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The solar collector at the front drives the absorption cooling system. The wine in the fermentation tanks (in the background) is cooled with a cold accumulator.
© Fraunhofer ISE
Solar technology for the south
06.05.2010

Cooling food with sunlight

In Tunisia and Morocco, Fraunhofer researchers are now utilising solar energy to refrigerate easily perishable foodstuffs such as milk, wine and fruit. “Cooled with sunlight” – this eco-label could be printed on food packaging in future: Solar energy is already used for air conditioning buildings, and now researchers want to use it to refrigerate fruit and other easily perishable food. Scientists from the Fraunhofer-Institute for Solar Energy Systems ISE in Freiburg are demonstrating its feasibility in the Mediterranean region using the example of a winery in Tunisia and a dairy in Morocco. In the MEDISCO project, which is short for MEDiterranean food and agro Industry applications of Solar COoling technologies, solar power systems for cooling milk and wine have been installed in cooperation with universities, energy agencies and European companies. Funded by the European Commission, the project is being run by Politecnico di Milano in Milan.

“Our method is suitable in countries that have many days of sunshine and in remote regions where there are no conventional means of refrigeration owing to a lack of water and non-existent or unreliable energy sources. It’s environmentally friendly and reduces the use of expensive electricity for conventionally operated refrigerators to a minimum,” says Dr. Tomas Núñez, a scientist at the ISE, in explaining the benefits. “The refrigeration is always available when the sun shines, which means that it is effectively produced during periods when it is needed most”.

The scientists have installed concentrating collectors that direct sunlight onto an absorber via a reflector. This makes it possible to convert the solar radiation into hot water with a temperature of 200 °C. “This extreme water temperature is necessary in order to drive the absorption cooling system, given the high ambient temperatures that prevail there. In contrast to refrigerators we do not use electricity to generate coldness but heat. The result is the same in both cases: refrigeration in the form of cold water or – in our case – a water-glycol mixture”, explains Núñez.

As the absorption cooling system generates temperatures of around 0 °C, the experts use the mixture to prevent the water from freezing. The water-glycol solution is “collected” in cold accumulators and then pumped through a heat exchanger that cools the delivered milk. “We use a slightly different system for cooling wine: Here the refrigerant flows through coiled pipes installed in the wine tanks”, says Núñez.
“MEDISCO is a demonstration project. The technology is not yet ripe for the market,” says the researcher. “But I certainly see opportunities for deploying solar cooling in agricultural enterprises or in the chemical and cosmetic industries”.

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