New solar-cooling technology for cooling-freezing
Refrigeration is often based on compressor technology which consumes electricity. A recently developed system making it possible to achieve relatively low temperatures solely using solar energy has been designed by PROMES, a laboratory working within the ENERGY framework of the CNRS, the French national scientific research centre. It uses a combination of two different processes: evaporation/condensation and absorption/desorption. The system operates as a thermochemical dipole with two distinct night and day phases. During the day, the solar collectors heat a reactive solid contained in the reactor. This causes the decomposition of the barium chloride (a salt) contained in it, releasing the gas that condenses at ambient temperature in the condenser and accumulates in the evaporator. During the nocturnal stage, the reactor cools down according to the ambient temperature, causing the reabsorption of the refrigerant gas; this in turn causes the refrigerant fluid to evaporate in the evaporator, thus inducing cooling. A simple process using a single dipole and conventional solar collectors producing temperatures of 70°C has a cooling capacity of 1-1.2 kW/m² of collector surface at 0°C. However, similar technology can be used for freezing when two dipoles are organized as a cascade: a primary dipole is used to bring down the temperature of the cold store and a secondary dipole cools the reactor of the primary dipole during the night. During the day, both dipoles are in regeneration phase. The system makes it possible to achieve temperatures as low as -45°C, solely with the energy provided by solar collectors commonly used for domestic water heating. A prototype was constructed in order to demonstrate the system's feasibility; it is autonomous and self-adapting, as it adjusts to external conditions without requiring any external regulation.