Inverter-less solar assisted farm level refrigeration system for fruits and vegetables

This paper gives a proof of concept of use of solar energy to cool down harvested fruits and vegetables at a farm level to an adequate farm storage temperature. The target storage temperature range was between 5 and 15°C. A model refrigerator was designed and constructed in the mechanical engineering workshop of Cape Peninsula University of Technology. It was installed and tested in outdoor conditions to get the effect of different weather conditions. The model consisted of a typical vapour compression system powered by a 12 V solar PV system. A DC compressor was used, and therefore, there was no inverter. The model was tested first without product and then with 20 kg batches of different fruits for a period of two weeks in April 2016. Wind speed, ambient temperature and solar radiation intensity data were monitored and collected from a Campbell Scientific weather station mounted on the roof adjacent the model. From hourly monitoring of temperatures and compressor current, refrigeration effect, power consumption and coefficient of performance were determined. The overall COP based on input solar energy was 2.8. It was thus proved that a suitably sized PV system could be designed and implemented at farm level to cool harvested fruits from ambient to storage temperature without use of an inverter. This could go some way to help retard deterioration of fruits and vegetables before delivery to a marketplace or to storage.