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Author Topic: Solar powered solar kiln  (Read 2102 times)

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Offline AnthonyW

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Solar powered solar kiln
« on: December 09, 2013, 09:00:38 AM »
The location of my solar kiln will not be conducive to being wired to an electrical source. For many years I have researched solar power. The systems consist of four main pieces:

1) The solar panels
2) Charge controller
3) Battery Bank
4) Inverter

The size of the inverter is based on the size of the load. Assuming a single circuit of 120V at 20A, that is 2400W. I have found a 3kW continuous inverter. The charge controller is based on the amperage output of the panels. The question that remains is how to size the array and the battery bank.
'97 Wood-Mizer LT25 All Manual with 15HP Kohler

Offline pineywoods

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Re: Solar powered solar kiln
« Reply #1 on: December 09, 2013, 11:22:50 AM »
Sounds like an interesting project. There is no need to run the fans off the inverter. Use 12 volt dc fans. (automotive radiator fans ? ) Another source is cooling fans out of old computers. 12 V dc and very low current draw. Just use more of them. This would reduce the required size of the inverter. If you put black sheet metal on the bottom of the rafters, there will be a good bit of convective air flow between it and the glazing. Might be enough to allow using smaller fans. Put a timer or photocel on the dh unit. No need to run it during the day, it does most of it's work after the kiln cools down at night. There's not going to be much of any way to calculate the optimum size of the pv array and battery bank. SWAG and then monitor.
You are deep into experimental territory  ;D Keep us updated, interesting..
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
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Offline AnthonyW

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Re: Solar powered solar kiln
« Reply #2 on: December 09, 2013, 11:37:22 AM »
I was actually looking at gable and attic fans as they should be rated to run at the higher temps as compared to the portable fans that PlanMan used. The gable fans looked to have higher CFM rating but also costs twice as much. I like the idea of the radiator fans. They should be able to be had from the junk yard for cheap (the new one in my wife's car cost $130, the motor alone was $25 and that was new and retail).

I never gave it much thought, but you are correct. The cooling coil of the dehumidifier can only cool the air so far, if it cannot cool the air below the dewpoint it will not be able to condense the water vapor from the air. Would a temperature controlled switch be better? It can turn off when the kiln temp is too high and back on when the temperature reaches the point where the dehumidifier can work.

I can't really SWAG, there is too much money on the line. If I start the race, I need to make sure I can finish it.

UPDATE: I did some searching around the 'net. It appears that the fan in my wife's car draws 10.5A at 12VDC, or 126W. That would take 10 of the HF 15W panels just to drive the fan! That would leave nothing to recharge the battery bank to run at night. Another 10-15 panels would be needed for that.

'97 Wood-Mizer LT25 All Manual with 15HP Kohler

Online Ianab

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Re: Solar powered solar kiln
« Reply #3 on: December 09, 2013, 02:12:46 PM »
In the normal solar kiln design the fans aren't run at night, and there is no de-humidifier? There's a "cool down" and equalise phase each night. Basically if the sun isn't shining, the kilns not heating, and you don't need the fans. That would simplify your build a lot. The moisture is removed by controlling the vents and letting the warm moist air out.

Or are you planning a hybrid solar / DH?

Ian
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Offline AnthonyW

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Re: Solar powered solar kiln
« Reply #4 on: December 09, 2013, 02:28:02 PM »
In the normal solar kiln design the fans aren't run at night, and there is no de-humidifier? There's a "cool down" and equalise phase each night. Basically if the sun isn't shining, the kilns not heating, and you don't need the fans. That would simplify your build a lot. The moisture is removed by controlling the vents and letting the warm moist air out.

Or are you planning a hybrid solar / DH?

Ian

I guess I'm not sure. The materials I have been reading don't appear to differentiate between the two types.

If the recirculation fans don't need to run while cooling (night), and the dehumidifier doesn't need to run when it is too hot (day). Then one could run the dehumidifier at night with the side benefit that it would act as a small recirculation fan.

I am more a novice on kiln operation as I am on the sawmill. Would this situation be too aggressive, causing checking or case hardening?

My primary driver for building the kiln is as a preventative measure against bugs. I have a high fear of trying to air dry my lumber only to have it chewed into sawdust. I definitely do not want to build something from infected wood, to have it in the house and have the house chewed to pieces. There are a lot of bugs, spiders, bats, and mice around. Each of which lend themselves to having more of the other.
'97 Wood-Mizer LT25 All Manual with 15HP Kohler

