Part of a commercial solar photovoltaic farm in the hot dry Negev Desert of Israel was modified by planting low-rise surface cover crops in the spaces between the rows and beneath the solar panels. In two test plots of about 0.22 hectares each, modifications to the microclimate resulted in lower air temperature, higher humidity and reduced radiant loads on the lower face of the panels compared to a control plot that was not modified. PV panel temperature in the planted test plots was up to 4.5oC lower, resulting in an increase of electricity output of 1.2% over the summer. The temperature reduction is attributed primarily to smaller fluxes of solar radiation reflected from the plants, which have a lower albedo than the bare soil, and to less infrared radiation emitted from the plants, which are cooler. Water consumption for irrigation was 24-30% lower in the partly shaded zones during the initial planting and growth phase (depending on the type of crop) but was only 7-11% lower in the height of summer once the crops had matured. The crop yields beneath a partly shaded area beneath the panels were about 60% of the yield in fully exposed areas of the site, but the Land Equivalent Ratio of the test plots was 1.67. An analytical model, adapted from the Faiman equation, can describe PV panel temperatures in the presence of crops accurately, providing a basis for estimating the electricity output based on their rated temperature coefficient.
1. Prof. Evyatar Erell
The Effect of Surface Cover Vegetation on the Microclimate and Power Output of a Solar Photovoltaic Farm in the Desert
Ben Gurion University of the Negev, Israel