Solar energy is central to models of environmental sustainability, but not all projects are built the same. One concern in energy development, renewable or otherwise, is the concept of “energy sprawl,” which is the dedication of land for energy production and distribution.
Environment California estimates rooftop solar could prevent the development of 148,000 acres of land versus a ground mounted utility-scale only model. This is based on a state regulator estimated deployment of 28.5 GW of rooftop solar through 2045 in order to meet clean energy goals. That is an area about half the size of Los Angeles that could be preserved.
Solar is hailed for its ability to be integrated into the built environment, placed on rooftops, integrated into building facades, on carports, etc. However, in order to meet aggressive decarbonization goals and achieve a 100% renewable energy system, ground-mounted solar will be also needed. This is where agrivoltaics, the practice of co-locating solar energy production with agricultural functions, can step in.
Research by Oregon State University found that solar and agricultural co-location could provide 20% of the total electricity generation in the United States. Wide-scale installation of agrivoltaics could lead to an annual reduction of 330,000 tons of carbon dioxide emissions while “minimally” impacting crop yield, the researchers said.
The paper found that an area about the size of Maryland would be needed if agrivoltaics were to meet 20% of U.S. electricity generation. That’s about 13,000 square miles, or 1% of current U.S. farmland. At a global scale, it is estimated that 1% of all farmland could produce the world’s energy needs if converted to solar PV.
Agrivoltaics does more than preserve land and make the most of an acre. There are synergies between the solar arrays and the agricultural activities below.
For example, a team of researchers with the University of Arizona, which operate an agrivoltaic test center at the Biosphere 2, a fully self-contained indoor “natural” environment, found that crops improve solar array performance, and the solar arrays improve crop yield in dry environments.
The Biosphere team found that the shade provided by the photovoltaic system reduced evaporation, meaning that water would stay on the surface longer and better feed crops than open-air land-based agriculture. Not only does this save water, but it makes the plants grow stronger, leading to a better crop yield. Additionally, the shaded space provided by the panels causes plants to spread out, searching for sunlight. In the trials, the agrivoltaic-shaded leaf was nearly twice the size of the open-air one.
In dry climates like the one that surrounds Biosphere 2, there can often be too much light and heat for plants to grow properly. The panel’s shade helps create better conditions for the plants. The same goes for solar panels, which produce less power at high temperatures. A conventional solar facility may remove all vegetation below, which, in large solar arrays, causes a studied effect of a heat island.
Excess sun energy that isn’t converted to electricity can leave the area in two ways: either as latent heat or sensible heat. Sensible heat is the type that we can feel, and the type that is damaging to solar PV production. Latent heat is the energy that is absorbed by nearby water, evaporating into vapor. By adding crops below in a dry climate, you are adding more latent heat absorption, taking heat pressure off the panels, and boosting production and lifecycle.
Dry-climate farmers may enjoy working with agrivoltaics, too. Preliminary data from the center suggests skin temperatures are about 20 degrees Fahrenheit lower than open-air farming.
The National Renewable Energy Laboratory (NREL) is exploring many possibilities for agrivoltiacs, including placing cattle or sheep, crops, pollinator-friendly native plants, or soil rehabilitation and other ecosystem services in the same plot of land as active solar arrays.
NREL’s main research project on agrivoltaics is called Innovative Solar Practices Integrated with Rural Economies and Ecosystems (InSPIRE). The InSPIRE project developed a financial calculator to quantify the benefits of the practice. It also developed a list of best practices for those interested in entering the field. Additionally, InSPIRE tracks all the active agrivoltaics site across the U.S., which can be found here.
“Through our work, which spans multiple regions, configurations, and agricultural activities, we’ve seen so many initial promising results,” said Jordan Macknick, NREL’s lead energy-water-land analyst and principal investigator for the InSPIRE project. “Now, our challenge is to figure out how to scale up and replicate these successes.”
NREL also developed a set of five basic principles for success in agrivoltaics, called the five C’s:
- Climate, Soil, and Environmental Conditions — The ambient conditions of a location must be appropriate for both solar generation and the desired crops or ground cover.
- Configurations, Solar Technologies, and Designs — The choice of solar technology, the site layout, and other infrastructure can affect everything from how much light reaches the solar panels to whether a tractor, if needed, can drive under the panels. “This infrastructure will be in the ground for the next 25 years, so you need to get it right for your planned use. It will determine whether the project succeeds,” said James McCall, an NREL researcher working on InSPIRE.
- Crop selection and Cultivation Methods, Seed and Vegetation Designs, and Management Approaches— Agrivoltaic projects should select crops or ground covers that will thrive under panels in their local climate and that are profitable in local markets.
- Compatibility and Flexibility — Agrivoltaics should be designed to accommodate the competing needs of solar owners, solar operators, and farmers or landowners to allow for efficient agricultural activities.
- Collaboration and Partnerships — For any project to succeed, communication and understanding between groups is crucial.
InSPIRE represents the largest, longest-running, and most comprehensive agrivoltaics research effort in the world, spanning 28 sites in 11 U.S. states, Puerto Rico, and the District of Columbia. Some of these sites involve direct research, some involve research design and consideration, and some involve ongoing consultation and mentoring of partners.
“One thing InSPIRE has done really well is to create a community of people who are thinking differently about PV solar design and management. Universally, following an InSPIRE conference call hearing scientists and industry practitioners share their results, there’s tremendous energy and optimism for the challenge and opportunity ahead of us,” said Rob Davis of Connexus Energy, the Midwest’s largest electric co-op.
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