Offline pineywoods

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Re: Solar powered solar kiln
« Reply #5 on: December 09, 2013, 03:06:50 PM »
A temp shutoff on the de-humidifier works fine. In fact, that's what I use. My dh is a cheap sears 1 room model, that has an adjustable high-temp cut off. I set that for about 110 degrees and just leave the power on 24/7. Planman is a neighbor. His kiln is an updated copy of mine. To get the moisture out, you have the option of vents or the dh unit. Vents are a bit cheaper, but require a lot of attention. With the d/h it's pretty much set and forget and will dry lumber quicker and to a lower moisture content. If your biggest concern is bugs, put the black sheet metal on the bottom of the rafters. You will get a lot more heat (some say too much). we have documented 180 degrees. Ianab makes a valid suggestion. with limited power available, running the d/h OR the fans but not both would probably be a workable approach. Automotive fans come in different sizes, I have one on my mill that only pulls about 5 amps...
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Online Ianab

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Re: Solar powered solar kiln
« Reply #6 on: December 09, 2013, 03:29:58 PM »
Dehumidifier and Solar are two different systems, although some guys have successfully combined the two. What you have to watch then is that you don't dry too fast, with the solar heat during the day, and dry D/H conditions at night. In Pineywoods case, a small domestic D/H probably isn't going to remove water fast enough to create a problem, so his system works fine, and should be faster then solar alone.

The beauty of the solar design is that it's very energy efficient. It's only using a little electricity to run a couple of small fans, the actual energy to dry the wood is from the sun. Also it need not have precise control because the drying goes in cycles. At night the kiln cools off, the humidity goes up and the wood has a chance to equalise. This lets moisture from the core migrate out to the dry surface, and reduces the chances of surface checking. Next day, sun comes out, kiln heats up and you drive a bit more moisture out. Repeat until the wood is dry.

At the end of the cycle you can close the kiln up and it should get hot enough to cook any bugs for you.

A dehumidifier works like a big air conditioner, with refrigerant, a compressor, fans and condenser / radiator. In that system the heat is usually provided by the compressor, and recovered and recirculated through the radiator. Also quite energy efficient, but takes a lot more power to run an Air-con pump (usually a couple of kW) and you are not collecting that free sunshine. More expensive to set up, and needs a proper schedule and control system as it's running 24/7, and it's possible to dry wood too fast  But for a commercial operation, you aren't relying on the sun. Wood is going to be dry in X number of days, even if the sun doesn't shine.

So that pure Solar kiln is what you want for your off-grid set up, because it is practical to power the fans from solar panels, only needing 50 or 100 watts of power to get useful air movement. I think they sell pre made kits with an attic fan and a matching solar panel? A couple of those and you would be in business. No messing about with batteries and inverters, just not needed.

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Offline MattJ

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Re: Solar powered solar kiln
« Reply #7 on: December 09, 2013, 03:35:56 PM »
Have you guys ever seen this article on a totally solar kiln using solar panels?

http://appropriatetec.appstate.edu/sites/appropriatetec.appstate.edu/files/HPSolarLumberKiln.pdf

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Re: Solar powered solar kiln
« Reply #8 on: December 09, 2013, 03:49:23 PM »
Have you guys ever seen this article on a totally solar kiln using solar panels?

http://appropriatetec.appstate.edu/sites/appropriatetec.appstate.edu/files/HPSolarLumberKiln.pdf

Hadn't seen that page, but that's EXACTLY the sort of thing I was trying to describe, with just the fans and solar panels.  :)
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Offline AnthonyW

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Re: Solar powered solar kiln
« Reply #9 on: December 09, 2013, 04:12:03 PM »
That was a good article, could have had a little more on the setup of the items I'm interested in and a few more photos of the construction in general. I have been looking for the low amperage fans like are described in the article (12VDC, 1.1A, 12-18" diameter 500-2000CFM) but I haven't found them yet. I found plenty of 12V fans but all are small diameter and CFM. The solar attic fans are going for $225 each. Fairly comparable to what they spent in the article. But I'd like to spend less. I would love to get all 3 for the $225 (HF 45W solar setup with 3 fans @ $25 each, would do it).

I'm not following their operation of the vent baffles. My thought was to base it on temperature, time of day (open during day, closed at night), humidity, or a combination of all. The VT design had no baffles, the air came in high, down past the collectors, through the stack and out the back at the bottom.
'97 Wood-Mizer LT25 All Manual with 15HP Kohler

Offline 21incher

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Re: Solar powered solar kiln
« Reply #10 on: December 10, 2013, 06:21:43 PM »
Take a look at the Renogy.com store. They have a solar calculator in the store. I recently installed one of their 100 Watt mono-crystalline solar panel kits for lighting in a pole barn and it works great. The mono panels are much lower cost per watt then the
HF panels and more efficient. I have it hooked up to (2) 125 AH deep cycle batteries and a 700 watt inverter. I installed 3 strings of temporary light sockets from Home Depot that each hold 5 of the 23 watt cfl bulbs. I am running about 350 watts and can get between 1/2 - 1 hour of lights a day with my setup depending on how much sun we get. The mono panels even make power when it is cloudy. I expect to get twice as much power in the summer. If you want to supply 2400 watts for any period of time you will need a massive bank of golf cart batteries hooked together with welding cables and a good size array of panels plus you may want to go with a 24 volt system. If you just want to run a fan one of their panels may do that for you.
Hudson HFE-21 on a custom trailer, Deere 4100, Kubota BX 2360, Echo CS590 & CS310, home built wood splitter, home built log arch, and a Logrite cant hook.

