Dual Use of Pasture for Grazing and Solar Electricity.

Growing interest in generation of electricity using photovoltaic panels has led to power companies offering to buy or lease farm land to use for solar photovoltaic arrays.  As a consequence is loss of agricultural land.  A system was installed at the University of Massachusetts to allow livestock to graze beneath the panels. The photovoltaic array consisted of two rows of twelve 3-solar panel clusters (5 ½ x 10 ½ ft). Panel clusters were mounted on a horizontal beam held up by steel posts pounded into the ground.  No concrete was used, so that soil disturbance was kept minimal, and land could easily be returned to other agricultural use if the solar array was removed. Rows were 30 ft on center, and panel clusters were spaced within the row at 2, 3, 4, or 5 ft.  Varying the spacing allowed for an assessment of shading effects on pasture quality/quantity. In the spring of 2011, one ft square pasture samples were taken 5 times over the growing season.  Samples were taken directly beneath the solar panels, between solar panels, and to the south of the panels, where shading would have no effect.  No effect from shading was observed in May or June, 2011 during the pasture recovery period.  In July, there was a trend toward higher yield as amount of shading decreased where no shading dry matter yield averaged 3.6 t/ha, while areas associated with the most densely spaced panels averaged 2.7 t/ha just prior to when the pasture was to be grazed.  In September and October the yield estimate was more variable and much less, ranging from 1.0 to 1.6 t/ha with shading effect not statistically significant.  The project will continue in 2012 to further determine the optimal panel spacing for combined grazing and electricity production.