A Refrigeration Facility for Milk Cooling Powered by Photovoltaic Solar Energy

The use of renewable energy sources is usually a reliable alternative in rural areas and developing countries, where the grid line does not exist or is at a great distance. In this work, the characteristics and working conditions of a refrigeration facility designed for cooling down an expected daily production of 1501 of milk are analyzed. The facility is a stand-alone, direct-coupled system where 20 photovoltaic modules, 120 W_p each, power two permanent magnet, direct current motors of 24 V, 650 W. Each motor drives a separate cooling system compressor, which provides the flexibility to operate the equipment with one or two motors and with various interconnections of the PV modules, depending on the available irradiance level and the thermodynamic state of the system. The photovoltaic energy obtained during daylight hours is stored in the form of sensible and latent heat of frozen water in a tank surrounding a milk container. Thermodynamic analysis of the system shows that the autonomy of the system is 2·5 consecutive cloudy days if the available stored ice energy is 80% of the nominal capacity of the water/ice tank. Results of the refrigeration efficiency are similar to those obtained by other commercial refrigeration facilities powered by a photovoltaic array, including batteries.