Direct-drive freezer operates at low levels of isolation

Sun Frost has been building vaccine storage refrigerators for the past 20 years. Sun Frost is now building a direct-drive ice pack freezer. Some new technologies incorporated into the design allows the freezer to run even at very low light levels. On a cloudy day if the output of the PV array is less than about 60 watts the compressor in a direct drive system will not start. The Sun Frost F-1 will run on cloudy days even if the output of the solar array is minimal. On a sunny day the number of run hours will be increased because the F-1 will run closer to sunrise and sunset leaving less night time hours for the ice to melt. On a standard poor solar day (3.5 KWH/m^2/day) the Sun Frost F-1 will freeze about 3 kg of ice by sunset while being powered by a 140 watt PV module. Some of the ice will melt overnight giving a net production of 2.4 kg. If these partially froze ice packs are left in for a second day they will be cooled well below 0 deg C by sunset. The following morning the coolth stored in the sub-cooled ice packs will keep them from thawing. Another major advantage of running at low levels of isolation is that performance on marginal solar days can be predicated using total daily solar data rather than hourly data. What makes sizing direct drive refrigerators difficult in developing countries is that this data is typically not available hence the comment in the PQS sheets “For solar direct drive units, the correct sizing of the solar panel array for a specific site is complex and critical. It must be agreed with both the appliance manufacturer and with the Qualified Supplier of the solar energy system at the time of ordering” Steve McCarney at Solar Electric Light Fund (SELF) is currently running long term tests on the F-1 in Columbia. Preliminary results look good. (attachment) Contact Sun Frost for more information. Larry Schlussler, PhD (Engineer and owner of Sun Frost) PQS-F1.pdf