Farmers in Japan can now generate solar electricity while growing crops on the same farmland. This co-existence or double-generation is known as “Solar Sharing” in Japan. The concept was originally developed by Akira Nagashima in 2004, who was a retired agricultural machinery engineer who later studied biology and learned the “light saturation point.” The rate of photosynthesis increases as the irradiance level is increased; however at one point, any further increase in the amount of light that strikes the plant does not cause any increase to the rate of photosynthesis.
By knowing that too much sun won’t help further growth of plants, Nagashima came up with the idea to combine PV systems and farming. He devised and originally patented special structure, which is much like a pergola in a garden. He created a couple of testing fields with different shading rates and different crops. The structures he created are made of pipes and rows of PV panels, which are arranged with certain intervals to allow enough sunlight to hit the ground for photosynthesis.
Based on the tests conducted at his solar testing sites in Chiba Prefecture, he recommends about 32% shading rate for a farmland space to reach adequate growth of crops. In other words, there is twice as much empty space for each PV module installed. Takazawa installed 348 PV panels on a small 750 square-meter of farmland. PV panels are installed on pipes, which are 3-meter high from the ground. Rows of PV panels are installed every 5 meters. Under the PV system, Takasawa’s father has been cultivating peanuts, yams, eggplants, cucumbers, tomatoes, and taros and will cultivate cabbages during the winter. These vegetables are sold at a nearby street and consumed by his neighbors.
Many have questioned stability and durability of the PV structure for solar shared family. Nagashima stated that his systems, which are made of thin pipes without concrete footings, even withstood strong winds and earthquakes during the Fukushima Tsunami disasters in 2011. These systems are extremely lightweight and installation of PV panels are spaced out, allowing air to flow through between the panels. This will eliminate concern that the panels will receive wind load and be blown away, therefore, reducing the need for complicated and expensive mounting hardware.