A review on opportunities for implementation of solar energy technologies in agricultural greenhouses

The greenhouse industry is an energy-intensive sector with a heavy reliance on fossil fuels, contributing to substantial greenhouse gas (GHG) emissions. Addressing this issue, the employment of energy-saving strategies along with the replacement of conventional energy sources with renewable energies are among the most feasible solutions. Over the last few years, solar energy has demonstrated great potential for integration with agricultural greenhouses. The present study reviews the progress of solar greenhouses by investigating their integration with solar energy technologies including photovoltaic (PV), photovoltaic-thermal (PVT), and solar thermal collectors. From the literature, PV modules mounted on roofs or walls of greenhouses cause shading which can adversely affect the growing trend of cultivated crops inside. This issue can be addressed by using bifacial PV modules or employing sun trackers to create dynamic shades. PVT modules are more efficient in producing both heat and electricity, and less shading occurs when concentrating modules are employed. In terms of using solar thermal collectors, higher performance values have been reported for greenhouses installed in moderate climate conditions. Further, in this review, the employment of thermal energy storage (TES) units as crucial components for secure energy supply in solar greenhouses is studied. The usage of TES systems can increase the thermal performance of solar greenhouses by 29%. Additionally, the most common mathematical models utilized to describe the thermal behavior of solar greenhouses are presented and discussed. From the literature, machine learning algorithms have shown a better capability to describe the complex environment of greenhouses, but their main drawback is less reliability. Notwithstanding the progress which has been made, further improvements in technology and more reductions in costs are required to make the solar greenhouse technology a solution to achieve sustainable development.