Collector Plate & Baffle


The purpose of the collector plate is pretty straight forward. The solar kiln needs as much surface as possible to convert the sun's energy to heat within the kiln. The black fan deck and end walls will both see direct sunlight and will both serve to create heat. Once the stack of lumber is loaded in the kiln, the top of the stack is a large horizontal area that can serve as a collector to create more heat. The material used for this collector isn't important as long as it is dark in color. Flat black is the optimal color for converting solar energy to heat energy. The VT demonstration kiln uses plywood that has been painted black. For my solar kiln, I chose two sheets of thin, corrugated metal roofing. The logic behind the choice was simple. The roofing was sold in 12 foot lengths so I could cut them to fit the exact length of the kiln, the price was reasonable, the roofing isn't subject to bowing and curling, and they are light which is important when I load and unload them alone.

The first step was to cut each of the two pieces to length. The interior length of this kiln is approximately 136", so I cut each piece to within a 1/4" of the overall kiln length. I wanted a good, close fit to minimize hot air bypassing the lumber stack by sneaking around the ends of the collector panels. If you use metal roofing, wear gloves as the edges of the panels are quite sharp. Then it was simply a matter of spraying on some primer and brushing on some of the exterior latex I had left over. I'm sure that as time passes, the panels will require some paint touchups, but I'll keep a can of flat black spray paint handy just for that purpose. The collector plates are placed on top of stickers, which are on the top row of boards.

Original corrugated roofing panels cut to length A coat of primer sprayed on Flat black paint brushed on..... along with a little bit of rain

The baffle is anything you use to span the variable distance between the bottom of the fan deck and the top of the lumber stack. The goal is to keep the air flowing in a direction that allows the greatest amount of moisture removal from the lumber. The fans blow air that has been heated under the polycarbonate, towards the front of the kiln where it enter the stack of lumber, collects moisture from the wood, exits the stack where some heads out the exhaust vent and some is drawn up towards the fans to begin the cycle again. The fan deck, baffle, and the collector plate create the primary boundary between the dry heated air and the moist, cooler air after it passes through the lumber.

A basic tarp seems to be the baffle of choice for most solar kilns. In my effort to maximize the amount of heat generated, I chose a "heavy duty" tarp from Northern Tools that has a silver side and the all important black side. The tarp is 10'x12' which is almost perfect since the interior length of my kiln is just under 12'. Ten feet was way more than enough height for the baffle, so I folded the baffle in half. A couple extra stickers were cut to length and placed in the fold of the tarp. Some washer head screws were used to attach the baffle to the stickers.

Some of the interior sheating offcuts were ripped to a couple inches wide and cut to length to fit the width of the kiln. I then sandwiched the loose edge of the tarp between the fan deck and the sheathing offcuts and screwed them together. I figured this was better than screwing or stapling the tarp to the fan deck, which would eventually create tears in the tarp. The couple inches of excess on each end were left in place and I just fold those back and against the end walls when the baffle is rolled down. The stickers in the bottom of the tarp make it easier to roll the tarp up out of the way or roll the tarp to the height needed for a load of wood. The stickers with some rolled up tarp can be easily tucked under the edge of the collector plate and it holds in place without the need of any additional attachment.

Northern Tools tarp that is used as a baffle Here the tarp is laid out, folded in half and the stickers are ready to be inserted into the fold Closeup view of the tarp and backer strip screwed to the fan deck
Another view of the baffle attachment The completed baffle hanging down to its full length View of the baffle and fan deck from the front side of the kiln 

With the black collector plate, black baffle, black fan deck and gap fillers, the only thing visible from the south side of the solar kiln is collector surface.

All of the solar kiln collector surfaces as the sun will see them
 
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