Solar Powered Kiln-Drying

Kiln-drying lumber involves maintaining strict control of temperature, relative humidity and airflow within the kiln. We carefully monitor these factors and are able to uniformly dry lumber down to the level you need.

The Benefits of a Solar Powered Dry Kiln

The primary benefit of using a solar powered dry kiln is the spectacular color that is brought out in the wood. In a solar powered dry kiln the day starts with the sun powering up the fan to start circulating the air inside the kiln. As the sun continues to heat the metal heat sink, the air passing over it increases in temperature which is then driven through the drying rack increasing the temperature of the wood. As the wood increases in temperature, the moisture inside begins to heat up also and then is removed by the passing air.

Prior to loading our kiln we air dry our wood to an average moisture content from 12% to 16%. This is accomplished in a drying shed where it air dries for 4+ months to attain the lowest moisture percentage level. This means that when the wood goes in the kiln, we only have to bring the moisture content down to 6% – 8% to meet standard specifications.

Back to the process. As the temperature continues to increase the wood is forced to give up its water through natural processes of evaporation. This leaves the wood grains themselves undamaged so the coloration as well as the structure of the wood cells is not damaged or modified. When the sun starts setting the intensity of the heat starts to diminish in a smooth decline. When the sun’s rays will no longer operate the fan, the air stops moving and the wood cools down gradually only to be repeated every day that the sun shines.

Solar powred kiln drying
Lumber display

Air drying lumber

We keep a recording thermometer in our kiln so we can monitor what has happened temperature wise during the drying period. Over time we have learned that if the ingoing moisture percentage is within design parameters, then it will take 3 – 4 weeks to bring the moisture content to the desired 6% to 8% level. If there have been several days of rain or cooler than normal temperatures, adjustments are made to the amount of time the wood is in the kiln. During the winter months this can range as high as 6 months in duration.

During an average hot summer day our kiln will heat up to 146 degrees F and will usually cool down to 100 degrees F overnight. We have recorded months where the average temperature in the kiln never went below 100 degrees F and the average temperature during a typical 24 hr period was 110 degrees F. The way our kiln is designed we expect a 40 degree to 60 degree increase from outside ambient temperature with a corresponding decrease in temperature overnight.

Green dry kiln building
Green dry kiln building

Green drying kiln building

The secondary benefit of using a solar powered dry kiln is reduced cost both in dollars and cents as well as saving energy. When the sun heats our wood, the electric grid doesn’t carry a cost, nor do we consume petroleum fuels to dry out our wood. Since our operation is on the smaller scale, we do not generate sufficient wood waste to fuel our own electric plant nor the manpower required to operate this kind of system.

The third benefit is the ability to fill the kiln and let it do it’s thing without constant supervision. With our setup we can fill the kiln and then saw the lumber to replace the lumber racks emptied, plane the wood that was just removed and get it ready for market, as well as produce sawmill time for log customers. We also make other wood products that we market.

The most unique feature of our kiln is the ability to be portable as required by the by-laws of Johnson County, Kansas. Attach a tow bar and a couple of wheels, and off we go. We would like to build a two more kilns for rental in the future but we’ll see what happens.