Solar Kiln - Is a small one worth the effort.

[Garbanzo62]

I am contemplating building a solar kiln to help expedite the drying of my wood. The only issue I have is that I have limited space that would get sufficient sun. (besides being smack dab in the middle of the back yard). I am just wondering if it is worth if to go through the effort and expense. At best I could probably get a 8 ft ln X 3ft W X 6 ft H. That might be a stretch. Also this would face South, which should get relatively good sun. Anyone have experience with small solar kilns?

 

[KDubU]

I am planning one or two solar kilns as well to get some of my wood drier hopefully for next fall/winter season. I have not built one before and have reviewed the thread on here about it several times. Seems straightforward although not the most attractive thing to have in one’s yard. I have plenty of space for it and will place it somewhere less intrusive and mine will be about 4 times your size.

Hopefully someone will answer you questions as the size you wrote is pretty small. Are you planning to burn full time or is it more for ambiance and add-on heating?

I think @Woodsplitter67 did this and has a write-up.

 

[stoveliker]

Woodsplitter67 is indeed likely the most knowledgeable to answer this, but I see no reason why a small one would not work similarly to a large one. It is a balance between total solar exposure versus heat loss. But both scale with surface area (and the latter with the air flow, i.e. holes in the plastic).

I'd put a thermometer in there somewhere so you can see the max temps reached and adjust the opening size at the top of the kiln to adjust the convective air flow. If you reach similar temperatures as larger kilns, the results with your wood will be the same.

And keep the plastic off the sides of the wood to avoid condensation soaking back into the wood.

 

[armanidog]

It may be a good year for using a solar kiln to speed up firewood drying time. A decent kiln will dry 2 inch sawn boards in 15 weeks.
Firewood will take longer due to bark and thickness.

"According to the CPC analysis, large parts of the country are likely to see above normal temperatures, with the best chances for above normal temperatures expected over the northeastern states of New Jersey, Delaware, Maryland, Pennsylvania, New York, Vermont, New Hampshire, Rhode Island, Maine, Massachusetts, New York, and Connecticut and the southwestern states of Nevada, Arizona, Colorado, and Texas. Above normal temperatures are also expected across much of Alaska and Hawaii this summer too. The only place where there’s a 50-50 chance of warmer or cooler than normal temperatures will be over the upper midwest."

Climate Prediction Center Releases Newest Summer Outlook: Warm and Wet

The National Weather Service's Climate Prediction Center (CPC) has released their newest outlook for the Summer of 2023; they're calling for warmer than...

weatherboy.com

 

[Garbanzo62]

Well to answer KDubu, I plan on burning as much as I can. I have a lot of Ash that is CSS from this fall, some pine and a good amount of Slab wood from a lumber mill that had too high a MC% to burn this year. I also have a bunch of Oak that will need time. I am assuming the Ash and Pine should be ready for the fall, but not sure I want to take a chance. Figured I could Run batches through the kiln to get stuff to a good MC and since it should be fairly far along already, I might be able to turn batches over faster. If all that gets to proper MC, I can start to work on the Oak.

 

[EbS-P]

The kiln is a good idea. Plan ahead so you don’t have to re stack anything. It’s such a pain. Keep everything not in the kiln top covered and off the ground as best as possible.

 

[KDubU]

Split smaller and yes ash and pine will likely be ready for late fall burning. Oak as you say will take longer but again splitting it smaller will allow it to dry quicker.

 

[Stove Cricket]

Last year a regular 8x12 tarp over an experimental 6’x6’x14” (42 cu. ft.) rack of wood, from late summer through fall, really helped dry out some oak.

This summer one thing I will be experimenting with is a clear tarp, with side grommets loosely laced up the sides for ventilation, in the same way as last year, full southern exposure. Thinking maybe imbedding a Hobo data logger would be informative?

 

[Garbanzo62]

Last year a regular 8x12 tarp over an experimental 6’x6’x14” (42 cu. ft.) rack of wood, from late summer through fall, really helped dry out some oak.

This summer one thing I will be experimenting with is a clear tarp, with side grommets loosely laced up the sides for ventilation, in the same way as last year, full southern exposure. Thinking maybe imbedding a Hobo data logger would be informative?

View attachment 311063

how much drop in MC did you see?

 

[Stove Cricket]

how much drop in MC did you see?

I wasn’t tracking mc at that time, but the wood was css in April, and burned fine in January. Bark came off when it was moved to the shed. Currently mc stands at 18%. It was a very dry and hot summer, the small stack was single width, stacked well off the ground, exposed to a lot of wind. I will be checking mc closer this year.

