Building my first solar kiln

[etd66ss]

sounds like it will fastened to the ground.  part of the size of the VT kiln, is so it can be picked up on forks and moved.  you could also make it wider to keep the 45° angle if needed, and it would also be less tall.  

I do want to use it in the winter, so the 55 degrees makes sense. I will cut the 12ft polycarbonate panels if need be, but was hoping to not have to. Wish they made 10 footers.

[doc henderson]

i would make the depth to accommodate the panels.  and they think they a few sizes, but maybe not stocked.  8, 10, and 12 I think.

[btulloh]

I do want to use it in the winter, so the 55 degrees makes sense. I will cut the 12ft polycarbonate panels if need be, but was hoping to not have to. Wish they made 10 footers.

not sure which polycarb panels you’re planning to use but be sure to make a double layer with sealed air space between if you use the corrugated ones. If you’re using the twinwall you’re all set. Just be sure to seal the ends as shown in the instructions. 
Good luck with your build. I’ve really gotten a lot of good use from mine.  It’s a good tool. 

[etd66ss]

I do want to use it in the winter, so the 55 degrees makes sense. I will cut the 12ft polycarbonate panels if need be, but was hoping to not have to. Wish they made 10 footers.

not sure which polycarb panels you’re planning to use but be sure to make a double layer with sealed air space between if you use the corrugated ones. If you’re using the twinwall you’re all set. Just be sure to seal the ends as shown in the instructions.
Good luck with your build. I’ve really gotten a lot of good use from mine.  It’s a good tool.

I planned to use Tuftex, like the VT document shows. However I did not intend to buy two layers. Why dual layers?

[btulloh]

Lots of heat loss through the glazing. The airspace helps a great deal. It’s highly recommended although I don’t think it was mentioned in the VT document. Easier to do it initially than adding a second layer after the fact. Having the airspace for insulation will be even more important when the days get shorter and the ambient temp is lower in fall, winter, and spring. 

[metalspinner]

Unlike other forums, forestry forum members have a gallery in which you can organize and store your pictures. This also houses the pictures permanently so that threads like this will always contain the photos used to  aid the discussion. 
I have pictures in my gallery that go back 15 years?? I have long lost access to my original photo storage and appreciate that these are here. 

[Larry]

I built and operated a solar kiln for 12 years.  It did an excellent job and even had a picture in one of Dr. Gene's articles in Sawmill & Woodlot years ago.

I've also been involved with two other builds.  One guy did not use double glazing with disastrous results.  During cool and cold weather moisture would condense on the single glazing.  Than it would drip off onto the floor.  If he had not fixed it the whole floor would have rotted out.

Second thought is lumber from treated poles does not last any longer than untreated lumber.  It has the smell and color, but not enough preservative makes it through the outer few inches of the shell to do much good.  I did not use treated lumber for my floor joists and did not have any problem, but I had it elevated off the ground maybe a foot.

[etd66ss]

Doubling up the glazing is not going to work for me, that would be over $1000 just for the glazing. I'm trying to make this thing out of sawn lumber and very limited purchased components.


It also seems like the Tuftex would be a nightmare to double layer with the way the joints overlap and how I'd have to make double sided closure strips with a jigsaw...

https://www.lowes.com/pd/Tuftex-Wood-Solid-Roof-Panel-Closure-Strip/3012462

Is this 6mm twin layer stuff what I should use?

https://www.lowes.com/pd/Tuftex-Multi-Wall-6mm-Panel-Clear-4-ft-x-8-ft-Corrugated-Polycarbonate-Plastic-Roof-Panel/1000689436

It doesn't seem as durable as the corrugated to me, and it only comes in 8ft long sheets, which means I'd have to have a roof overlap somewhere.

Second thought is lumber from treated poles does not last any longer than untreated lumber.  It has the smell and color, but not enough preservative makes it through the outer few inches of the shell to do much good.  I did not use treated lumber for my floor joists and did not have any problem, but I had it elevated off the ground maybe a foot.

I'm using sawn creosote utility poles for the floor joists and rim boards.

