Solar Kiln Assistance

JackLeg · 01-29-2008, 11:02 PM

Anyone know where I can find the roofing material for the solar kiln I am building? Polycarbonate panels seem to be the material of choice for greenhouse applications, but MAN that stuff is expensive!!!

I'm also open to other suggestions (come on Scott, I know you can offer something here!) so all input is welcome.

I need to find a source that I can "pick-up" as the freight on this stuff will eat you alive!

Thanks in advance!!

junquecol · 01-29-2008, 11:52 PM

Both Lowes and Home Depot carry polycarbonate panels, over by the roofing sheets (tin). They come in 8', 10', and 12' lengths only. Be sure and buy the galvanized roof screws, that are made for these panels.

scsmith42 · 01-30-2008, 12:08 AM

Reggie, in addition to Lowes and HD you can also check Farmtek (www.farmtek.com). They sell a lot of greenhouse related stuff.

You can also keep an eye out for a used greenhouse for sale on either craigslist or the NC Agricultural Review.

Scott

jeff... · 01-30-2008, 01:06 AM

A few years ago I started collecting materials to build one. I had 15 clear sheets of 12' long polycarbonate but I gave it away to a friend who wanted to use it for sky lights in a barn he is building. Jack please please don't get me wrong for what I'm about to say, I'm only trying to save you some expense by sharing my experiences and understanding.

At one time I was gun-ho to build a solar kiln. That is till I paid I guy to dry several 1000 BF of quarter sawn 4/4 oak for me in his. Several weeks after helped load the kiln he calls me up and said my lumber was ready. I got there and as we were pulling the boards out of his solar kiln and loading them on my trailer. They looked looked like a bunch of twisted dried up snakes, never had I seen so much drying defect in my life out of a batch of lumber. There truly was not a single board that I would have thought about selling to someone, I ended up unloading it into a big pile and put a match to it. Yes it really was that bad.

So I figured it was just this one guy and he not knowing what he was doing so I found another guy hauled my trailer over 2 hours to his solar although this time it was maple instead of oak. Same thing happened, each and every board was so crook and twisted they were unusable and not only that most of them looked like they exploded they were split so bad.

What went into those solar kilns was just as good if not better than what I take to Scott to dry and have not had any problems like this from Scott or his dehumidification kiln. Personally I think a solar kiln gets too hot and the lumber that's in there looses to much moisture in one day and literally explodes.

If your serious about a solar kiln, figure out some way to regulate the temperature even if it means throwing something over the roof to prevent the sun from beating down on your collector and building up excessive heat in the the chamber. I don't know an effective way to do this, specifically in the summer when temperatures hover around 100 degrees and humidity is high, vents are only so effective. Maybe an air conditioner might work? Another thing may be to figure out how to supply supplemental heat on those days when it's raining or cloudy. Constant changes in temperature and humidity has got to be bad for the lumber trying to dry in a solar kiln.

I don't think I would ever consider placing fresh cut green lumber in a solar kiln after my experiences. It seems like air drying to around 15% then "polishing off" in a solar kiln might be the way to go?

I do know that even laying a fresh cut board like oak in the direct sunlight during the summer will cause it to surface check and possibly split in no time flat, because the sun dries it to fast. I think the idea is to keep the lumber in the dark, stay within the maximum allowable moisture content loss per day, dry slow and steady and not "cook" the lumber.

sorry for blabbing

Thanks

Alan in Little Washington · 01-30-2008, 01:53 AM

If you are going to build a solar kiln you need to build it AND OPERATE it correctly. Dr. Eugene Wengert has written a number of publications for USDA and others, and is THE EXPERT. VA Tech has a Forrestry Dept that designed a home sized solar kiln, and publishes plans. A Google search on solar kilns and/or Dr. Wengert will lead you to all the info, including solar kiln info and downloadable plans, and USDA pubs on drying lumber.

Polycarbonate is the kiln glazing material of choice, specifically dual, or triwall. It is available from a number of sources but is not cheap. Corrugated single wall sheets like on the kiln below are available at big box stores. There are suppliers of the bi/triwall in Charlotte and Raleigh.

Piedmont Plastics

Ecologic

Sundance Supply

Complex Plastics

US Plastics

Greenhouse Meg Store

Like Jeff said it is easy to over heat wood in a solar kiln especially here in the South. That can cause warping and case hardening. The kiln that was offered to me, which I have yet to get has fans that are both timer and thermostatically controlled. All kilns require monitoring and some control, except very expensive computer controlled ones. Like Jeff mentioned, I think some of the sources actually recommend air drying to 20% before putting the lumber in the kiln. Different species have different drying schedules also- exceed the recommended schedule and you risk warping and splitting the lumber.

(This is my kiln, as soon as I find a place to put it and a way to get it there)

JackLeg · 01-30-2008, 08:39 AM

Thanks for all the responses so far. This is where I am at this point.

