Apart from harnessing solar thermal energy to directly (through heated greenhouse air) or indirectly (through heated water) meet the greenhouse heating demands, energy from the incident sunlight can also be converted to electricity through the photovoltaic (PV) effect. Despite the abundant amounts of solar energy reaching the earth, on the local scale, it is intermittently available over the day and around the year - this means that the electricity generated during periods of high availability would need to be stored using battery systems to supply it during times of deficient availability.
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Recently, there is significant research dedicated to semi-transparent PV panels that allow partial transmission of wavelengths considered important for photosynthesis, while using the rest for electricity generation. However, such panels still decrease the overall PAR transmission, compromising with crop production. PV panels can be mounted on administrative buildings, offices, or parking spaces associated with greenhouses.
Contribution to energy balance and resource use of greenhouses:
Electricity generated from PV modules can be used to supply power to climate-conditioning equipment such as heat pumps, forced ventilation, mechanical dehumidification, as well as for artificial illumination, which contribute to the internal climate of the greenhouse and its energy and resource use.
However, with limited efficiencies of PV modules and with constraints on the area available for mounting the PV panels, the total electrical demand of the greenhouse is difficult to be met completely by PV modules alone, and other sources of electrical power are required.
Possible steps towards sustainable, energy-efficient greenhouses
The development of more efficient PV modules would enable much better utilization of the freely available solar energy to power the greenhouse climate-management in a sustainable and energy-efficient way.
If electrical power is generated in excess of the electrical demand of the greenhouse, this can be stored in batteries to be used during times of lower PV power output due to reduced availability of solar energy (e.g. at night-time and in winter months).