One might think this would be a good time to be in the solar power business in the U.S. After all, federal and state subsidies are reducing the costs of installing solar energy systems, and renewable portfolio standards in 29 states require electric utilities to generate some portion of the energy they deliver from renewable sources.

Yet in the past month, three U.S. solar power companies have gone bankrupt -- most recently Solyndra Inc. of California. Solar power hasn’t become a major player on the nation’s energy stage.

The industry faces a number of difficulties. The weak economy has made it challenging to secure financing for new plants. Chinese competition is aggressive. Creating new solar-power generation facilities in the U.S. has been difficult partly because water, needed to run most large-scale plants, is scarce in the sunny desert Southwest where it makes most sense to build them.

But the biggest challenge for expanding solar energy use in the U.S. is to find the enormous tracts of land it will need.

A 1,000-megawatt power plant fueled by natural gas, coal or nuclear fission occupies less than 1,000 acres. Solar, in contrast, needs thousands of acres. A concentrated solar power plant uses a steam cycle to spin a turbine, which generates electricity, and each one of these requires 6,000 acres. As for photovoltaic plants, whose cells directly convert solar radiation into electrical current, each one requires about 12,000 acres.

Limited Capacity

Even these large numbers don’t fully capture how much land is needed, because they don’t take into account solar’s limited production capacity. A typical fossil-fuel power plant works around the clock at 90 percent capacity. A solar plant can’t match that, because darkness and inclement weather restrict its output to about 20 percent to 30 percent. So it takes three or four solar plants to generate as many megawatt hours of electricity as can be produced by one fossil-fuel plant.

This is why we can’t expect to draw enough energy from solar systems constructed on city rooftops to replace fossil-fuel generated power. Two ambitious photovoltaic projects in Southern California in 2009 and 2010 succeeded in installing only a few hundred megawatts of solar capacity. While this is nothing to sneeze at, it’s about the same amount that just one large concentrated solar-power plant would generate. To get the amount of power we need, solar plants will have to be spread out on enormous tracts of land.

Consider what this means, for instance, in California, where the state government has set a goal of generating 33 percent of its electricity from renewable sources. To get all this power from solar energy would require building solar plants on at least 270 square miles of land.

California is a big state, to be sure, but solar companies have so far found it difficult to find even the five or six square miles needed for a single plant. Private land is appropriate for solar-power plants, especially low-quality farmland. But few farmers own the amount of contiguous land needed, which means solar companies must negotiate with multiple landowners in order to secure enough land.

For this reason, land owned by the federal government is vital. Of course, some kinds of federal land aren’t well-suited for solar development. National parks, monuments and forests are obviously inappropriate.

But some lands controlled by the Bureau of Land Management could work -- particularly those that have been severely degraded by past uses, such as gravel pits or mine tailings. However, it has proven difficult to obtain the agreement of all stakeholders that specific parcels of federal land are appropriate for solar plants.

Arizona Land

In Arizona, for example, where sunlight is plentiful, the bureau controls 12 million acres. Yet, a two-year effort by the BLM to identify possible sites for solar-power plants on its land in Arizona yielded consensus on only 25,000 acres. Every acre of the bureau’s land in Arizona seems to have at least one environmental organization or citizen’s group that wants to preserve it.

American Indian lands offer another potential option for solar projects. However, many reservations are remote from the urban centers that need more power, so building there would mean also constructing new high-capacity transmission lines, which would require still more land.

Rooftops, agricultural land, severely degraded public lands and Indian reservations will provide some space for solar power. But even collectively, these options aren’t enough to wean the country from electricity generated by fossil fuels. If we are serious about significantly increasing the percentage of the nation’s power generated by solar energy, we must locate a large number of solar plants on low-value public lands.

Southwestern deserts provide accessible and truly appropriate areas for building solar power plants. For example, the Mojave Desert, located in the triangle of southern Nevada, southeastern California and western Arizona, occupies about 54,000 square miles, much of it controlled by the BLM. High-quality habitat, as well as valuable recreational and scenic land, has already been preserved. Much of the rest is scrub desert, which provides only marginal habitat for threatened and endangered species. It makes sense to locate solar plants on this land, especially along interstate highways and in areas already bisected by high-voltage transmission lines and trampled from decades of grazing cattle and driving off-road vehicles.

Environmental groups have opposed the bureau’s granting of permits for solar-power plants on these marginal lands because surveys have disclosed small numbers of important species, particularly the threatened desert tortoise. This opposition is understandable because all undisturbed land is habitat for some species. But not all habitats are crucial for the protection of endangered and threatened species.

Failure to act aggressively to develop renewable energy sources means allowing global climate change to continue apace. The potential effects would devastate the very species that environmental groups wish to protect.

The future of solar power in the U.S. is in doubt. In 2009, it produced only about 0.02 percent of the nation’s power. If we are serious about making solar energy a viable option, we must invest in the land necessary to make that happen.

(Robert Glennon, a professor of law at the University of Arizona, in Tucson, is the author of “Unquenchable: America’s Water Crisis and What to Do About It.” The opinions expressed are his own.)

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To contact the writer of this article: Robert Glennon at glennon@law.arizona.edu

To contact the editor responsible for this article: Mary Duenwald at mduenwald@bloomberg.net