The vaccine cooler has been tested in climate chamber at DTI. The holdover time for the vaccine cooler was measured to be about four days at 32 °C ambient temperature. For the upright version, the hold-over time is one day less due to the geometry and smaller ice volume. The tests have been used to determine the necessary PV panel size for the selected locations. As the critical parameter is the minimum current for start of the compressor, it was decided to use a panel with a short circuit current of 2.5 times the start current. In this way it is ensured that the compressor will also start at most overcast days, but the economical optimum may be found at a smaller panel size.

Fig.2 Typical current consumption on a good solar day. The many spikes in the early morning represent non-succesful start attempts.