It has seemed for a long time that generating electricity from the sun and the wind would eliminate a lot of environmental problems.

We would not have the pollution that comes from mining coal or extracting oil from the ground or the greenhouse gases that come from burning them. But before we get too excited about renewable energy, we need to be aware of land use issues.

This post will concentrate on land use for solar energy. Wind energy presents somewhat different problems.

Solar power remains popular; 82% of Americans favor tax rebates for solar panels and other aspects of renewable energy. But a favorable opinion of solar energy in general doesn’t mean that solar projects won’t face opposition locally.  Concerns include water requirements and loss of property values, farmland, woodlands, scenery, or wildlife habitat.

All these issues have more to do with land use than the desirability of solar energy.

Energy and power density

Different forms of energy make different demands on land. To make meaningful comparisons requires understanding some technical vocabulary, particularly energy density and power density.

Energy density refers to how much energy a fuel produces by weight or volume. Coal and oil have high density by both measures. Natural gas has low energy density by volume but high density by weight. Fuels with high energy density are easy to move from one place to another.

That is, it is easy to put coal on a train and send it from the mine to wherever it’s needed. We easily move oil and natural gas through pipelines. We cannot move sunlight.

Power density refers to the amount of land surface needed to produce a given amount of energy. It is impossible to calculate any exact figures. The power density of fossil fuels ranges from less than 200 watts per square meter to more than 1,000 watts per square meter. If an average house requires an electricity flow of 2,500 watts, it requires disturbing somewhere between 27-135 square feet of land to provide it from fossil fuels. That range amounts to the average size of a bathroom or a bedroom.

Fossil fuels have much greater power density than solar energy. I have seen estimates anywhere from ten times as much to four hundred times as much.

Taking a middle figure of one hundred times as much, providing that same house with the same power from renewable energy would mean disturbing one hundred times as much land. That is, instead of using the equivalent land of a single room as with fossil fuels, using solar energy would use land equivalent to the floor space of the entire house.

One offsetting benefit of solar energy land use

I do not want to leave the impression that, in terms of land use, fossil fuels are good and solar energy is bad. Solar energy has one land use advantage over fossil fuels.

Once building a solar farm has disturbed a parcel of land, that land can produce solar power indefinitely. Extracting fossil fuels from one parcel of land eventually exhausts the supply there. Companies have to find new land to drill on. And then they must restore the land after production ends.

A post of this length cannot begin to deal with all the nuances of the figures in the last few paragraphs. That impossibility does not change the fact that solar energy requires a lot of land.

Some reasons for opposition to solar energy development

With some limitations, it is possible to choose where to put an oil refinery or a power plant. Solar farms can only go where there is enough sunshine.

Very often, power from a proposed solar farm has no apparent local benefit. The electricity will be sent far away, and that requires long-distance transmission lines. New transmission lines will require additional land. Transmission from the Great Plains to cities in the East means the new lines will require easements for ugly transmission towers and lines through areas that will not benefit from them. They cross multiple state lines. Varying state laws govern whether the process of eminent domain can procure the necessary land.

Solar resources in the US are best in the Southwest and very strong in the Southeast. Solar generation there at utility scale requires development in areas where the population is not used to siting industrial-scale facilities.

Densely populated states such as New York face a somewhat different problem. The state aims to derive half of its energy from renewable sources by 2030. Doing so will require that solar and wind farms occupy almost 325 square miles of land. Almost a quarter of the state’s land area is used for agriculture. Woodlands and forests occupy half of the state. Where is that extra 325 square miles of land for renewable energy supposed to come from?

Marginal land and other appropriate places for solar development

We can put solar panels on many, though not all, roofs. The large, flat roofs of big box stores, factories, and warehouses provide a lot of usable space.

I have also read about projects to cover parking lots with solar panels, which would enable cars to park in their shade. All the flat roofs and parking lots in the country taken together do not provide enough area for us to meet the goal of using solar power to replace fossil fuels.

Marginal land means land with little or no agricultural or industrial value. It includes reclaimed Superfund sites, other brownfields, capped landfills, and capped coal ash pits.

One large-scale marginal land opportunity

The Tennessee Valley Authority, America’s largest public utility, has proposed building a $216 million solar farm on one of its capped coal ash storage pits in Kentucky. It can potentially generate 100 megawatts of electricity.

Solar farms on all of the TVA’s closed coal ash sites could have a combined capacity of 1,000 megawatts. The TVA manages almost 300,000 acres. It still bears responsibility for reclaiming all the land ruined by burning coal, but it claims that the solar panels would not compromise the turf that caps the site or interfere with the cleanup.

In case that seems like a lot, the US currently has more than a million megawatts of generating capacity. Natural gas and coal account for more than 60% of it. Do we have enough sunny marginal land to replace it?

A smaller-scale marginal land opportunity

A lot of unused disturbed land suitable for solar panels exists near interstate highways: along the shoulder, in median strips, and by on- and off-ramps. Maryland alone has about 3,000 parcels of land near its highways.

Some of this land is wooded, and it’s not a good idea to cut down trees to install solar panels. Therefore, identifying which parcels are suitable can be difficult.

A Georgia non-profit company has recently installed 2,600 solar panels on a 5-acre triangle of land near exit 14 on Interstate 85. Formerly, it was completely cleared, ugly, and suffering erosion. The panels were installed higher off the ground than usual so they could coexist with wild flowers.

The same non-profit has developed a digital tool to help identify parcels suitable for solar panels. It can also express the outcome of proposed solar projects in terms of their economic value, the number of homes they serve, or how much carbon they offset.

Such small parcels of disturbed land will not produce electricity on a large scale. They can make highways more sustainable and possibly even more attractive. They may total more than 52,000 acres of marginal land nationwide. Some states have targets for reducing emissions. Roadside solar—and a tool to help determine where to develop it—can help their efforts.

Coexistence of solar energy and farmland

Farmland already faces pressure from housing developments and new highways. Land use needs of solar farms and wind farms only add to the competition.

Fortunately, land used for a solar farm can also serve other purposes at the same time. Cattle can graze near solar panels. Solar farms may also be able to coexist with low-growing crops that will not cast a shadow on them.

Unfortunately, state and local officials have access to too little information on how to site solar farms to have the least detriment to productive farmland.

We are beginning to learn that sustainability is an elusive goal. Something that solves or helps solve one problem can make another worse. Many today fear that we have very little time to curb greenhouse gas emissions. The worst fears are probably exaggerated. We must certainly find the best way to deploy solar power, but being in too much of a hurry to plan intelligently can only get us into different crises.

Sources:

Georgia group helps turn unused roadsides into solar fields / Emily Jones, Albany Herald. November 12, 2022
Renewables, land use, and local opposition in the United States / Samantha Gross, Brookings. January 2020
To combat climate change: Encourage solar energy that doesn’t sacrifice agricultural land / American Farmland Trust
Utility backs solar farm atop capped Kentucky coal ash pit / Jonathan Matisse, Associated Press. November 11, 2022