Agrivoltaics: can farming and solar panels coexist?

On September 21, Rutgers University had open houses at two of its Agriculture Extension Service demonstration farms. I was able to attend the one near Bridgeton, NJ, approximately midway between Kendal and Cape May. A major project there is studying agrivoltaics: mixing solar panels with growing crops. I learned a lot.

New Jersey’s governor Murphy is pushing to move New Jersey to 100% renewable generation by 2035. One of the ways to get this done is to install lots of solar panels in existing farm fields, while still allowing farming to continue. New Jersey (the “Garden State”) has vast amounts of farmland in its southern half, so the solar potential is enormous.

The Bridgeton location (called “RAREC”, for Rutgers Agricultural Research and Extension Center) has both state and federal funding, plus some money from Rutgers. (Unfortunately, $1.8 million of allocated federal funding was recently cut off, apparently due to anti-renewable sentiment in Washington.)

Choosing the crops and the panels. Given the objectives of the RAREC project, the crops chosen for the experiment were some of the major New Jersey cash crops. When I visited, soy beans, tomatoes, eggplants, and bell peppers were being grown. Most of the acreage was in soy beans.

The panels are laid out in parallel rows, spaced 34’ apart. That gives enough space for five parallel beds of vegetables between them. Between the beds is an access pathway for manual harvesting. Vegetable harvesting is done by a locally-recruited team of “master gardeners”, who also grade and weigh the produce. Harvesting occurs every week or two, on a schedule that depends on the type of vegetable, the weather, and the soil conditions.

The soy beans, which are machine-harvested, do not need to be planted in beds, so the whole 34’ space between panel row is filled with soy beans.

The panels are mounted on “single-axis trackers”, which means that during the course of the day they pivot on a horizontal axis that is oriented north and south. In the morning, they point east; at noon they are flat; and in the evening, they point west.

The panels are on top of 8’ steel posts. That height was chosen so that, when the panels are in their flat position, farm machinery can pass beneath them. This height also allows more sunlight to reach the crops than if the panels were lower. Bifacial panels were used, which means both the front and back of the panels can generate electricity. The back side never faces the sun, but diffuse light from the sky does allow them to generate a significant amount of electricity—somewhat less than 30% of the amount generated by the front side.

Early results. This is the second year that the project has been up and running. Last year was unusual in that it was much drier than normal, and there was more sun (fewer clouds). That means that last year’s harvest may not be representative of what can be expected in future years.

With that caveat, here is the outcome from last year. The soybean yields were actually slightly better close to the panels than in the “control” area out in the open. Eggplant yields, however, were lower near the panels (where they were shaded part of the day). Pepper yields were better than the eggplants, but still not as good as the controls. Tomatoes yields were hardly different between the two environments.

Results this year (with more typical weather) may be different.

The solar facilities have not worked entirely as planned. Two of the tracking systems (out of 18 total) were out of commission when I visited, leaving the panels mounted on them stuck in one orientation.

The trackers will be fixed. But another problem won’t be. Planning for the RAREC solar facility was based on capacity maps from the local power utility, Atlantic City Electric. According to those maps, there should have been plenty of substation capacity for RAREC to send its surplus power to the grid.

However, the maps were wrong, and RAREC would have had to pay $790,000 to upgrade the nearest substation in order to correct the capacity limitation. They didn’t have the money, so they have ended up with only a third of their panels delivering electricity to the grid. The experiment continues, however, with all the panels tracking the sun as if they were working properly. The two-thirds of the panels that can’t be connected can still generate electricity, but it is not used. It is just dissipated as heat.

The future. As the RAREC experiment begins to produce statistically-significant results, those results will be used by the New Jersey Utility Commission to determine what rate will be paid for agrivoltaic electricity. There will be an “adder”—a little extra above the normal rate—to encourage the development of agrivoltaics.

It is anticipated that solar developers (not the farmers themselves, who often lack the necessary access to capital) will fund the building of the solar systems. The farmers will get a cut of the profits.

Certain parts of the state are off-limits for this type of solar (most of the pine barrens, some coastal areas, and areas of historic importance) but the major agricultural areas should benefit from it.

Another of the Rutgers sites, near the main campus in New Brunswick, is experimenting with two-sided vertical solar panels that don’t track the sun. The rows of panels can be thought of as a “dark fence”, with one side facing east and the other west. That approach is cheaper because it doesn’t require trackers, and the arrangement minimizes the issues related to running farm equipment among the panels. But it does generate less electricity. At that site, Rutgers will also be experimenting with grazing cattle among the panels.

Having seen agrivoltaics in action, I wonder whether it might be used at the Kirkpatrick Farm site, adjacent to Crosslands. I now see that there are a lot of factors that would need to be carefully considered if KCC were to move in that direction.