of available sunlight, you would need even more: about 11 billion solar panels in total.

How much land would you need for all those solar panels?

Because each of our solar panels is 1.64 square meters, those 6.5 billion solar panels would take up 10,632 square kilometers or 4,105 square miles. Given that the little state of Rhode Island is 1,034 square miles, you would need 4 Rhode Islands covered in solar panels to power the USA.

If you’re instead talking about the 11 billion solar panels you’d need if they were near seattle, those would take up 18,040 square kilometers, or 6,965 square miles, or nearly 7 Rhode Islands.

However, this is an idealized case because it assumes that the solar panels are packed tight together. In reality, ground-mounted solar panels are installed on racks and need space between rows of racks to provide access and to prevent panels from shading each other. This means you would need even more space.

Fortunately for those of us interested in this question, the National Renewable Energy Laboratory has done the analysis for us. The United States would realistically need 22,000 square miles if it wanted to power the US with only solar power, which is about the area of Lake Michigan.

Bottom line: you wouldn’t power a country with only solar power anyway

While it’s an interesting question to ask how many solar panels you would need to power an entire country, it’s ultimately just an academic exercise. You would never power the US with only solar, wind, hydro, or any other single technology. These technologies are complementary, with each able to provide electricity when one can’t. For example, hydroelectric dams can often act as giant batteries, storing excess electricity and releasing it when the sun isn’t shining or the wind isn’t blowing.

That means the United States would need a lot less than 22,000 square miles for solar farms. Still, we’re talking about billions of solar panels and thousands of square miles. If meeting these huge numbers seem like an impossible task, that’s understandable.

But it’s more realistic than you might think. According to Bloomberg, two million acres (3125 square miles) are used just for golf courses in the US. If it’s possible to devote that much land to one sport, certainly we can use at least the same amount of land for something as important as renewable energy.

As far as manufacturing goes, the number of solar panels installed around the planet amounts to about 720 terawatt-hours of generation, which already is a significant fraction of the 4,000 terawatt-hours the United States requires. Solar manufacturing and installation is projected to increase at an exponential rate, so we can expect this capacity to rapidly increase over the next coupld decades.

This is one of the great things about rooftop solar. While the numbers are daunting, every square foot of rooftop devoted to solar panels helps the United States reach its goal of net-zero carbon emissions by 2050.

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