Solar kiln for hardwoods

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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
how long is a run?

So how long you run your kiln will depend on a couple of things. Time of year, species of wood, and sunlight. All of this will factor into how long you will need to run the kiln to achieve the desired MC. Your in PA so your not far from me, but its going to be hard for me to help you with the seasoning time. Im in direct sunlight, and I dont have any real experience with partial sun. If I were in an area with partial sun I would do multiple Kilns and more likely have to run the kill the entire summer to achieve the desired moisture content I would do a run with Hardwoods splitting the wood this spring letting it season for a couple of months and run the kiln for the entire summer. I would take some internal temp readings when the sun hits it to see what the solar gain is and pull a split to see how much MC you have dropped. Once you do one run in the kiln you will have a better idea of what to expect. From what i can remember @Poindexter needs to run his most of the summer, while i can do 2 runs in the summer if needed. How much will you need to season
 
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Dmitry

Minister of Fire
Oct 4, 2014
1,049
CT
My solar kiln, was made from the big box store wood racks as an experiment to see if i could season hardwoods like @Poindexter has done with softwoods.
Materials used were wood racks, 2x4 pressure treated, 6 mil clear plastic, a small roap, contractors stretch wrap and a staple gun
My wood racks were 5 inches above ground and sitting on 2x4 for a total of aprox 8 inches. I secured some two-by-fours on the ends and tied a rope between them making a roof over the top I put plastic around the racks and secured the bottom of the plastic to the first row of firewood with contractors stretch wrap and some Staples I cut in 3 vents to on either end approximately the size of a grapefruit and one smaller one in the middle this would was split in May and sat on the racks until the week of July 8th in which I started the kilm all of my splits were large 6 to7 in thick and 18 in Long and those splits at in the kiln until October when I open the Kiln the Cherry splits were down to approximately 2% and all of the oak was down to 9% so given that you could easily do two runs with in a rack
The way that the kiln needs to be set up for Hardwoods is you need it in a full sun area you do not want the venting to be too much as you want the temperatures to get extremely warm within the kiln it does need to vent the moisture out so typically my kiln Ran from anywhere from 110 degrees and I've gotten it as high as 121 degrees
The first day I ran my kiln it was a cooler day no more than 76 degrees and within a couple of hours of setting up the kiln it was over a 110. I used an air probe for my smoker to measure the internal temperature of the Kiln at various points.
I did all of this to see if I ever get jammed up that I could actually season a Year's worth of firewood over the course of the summer I also did another experiment with nothing but Oak and even larger splits those splits started in the upper 30s to low 40s and I got them down to sub 20% moisture content in 2 months
View attachment 231154 View attachment 231155
Where do you cut holes and how to make sure that no water can get in those holes
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
Where do you cut holes and how to make sure that no water can get in those holes

I cut a hole on eather end in a u shapr not removing the plastic bit making it into a flap amd i just taped it up. I also did one in the middle of the apex of the roof. You may get a little water in but not much. All the vents are at the top so not alot of water will run down the plastic into the hole.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
Can you post more pictures from different angles? Do you have any pictures of the rack and stack before wrapping?

Check out post 15. Thats what itlooks like, thats how the wood is stacked nothing special. It can be any rack all wood bottom, metal ends it dosent matter the lenth could be 20ft, 16, 8ft. You can do 3 racks deep and 6ft high. One kiln 20long 4.5 wide and 6ft high will yeald 4.21 cords per run.
I dont have additional pics as i had no plans to start a thread like this. I will do a better job of this in the future and will be able to post more indepth
I encourage you to experiment with it. The worst thing that happened to me was my cherry was 2% and my oak was 9%. . You really cant go wrong. Your woods not going to spontaneously explode it's either going to be perfectly seasoned a little under seasoned or a little over seasoned. Eather way.. you've made progress and learnd something and now you know for next time.
 
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
Check out post 15. Thats what itlooks like, thats how the wood is stacked nothing special. It can be any rack all wood bottom, metal ends it dosent matter the lenth could be 20ft, 16, 8ft. You can do 3 racks deep and 6ft high. One kiln 20long 4.5 wide and 6ft high will yeald 4.21 cords per run.
I dont have additional pics as i had no plans to start a thread like this. I will do a better job of this in the future and will be able to post more indepth
I encourage you to experiment with it. The worst thing that happened to me was my cherry was 2% and my oak was 9%. . You really cant go wrong. Your woods not going to spontaneously explode it's either going to be perfectly seasoned a little under seasoned or a little over seasoned. Eather way.. you've made progress and learnd something and now you know for next time.
WS67, you are creating a revolution!