EDIT: Found this place:

https://www.interstateplastics.com/Polycarbonate-Twinwall-Clear-Sheet-POLCE~~SW.php?kitoptionpk=197&src=adwordspla&thisisforcallrail=1&campaignid=225228743&adgroupid=37851262274&creative=153445283219&matchtype=&network=g&device=c&keyword=sheets-POLCESW-kits197&gclid=Cj0KCQjw5auGBhDEARIsAFyNm9Fa1Zo6h62CavAZdq8fHvPzeYlDnBP660EKndqbbi6vnU-NfIWsBa4aAjX7EALw_wcB

Anyone order from Interstate Plastics before?

Does the thickness of the twin wall matter? I imagine the farther apart the twin walls are, the higher the R-value of insulation. They have 6mm, 8mm, 10mm & 16mm, they also have triple wall, but that's $320 for one sheet...

[etd66ss]

Well, I just built up a cart of what I would need for the glazing:



 

Might have to rethink this solar kiln build. Thought it was going to be cheaper than this...

The whole reason I wanted to build a kiln was to saw and dry ~1000 bd-ft of 1x8 Scots pine to turn into T&G for the ceiling of my house build. As well as 6x10x24ft & 6x6x12ft beams from the same wood. Maybe I'm dreaming that a kiln + me felling the trees and milling the rough boards & timbers would be cheaper. I still need them finished into T&G and re-sawn beams. Though I was thinking I can re-saw the beams and sand them.

[doc henderson]

the original design is only 14 feet long if I recall.  you can build it with the corrugated stuff, but will not be as great in the winter compared to the summer.  but I think as long as you get a differential of 20 or 30 degrees inside vs outside, it will dry faster than air drying.  the big beams may do well just to be well covered and air dry down to 12 %.  

[etd66ss]

I might be money ahead to just air dry the beams as suggested and have the general contractor acquire the T&G for the ceiling, though I really wanted the look of Scots pine for the T&G vs the bland white pine available.

-or-

I build a 16ft Kiln and not try to kiln dry the beams.

I have to mull it over I guess...

[doc henderson]

some will add sheet plastic as a first layer, with tuffex over the top to protect and develop an air layer to help insulate.  You are suffering the same as me.  want a cheap kiln, but also very efficient.  you will either wind up with time and or money invested.  too many short cuts, and it will not last and or will not work well.  It does not need to pretty as much as air tight, and insulated.  many have discussed adding supplemental heat, but the glazing is the weakest link.  to do that, you need a separated solar panel and container.  now you are talking more money in materials and insulation, with more complexity, fans electricity.  you can do all kinds of foamboard, air dams and valves to stop air flow and insulate at night.  so the greatest thing about this solar kiln, is keeping it simple.  "it is just a solar kiln"!  

[doc henderson]

or mill the boards, air dry with fans quickly to 12%, and find a kiln to dry on down, or put in place at 12% accounting for a bit of shrinkage.  I struggled as well.  there is info on a "simple cycle solar kiln"  that is just  a stack of wood and plastic, that might work for your beams.  It also illustrates how containing a bit of heat can speed things up.

[doc henderson]

I have dried 2 inch slabs down to 7% using something like this.  Elm out on the driveway.

Simple Solar Cycle Kilns at Timbergreen Farm (timbergreenforestry.com)

I left the bottom open to let water run out, used 16 dollar box fans in the middle of the stack and used a 14 dollar remote temp and humidity monitor.  accurite i think.  

[etd66ss]

I just bought a 40ft container for storage when moving out of my house. For the beams, I place them in the container with a heater and dehumidifier for a couple months? This would be a one time drying event, and I'd do it in the summer/fall before it gets cold as the container is not insulated.

[doc henderson]

I put my air dried lumber in there, and have a dehumidifier in there.  after the wood is dry I only run it once a month or so.  It has been suggested that you could paint the container black at least on the top and southern exposed walls.  keep it stickered with some cheap fans running.  it is fun to see the bucket daily and how much water literally is coming out of the wood.  I keep a remote temp and humidity probe/monitor in there as well.





