Inspired by the solar plane utilising the free energy source that is commonly referred to as ‘the sun’, I felt an impulse 😉 to build a solar kiln for drying timber. Most of our timber is cut green, great for cutting frames but not so stable for joinery type use. Typically with a moisture content upwards of 35%.

Kiln dried timber has a moisture content of ~15% or less. The process takes time in power hungry kilns, hence the timber is approximately twice the price of green.

A recently completed frame is to have a direct glazed gable, and the cover boards need to match the curved timbers used for the main rafters. The thin slabs (ex 40mm) were cut from the same timber used for the rafters and needed have a moisture content of at least 15%.

After a little online research a simple box was constructed using OSB & insulation, with a 50° angled clear front, behind which is a black solar collector. With a high power solar fan in the middle, circulating the hot air downwards and through the slabs below. The following pictures shown this quite clearly.

solarkiln

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Loaded with a some new slab material.

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There are vents at the back in each corner, the air flow to these can be adjusted according to the seasons.

After two months of operation, the first test timbers successfully dried without too much distortion down to 10%, which is probably a little too low. But bringing them outside will allow them to stabilise.