Outlook: sunny, but the milk's still cold

Spanish food equipment manufacturer, Tarre, in collaboration with the Public University of Navarre has built a prototype for cooling milk using energy from the sun.

The cooling and maintenance system for use in dairies takes energy directly from a photovoltaic system and so there is no need to use batteries, its developers claim.

The prototype integrates two concentric cylindrical tanks in a single structure: the first one is a cooling chamber for the milk and the second one is a tank of frozen water. In this system the first tank is inside the tank of frozen water. That way the milk is cooled without using any pumping system.

Because it is impossible to maintain an adequate balance between the moment when the energy requirement is greater, that is, right after milking, and when the sun's irradiation is sufficient, the cooler had to be designed with a solar energy storing system. It was at this point in the development of the machinery that Maria Angeles de Blas, from the Public University of Navarre​ proposed the use of energy produced during the state conversion from ice to water, as an alternative to the usual electrochemical batteries. Usually such batteries have a lot of problems, including high costs, need of maintenance and high contaminant levels.

The system has added a new concept to the cooling systems: the assembly of the photovoltaic system directly to the milk tank without using any kind of intermediary power conditioning system or any microprocessor. This way the technology used is simplified and the energy requirement is reduced. As all dairy processors know, milk needs to be cooled to 4 º C in a specific period of time and then it must be maintained at that temperature until it is taken away from the cooling chamber.

The storing range of the system is two and a half days and when in the tank ice is takes up 80 per cent of its capacity. According to Maria Angeles Blas the results of the cooling efficiency of the system are similar to those reached by the usual systems, which use electrochemical batteries to store energy.

After studying several alternatives, the development team decided to have two cooling systems, similar but independent. So depending on the power consumption and on the photovoltaic energy storage levels, one or two systems would always be operational. So, when the sun irradiation is high, the system will store energy, and that energy will be used for the second milking at night.

In order to provide an adequate working level for the equipment the configuration of the photovoltaic field and the number of cooling circuits that are operating is flexible. This means that either one or both of the cooling circuits can work simultaneously.