Effects of greenhouse photovoltaic array shading on Welsh onion growth

The use of renewable energy for greenhouse environment control to replace or reduce the consumption of fuel and power-line electricity is an important objective for sustainable greenhouse crop production. This study was undertaken to apply a solar photovoltaic (PV) array to supply electricity for greenhouse environment control. The PV array was mounted inside the south roof of an east–west oriented single-span greenhouse, in which Welsh onion (Allium fistulosum L.) was cultivated hydroponically. Effects of PV-array shading on the Welsh onion growth were assessed. Two PV-array formations were tested: straight-line and checkerboard. For each arrangement, the PV array covered 12.9% of the greenhouse roof area. Beside the PV greenhouse, a control greenhouse was built with identical dimensions and orientation to those of the PV greenhouse. Welsh onion was cultivated also in the control greenhouse. The straight-line arranged PV-array (PVs array) cast shadows on a specific area of the cultivated plants continuously during the growth period. The fresh weight (FW) and dry-matter weight (DW) of Welsh onion cultivated under the PVs array shadow were significantly less than those of Welsh onion cultivated in the control greenhouse. The checkerboard PV-array (PVc array) cast shadows in the PVc greenhouse intermittently during growth. Consequently, the inhibitory effects of the PV-array shading on the FW and DW accumulations of Welsh onion were diminished. The electrical energy generated by the PVc array was comparable to that of the PVs array, which is another advantage of the PVc array.