They nourish and give energy

Agriculture has large open, sunny areas. Why not combine food production with energy production (1)? Moreover, the electricity generated by solar panels could be used locally, for example, to power irrigation pumps, and the surplus could be sold to the grid, increasing the income of the owner.

It is worth knowing that many plants do not like strong direct sunlight. Panels placed above them would not interfere, and even optimized the harvest. In general, they can be adjusted and change the level of incoming light according to extremely precisely programmed patterns. You can also think of these as modern greenhouses that use them instead of regular glass panels. solar panels.

A year ago, Scientific Reports published a study from the University of Oregon that showed that covering as little as one percent of the world's arable land with such installations should be enough to provide electricity to all mankind.

Instead of competing for space, divide the field

In 1981, Adolf Goetzberger and Armin Sastrow were the first to propose the concept of dual use of arable land for production. solar energy and growing crops to improve overall agricultural productivity. This was their contribution to the then-ongoing debate about competition for arable land between solar energy production and arable crops.

Based on the assumption that there is such a thing as a light saturation point, and increasing the number of photons does not lead to improvement, Japanese researcher Akira Nagashima proposed a practical combination of photovoltaic systems and agriculture in order to use excess light. He developed the first prototypes in 2004.

By 2017, more than a thousand photovoltaic systems have been installed on Japanese farmland, coexisting with traditional agriculture. To obtain a permit to operate solar panels on crops, farmers in Japan must meet the maintenance requirement of at least 80 percent under local law. normal agricultural production.

In 2017, a 35 MW power plant was put into operation in Japan, installed on 54 hectares of crops. The degree of shading of this power plant is 50 percent, which is more than 30 percent. shading commonly used in Japanese agro-power plants. Farmers cultivate ginseng, ashitaba and coriander, among others. A 480 MW solar power plant, including agro-power plants, is to be built on Ukujima soon.

The term "agrovoltaics" appeared in one of the publications in 2011. In Asia, the term "solar sharing" is also sometimes used. Following the example of Japan, many countries of this continent are undertaking similar projects, including, of course, China and India. In the latter case, agro-energy is seen as a great opportunity to increase the incomes of the rural poor. In Malaysia, attempts were made to install solar panels on tea plantations, and in Vietnam - on shrimp farms.

Of course, this concept also reached Europe. Earliest and greatest extent in France. Photovoltaic greenhouses have been built here since the beginning of 2007. An example of French technology is the Agrinergie project, developed by Akuo Energy since XNUMX.

Since 2009 the French companies INRA, IRSTEA and Sun'R have been working on a program developed for fields called Sun'Agri. The first prototype was installed on an area of ​​0,1 hectares in Montpellier. Further prototypes of the unit with mobile single axis panels were built in 2014 and 2017. Sun'R's first outdoor agro-electric plant was built in the spring of 2018 in Tresser in the Pyrenees-Orientales. The power plant has a capacity of 2,2 MW from panels located on 4,5 hectares of vineyards (2). And these are not the only French projects of this type.

2. Growing vines with solar panels

Excess light from photosynthesis

In the United States, these projects are managed by SolAgra (3) in collaboration with the UC Davis Department of Agronomy. The first power plant with an area of ​​0,4 hectares is under development. The area of ​​2,8 ha is used as a management object. Several types of crops are being studied: alfalfa, sorghum, lettuce, spinach, beets, carrots, radishes, potatoes, arugula, mint, turnips, cabbage, parsley, coriander, beans, peas, shallots, mustard. Agroelectric experiments are also being conducted at a number of American universities.

3. Photovoltaic installations next to SolAgra crops

According to a National Science Foundation-funded study led by engineers, plant biology researchers and physics researchers at North Carolina State University, many greenhouses can become energy neutral by using transparent solar panels to generate energy (4). We are talking about the energy use of light wavelengths that plants do not use for photosynthesis. The results of the study were published in February this year in the journal Joule.

4. Agro-electric greenhouse

"Plants only use some of them for photosynthesis wavelengths of light. The idea is to create greenhouses that generate energy from this unused light while letting in most of the photosynthetic light,” explains Brendan O'Connor, one of the study's authors. “We can achieve this with organic solar cells because they allow us to fine-tune the spectrum of light absorbed by the solar cell. However, until now it was not clear how much energy a greenhouse could get if it used these translucent, selective, organic solar cells.”

To answer this question, the researchers used a computational model. “Most of the energy used in greenhouses is related to heating and cooling, so our model was focused on calculating the energy load required to maintain the optimal temperature range for growing tomatoes,” says O'Connor. "The model also calculated the amount of energy the greenhouse would produce if solar panels were placed on its roof."

For plants that love shade

Three main types of agrovoltaics are currently being researched: solar panels in the space between crops, flat solar panels above crops, and greenhouse solar system. The main parameter taken into account for agrovoltaic systems is the angle of inclination of the solar panels. Other variables that are considered when installing an agro-electric system are the type of crop, the height of the panels, the solar radiation in the area, and the climate in the area.

Wen Liu from the Hefei University of Science and Technology in China proposed a new idea for agrovoltaics in 2015, using curved glass panels coated with a polymer film to selectively transmit the wavelengths of sunlight needed for plant photosynthesis (blue and red light). . All other wavelengths are reflected and concentrated in concentration solar panels for power generation.

Modeling and research in agrovoltaics show that the production of electricity from crops does not reduce agricultural productivity. Of course, this works best for plants that are shade tolerant or even prefer less sunlight.

In a recent study in Arizona, scientists compared plants grown under solar panels with plants grown in direct sunlight. They noted in particular that total chiltepin production was three times higher in plots under solar panels, and cherry tomato yields doubled under solar panels. Some plants in agroelectric systems required much less water, in part because shady soil retained more moisture.

A research project in South Deerfield, Massachusetts, provided similar perspectives. Tests have shown that growing broccoli and similar vegetables produces 60 percent more plant weight than plants in full sun.

So maybe the field for the development of great solar farms is not the Sahara and other deserts, as is often predicted, but fields known so far only as food?