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The self-cooling greenhouse is a concept to enable crop cultivation in adversely hot climates. It sacrifices a fraction γ of the incident solar energy to drive a refrigeration system, thus lowering the internal temperature below ambient. Heat is actively rejected to a stream of coolant such as air or water. To maintain availability of sunlight for photosynthesis, γ should be as small as possible. Nonetheless, the laws of thermodynamics dictate a minimum value of γ. Using the approach of endoreversible thermodynamics and the theory of selective blackbody absorbers, we determine ideal minimum values achievable for cases of both thermal and photovoltaic solar collection with and without solar concentration. To achieve an internal temperature 10 °C below that of the incoming coolant, a minimum γ = 0.056 is needed using multicolour absorption at maximum concentration C = 46300 – representing an absolute minimum for either type of solar collection. Without concentration (C = 1) a selective thermal collector permits minimum γ = 0.089 and a single-junction PV solar collector permits minimum γ = 0.15. We discuss briefly implications for development of a real self-cooling greenhouse to approximate the performance of these ideal cases.

A stand-alone small-scale renewable heat powered polygeneration system to provide cold for space cooling, electricity, and seawater desalination was proposed and numerically modelled. The system is based on Permeate/Conductive-gap MD modules (P/CGMD) and an ammonia/water absorption power-refrigeration system driven by heat from an evacuated flat plate solar collector field with a biomass-fired backup boiler. Energy and exergy performance of the system was analysed using climate conditions of a typical location well-endowed with solar irradiation and characterized by a potential shortage of freshwater supply and high cooling demand. In the base-case, the system provided 130 kW of cooling capacity at 11 °C, 6.4 kW of net electrical power, and 41.4 m3/day of desalinated water based on annual average weather conditions of Almeria (Spain). The overall system's resource utilization efficiency and exergy efficiency were estimated at 44.2% and 6.9% respectively. The use of CGMD reduced the required specific membrane surface area by 53% compared to the PGMD. The results of this study show that a thermally coupled absorption refrigeration system and MD process can be implemented (i) to increase the efficiency of the entire thermal energy conversion process and (ii) to cost-effectively utilize the solar thermal installation, particularly in regions where desalination is a necessity.

The performance of a double-effect LiBr–H 2 O absorption heat pump connected to a solar multi-effect desalination plant has been analyzed experimentally. A detailed study of the main operation problems has been carried out in a first experimental campaign with the aim of identifying new control strategies to improve the behavior of the system at stationary nominal conditions, as well as to increase its thermal efficiency. An improved control strategy is proposed to deal with the identified problems and has been validated in a second experimental campaign. Results of these experiments have shown an improvement of the heat pump performance when the refrigerant flows continuously between the low-temperature generator and the condenser. By avoiding intermittent water flow, it is easier to keep LiBr solution levels in both generators constant, gas consumption is lower, it takes less time to reach steady state and a higher average coefficient of performance is reached.

Different alternatives for the effective integration of desalination technologies in the cooling of concentrating solar power (CSP) plants in the Mediterranean area are discussed and evaluated. Two cases are considered where a low temperature multi-effect distillation (LT-MED) plant is integrated into a CSP plant replacing the condenser of the power cycle. In one case, a LT-MED plant is fed by steam at the outlet of the turbine expanded to 70 °C. In the other case a LT-MED is fed by the steam obtained from a thermal vapour compressor (TVC) which uses the exhaust steam of the CSP plant (at 37 °C, 0.063 bar) together with some from the high pressure turbine extraction (17 bar). The two cases are compared with that of a reverse osmosis (RO) unit powered by the electricity produced by the CSP plant. In this case, two different wet cooling technologies, once-through and evaporative water cooling, and a dry air cooling are considered for the CSP plant. Thermodynamic simulations are presented for all cases, together with an economic analysis.