Plans for a large solar kiln

labradorguy · August 11, 2019, 07:07:37 PM

Does anyone know where I can find plans for a large solar kiln, say 5000bf+??

Everything I have come across seems like it's 1000 or less....

Thanks!

doc henderson · August 11, 2019, 07:20:37 PM

that has been asked before and the answer is you loose some efficiency getting wider or need more air flow, but you can go long. i think @GeneWengert-WoodDoc however has recommended just building more kilns so you can segregate wood species and not tie up one big kiln, and accommodate smaller loads ect. we will see if he can chime in. the nice thing is you can build a small one and get started, then 2 then 3 and just keep going as far as you need, as you need. tell us more about your plans

YellowHammer · August 11, 2019, 07:41:08 PM

Woodmizer sells plans and hardware for a 6Mbf solar kiln.

longtime lurker · August 11, 2019, 08:23:51 PM

Not plans but a turnkey system, and with the USD/AUD exchange rate where it currently is it might be surprisingly competitive. the smallest model is about 7000BF

http://solarkilns.com/t1-mini-pro/

Industry gossip here is these guys are every bit as good as they say they are... I know a couple big mills have installed multiple 120MBF units and intend to install more.

GeneWengert-WoodDoc · August 11, 2019, 08:35:55 PM

Small kilns are almost always more versatile, in terms of species, thicknesses and starting MC, than a large kiln.

The key for a solar kiln is 1 sq. Ft. Of roof for every 10 BF of lumber. The roof area is measured as the area perpendicular to the sun at noon, or the shadow that the roof makes at noon. So, a 5000 BF solar kiln needs 500 sq. Ft. of sloped roof. If the roof is 12' wide, then you need a kiln that is 40' long to get 500 sq ft. Pretty ridiculous indeed. So, if you take three VT solrar kilns and put them so that they side walls are in common, you will have about 4500 BF in a kiln that is 50 feet long. The cost of a kiln with one chamber that is 50' or with three adjacent chambers that are 17' each is essentially the same.

You could take the VT kiln and make it twice as tall and get 4000 BF, but the roof area would be only 35% of the required area. You could extend the size of the roof, but that would Be expensive compared to three solar kilns.

If you make the kiln wider, you will likely see air flow issues unless you spend a lot of money for high quality fans.

longtime lurker · August 12, 2019, 08:00:27 AM

Gene how does latitude affect that calculation of 1 sq.Ft per 10 BF? Obviously the more equatorial we get the more sun but is there any rule of thumb?

Couple of years ago I visited a small slaughter facility and they had solar hide dryers, which were basicly a 4000 gallon or so black poly water tank, side door, a raised roof with a whirlybird type vent in the apex and a couple air ingress points in the bottom. (not sure what whirlybird translates to but I think its what you guys call a turbine vent.) It was a still day and that turbine was spinning because of the convection current. I stuck my head in one and my best guess would have been around 110°F or so, maybe 20° above ambient on that day

It makes me wonder about having a black coloured chamber exterior, possibly even a black collector. Curious if thats ever been trialled and if there was any significant difference?

scsmith42 · August 12, 2019, 10:16:29 PM

One other challenge that you have with long solar kilns is door and header sag.

I have a pair of modified VT design 20 footers / 2K bd ft capacity with 10 wide, 8' tall doors, and the doors can get problematic at different times of the year.

GeneWengert-WoodDoc · August 14, 2019, 09:45:57 AM

The 1:10 ration applies at all latitudes. The secret is that the roof area is the area perpendicular to the sun, or the shadow the roof casts at noon in a sunny day at the time of the equinox. This is why we would have a flat roof at the equator but a 45 slope in the norther US.

Of course, the kiln works more poorly as we move north because of less hours of direct sunlight. Plus in the summer, the sun rises in the NE and sets in the NW, but the kiln only looks southward, so early and late summer sunlight does not easily get into the kiln.