Poindexter came before you, but he was a little too intellectual (or maybe a lot) for the masses. It's often the reluctant who spark such things.

I've wanted a kiln system myself for a few years now. But you did it.

I hope to see shrink wrapped woodstacks popping up everywhere soon.

Good work!
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
WS67, you are creating a revolution!

Poindexter came before you, but he was a little too intellectual (or maybe a lot) for the masses. It's often the reluctant who spark such things.

I've wanted a kiln system myself for a few years now. But you did it.

I hope to see shrink wrapped woodstacks popping up everywhere soon.

Good work!

Thanks ED..
 

chemie

Feeling the Heat
Aug 11, 2018
267
New York City
Check out post 15. Thats what itlooks like, thats how the wood is stacked nothing special. It can be any rack all wood bottom, metal ends it dosent matter the lenth could be 20ft, 16, 8ft. You can do 3 racks deep and 6ft high. One kiln 20long 4.5 wide and 6ft high will yeald 4.21 cords per run.
I dont have additional pics as i had no plans to start a thread like this. I will do a better job of this in the future and will be able to post more indepth
I encourage you to experiment with it. The worst thing that happened to me was my cherry was 2% and my oak was 9%. . You really cant go wrong. Your woods not going to spontaneously explode it's either going to be perfectly seasoned a little under seasoned or a little over seasoned. Eather way.. you've made progress and learnd something and now you know for next time.

Let us know when you do a new run in Spring. And please take lots of pics for people who are not so handy like me.
I’d like to run a trial test at the same time with you in Spring. Then we can compare the results.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
Let us know when you do a new run in Spring. And please take lots of pics for people who are not so handy like me.
I’d like to run a trial test at the same time with you in Spring. Then we can compare the results.

Ok.. rhats cool.. im going to do white oak.. and im going to do it 2 kind of ways..
 

showrguy

Minister of Fire
Aug 2, 2015
515
Marysville, Pa.
Ok.. rhats cool.. im going to do white oak.. and im going to do it 2 kind of ways..
Did I read somewhere that you tried the same thing over winter with not much for results ??
I'm working up a couple of cords of Standing dead Oak, and was thinking of wrapping it, then was thinking just top cover for winter ??
 

mcstatz5829

Member
Jul 11, 2018
150
Indianapolis
Check out post 15. Thats what itlooks like, thats how the wood is stacked nothing special. It can be any rack all wood bottom, metal ends it dosent matter the lenth could be 20ft, 16, 8ft. You can do 3 racks deep and 6ft high. One kiln 20long 4.5 wide and 6ft high will yeald 4.21 cords per run.
I dont have additional pics as i had no plans to start a thread like this. I will do a better job of this in the future and will be able to post more indepth
I encourage you to experiment with it. The worst thing that happened to me was my cherry was 2% and my oak was 9%. . You really cant go wrong. Your woods not going to spontaneously explode it's either going to be perfectly seasoned a little under seasoned or a little over seasoned. Eather way.. you've made progress and learnd something and now you know for next time.
Are you going to burn those as is or let them regain moisture?
 

Akon

Member
Dec 1, 2016
18
Maine
I am going to do a run or two in the spring or summer with red oak and ash on yet to be cut trees. Need to finally get ahead on my supply. Don't have a great spot for a kiln that gets good sun near my wood, so am considering putting it temporarily on part of the asphalt driveway that is out of the way for ~ 4 weeks.
 

mtarbert

Minister of Fire
Feb 23, 2006
547
Maryland
My solar kiln, was made from the big box store wood racks as an experiment to see if i could season hardwoods like @Poindexter has done with softwoods.
Materials used were wood racks, 2x4 pressure treated, 6 mil clear plastic, a small roap, contractors stretch wrap and a staple gun
My wood racks were 5 inches above ground and sitting on 2x4 for a total of aprox 8 inches. I secured some two-by-fours on the ends and tied a rope between them making a roof over the top I put plastic around the racks and secured the bottom of the plastic to the first row of firewood with contractors stretch wrap and some Staples I cut in 3 vents to on either end approximately the size of a grapefruit and one smaller one in the middle this would was split in May and sat on the racks until the week of July 8th in which I started the kilm all of my splits were large 6 to7 in thick and 18 in Long and those splits at in the kiln until October when I open the Kiln the Cherry splits were down to approximately 2% and all of the oak was down to 9% so given that you could easily do two runs with in a rack
The way that the kiln needs to be set up for Hardwoods is you need it in a full sun area you do not want the venting to be too much as you want the temperatures to get extremely warm within the kiln it does need to vent the moisture out so typically my kiln Ran from anywhere from 110 degrees and I've gotten it as high as 121 degrees
The first day I ran my kiln it was a cooler day no more than 76 degrees and within a couple of hours of setting up the kiln it was over a 110. I used an air probe for my smoker to measure the internal temperature of the Kiln at various points.
I did all of this to see if I ever get jammed up that I could actually season a Year's worth of firewood over the course of the summer I also did another experiment with nothing but Oak and even larger splits those splits started in the upper 30s to low 40s and I got them down to sub 20% moisture content in 2 months
View attachment 231154 View attachment 231155



Do you think a small solar powered vent fan would help ?
 

