Solar Panels Reduce CO2 Emissions More per Acre than Trees — and Much More than Corn Ethanol

by Matthew Eisenson (Columbia Climate School) ... On September 21, the New York Times published an essay by Gabriel Popkin titled “Are There Better Places to Put Large Solar Farms Than These Forests?” Popkin describes a recently approved 4,500-acre solar project in Virginia that will remove approximately 3,500 acres of forest and asks whether such projects could be sited instead on rooftops, parking lots, and other degraded land. This blog post provides some additional information and context to Popkin’s essay.

First, only a very small percentage of solar projects in the United States are currently being sited on forested lands. While Popkin correctly notes that approximately 50% of solar energy facilities, as measured by land area, are sited in deserts, the assertion that “more than four-fifths of the rest go on farmland, forestland or grasslands” requires additional context. Specifically, it is important to understand that solar is not being sited in equal quantities on these three types of land, as farmland hosts far more solar projects (33%) than either grassland (6%) or forests (4%). For comparison, nearly 3% of solar power is currently sited in urban areas.

Second, while Popkin correctly notes that forests, like solar farms, offer climate-change benefits, the essay does not provide any information on the relative emissions benefits of forested land versus solar farms.

However, on the narrow but important issue of carbon dioxide emissions, an acre of solar panels appears to offset more emissions each year than an acre planted with trees can sequester. In Virginia, where the primary source of electricity is natural gas, the emissions intensity of electricity is 679 pounds of carbon dioxide per megawatt-hour (MWh), not including other greenhouse gases. According to the Lawrence Berkeley National Laboratory, utility-scale solar power produces between 394 and 447 MWh per acre per year. Thus, an acre of solar panels producing zero-emissions electricity saves between 267,526 to 303,513 pounds, or 121 to 138 metric tons, of carbon dioxide per year. By comparison, according to the EPA, the average acre of forest in the United States sequesters 0.84 metric tons of carbon dioxide per year. Thus, an acre of solar panels in Virginia reduces approximately 144 to 166 times more carbon dioxide per year than an acre of forest.

Third, Popkin suggests that siting solar projects on farmland may interfere with an “obvious an important use: growing food.” However, solar projects can coexist with and complement agriculture, including by improving pollinator habitat and allowing animals to graze between rows of panels. The Great Plains Institute has found, for example, that “utility-scale solar can be compatible with other forms of non-cultivated agriculture like pasture and grasslands.” In addition, recent research has shown that growing crops, such as tomatoes, in between rows of solar panels in hot, dry climates may increase yields by creating shade, which conserves water, increases humidity, and lowers temperatures.

Moreover, any discussion of a purported conflict between agriculture and energy production must also acknowledge that more than one-third of all corn grown in the United States is used not for food—or even to feed livestock—but for energy.

Importantly, converting the land currently used for growing corn ethanol to solar energy would greatly increase the amount of energy produced on that land.

Fourth, as Popkin correctly acknowledges, rooftops and parking lots are “generally more expensive to develop than forest or farmland.” However, Popkin does not explain how much more expensive it is to build solar on rooftops or parking lots. According to the National Renewable Energy Laboratory, the average cost per watt of installing rooftop solar projects is approximately 1.75-3 times as expensive as utility-scale solar.

Constructing solar canopies over parking lots also appears to be more expensive than utility-scale solar. READ MORE