When it comes to land impact, does solar, wind, nuclear, coal, or natural gas have the smallest footprint?

The problem with renewable energy, so claim its critics, is that it is too diffuse. Solar and wind farms require vast amounts of land to harvest the low-density energy from the sun and wind. In contrast, they point out that power plants, like coal, natural gas, and nuclear, have relatively tiny footprints, requiring hundreds of times less land than renewables for the same power. 

This argument has merit but it overlooks two essential points. First, it conveniently ignores the very large land footprint of the mines that produce the fuels for coal and nuclear plants. Second, each acre can only be mined once. After that, the acre is depleted forever and the mining companies must move on to the next acre. In contrast, an acre of solar, wind, hydro, or biomass will continue producing energy, year after year, forever. In other words, an acre is not just an acre.

This relationship reminds me of a goose that lays golden eggs, where the goose is an acre of land and the eggs are revenue. If I want money immediately, I can sell the goose but I’ll never see any more value from it ever again. But, if I hold onto the goose, and sell its golden eggs over a longer period of time, the value of those eggs will eventually be worth much more than I could have ever made selling the goose. An acre devoted to solar and wind will generate energy in perpetuity.

The use of land shouldn’t be measured in acres alone but instead, acres over time

The table below normalizes all major electricity generation sources to a common unit, a gigawatt hour. One GWh of electricity can power about 100 American homes for a year and it is roughly the electricity consumed by a person over their lifetime.

(click here to see as an image; sources available here)

Let’s start by looking at land-use as a renewable critic might — a snapshot of the electricity generated per unit of land. This narrow analysis shows that a solar or wind farm uses hundreds of times more land than the relatively tiny footprint of a coal or nuclear plant. But, analysis like this often overlooks the much larger footprint of mining coal and uranium. The column “Acres per GWh per year” contains land use, including mining, to better compare land efficiency. When measured as a snapshot in time, land used for mining coal (0.09 acres per GWh) and uranium (0.06 acres per GWh) uses less land than solar (3 acres per GWh) and wind (26 acres per GWh). So, when you include mining, does this confirm that fuel-based land use is still the most productive?

Not at all, because it ignores the value over time. Imagine this was your land and that you planned to own for many years.  Suddenly the economics look very different. If you build a solar farm on your land and operate it for 25 years, you can produce 8.33 GWh of electricity, making that land’s energy output more competitive with an acre of coal (11.11 GWh) and nuclear (16.66 GWh). However, if you measure that same land over your lifetime, an acre of solar can generate 25 GWh of electricity, more than an acre of nuclear or coal!

Even with solar shining over time, there are many considerations beyond energy output when assessing the footprint of electricity generation. There is a fixed amount of land on earth and we need to consider the health of each acre we use — the environmental impact of mining land versus hosting solar panels is very different.

Beyond acres and kilowatt hours: dual-use and reclamation

Renewables can hold their own against mining fuel on an energy per acre basis but it is the health of that acre where renewables demonstrate the best land footprint. The towers that hold those enormous turbines only require a tiny portion of a wind farm’s total land footprint—the rest can serve other purposes. Increasingly, land in wind farms has become “dual-use,” simultaneously supporting livestock grazing and agriculture. Solar farms, because they are typically more densely packed than wind farms, make dual-use more of a challenge, but pilot projects all over the world are proving that panels can co-exist with grazing and certain kinds of agriculture (see Will the growth of solar power crowd out farmland?). Even hydropower reservoirs and biomass forests allow for recreation while they are producing energy. 

Mining is far less flexible or forgiving. While mines are open, they are too dangerous for any purpose other than fuel extraction. However, advocates of fossil fuels and nuclear make the case that when mines eventually close, the land can be reclaimed and given back to nature. This is difficult to assess with uranium mines because 95% of this nuclear fuel comes from outside the US where there is less accountability for environmental initiatives. What we do know is that uranium mining brings radiation-laden rocks permanently to the surface, requiring extraordinary cost and care for putting the land back to its original state. Nuclear plant disasters like Chernobyl and Fukushima have also left hundreds of thousands of acres unfit for human habitation.

Reclaiming coal mines is a bit easier to analyze because coal is mined domestically. A report by the Appalachian Law Center found the US had spent $5.7 billion over 40 years to reclaim 800,000 acres of land damaged by mining but they also found 6.2 million acres were still awaiting reclamation (this federal fund is set to expire in 2021). Storing the 2 billion tons of coal ash left over from a century of coal power requires 1,100 ash ponds across the US. While the land required for ash is relatively small in terms of acres per GWh, the coal ash contains arsenic, mercury, uranium, and other toxic heavy metals. Reclaiming those acres will cost billions of dollars.

When you put all this together, the environmental impact of mining coal and uranium diminishes many of its benefits in land usage efficiency.

Why solar is the most land-efficient type of renewable energy

Now, let’s look at how much electricity each type of renewable power plant can produce per acre. At first glance, solar’s 3 acres per GWh is roughly 10-times more efficient than wind and almost 100-times more than hydro or biomass. How is that solar requires so much less land?

It helps to remember that nearly every form of energy began, at some point, as solar power. Wind is just moving air, set in motion by heat from the sun. The water for hydroelectric plants started out at lower elevations before the sun evaporated it and delivered it as rain. And, of course, the trees used in biomass plants get all their energy from sunlight. Solar panels shortcut all these complex flows and convert sunlight directly into electricity, faster and more efficiently than any other renewable energy system. It’s not surprising that solar panels require far less land than any other form of renewables.

