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How Many Solar Panels to Power the United States?

It seems like every day, we read about significant breakthroughs in producing power from renewable energy sources like solar energy. Over the last few years, there has been a dramatic increase in the efficiency of solar panels. The technology has improved so much that home solar systems are now a viable and affordable way to save on your energy costs while helping the environment.

A question that occurred to me the other day was that if we were to rely purely on solar energy, just how many solar panels would we need to power the whole country?

It might seem like a throwaway thought, but the question speaks to the long-term potential of solar power, and it’s an excellent way to explore just how far solar technology has advanced.

So I decided to answer the question, and you’ll be fascinated to learn the answers I came up with. So, just how many solar panels power the United States?

Measurements

We will be looking at some pretty big numbers as we answer the question. The US uses a lot of energy. Let’s just take a moment to make sure we understand all the measurements we’ll be using.

We measure power in watts (W). A Watt is a tiny unit of power, so more typically, we use Kilowatts (kW) to represent  1,000 Watts.

So that’s power, but when we look at energy usage, we use another measure to describe the quantity of power that we use over a period of time.

We measure energy usage in Kilowatt-Hours (kWh). A kilowatt-hour represents the usage of one kilowatt for one hour, it makes perfect sense.

How Much Energy to Power The United States?

The best place to get reliable information about how much energy we use in the United States is direct from the government. So I headed straight to the US Energy Information Administration (EIA) website. And sure enough, they had the information I was looking for, for 2019.

how many solar panels to power the us
Source: U.S. Energy Information Administration

The EIA website gives figures for total energy use for the US and breaks it down into contributions from different energy sources. We don’t need that breakdown to answer our question. It’s interesting, though, to note that already 11% of the total energy supply of the United States comes from renewable resources, although solar power is currently just 9% of that total.

In 2019 the United States used 100.2 quadrillion British thermal units (Btu) of energy.

What’s a British Thermal Unit?

It turns out that a British Thermal Unit or BTU is a unit that we use when measuring the energy that derives from several sources. That’s great, but it’s not much use to us yet since we need to make our calculations in kilowatt-hours. Fortunately, it’s easy to convert between the addition thermal units and kilowatt-hours. Here’s the conversion rate:

 1 BTU/hr =0.293071 W 

When we convert those numbers from BTU into kWh, we find out that;

The US uses 0.029 quadrillion kWh of power a year.

What’s a Quadrillion?

So, we’re making progress, but what exactly is a quadrillion? Things start to get incredibly confusing when you add a lot of zeros to numbers.

Here is a great page that explains the terms that we use to describe really large numbers. The fact that we define big numbers differently in the US than they do in the UK doesn’t make things any easier, but I’m using US number definitions here. So, a quadrillion is a thousand billion, or a one followed by fifteen zeros, like this;

 One Quadrillion = 1,000,000,000,000,000 

Now we have enough information to work out that total 2019 energy usage figure in kilowatt-hours. Here’s how we calculate that:

 0.029 quadrillion kWh x 1,000,000,000,000,000 = 29,000,000,000,000 kWh 

So the total energy usage for the US in 2019 was 29,000,000,000,000 kWh.

That’s 29 Trillion kWh!

How Much of This Energy Use Was Domestic?

We use only around 18.1% of this national energy total in our homes. The largest users of energy are transport and industry. In 2019 we only used 5,250,000,000,000 kWh in our homes .

Now that we have the first part of our answer, we just need to figure out how many solar panels we would need to make this enormous quantity of energy.

ENERGY CONSUMPTION BY SECTOR
Data Source: U.S. EIA (2020) Annual Energy Outlook 2020.

How Much Energy Do Solar Panels Produce?

There are many types and sizes of solar panels, and they all produce different amounts of power.

Solar panels vary inefficiency, which is a measure of how much of the sun’s power they can convert into electricity. Most domestic solar panels have an efficiency of between 15% and 20%. These efficiency ratings are increasing as technology advances.

How Much Energy Do Solar Panels Produce

To add another complication, solar systems are more effective in some places than others. Solar cells located in areas with lots of direct sunlight generate more power.

Let’s take a look at the different kinds of panels so that we can make some reasonable assumptions and develop a representative ‘standard panel’ that we can use in our calculations.

What Is a Typical Solar Panel?

Domestic solar panels are collections of individual solar cells. They come in two sizes, panels with 60 or 72 solar cells. Other things being equal, the 72 cell panels generate more power than the smaller sixty-panel units since they have more solar cells.

60 vs 72 cell

The output of a typical domestic solar panel is rated between around 300-450 Watts. This is a measure of how much energy they produce under factory testing conditions. Home solar systems rarely replicate these lab results, but the measures are a good way to compare the power output of different panels.

For the sake of our calculation, we’re going to use a 72 cell solar panel with good efficiency that gives us 370 Watts of power.

Where Is The Best Place to Put Solar Panels?

The amount of solar energy that gets through to the Earth’s surface varies from place to place; here’s a very detailed website that shows solar energy availability everywhere in the world. We use a measure called Peak Solar Hours to calculate how much solar energy a solar panel can collect from place to place.

It’s important to mention that this number doesn’t represent how many hours a day the sun actually shines. Instead, it measures all the day’s full and partial sunlight and converts this into the number of hours over which that energy could power a solar panel at peak capacity.

Peak solar hours in the US vary from three and half hours in the Northwest to six hours or more in some Southern states.

Peak Sun Hours Map

The U.S. national average peak solar hours is around 4.75, so we will use this number.

Our 370 W solar panel receives an average of four and a half hours of direct sunlight a day, every day of the year.

 370 Watts x 4.75 hours x 365 days = 641 kWh 

How Many Solar Panels to Power the us

The Answer

The number of domestic solar panels that we would need to power the whole of the US is:

 29,000,000,000,000 kWh /641 kWh = 45,000,000,000 

How Many Solar Panels To Power usa

We would need 45 Billion solar panels to produce the 2019 energy usage of the United States

If we decide just to cover the domestic energy usage of the US, then we would need this many solar panels:

 5,250,000,000,000 kWh /641 kWh = 8,200,000,000 

We would need 8.2 Billion solar panels to produce the 2019 domestic energy usage of the United States

Sure, that’s a lot of panels in anyone’s book, but the United States is an enormous country with a massive population of 328 million (2019 figures).

Even though it’s not part of our question, we can get a better understanding of these results by working out how many solar panels per person we would need to produce this domestic energy requirement. Here’s how we work that out:

 8,200,000,000 /328,000,000 = 25 
We would need just 25 solar panels per person to cover the total US domestic energy usage.

What Do These Results Mean?

We’ve looked at some extremely large numbers in this exercise, but at last, we’ve come to something a bit more manageable.

It would take some 45 billion solar panels to provide enough power for all of the United States’ fuel needs.
But when we consider domestic energy use on its own and spread it out over the whole population, we find that we would only need 25 solar panels per person to cover all our domestic energy needs.

how much land would it take to power the us with solar
Area of solar panels needed to power the U.S

These results show that solar power is a viable solution to cover more and more of our domestic energy needs. And don’t forget that solar power is becoming ever more efficient and there are lots of government incentives to help you invest in a solar system.

What began as a casual inquiry has produced an interesting answer that suggests that solar power has the potential to make a significant contribution to our energy needs, now and in the future.

If you have any questions or comments, then please share them with us.

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