Prototype semi-transparent photovoltaic modules for greenhouse roof applications

Improved energy efficiency and the increased use of renewable energy are important objectives for sustainable greenhouse crop production. Two prototypes of semi-transparent-bifacial photovoltaic modules intended for greenhouse roof applications were developed. A module (PV1) using 1500 spherical solar microcells (1.8 mm diameter, crystalline silicon) with 15.4 cells cm−2 density in 108 mm × 90 mm area was produced. Thirty-nine percent of the area was covered with the cells. The remaining 61% was transparent to allow the most sunlight to enter the greenhouse for promising plant photosynthesis. Similarly, a module (PV2) was made using 500 cells with 5.1 cells cm−2 density. Thirteen percent of the area of this module was covered with the cells. The peak power output was 540 mW when the PV1 module was irradiated with 1213 W m−2 sunlight coming directly from the sky and via ground reflection. The peak power output was 202 mW when the PV2 module was irradiated with 1223 W m−2 sunlight. The conversion efficiencies from sunlight energy irradiated on the 108 mm × 90 mm area into electrical energy were 4.5% for the PV1 module and 1.6% for the PV2 module. Calculations of the annual electrical energy production per unit greenhouse land area indicated that these modules are potentially suitable for greenhouses in high-irradiation regions where electricity production could be high and winter demand low.