Even coal and natural gas began life as sunlight-powered biomass, albeit a very long time ago (see the article, Where does coal come from?). Back then, the energy in this biomass was just as diffuse as it is today but tens of millions of years of geologic heat and pressure concentrated it into a much higher energy density.

Solar makes the best of use of land because it often doesn’t need any land at all

It turns out there are lots of acres that few people will ever want to visit. These can be an ideal place for solar. The largest footprint of such land is deserts. While care must be taken for local flora and fauna, the land available is vast, even in the US. For example, the Mojave Desert, located in the US Southwest, occupies almost 50,000 square miles – more than twice the land needed to power the entire US with solar panels (see How much solar would it take to power the US?)(obviously, we don’t want to and don’t need to cover a single desert with solar panels but there is clearly a lot of uninhabited land in the US).

Sadly, there is also a lot of land that was once habitable but is now destroyed or even toxic — solar panels can give this land new value. The industry refers to these places as “brown fields” and they include closed landfills, old coal mines, and Superfund sites. Even the area around the Chernobyl nuclear reactor is now hosting a 4 acre of solar plant.

Another kind of land that is otherwise usable is the surface of water treatment ponds, dams, reservoirs, and even the lakes behind hydroelectric dams. The industry has adopted the term “floatovoltaics” (seriously) to describe this fast-growing venue for solar panels. There are benefits beyond leveraging unneeded space — the proximity to water helps cool the panels, making them more efficient and the panels reduce evaporation and limit algae blooms. 

The most exciting story for solar and land footprints is building integrated photovoltaics or BIPV. This is where common building components are upgraded to include solar cells. Everyday things like shingles, windows, driveways, awnings, and walkways become electricity generating solar installations. Since these components already need to be purchased and installed, the added cost of making them solar-powered will be relatively smaller than stand-alone solar panels. BIPV is not only reducing the overall land required for solar power, it is one of the most promising areas to continue driving down the costs of solar.

There is more characteristic of solar that makes its land use truly unique. Sunlight is everywhere. Every acre of land and water on earth receives sunlight at some point. Mines and wells can only be put on top of rarified underground deposits. Wind and hydro require unique geographies. Even biomass only makes sense in places with rich soil and rain. Among all the mechanisms for generating electricity, only solar can be put anywhere on earth. It is the most equitable and universally available source of energy that exists.

Geothermal and natural gas use the least amount of surface land

What about geothermal and natural gas, you may ask? When measured by surface land usage, geothermal is the clear winner. There is no fuel extracted from the earth, just heat. Geothermal power plants sit atop the land being drilled and process the heat directly. Were it not for occasional earthquakes and the very limited number of places that can be cost-effectively tapped for heat energy, geothermal might be the ideal source of electricity generation. Until there are substantial advances in technology, geothermal will be relegated to a niche solution.

Much as it may pain those adamantly opposed to fossil fuels, natural gas also enjoys one of the smaller land footprints among electricity generators. Like geothermal, all the action is underground. Both can use as little as a few acres on the surface but can easily drill downwards and outwards for miles. But unlike geothermal, natural gas is a fuel that must be extracted and burned to generate electricity. This means it has a wide range of non-land environmental impacts including methane leaks at wellheads and along pipelines, chemical leaks into water tables, and emissions like SOx and CO2 (these impacts will be covered in another article).

The Freeing Energy Perspective 

While renewable energy initially requires more land than fuel-based power plants, this is a short-lived advantage. Over time, an acre of solar panels will produce more energy than any mining operation, whether it is coal or nuclear.  During operation, a solar or wind farm will have so little impact on its land that it is increasingly common to allow grazing and farming on the same acres at the same time. Because solar panels and wind turbines sit on the surface of land, and because most of the materials can be recycled profitably, we can hope that land reclamation will be far more successful than gas wells, coal, or uranium mines. Best of all, the land footprint of solar will continue to shrink. As technology makes panels and panel placement more efficient and as more solar is built into rooftops, parking lot canopies and buildings, the total acreage of land needed per gigawatt hour will continue declining.

Overall, the footprint of solar energy is uniquely small for several reasons:

1. Solar can be put anywhere on earth because the sun shines everywhere. No other type of electricity generation can match this flexibility.
2. Over time, an acre of solar can generate more electricity than any other renewable, and more than coal and uranium mines.
3. Solar can be placed onto existing structures like roofs, driveways, roads, etc, thus not requiring any dedicated land.
4. Solar can revive the value of land lost to misuse like old coal mines and Superfund sites.
5. Solar can be built in places that are not otherwise habitable, like deserts and lakes.
6. Solar farms are already proving they can “dual-use” and co-exist with agriculture and grazing.

Every source of energy has its own set of challenges and benefits. My hope is that this article helps reduce the concerns that the land footprint of renewables like solar should be used to justify putting the brakes on continuing global adoption.

Disclaimer: the metrics in this article are gathered from many sources and normalized for the sake of illustration. This analysis does not include the land used for waste disposal or for the materials used to construct the plants themselves (solar, wind, nuclear, coal, and natural gas power plants all use a lot of steel, copper, and cement). Both of these topics will be covered in upcoming articles.