Analysis by Paul Mathewson, PhD, and Nicholas Bosch
Overview
Despite the huge amount of agricultural land dedicated to growing corn for ethanol, solar photovoltaics have been proven to be a more efficient source of energy production. This analysis quantifies the difference in energy production between corn for ethanol and solar photovoltaics, comparing energy return on investment (EROI), vehicle miles powered per acre, and overall land-use efficiency, while exploring the policy implications for Wisconsin’s clean energy transition.
Key Points
- Energy Efficiency: Solar photovoltaics have an EROI of ~8 compared to corn ethanol’s ~1.2, meaning solar delivers significantly more net energy to society per unit of input.
- Land-Use Efficiency: Assuming average EROI, net energy production per acre is 100-125x greater for solar photovoltaics than for corn-based ethanol.
- Potential For Renewable Transition: Wisconsin could meet its carbon-free goals using 240,000–285,000 acres of solar. That’s less than one-third of the land currently used for ethanol.
Summary
Wisconsin currently dedicates over 1 million acres of farmland, about a quarter of all corn planted in the state, to grow corn for ethanol production. The practice was originally designed to support cleaner-burning fuels, but emerging data shows that energy production by solar photovoltaics is exponentially more land- and energy-efficient than corn ethanol. Technological advances continue to improve solar energy density. Meeting Wisconsin’s carbon-free goals would require only a small fraction of farmland for utility-scale solar, freeing land and vastly increasing energy output compared to corn ethanol.
Important Takeaways
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Solar Vastly Outperforms Corn Ethanol: In net energy production, solar delivers 88% of generated energy to society versus only 20% for ethanol.
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Ethanol Requires More Agricultural Land Than Solar: Solar energy would need just 1.7-2% of Wisconsin’s total agricultural land to produce the same amount of energy currently generated via corn ethanol production.
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Technological Improvements Make Solar More Promising: Energy density per acre for solar photovoltaics increased 25-33% from 2011–2019, while ethanol remains limited by photosynthesis efficiency.
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Corn Ethanol Is a Low-Return Energy Source: Some EROI estimates for corn ethanol fall below 1, meaning it could consume more energy than it produces. Meanwhile, solar is consistently high-return.