 

this is how I bundle logs, and sticker.  the fans go in between and all get covered with plastic, and a plywood cover.  A remote sensor can go into the stack as well.  after airdry, these get moved to the 20 foot container, with fans and a dehumidifier.
 

[btulloh]

Well, I just built up a cart of what I would need for the glazing:


Might have to rethink this solar kiln build. Thought it was going to be cheaper than this...

The whole reason I wanted to build a kiln was to saw and dry ~1000 bd-ft of 1x8 Scots pine to turn into T&G for the ceiling of my house build. As well as 6x10x24ft & 6x6x12ft beams from the same wood. Maybe I'm dreaming that a kiln + me felling the trees and milling the rough boards & timbers would be cheaper. I still need them finished into T&G and re-sawn beams. Though I was thinking I can re-saw the beams and sand them.

Yeah that's the stuff.  When I figured the cost and hassle of doubling the corrugated stuff I ended up with the twinwall.  At the time I was able to get from Home Depot and had it shipped to the store for free.  They don't seem to have 48" wide panels now, just 24", but Lowes has the 48".
I was trying to limit my costs for the kiln just like you and I was able to scrounge a lot of the framing and plywood, but the glazing and insulation costs were the big cost drivers.  Mine was sized to dry 12' lumber, so that's way different from your length.  I also redesigned it a bit so that I could use 8' lengths of the twinwall for my collector.  This of course cut down the collector area and the size of the load, but for me that was an acceptable tradeoff.  I ended up spending about $1600 on the build, which was pretty good and I could have knocked that down a little more if I tried.  Of course your overall length will change that equation.
The one thing I can say is that the value added by building the kiln was such that I would be happier spending more than my original investment even though I only use my lumber for myself.  Having the ability to produce KD lumber easily without any real energy costs gave me much more useful product and really changed my whole dynamic on finished lumber product.
Everyone has their own budgets and requirements to manage, so whether it's worth it for you is another question you'll have to figure out.  Maybe you can get by with a shorter (less expensive) version, or maybe not.  Or maybe it's worth it in the long/short/medium run to proceed with your current size.  Your call.  Anyway, good luck with your kiln project, and especially your ultimate projects.

[scsmith42]

Of my 4 solar kilns, three use double pane polycarb panels designed for green houses (greenhousemegastore.com), and one uses a single pane polycarb similar to what you're looking at from the Home Supply store.

I can effectively dry for 2 -3 months more a year with the double pane kilns versus the single pane.  They have the advantage of having closed cell spray foam insulation too though.

About 10 years ago one of our FF members did an analysis of the effectiveness of drying with a double pane glass versus a single pane. It was quite informative in terms of the benefits of the better insulated panel.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

I've had zero issues with moisture in mine.

[etd66ss]

Of my 4 solar kilns, three use double pane polycarb panels designed for green houses (greenhousemegastore.com), and one uses a single pane polycarb similar to what you're looking at from the Home Supply store.

I can effectively dry for 2 -3 months more a year with the double pane kilns versus the single pane.  They have the advantage of having closed cell spray foam insulation too though.

About 10 years ago one of our FF members did an analysis of the effectiveness of drying with a double pane glass versus a single pane. It was quite informative in terms of the benefits of the better insulated panel.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

I've had zero issues with moisture in mine.

Did you use the 6mm twinwall polycarbonate or thicker?
I think I would have condensation issues being up in the northeast right near the Great Lakes.

[btulloh]

Of my 4 solar kilns, three use double pane polycarb panels designed for green houses (greenhousemegastore.com), and one uses a single pane polycarb similar to what you're looking at from the Home Supply store.

I can effectively dry for 2 -3 months more a year with the double pane kilns versus the single pane.  They have the advantage of having closed cell spray foam insulation too though.

About 10 years ago one of our FF members did an analysis of the effectiveness of drying with a double pane glass versus a single pane. It was quite informative in terms of the benefits of the better insulated panel.

https://forestryforum.com/board/index.php?topic=84982.msg1302695#msg1302695

I've had zero issues with moisture in mine.

That might have been @YellowHammer that did the analysis. I know he went back and added a second layer to his first kiln. And he’s in Alabama, home of copious sunshine and Auburn University.