I’ve seen some pieces in the media lately questioning this, so allow me to point to some facts based on real-world data.

tl;dr: We’ll probably never power the world entirely on solar, but if we did, it would take a rather small fraction of the world’s land area: Less than 1 percent of the Earth’s land area to provide for current electricity needs.

First, let me be clear: I doubt the future is 100% solar or anything like it. We are in the midst of a multi-decade transition. And while solar is the most abundant renewable on the planet, and plunging in price faster than any other, there’s a role for solar, wind, hydro, nuclear, and geothermal in the distant future based on ideal geographies and scenarios. I very much hope to see highly advanced, high-yield biofuels come into the mix in the next decade. And for a number of decades to come we’re going to have fossil fuels in play. This article is a ‘what if?’ and not a prediction of or call for 100% solar.

Second, to move to a high-renewables world, we need low-cost energy storage. We’re making progress on that. But there’s still quite a distance to go.

For the data, let’s use two examples.

Example #1 comes from a Breakthrough Institute article complaining about the vast amount of land that solar needs. Guest writer Ben Heard complains that solar’s land footprint (specifically at the Ivanpah plant) is 92 times that of a small modular nuclear reactor. (If you’ve read The Infinite Resource you may know that I wrote a whole chapter in praise of nuclear power and of small modular reactors in particular. I’m a fan.)

What Heard’s Breakthrough Institute article doesn’t tell you is how tiny that land footprint, in the grand scheme of things, actually is. Do the math on the numbers he presents: 1087 Gwh / yr, or 0.31 Gwh / acre / year.

At that output, to meet the US electricity demand of 3.7 million Gwh per year, you’d need about 48,000 square kilometers of solar sites. (That’s total area, not just area of panels.) That may sound like a stunningly large area, and in some sense, it is. But it’s less than half the size of the Mojave desert. And more importantly, the continental United States has a land area of 7.6 million square kilometers. That implies to that meet US electrical demand via this real world example of Ivanpah, would require just 0.6 percent of the land area of the continental US.

This fact – which puts the land area requirements in context – is completely missing from Heard’s piece at the Breakthrough Institute site.

Asked about this on twitter, Heard replied that larger size nevertheless is a disadvantage. It threatens ecosystems and endangered species, for instance. And this is a legitimate point, in some specific areas. (Though certainly far less so than coal and natural gas.)

But, for context, agriculture uses roughly 30% of all land in the United States, or 50 times as much land as would be needed to meet US electricity needs via solar.

Ivanpah, of course, may be an atypical site. So let’s look more generally.

Example #2 is a convenient reference from NREL: Land Use Requirements for Solar Plants in the United States (2013) It’s excellent reading. I recommend pulling it up the next time Bjorn Lomborg writes an op-ed.

The second to last column tells us that, weighted by how much electricity they actually produce, large solar PV facilities need 3.4 acres of total space (panels + buildings + roads + everything else) for each Gwh of electricity they produce.

That leads to an output estimate of 0.294 Gwh / year / acre, and virtually the same total area, around 50,000 square kilometers in the US, or 0.6% of the continental US’s land area.

Update: In my original post I didn’t take the time to compare this area to other suitable areas in the US, such as rooftops, parking lots, and built land. Various people pointed me to pieces of data. So, consider that:

1. The built environment in the US (buildings, roads, parking lots, etc..) covered an estimated 83,337 square kilometers in 2009, or roughly 166% of the area estimated above. (Likely this area would not be as efficiently used, of course. But it could make a significant dent.)

2. Idled cropland in the US, not currently being used, totaled 37.2 million acres in 2007, or roughly 150,000 square kilometers, roughly three times the area needed.

3. “National Defense and Industrial” lands in the US (which includes military bases, department of energy facilities, and related, but NOT civilian factories, powerplants, coal mines, etc..) totaled 23 million acres in 2007, or roughly 93,000 square kilometers, nearly twice the area needed to meet US electricity demand via solar. Presumably much of that land is actively in use, but it gives a sense of the scale.

4. Coal mines have disturbed an estimated 8.4 million acres of land in the US. That works out to around 34,000 square kilometers, not too far off for the estimate from solar, and doesn’t include the space for coal power plants. And coal currently produces around only 40% of US electricity and hasn’t been above 60% in decades. To scale coal to 100% of US electricity would have required far more land than is required to meet that same demand via solar. Other analysis says the same: Counting the size of coal mines and their output, solar has a smaller land footprint per unit of energy than coal.

And the solar estimate of ~50,000 square kilometers, of course, is with solar systems already deployed. It doesn’t take into account the possibility of future systems with higher efficiencies that could reduce the land footprint needed.

Again, the point here is not that we’ll see a 100% solar world. The more solar we deploy, the more sense it makes to deploy wind to complement it. And frankly, I want to see the nuclear industry succeed. Nuclear is safe baseload power that we should be rooting for. I hope the nuclear industry can get costs and construction times down and under control.

But, when it comes to solar, land is not a blocking issue. Be skeptical when it’s brought up as one.