Solar Crops

Solar Crops and Agro-photovoltaics

You have heard about solar fuel, solar energy, solar cells, solar irradiation, and plenty of other things solar.  You have also heard about solar photovoltaics, solar thermal photovoltaics, and many other technologies solar. Add to that now the solar crops from Germany. The smart Germans have invented the science of agrophotovoltaics.

What is Agrophotovoltaics?

All science and engineering is primarily, commonsense supported and sharpened by the subject of mathematics (which baffles so many people and is loved by so many). Agrophotovoltaics is no exception. It is simple and pure commonsense. Germany is leading the shift towards clean energy, and have recently celebrated a day which was totally carbon free. I this drive, they realized that a lot of cultivable land was going to solar generation. As the drive towards totally green energy in Germany continued, more area will be needed for solar farms. At the same time, as population increases, more land will be needed for food. That is a serious issue for small-area countries like Germany.

Polyculture of a New Kind

Polyculture means growing two crops simultaneously in the same piece of land. An example is onions and carrots being planted together. Together they protect each other from pests.  Why can’t we grow crops and generate solar energy simultaneously over the same piece of land? Fraunhofer Institute for Solar Energy Systems (ISE) started the experimental project called Agrophotovoltaics (APV).

Co-existence

The basic problem was how to make solar panels and crops coexist without grabbing land from each other. Further, solar panels are taller. They will deprive the crops of sunlight.  How would that affect the yield?  ISE found a very ingenious solution.

The Two-Story-House

Solar panels are neither carrots nor onions. They do not need ground. They need space. If they can perform over rooftops, they can perform over elevated structures- something like a solar roof. So why not position the panels high up, leaving the space below for crops. Sure, but that will cause even more shading! There was another concern. The elevated structures housing the panels will have to be mounted on the ground. Would the support structures obstruct the farm machinery?

The Solution

The Germans tried a trick. Place the solar panels in rows facing south-west at a height of 15 meters. And leave a carefully calculated large enough space between the rows. As the sun moved, it will gradually move over most of the area below. Averaged over the day, the plants below will receive a uniform amount of sun. Scattered light will also help fill the gaps. The height and spacing should also permit unhindered movement of the farm machinery.

Will it Work

The best of theories must be verified experimentally. That is why the ISE experiment was conducted. The results of a one-year trial, reported recently, are very encouraging.

Crop Performance

They cultivated a variety of crops in the first trials: potatoes, winter wheat, celeriac and clover grass.  Not that the shading did not affect the crop yield. It did. What was remarkable was that the effect was much below what could be. Compared to a reference plot, wheat, potatoes, and celeriac showed a yield loss of only 18 to 19 percent. Clover gross showed a much smaller loss in yield-just about 5.3%.

Net Gain

The solar power output more than compensated for the little loss in crop yield. In one farm, 720 bifacial solar panels had a rated power of 194 KW, and produced 1266 KWh of electricity per installed capacity of one KW. That solar ‘yield’ of electricity is 33% above the national average of 950 KWh/KW. bifacial panels also generate electricity  from scattered light on the rear side and promise another 25% when snow cover is available.

Land Gain

This experiment provides additional virtual land area to small countries. Even with a crop yield loss of 18%, land gain in this technique is close to 82%. One hundred hectares will now produce as much as 182 hectares. That is phenomenal.

Still to Work

Researchers caution against complacence. A lot more needs to be done. Other crops must be tested. Utilization of the produced energy needs optimization. Storage facilities will have to be developed and integrated. Currently the surplus power is fed to the Elektrizitätswerke Schönau grid, an electric company which derives 100% of its power from renewable energy sources. Also, the company is  a partner in the project.

Funding

The project was supported by funding from Federal Ministry of Education and Research (BMBF) in addition to Research for Sustainable Development (FONA).