The practice of food and energy double-generation, known as “solar sharing” in Japan, was originally developed by Akira Nagashima in 2004. Nagashima, a retired agricultural machinery engineer, studied biology and learned of the light saturation point at which increase in the level of sunlight does not cause any further increase in the rate of photosynthesis. (Actually, only a small fraction of the incident sunlight is needed for plants to reach maximum rate of photosynthesis; too much light can be damaging, and plants have evolved mechanisms to protect themselves from being ‘sunburnt’; see [2] Harvesting Energy from Sunlight with Artificial Photosynthesis, SiS 43).
Nagashima came up with the idea of combining PV with farming. He devised and originally patented a special structure like a garden pergola, which was tested in fields with different crops and shading rates. The structures are made of pipes and rows of PV panels mounted above ground, and arranged at certain intervals to allow enough sunlight for photosynthesis. There is no concrete footing so the structures can be easily dismantled; the system is designed to allow adequate sunlight for crops and space for agricultural machinery to be used, as stipulated by MAFF guidelines.
According to Nagashima, the MAFF guidelines are to ensure that farmers remain farmers, and not to fully convert productive farmland into solar facilities. Based on his tests in the Chiba Prefecture, he recommends about 32 % shading rate. Farmers are required to report their annual crop cultivation, and if the amount cultivated on the solar-shared farmland falls below 80 %, they will be required to dismantle the PV system.
Solar-sharing pays
Japan requires about 2.5 million acres of land to supply the entire country’s electricity with PV [1]. Under the solar-share scheme, it will take about 7 million acres of farmland to supply the same amount of electricity. Japan currently has more than 11.3 million acres of available farmland.
Solar sharing could well be a readily available alternative to artificial photosynthesis [2] in harvesting sunlight, as batteries for energy storage improve and come down in price [4] (Renewable Ousting Fossil Energy, SiS 60).
Before the industrial revolution, farmers provided both crops and energy in the form of firewood and charcoal to society, Nagashima said [1], solar-share farming will do the same again and revitalize the farming sector.
Sources: CECHR@CECHR_UoD
MORE: Japanese Farmers Producing Crops and Solar Energy Simultaneously
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