Solar radiation manipulations and their role in greenhouse claddings: Fresnel lenses, NIR- and UV-blocking materials

From the global solar radiation which enters the greenhouse interior space only Photosynthetic Active Radiation (PAR) is absorbed by the plants and is important for their growth and photosynthesis. Thereby, sunlight spectral modifications which affect the quality and quantity of the incoming solar radiation are valuable and can be achieved by using specific kinds of cladding materials. In the present paper, some critical kinds of greenhouse claddings which are related with sunlight modifications are reviewed. The claddings considered include: Fresnel lenses, Near-infrared (NIR)- and Ultraviolet (UV)-blocking materials. The authors of the present article refer to some representative studies from the literature and make critical comments on each cladding category based on factors such as the feasibility for practical applications. Regarding the presented types of greenhouse covers, they have the potential for further development in a cost-effective way. Certainly, the penetration of renewable energy sources technologies is important and should be promoted. Towards this direction, cost-effective solar energy technologies, for example Fresnel lenses combined with simple Concentrating Thermal (CT) systems can provide advantages such as temperature/light control of greenhouse interior space along with production of thermal energy for greenhouse energy needs.