I am building the 800-1000 ft kiln from downloaded drawings from VA Tech. The "sketches" require you to really use your imagination. I have
e mailed VT and asked if they have plans. Haven't heard from them yet.

Jeff, I've heard similar stories to yours. I plan to attend a workshop at VT in April on solar drying. It does seem some air drying is helpful prior to loading the kiln. I realize I have a lot to learn.

Alan, wish I was nearer you. We'd get that thing home somehow!

I'll check the BORG's for the polycarbonate sheets.

Keep the input coming. And thanks!

woodydiver · 01-30-2008, 09:03 AM

hello all,
i just wanted to ask if there is a formula that some one has on drying the woods. i was thinking about building a solar kiln, but i was going to put fans to help regulate the temp and humidity. If you guys can come up with something ill build a controller and see if it helps.
curt

Bernhard · 01-30-2008, 10:56 AM

Originally Posted by JackLeg

..... I have
e mailed VT and asked if they have plans. Haven't heard from them yet.

. ....

You may want to call Brian Bond of VT directly, he is a pleasant to work with and quite helpful.

Phone: (540) 231-8752
Fax: (540) 231-8868
Office:

Brooks Forest Products Center (0503)
Virginia Tech
1650 Ramble Road
Blacksburg, VA 24061

Related Website(s):

Dr. Bonds non-work activities

Email: bbond@vt.edu

I have a copy of the plans, just need to find them, but they are available on the web.

As for solar kiln operation: As with any process, success is dependent on the operator. IMHO, a solar kiln is the way to go. And I will build one this year in spring.
Cheers,
Bernhard

jeff... · 01-30-2008, 12:33 PM

Originally Posted by JackLeg

Thanks for all the responses so far. This is where I am at this point.

I am building the 800-1000 ft kiln from downloaded drawings from VA Tech. The "sketches" require you to really use your imagination. I have
e mailed VT and asked if they have plans. Haven't heard from them yet.

Jeff, I've heard similar stories to yours. I plan to attend a workshop at VT in April on solar drying. It does seem some air drying is helpful prior to loading the kiln. I realize I have a lot to learn.

Alan, wish I was nearer you. We'd get that thing home somehow!

I'll check the BORG's for the polycarbonate sheets.

Keep the input coming. And thanks!

Jack if I had to put my thoughts about kilns men into single sentence it would be something like Kiln Drying Lumber is where Science and Art meet at the headwaters of Experience.

contrary to what some people believe - you can't just toss lumber into any kiln turn it on and expect it to come out perfect. That's why kilns men get paid the big bucks...

Later Gator

gordonmt · 01-30-2008, 12:59 PM

I can offer one Scottish solution that I did when I lived in Illlinois.
I went to a building salvage yard and purchased old reclaimed windows from various demolition jobs. I tried to get them from one demolition job so they would each be about the same size. I got each window (from memory now) for about $3.00 a window. I fitted them into a long frame with nails and a caulk. I dried over 400 bf of lumber in that thing before I left it with the farmer that owned the land it was sitting on. It was obviously not a transportable device. It worked well though.

junquecol · 01-31-2008, 07:29 PM

Somewhere here, I have a set of the Wood magazine solar kiln plans, along with the original article. Recently either American Woodworker, or Wood did a small solar kiln article. Also have two different articles on small DH kilns.

JackLeg · 02-01-2008, 10:01 PM

Originally Posted by junquecol

Somewhere here, I have a set of the Wood magazine solar kiln plans, along with the original article. Recently either American Woodworker, or Wood did a small solar kiln article. Also have two different articles on small DH kilns.

Bruce, if you find those articles/plans, I'd love to see/read them. I'm underway with construction, but nothing is irreversable. Thanx.

jeff... · 02-01-2008, 10:19 PM

Jack good for you - please keep us posted on how it turns out. I hope you have a better experience that I have had.

Thanks

Ivey · 02-01-2008, 10:32 PM

Reggie,
Good luck on that project. I'll bet you make it work, I think fans, and vents will be the key to success on the solar kiln.
If you need any framing lumber, let me know, I will donate to your kiln project.
Again good luck.... Keep us posted.

JackLeg · 02-02-2008, 10:13 AM

Originally Posted by Ivey

Reggie,
Good luck on that project. I'll bet you make it work, I think fans, and vents will be the key to success on the solar kiln.
If you need any framing lumber, let me know, I will donate to your kiln project.
Again good luck.... Keep us posted.

The plans I'm building from include 3 fans and a total of 6 vents, high and low. I fully realize that this is going to take some learning and experimenting, but, the one thing I have is time!

I did find the poly sheets at my local Lowes, so----

Again, thanks to all who are contributing and keep the ideas and opinions coming.

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