P.O. Box 64, Bridgetown, Barbados. Dryers have varied in size from the 2.2 m 2 wire basket dryer to the 149 m 2 roof collector.
Most solar dryers use solar air heaters and the heated air is then passed through the crop.
The roof of an existing barn is converted into a solar collector after it is painted flat black and fitted with a ceiling which becomes the duct through which air, the heat transfer fluid, is pumped. The advantage of using the roof of an existing farm building as a solar collector is that the dryer costs less than if it employs a dedicated collector. Bags of onions or bales of hay are placed on the top of the plenum whose roof is perforated to allow the air to flow through it and then through the crop. The crop is stacked so that heated air does not bypass it and escape to the ambient without removing moisture. This dryer does not employ an auxiliary heating system since the farmer for whom it was built did not think it was necessary.