Smart greenhouse covers: A look into the future

In a greenhouse, the cover is the main element determining the amount and quality of entering and outgoing radiation, both short and longwave. The cover properties are therefore essential in determining inside climate and the amount of external resources (such as heating and water) required to maintain the greenhouse climate within the boundaries required for crop production. There is not a single “ideal” greenhouse cover for the entire world. Growers use different systems like different shading techniques and/or different types of thermal screens to optimize the radiative fluxes in the greenhouse on each season, but no system is optimum. Therefore, the development of new “smart” covering materials that would allow for the instantaneous modification of the radiometric properties of the cover, could potentially serve a large market worldwide. Some of these materials already exist in the market, such as the electrochromic glass or polymer dispersed liquid crystals, but they have not technically and economically been optimized for their use as greenhouse covers. So, companies operating in this sector have a need to identify which properties are useful in various conditions and to quantify the advantage of (some of) them being switchable. A number of theoretical covering materials with filters transmitting selectively certain ranges of wavelength (PAR, NIR, TIR) for which the effect on greenhouse microclimate and crop growth can be simulated, have been considered for analysis. The present work uses existing simulation models to quantify the benefit (in terms of production and reduced resource requirement) of improving the optical properties of the cover and the added value of making some of them switchable, for greenhouses typical of a mild winter region, represented by Agadir (Morocco), and a very popular crop, tomato. Results indicate an interesting potential for improvement of greenhouse microclimate and tomato yield, for the individual simulated switchable optical filters. However, the simulated yield increases are comparable to those obtained with existing technology, such as shading mobile screens in these regions, as reported in the literature. Therefore, newly developed smart covers will have to be competitive in price with the price of these types of screens to be competitive in these regions or they must lead to other benefits for crop production not simulated with the models (e.g., fruit quality, less risk of diseases)