Solar drying is a type of thermal drying that reduces the total solids content by using readily available, free energy: solar radiation. Solar drying depends on the sun and ambient air to dry the solids without the use of fossil fuels. It is a slow process, requiring a larger footprint than heated thermal drying; however, because lower temperatures are applied, there is less odor. Unlike drying beds, solar drying beds are covered to prevent the biosolids from becoming wet again when it rains, while allowing air to travel across and help dry the biosolids.
Also, see Drying of Wastewater Solids.