Solar panels reduce CO2 emissions per acre by more than trees—and far more than corn ethanol
The following story was originally published in Climate Law Blog From the Sabin Center for Climate Change Law at Columbia University.
September 21, New York Times Gabriel Popkin published an article titled “What better place to put a large solar farm than these forests?” Popkin described the recent approval of a 4,500-acre solar project in Virginia that will clear about 3,500 acres of forest, and asked if such a project could be sited on rooftops, parking lots and other degraded land. This blog post provides some additional information and background to Popkin’s article.
First, very few solar projects in the U.S. are currently located in woodlands. While Popkin correctly points out that about 50 percent of solar installations, measured by land area, are located in deserts, the assertion that “more than four-fifths of solar installations are located in cropland, woodland, or grassland” requires additional context.Specifically, it is important to understand that the amount of solar energy is not the same on these three types of land because Farmland has more solar projects (33%) higher than grassland (6%) or forest (4%). By comparison, nearly 3% of solar energy is currently located in urban areas.
Second, while Popkin rightly points out that, like solar farms, forests can provide climate change benefits, the article does not provide any information on the relative emissions benefits of woodlands relative to solar farms. To be clear, forests provide enormous benefits unrelated to carbon sequestration, including serving as critical habitat for native flora and fauna, filtering drinking water, preventing erosion, and providing scenic and recreational benefits to millions of people. On the narrow but important issue of carbon dioxide emissions, however, an acre of solar panels seems to offset more emissions each year than an acre of trees can absorb.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), excluding other greenhouse gases.According to Lawrence Berkeley National Laboratory, utility-scale solar power generation is between 394 and 447 MWh per acre per year. Thus, an acre of solar panels producing zero-emission electricity could save 267,526 to 303,513 pounds or 121 to 138 metric tons of carbon dioxide annually.By comparison, according to the EPA, the average forest area in the U.S. 0.84 metric tons annual carbon dioxide. As a result, an acre of solar panels in Virginia reduces carbon dioxide emissions by approximately 144 to 166 times as much annually as an acre of forest.
What about the carbon released by clearing an acre of forest?According to the EPA, the average acre of forest contains 81 metric tons of carbon, although the exact number depends largely on the species of trees in the forest. About half the amount was sequestered in the soil. Even if all 81 metric tons of carbon (including 297 metric tons of carbon dioxide) are released after conversion to the solar farm, these emissions will be offset within 2-3 years of operation.
Third, Popkin argues that siting solar projects on farmland could interfere with “one clearly important use: growing food.” However, solar projects can coexist and complement agriculture, including by improving pollinator habitat and allowing animals to graze between rows of panels.For example, the Great Plains Institute found that “utility-scale solar can Compatible with other forms of non-till farming Like pastures and grasslands. Additionally, recent research suggests that in hot, dry climates, growing crops such as tomatoes between solar panels may Increase production By creating shade, you save water, increase humidity, and reduce temperatures. Likewise, the Michigan Department of Agriculture and Rural Development has identified “the placement of commercial solar power structures… Consistent with agricultural operations,” provided that certain measures are taken to maintain the integrity of on-site agricultural land, including planting pollinator habitat and protecting mulch. In addition, the income farmers can earn by renting out portions of their land for renewable energy projects allows them to Keep the rest of the land productive while producing. shield them from low-income years.
Furthermore, any discussion of the so-called conflict between agriculture and energy production must also acknowledge that, more than one third Half of all corn grown in the United States is not used for food—not even to feed livestock—but for energy.total more than 30 million acres of farmland, Covering an area roughly the size of Louisiana, it is currently used to grow ethanol corn. All of this land can be reused for solar energy production without affecting food production.
Importantly, converting the land currently used to grow corn ethanol to solar energy would greatly increase the amount of energy produced on that land. indeed, an analysis from pv magazine It was recently discovered that converting land currently used for corn ethanol to solar could meet all of the nation’s electricity needs.Similarly, an analysis from the United Kingdom Introduction to Carbon It was found that “one hectare of solar panels used to charge an electric vehicle provides 48 to 112 times the driving distance of a car used to grow biofuels.”
By my own calculations (below), an acre of solar panels produces about 40 times as much energy as an acre of corn used to produce ethanol—and that doesn’t take into account the fact that electric vehicles use energy more efficiently than gasoline power. Facts Cars:
- As mentioned above, solar power is 394 and 447 MWh (MWh) per acre per year.
- According to the University of Nebraska-Lincoln, an acre of corn yields about 462 gallons of ethanol.[2]
- Calories are 76,300 BTU per gallon Ethanol, 462 gallons of ethanol contains 35,250,600 BTU.
- Apply standard conversion factors 3,412,000 BTU per MWhthe amount of ethanol produced from one acre of corn is equivalent to 10.3 MWh.
- Thus, even assuming a relatively high yield per acre of corn, an acre of solar panels can produce approximately 38 to 43 times as much energy per acre as corn ethanol.
Fourth, as Popkin rightly concedes, rooftops and parking lots are “often more expensive to develop than forests or farmland.”However, Popkin did not explain How much Even more expensive is to build solar on rooftops or in parking lots. According to the National Renewable Energy Laboratory, Average cost per watt The cost of installing a rooftop solar project is approximately 1.75-3 times that of utility-scale solar. The average cost per watt for utility-scale solar systems is $0.89, compared to $1.56 for commercial rooftop projects and $2.65 for residential rooftop projects.
Installation cost comparison of residential solar, commercial rooftop solar, and utility-scale solar. resource: National Renewable Energy Laboratory
Building solar canopies over parking lots also appears to be more expensive than utility-scale solar.Industry publications pv magazine used $3 per watt As a rough figure, Energy Sage estimates, based on data from its solar market, that the average installation cost is $3.31 per watt. For a real-world example, the 12.3 MW solar canopy under construction at JFK Airport will cost $56 million, or $4.55 per watt.Although in some cases the construction cost of solar canopies may be offset Additional charge for shaded parking spaces below, it will be more challenging to recoup these costs where free parking is available.And these are just installation costs; also More expensive Maintain small, widely dispersed units compared to one large system.
Comparison of operating and maintenance costs for residential, commercial, and utility-scale solar. resource: National Renewable Energy Laboratory
Ultimately, net-zero CO2 emissions by the early 2050s, with Limit warming to 1.5 degrees Celsius An unprecedented number of renewable energy facilities will need to be built in a very short period of time. Currently, the siting of solar projects on forest land is relatively rare. In rare cases, when solar energy is located in woodland, these projects appear to offset more emissions per acre than trees can isolate; 30 million acres of cropland currently used to produce corn ethanol could produce as much energy as solar farms , without affecting food production; utility-scale solar projects are much less expensive to install and maintain than rooftop and parking lot solar projects.
Matthew Eisenson is dedicated to Renewable Energy Legal Defense Initiative exist Sabine Center for Climate Change Law.
