Direct drive solar coolers.

Many people in developing countries are living in areas without electricity from grid. Therefore, obtaining a correct temperature storage of vaccines has been a challenge due to the lack of electricity to maintain the recommended storage temperatures. Currently, most of the vaccines have to be stored at temperatures between +2 °C and +8 °C at the service delivery points. For many years, photovoltaic power has been used for vaccine refrigerators with a lead-acid battery to store electric energy and to provide the start-up current that drives the compressor. The problem with this technology is that the lifetime of the battery is short due to deep discharging of the battery during periods with low sunshine/irradiance. The development of solar “direct drive” refrigerators started in 1999 at Danish Technological Institute (DTI). It was demonstrated that the energy capacity of ice produced by a compressor is at least of the same magnitude as the lead-acid battery. As of to date (February 2016), 24 direct-drive vaccine coolers from eight different manufacturers are listed on the WHO PQS website, with the technology being one of the fastest growing technologies in the vaccine cold chain. This paper endeavours to expound on the current status and discusses how the technology could be used
for other purposes in the future.