A solar kiln is a structure used to dry and cure lumber with solar power. Solar kilns can be used by people like woodworkers and hobbyists, as well as timber processing facilities. Depending on the location, season, and amount of lumber, it can take less than a month to almost two months for lumber to finish drying in a solar kiln.
When timber is initially cut, it is in a state known as “green.” It has a very high moisture content and is swollen with fluids. Green timber can be processed into lumber, but it cannot be used right away. If green lumber is used in construction, it has a tendency to warp and distort as it dries. Consequently, lumber needs to be cured before use. One option is to leave it stacked outdoors, but this can take a long time, as ambient humidity traps moisture inside the lumber. The solution is a kiln, a heated environment that will dry the lumber quickly and evenly.
The problem with using lumber kilns is that they use a great deal of energy and require an energy source. A solar kiln relies on solar power to heat the air and power fans to draw hot air across the lumber to dry it out. Solar kilns can also be mobile, allowing for processing of timber anywhere, and they are usually very inexpensive to build. This can be important for people who want to process their own lumber on a budget.
Solar kilns are designed a lot like a greenhouse. A slanted roof is angled to take advantage of the sunlight, and fans are used to keep air circulating through the kiln. Fans at the top draw air into the hottest part of the solar kiln while fans at the bottom pull the heated air across the curing lumber and vent it once it becomes laden with moisture. The fans can be powered with a photovoltaic panel.
The initial investment required to build a solar kiln depends on the size and the building materials. Once built, the kiln is free to operate although periodic expenses may be needed for maintenance, to perform tasks like replacing broken panels in the roof. Once cured, the lumber can be put into storage or used immediately.
Several innovative people have explored the idea of building a solar kiln for pottery. Pottery firing requires temperatures much hotter than those reached in a lumber kiln. Most solar pottery kilns use a parabolic reflector that focuses heat onto a very small chamber. The chamber is small enough that it can heat sufficiently, but it usually cannot hold more than one or two items for firing, making the kiln rather inefficient.