 

[Poindexter]

I do think a small kiln is worth the trouble as a learning experiment. From reading here, you can just stack and top cover your split pine and split Ash. I don't have access to cheap Ash, plenty of spruce, I wouldn't bother kilning those for winter 23/24 from what I have read here. Put your oak in the experimental small kiln and see what happens before you scale up.

Yes to not letting the splits touch the membrane. I want condensate to drip out down the inner surface of the membrane, not get resorbed by the end grain of splits touching the membrane. Most of the time. Somebody used shrink wrap on cord wood stacked on pallets with a top opening and managed to get all (enough of) the moisture out the top vent.

Also, I have verticals for the stacks to butt on every 6-8 feet. When the heat is on and the wood is changing shape quickly (under FSP) I haven't had to restack and fallen areas yet. 8 feet is about my limit between uprights.

Good luck and best wishes.

 

[Poindexter]

Also, airflow can be the bugger. You want a combination of heat and airflow that gets the water out of the wood as vapor - AND- carries the vapor out of the kiln before it re-condenses on your splits.

If you have enough solar gain in the kiln for the air temp in there to be about say 30 to 50dF warmer than ambient you have enough airflow. If the air temp inside your kiln is say 70 to 80 dF above ambient I would open the vents to allow more air flow and carry more water out.

 

[Woodsplitter67]

I am contemplating building a solar kiln to help expedite the drying of my wood. The only issue I have is that I have limited space that would get sufficient sun. (besides being smack dab in the middle of the back yard). I am just wondering if it is worth if to go through the effort and expense. At best I could probably get a 8 ft ln X 3ft W X 6 ft H. That might be a stretch. Also this would face South, which should get relatively good sun. Anyone have experience with small solar kilns?

To me the deciding factor would be .. how much impact will it have on my wood supply.. If its only 25-30% of my usage it may not be worth it. If you load it early and dry 2 loads per season and that gets you close to something that you burn in a season,then definitely worth it.

If this is going to be a permanent thing, Id go all polly carb panels except the north wall

 

[Woodsplitter67]

Also, airflow can be the bugger. You want a combination of heat and airflow that gets the water out of the wood as vapor - AND- carries the vapor out of the kiln before it re-condenses on your splits.

If you have enough solar gain in the kiln for the air temp in there to be about say 30 to 50dF warmer than ambient you have enough airflow. If the air temp inside your kiln is say 70 to 80 dF above ambient I would open the vents to allow more air flow and carry more water out.

So for some basic data.. if the OP puts together a pollycarb kiln with basic ventilation the temperature would be well higher. CT is not far from NJ and the sun angle right now would be negligible.

It was cloudy in the morning yesterday with bright sun in the afternoon. My greenhouse is all pollycarb.. it was 55 degrees out with a 20 mph wind at 4pm it was 95 degrees and 20% dew point in the greenhouse.. thats plenty to start to dry that wood on the fast side.. put a solar powers attic fan in it and that set up will strip the water out.. even lareg splits of hardwood like 5x5 inches thick.. This isnt even april and the suns angle is only going to increase every day.. Realistically you could load the kiln in mid march.. empty it july 1 and dry another batch, then 2nd batch should be dry by October..

 

[KDubU]

So for some basic data.. if the OP puts together a pollycarb kiln with basic ventilation the temperature would be well higher. CT is not far from NJ and the sun angle right now would be negligible.

It was cloudy in the morning yesterday with bright sun in the afternoon. My greenhouse is all pollycarb.. it was 55 degrees out with a 20 mph wind at 4pm it was 95 degrees and 20% dew point in the greenhouse.. thats plenty to start to dry that wood on the fast side.. put a solar powers attic fan in it and that set up will strip the water out.. even lareg splits of hardwood like 5x5 inches thick.. This isnt even april and the suns angle is only going to increase every day.. Realistically you could load the kiln in mid march.. empty it july 1 and dry another batch, then 2nd batch should be dry by October..

How would you build one from polycarbonate panels? Specifically the sealing of each piece? Would you frame it like a greenhouse? I am curious as I plan to create a solar kiln in the coming weeks.

 

[Woodsplitter67]

Me personally.. How I built my greenhouse will be very similar to how a pollycarb kiln should be constructed. Of course how the structure looks will be different. The basice are.. You notch each stud approximately 6mm for the carb to fit into.. so if 2 carbs meet on 1 stud you take your tablet saw and rip 2 notches for the carb to seet into.. but leaving a pice of wood in the middleto separate. Seal with Clear Silicone calk.. screw a .5 in thick ripped 2x4

Ill get into detail later.. headding out with my boy