Poindexter

Minister of Fire
Jun 28, 2014
2,366
Fairbanks, Alaska
@ED 3000 , point well taken.

I posted a link to a journal article in one of my threads about how hot how fast. The guys running lumber kilns trying to make finished boards keep the kiln temperature below 95dF until the wood starts to shrink.

When your stacks are moving, tipping, leaning, whatever, when they are shrinking you have all the water out of the sap tubules and it is "time" to turn up the heat.

As burners we aren't too terribly worried about warping and cupping and end grain checking. The folks with a kiln full of clear mahogany are worried about that. So it could be we could let out kilns get hotter sooner then those guys, but is is a place to start.

FWIW I keep my kilns internal temp below 95dF until I see shrinkage. I have zero data on what the limit really is. If you have a split that measures 15% MC on the outside and 30+%MC on the inside, you turned your kiln temperature up too soon.
 
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
@ED 3000 , point well taken.

I posted a link to a journal article in one of my threads about how hot how fast. The guys running lumber kilns trying to make finished boards keep the kiln temperature below 95dF until the wood starts to shrink.

When your stacks are moving, tipping, leaning, whatever, when they are shrinking you have all the water out of the sap tubules and it is "time" to turn up the heat.

As burners we aren't too terribly worried about warping and cupping and end grain checking. The folks with a kiln full of clear mahogany are worried about that. So it could be we could let out kilns get hotter sooner then those guys, but is is a place to start.

FWIW I keep my kilns internal temp below 95dF until I see shrinkage. I have zero data on what the limit really is. If you have a split that measures 15% MC on the outside and 30+%MC on the inside, you turned your kiln temperature up too soon.
You know I'm a big fan of your work, PD. I'm just way too lazy (or worn out from other stuff that requires attention) to do a build that requires too much effort.

So far, I've filled a couple of round cages made of welded fencing and dropped big clear bags over them. After a few weeks, the bags stopped showing condensation on the inside. Clearly it worked!

Here's an idea for a commercial modular solution:. Shelterlogic sells big solar firewood kilns, but no matched racking solutions. Couple the racks that WS67 used with covers made of the material Shelterlogic uses on their kilns and greenhouses. The options should start with a "face cord" model, a 2/3 cord model (two racks back to back), and a one cord model (3 racks). You'd have to figure out the venting. Plug and play.

I don't think this is an idea that would make a ton of money, but it would probably be worth doing.
 

SuperJ

Feeling the Heat
Sep 10, 2017
307
St.Jacobs, ON, Canada
The kiln need to get warm.. winter sun and cold temps are not ideal

Wouldn't the low OA dewpoint in the winter play to your advantage? You need less of a temperature lift when it's really cold, to a have really low %rh.
The low angle and shorter daylight hours would be a downer though.

This is a nice simple dewpoint/humidity/temp converter to play with http://www.dpcalc.org/
 

mcstatz5829

Member
Jul 11, 2018
150
Indianapolis
I like this idea more and more. I may relocate to another state in a few years. A cheap kiln will keep the wood stockpile low and prevent overinvestment.

I suppose if I had roots and plenty of acres it wouldn’t matter much, but in my situation a kiln makes much more sense than stockpiling 3 years of wood.
 
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Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
I like this idea more and more. I may relocate to another state in a few years. A cheap kiln will keep the wood stockpile low and prevent overinvestment.

I suppose if I had roots and plenty of acres it wouldn’t matter much, but in my situation a kiln makes much more sense than stockpiling 3 years of wood.


At one time i was sitting on 13 to 14 cords. I burn just about 4 cords. I now sit on 9. my wood is cut down because if i need more i can just season more up kinda on demand.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
1,955
Woolwich nj
Did I read somewhere that you tried the same thing over winter with not much for results ??
I'm working up a couple of cords of Standing dead Oak, and was thinking of wrapping it, then was thinking just top cover for winter ??

So far i havent run the kiln in the winter. The kiln needs heat to work. The low sun and cold temps are ont ideal for wood drying. If you were to get temps in the 70s for a couple weeks you could see some progress, but were past that point