Composting is a natural process of recycling that uses heat to turn organic material into usable fertilizer. Although heat is required for composting, it does not require the use of sunlight as the heat source. In certain situations sunlight can prove detrimental to the composting process, but when composting and sunlight are combined in proper amounts effectively it balances out.
The process of composting occurs from decomposition of organic material and the digestion of the decomposing material by microorganisms and worms. Composting works by heating up the interior, or core, of a compost pile up to 160 degrees F. Composting works similar to microwave ovens in this manner by cooking material from the inside out.
The only effect of sunlight in relation to composting is the moisture control of the compost pile. Finding the proper amount of sunlight helps keep the compost pile from drying out from the evaporation of moisture. Since the organisms within the pile require moisture to sustain themselves and thereby aiding decomposition, without this moisture the process will slow or eventually halt depending on the amount of sunlight.
Since composting works from the inside out, the exterior area of the pile will be much cooler than the core. Having a high internal temperature will eliminate pathogens and seeds year round. Sunlight helps keep the pile exterior warmer during colder seasons as well as melt trapped moisture from snow, frost and ice.
The amount of sunlight in relation to composting depends on the location. The ideal amount of sunlight for a location depends on the climate. Compost should be in a partially shaded area where the sun can deliver heat but not to excess. The shade slows down the evaporation rate along the outside of the pile. Placing the pile under trees helps maintain consistent temperature because the canopy of the trees traps the heat from the sunlight.
If a compost pile gets too much sunlight it begins to dry out. Precautions against this can be taken by monitoring the pile's exterior and applying water as needed. Building a semi-enclosed structure around the pile or using a bin also helps maintain heat while controlling moisture. Using a dark colored, covered container allows the sunlight to heat the container thereby aiding the heating process within the core and maintaining a constant temperature.