Optimal spectra management for self-power producing greenhouses for hot arid climates

Abstract

The air conditioning in hot and arid climates remains one of the grand challenges for food production in greenhouses. Therefore, significant efforts are given to determine the suitable techniques for effective cooling of greenhouses. Usually, greenhouses are used in colder climates to gather sunlight for heating purposes. However, hot climates with elevated solar irradiation characteristics suffer from high temperatures within the greenhouse. In this study, we propose a unique method solving the extensive cooling requirement of greenhouses in hot arid climates by employing an optimal spectra management strategy. The novel sun-tracking roof design of the greenhouse incorporates hot dielectric mirrors and solar panels, which help to reduce the cooling load and provide electricity to the vapor compression cooling unit. The spectrum above 750 nm is reflected to vertically aligned InGaAs solar cells for additional power generation, whereas the c-Si solar cells are able to provide effective shadowing at noontime without significant comprimise on photosynthetically active radiation (PAR) while producing power. The results showed an average reduction of 28.9% and 25.4% in the cooling load of the proposed greenhouse compared to the conventional greenhouse during the summer and winter seasons for sun tracking hours (10:00 a.m. to 1:00 p.m.), respectively, at a set greenhouse temperature of 28 °C. The proposed greenhouse produced an average of 22.18 kWh/day of electrical energy throughout the year. The novel roof significantly lowers the cooling load and partially meets the energy demand of greenhouses without compromising on photosynthetically active radiations to enter the greenhouse.