System design, operation and performance of roof-integrated desalination in greenhouses

This paper is focused on applications in remote and arid locations where the source water is assumed to be brackish. In this concept the roof transmission is reduced as solar irradiation is absorbed by flowing water on a glass sheet covered by a top glass sheet. Fresh water is evaporated, condensed on the top glass and collected at the roof eaves. For the assessment of this concept compared to conventional, single glassed greenhouses, extensive computer simulations and field experiments were performed in Tunisia. Considerably less extreme climate conditions were registered in an experimental greenhouse with roof desalination compared to a conventional house. The simulation inaccuracy was around 5% for the water demand and production. In a more general analysis, various design cases, including crop cultivation examples were simulated. A system integrated in 50% of the roof area had the capacity to cover the annual demand for a low canopy crop. A similar capacity for a high canopy crop requires asymmetrical roof design and desalination system in the whole roof area. The yield problem could be solved with more light selective glass materials (NIR-absorption). Interesting future prospects are expected for electrochromic glasses with dynamic absorptance control. This could improve crop yields and eliminate the seasonal storage demand. (C) 2004 Elsevier Ltd. All rights reserved.