Agrivoltaics (APV) is a promising new field that looks to double-up land use, combining solar power arrays with agriculture. Essentially, it tries to use the same plot of land for two different purposes without a corresponding drop in efficiency. So far, experiments worldwide have ranged from disappointing to encouraging, and the search continues for ways to improve configurations and cultivation. This article examines the crops that seem to work best with APV and what we can learn from their success.
What Crops Work Best? The Short Answer
APV projects have shown the most promise when paired with leafy greens (lettuce and spinach) and root crops (potatoes, radishes, beets, and carrots). While results for each of these crops (and several others) have been positive in various installations worldwide, a recent report from Oregon State University's Department of Biological and Ecological Engineering focuses on them. It highlights their excellent compatibility with solar panels.
However, the local climate may be as crucial to the success of an APV project as the crops in question. For example, the Oregon State report revealed that, while barley and other grasses worked well in the Pacific Northwest, tomatoes and peppers require hotter temperatures and might not be the best fit at that latitude.
For the study area, the researchers concluded that a combination of berries (blueberry, raspberry, and strawberry) could offer the highest crop yields and increased solar panel efficiency. On the other hand, excessively tall crops like apples and corn or sunflower were the least effective.
Defining "Best" Is a Complex Challenge
The "best" can be challenging to define. In the APV context, does it mean the highest solar panel efficiency? What about crop yield? The proper context may be one of sustainability. Can agrivoltaic projects improve food, water, energy, and climate sustainability at the same time?
In the right circumstances, it seems so. The technology is scalable, so we could deploy it widely and enjoy tremendous positive results. Moreover, agrivoltaics maps favorably onto all 17 United Nations Sustainable Development Goals (SDGs). Proponents like the Oregon State researchers believe it is scientifically viable, economically feasible, and can significantly impact societies where it's needed most.
It's all About Efficiency and Microclimate
The crops used in APV installations are just one component among many that factor into what is the "best" configuration. The Oregon State report illustrates that the interplay of solar efficiency and microclimate (partially determined by crop type) is complex but knowable. Using data collected from agrivoltaics projects, the study devised a way to rank the effectiveness of an APV installation.
The scientists determined that underlying land use was one of the most essential factors in solar panel efficiency, along with air temperature, wind speed, and relative humidity. Each of these factors has a marked effect on the ability of a panel to capture solar light and convert it to electricity.
According to their report, every 10 degrees C lowers efficiency by .5%. But, of course, wind speed affects heat dispersion, so they determined that every .5 m/s of wind speed improved efficiency by .5%. Moreover, the water evaporated from shade-loving plants cooled the solar arrays, even more, giving the highest energy efficiency rating. The symbiotic relationship between the water released by the crops and the shade provided by the solar arrays maximized the effect of the dual-use land model.
Global Data Can Help Determine Areas and Crops with the Largest Potential Impact
The study used its data to calculate agrivoltaic potential across a global map. It factored in temperature, wind speed, humidity, and a host of other factors. The results suggest that the western United States, southern Africa, and the Middle East have the most to gain environmentally, economically, and socially from a concerted agrivoltaics initiative.
The paper concluded by rank-ordering different types of land according to how much benefit they stood to gain from APV installation. Croplands, grasslands, and wetlands took the top three spots. Ironically, barren land (the most common site for conventional solar arrays) came in fifth place.
There Is No Final Word on Crops
It isn't easy to give a final word on what crops work best with agrivoltaics. Nevertheless, some trends emerge from the data. In a best-case scenario, according to a recent University of Arizona publication, an agrivoltaics setup may help generate two or three times more fruit and vegetables than traditional agricultural settings. The stud focused on chiltepins, jalapenos, and cherry tomatoes in a hot environment.
On the other hand, and in a less hot and dry arrangement, even shade-loving lettuce saw no benefit from the experiment, yielding the same amount under the open sky and under a solar panel. Therefore, as the microclimate study suggested, the best results for agrivoltaics come in a hot, dry environment with shade-loving plants. There, farmers can expect the greatest symbiosis between the crops and solar panels.
Go Native – The interplay of crop type, location, and other factors in agrivoltaics reinforces how well-balanced nature can be. Try to add more locally-grown foods to your usual diet. Without the extended supply chain, they will have lower emissions and keep the proceeds in your community.
Stay in Season – Likewise, try to get produce in season. If it's out, it's likely coming from far away. In-season means "low-impact" almost by definition. Also, who doesn't like pumpkin pie in the fall?
Follow Peak Efficiency – Solar panels are not the only things that lose efficiency in the heat. Air conditioners are similar. Enjoy some shade in the daytime if you live in a hot climate. Save the AC for after the sun goes down.