Crops vs Solar to Produce Vehicle Miles Travelled

November 7, 2023 By , ,

November 7, 2023

By Allison Bergquist

One of Stillwater’s own was recently approached by a land developer to consider turning farmland in Oregon into a solar farm. The lease payment amounts proposed in the out-years would provide approximately four times the income for the land compared to farming the same acres – a significant incentive and a difficult one to dismiss without thoughtful analysis. In a robust discussion via Slack and on a company-wide conference call, several of Stillwater’s Senior Associates raised multiple ramifications concerning the potential indirect land use change (ILUC) issues high value solar may drive. ILUC is an assessment incorporated into the lifecycle analysis for biofuels to account for the use of productive agricultural land for biofuel feedstock production instead of food crops. In this article, we will focus on considerations around farmland usage for solar arrays especially as it pertains to the transportation industry.

Agriculture AND Solar Is Already a Thing

There is a fancy name for this practice – agrivoltaics, which means co-locating agriculture underneath or between solar panels; also called agrivoltaic farming. To be clear, this is different than the idea of solar completely replacing agriculture on a piece of land. The U.S. Department of Energy (DOE) office of Solar Energy Technologies provides farmers with a guide to help them incorporate solar into their farming practices. In 2022, the National Renewable Energy Lab (NREL) published a technical paper resulting from their research about success factors in the United States for agrivoltaic projects. The figure below comes from this report and depicts the “5 Cs of success” for agrivoltaic projects: Climate, Configuration, Crops/Cultivation, Compatibility, and Collaboration.

The 5 Cs of Agrivoltaic Project SuccessSource: August 2022 NREL Technical Report

According to Colorado Agrivoltaics, Japan, Germany, and France have already implemented these agrivoltaic practices; India and China are starting to adopt them as well. Two key benefits of agrivoltaic farming include economic opportunity for farmers and doubling land use. Multiple articles dive into more details about agrivoltaic farming – World Economic Forum, National Resources Defense Council, North Carolina State University, Oregon State University, and the American Farmland Trust, among many others.

What About Solar Without Farming?

Agrivoltaic farming is not the only option. If significant revenue can be made from leasing land for solar panels, a farmer might opt for that rather than continuing to farm the land. To provide an idea of the dollar figures potentially on the table, consider these few data points. In California, a farmer was offered $1,600 per acre per year for a lease, with a 2% annual increase for 25 years. Elsewhere in California, a farmer was offered $10,000 per acre to buy, and the leasing option would have been 10% ($1,000 per acre). In Oregon, a farmer was offered $1,500 per acre per year.

Some states are already thinking about potential land use change issues around solar farms and working to manage it. In 2019, Oregon’s Department of Land Conservation and Development pursued a rulemaking about solar facilities on high-value farmland, which they finalized later that year. In 2023, Washington State passed HB 1216 about clean energy siting, including solar. The situation in California seems a bit more complicated, as the state wrestles with increasing drought and efforts to meet ambitious climate goals like the Renewable Portfolio Standard. California seems to be focused more on the research phase of determining how agrivoltaics would affect the land, farmers, and environmental challenges. During the 2023 session, California Senators proposed SB 688 for agrivoltaics research funding, but it made minimal progress.

How Does This Apply to Transportation?

As transportation fuels move away from fossil fuels, many renewable fuels rely on crop-based feedstocks. These feedstocks are grown on the same land where farmers might consider adding or transitioning to solar, thus raising the question around a new phase of ILUC considerations. Importantly, when we think about the topic from an ILUC perspective, the crop-based feedstocks aren’t the only consideration; co-products are significant and complicate the discussion. Soybeans, for example, are grown for high protein meal which represents about 80% of the whole bean and is used primarily as animal feed.  Soybean oil was previously a waste product but is now considered a byproduct or co-product as it is used for the production of biodiesel (BD) and renewable diesel (RD). As such, biofuels aren’t the only markets impacted by the conversion of farmland for solar array installation – the primary markets for these feedstocks are also impacted. For purposes of this article, however, we will remain focused on the transportation fuel impacts.

The mass of feedstock required to produce one gallon of fuel is generally known. For example, 7.5 pounds or 9.5 pounds of soy is required to make one gallon of BD or RD, respectively. Much less consistent is the volume of fuel produced per acre of farmland. This is understandable, as numerous factors affect the productivity of land, which then impacts the volume of fuel ultimately produced from one acre. Research from the University of Nebraska indicated the volume of BD produced from Nebraska farmland is 48-63 gallons per acre of soybeans, 63-100 gallons per acre of sunflowers, and 63-127 gallons per acre of canola. The Alternative Fuels Data Center estimated the average yield of soy biodiesel is 53.4 gallons per acre, with an industry best of 62.5 gallons of soy biodiesel per acre. There is generally one harvest of soybeans per year, making these volumes annual production numbers from one acre of land.

For simplicity, we will assume one acre of farmland produces 60 gallons of BD or RD per year. Using this assumption, we will compare the impacts on transportation. At 25 miles per gallon (mpg) for a diesel pickup truck, one acre of farmland will result in 1,500 vehicle miles traveled (VMT) using RD as a 100% drop-in fuel replacing fossil diesel. BD is not a drop-in fuel but is instead blended with fossil diesel before being used to fuel a vehicle. If 60 gallons of BD was blended to make B20, that would provide a total of 300 gallons of B20. At 25 mpg, a diesel pickup could travel 7,500 miles on that volume of B20 fuel (6,000 miles further than on RD). However, since the B20 did not displace all the fossil diesel, the overall emissions in these two scenarios would not be equivalent. (Additional detailed analysis on this subject is both interesting and warranted but is beyond the scope of this article.)

Next, let’s look at the amount of power the same acre of land could produce to “fuel” electric vehicles with solar energy. Numerous variables affect power output of solar panels. For simplicity, we will use NREL’s total area generation-weighted average of 3.5 acres per gigawatt-hour per year. One gigawatt-hour equals one million kilowatt-hours (kWh). That means one acre could produce 285,714 kWh per year of energy.

Among the current and announced electric vehicle and truck population, significant variability exists regarding battery size, usable battery capacity and stated range. According to the electric vehicle database, the average usable battery capacity for fully electric vehicles is 68.7 kWh and the average range is 357 km or 222 miles. Viewed from another perspective, light-duty EVs get 3-4 VMT per kWh, while medium-duty electric pickup trucks are closer to 2 VMT per kWh. Using those numbers, the resulting EV miles powered by 1 acre of solar panels would be between 800 thousand and 1.14 million miles for light-duty EVs and roughly 570 thousand miles for medium-duty pickup trucks. Ignoring all the logistics required to support this very specific use of solar power from one acre of land, the numbers are impressive. Worst case (7,500 miles on B20 vs. 570,000 miles on solar), this could be a 380x increase in VMT on clean energy, not to mention the implications for GHG emissions.

Unfortunately, the situation is not that simple or clean. Recall the discussion above about co-products from soybeans, which would be lost if the land were completely converted to solar. Additionally, numerous complexities around logistics, efficiency, storage, and daily electrical use for EVs compound the challenge of easily leveraging the solar output from a geographically dispersed piece of land. For example, most EVs are charged at night, putting a heavy load on battery-stored renewable power at the utility stations servicing residential areas. Home charging also means a higher load across the residential whole system, rather than consolidating heavy loads at fewer industrial fast-charging stations. Accommodating this increased load will be expensive; a Kevala study in May estimated up to $50 billion would be required by 2035 to update California’s distribution grids so they could handle the increased EV demand.

Want to dig deeper? Stillwater can help. Contact us to learn about how we would approach a more robust analysis.


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