In densely populated areas land-use and water-use conflicts have started to slow down the spread of solar power.  Water used to clean solar panels is often lost from irrigation and other uses, while the installation of solar power plants has started to compete for land with agriculture and many other uses.

The electrodynamic cleaning system devised by Professor Jitendra Nath Bera and his colleagues in the Calcutta University may be able to solve the water-use conflicts, or at least most of them. But it cannot mitigate the more general disagreements on how a certain patch of land should be used.

Some countries, including Italy, have already banned the instalment of photovoltaic panels on agricultural lands. Similar proposals have been put forward in many other countries, as well. With the world planning to establish 70 000 gigawatts of solar power within the next half a century, land-use conflicts related to the production of solar power are bound to become worse and more numerous, unless we find ways to overcome them.

Could solar power installations be planned so, that it would be possible to produce both food and electricity on the same land? Could solar power and agricultural production complement each other? Could solar power plants increase agricultural production, instead of competing with it?

In the tropical and subtropical regions, the amount of sunlight is almost never the factor limiting agricultural production. During the day a single layer of crops receive up to eight times more sunlight than it can actually utilize for photosynthesis.

The most important factors limiting the potential of agricultural production are the availability of freshwater and nutrients, and the temperature, which is often uncomfortably high for photosynthesis.

As a very general thumb rule it could be said that the most optimal temperature range for photosynthesis is roughly between 25 and 35 degrees Celsius. The efficiency of photosynthesis increases steeply until 25 degrees Celsius, and then only much slower. After 25 degrees Celsius the efficiency almost plateaus, and then begins to slow down, first slowly and then steeply.

This, of course, is only a very rough generalization: there is significant variation between the adaptations of different species.

However, there is a reason for why numerous tropical agroecosystems have traditionally used and are still using shade trees or shade nets. The use of shading trees was still much more common before the colonial period, before the European powers introduced their own farming systems, developed for colder climates, into the tropics.

The partial shading not only reduces evaporation of water from the soil but also lowers the temperatures of the soil and surface air closer to the range that is optimal for photosynthesis. It should be remembered, in this context, that in the tropics black surface soil can heat to 50 – 80 degrees Celsius, when exposed to direct sunlight at noon, during cloudless days.

In experiments conducted in Abu Dhabi, food plants produced eight times more with the same amount of water when the temperature was dropped from 45 degrees to 30 degrees Celsius.

Could photovoltaic panels or narrow photovoltaic modules be installed on agricultural lands so that they would function like shade trees or shading nets, providing partial shading for the crops, reducing evaporation from the soil and lowering temperatures?

In such systems water used to clean the photovoltaic panels – when electrodynamic cleaning will not be applied – would almost automatically double as irrigation water, watering the food crops growing next to the panels.

Theoretically, such co-production of solar power and food could significantly increase the productivity of most food crops. *Illustrative Image.