Effects of Agrivoltaics (Photovoltaic Power Generation Facilities on Farmland) on Growing Condition and Yield of Komatsuna, Mizuna, Kabu, and Spinach

Due to a growing human population and the concomitant increased demand for resources, the simultaneous production of sufficient food and energy without overly damaging the environment remains a serious issue that continues to limit sustainability (Tilman et al., 2009; Beddington, 2010; Harvey and Pilgrim, 2011; Steinbuks and Hertel, 2016). The need for new sources of renewable energy and the rising price of fossil fuels have created the anticipation of agricultural crops as a source of renewable energy in the future. With the rapid worldwide increase in photovoltaics to provide renewable energy, large areas of flat agricultural land are being converted to photovoltaic systems. Installation on flat land is optimal for harvesting solar radiation and has lower construction and maintenance costs than that in non-flat areas (Prados, 2010). Consequently, less land is now available for agriculture, raising the concern of decline in food production and rise in food prices in the future. In order to develop a sustainable system, it is therefore important to balance the production of renewable energy and food in utilizing the land (Nonhebel, 2005; Sacchelli et al., 2016). Agrivoltaics—the installation of photovoltaic equipment onto farmland—are a novel approach for using a limited amount of land effectively. An agrivoltaic system integrating renewable energy sources into food production could provide extra income for growers (Dupraz et al., 2011). The shade created by photovoltaic panels above farmland, however, limits photon flux density at the ground level where the plants are grown, thereby reducing crop productivity. The Ministry of Agriculture, Forestry, and Fisheries of Japan therefore does not allow farmers to install agrivoltaic systems in agricultural fields unless productivity can be maintained above 80% of the yield generated without the system. The introduction of renewable energy sources into agricultural fields has consequently been limited. It is therefore necessary to examine crops that do not suffer much decrease in growth and yield due to shading. Here, we examine strategies for converting solar radiation into both electric energy and food using agrivoltaics. Although some previous studies examined the effects of solar panels installed on the roofs of greenhouses (Tani et al., 2014), studies conducted in open agricultural fields are limited (Marrou et al., 2013a; 2013b). Particularly, the only crop used for those studies was lettuce. We therefore investigated the effect of shade generated by agrivoltaic systems on the yields of four vegetables (komatsuna, mizuna, kabu, and spinach) in an open field that, in winter, is otherwise not suitable for vegetable cultivation due to low temperatures and low levels of solar radiation, as well as examine the shading rate and identify the cropping systems suitable for agrivoltaics.