Offline AnthonyW

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Re: Solar powered solar kiln
« Reply #11 on: December 16, 2013, 04:04:31 PM »
I have reviewed both the Appalachian and VT solar articles plus the posts here and started sketching the design for a solar kiln.

The design basis was:
1) As small as possible, but still able to hold a 10' board. I would like to be able to relocate it.
2) Use the 8' long sheets of clear plastic from the hardware store without cutting them.



The angle from the rear door to the glazing is 48.6 degrees. According to the charts, the angle from the sun will vary from 22 to 70 degrees in my latitude. I actually wanted to reduce some of the collection in the summer so it doesn't dry too fast which has the benefit of better collection earlier and later in the year.

For the foundation, I'm thinking 6x6 PT to form a sled with an insulated "torsion box" (2x6 frame and floor joists covered on either side with exterior rated plywood. I want to be able to move it around my own property, but I'm trying to avoid axles and wheels. I'm starting to think it may be to big and heavy to make a sled work.

The length of 12' based on the 2' wide panels. The depth of 6' was set based on a stack 4' wide with 12" on either side for circulation. The height is what it is based on the stack up dimensions of the door, header, vents, and rafters.

There are a pair of doors. Each 5' wide (perhaps 2 1/2' bifold if I can figure out how to make them) and 7' tall. I'm 6' tall so I don't want to be bumping my head. I already made that mistake with my shed. The door header is 11 1/2" tall and the rafters supporting the glazing are 2x6.

I still need to source the solar panel and fans. Vent control still needs to be considered.

I think the 12' length is fixed if I want to fit 10' long lumber. I am open to any suggestions on how where I can make it shorter or narrower, keeping in mind my height, the angle required for the glazing, and the length of the glazing panels available (8' and 12') as I don't want to make any scrap.
'97 Wood-Mizer LT25 All Manual with 15HP Kohler

Offline GeneWengert-WoodDoc

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Re: Solar powered solar kiln
« Reply #12 on: December 17, 2013, 08:54:23 AM »
12' lumber is often 12'4, so consider that.

Your design seems wonderful.  Will you have two layers of glazing?  If so, the spacing between them is not critical.

For the doors, consider how barn doors are made and hung.  The hardware is substantial but can easily support a heavy door.  You can easily put the vents in the doors.  They rarely need adjustment...once a week, probably.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline AnthonyW

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Re: Solar powered solar kiln
« Reply #13 on: December 17, 2013, 10:22:09 AM »
12' lumber is often 12'4, so consider that.

Your design seems wonderful.  Will you have two layers of glazing?  If so, the spacing between them is not critical.

For the doors, consider how barn doors are made and hung.  The hardware is substantial but can easily support a heavy door.  You can easily put the vents in the doors.  They rarely need adjustment...once a week, probably.

I was thinking of just a single layer of glazing. The overall size is larger than what I really think I need and the cost is getting substantially higher than I expected. Putting the vents in the doors would reduce the height by about 7" and knock a few bucks off.
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Offline GeneWengert-WoodDoc

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Re: Solar powered solar kiln
« Reply #14 on: December 17, 2013, 04:29:22 PM »
The second layer of glazing can be inexpensive, but thick, polyethylene sheet.  It does get brittle, but the replace cost is low.  The second layer will make a big difference.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Planman1954

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Re: Solar powered solar kiln
« Reply #15 on: December 17, 2013, 06:26:26 PM »
Have you guys ever seen this article on a totally solar kiln using solar panels?

http://appropriatetec.appstate.edu/sites/appropriatetec.appstate.edu/files/HPSolarLumberKiln.pdf
Wow...sure takes that design a lot of TIME to dry wood. I dry pine in my pineywoods design to 14% mc in less than a week, and 6-8% in another week.
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Offline GeneWengert-WoodDoc

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Re: Solar powered solar kiln
« Reply #16 on: December 17, 2013, 07:20:23 PM »
A square foot of solar collector has 1000 BTUs per day on the average.  If the solar collector was 100% efficient and all the energy collected was used for evaporation (that is, no building heat losses), then this 1000 BTUs would evaporate 1 pound of water.  For 1000 BF of oak lumber, each 32 pounds of water evaporated drops the MC by 1%, so, if we have 1 sq ft per 10 BF (that is 100 sq ft per 1000 BF), a 100 sq ft collector and a 1000 BF kiln load of oak will dry (at 100% efficiency) will collect 100,000 BTUs average per day which will evaporate 100 pounds of water or 3% MC loss.  Of course, there are heat losses, so we might find 50% efficiency or 1.5 % MC loss per day.  If we want faster drying we can add energy...external source or larger collector.

Note that for pine, which can be about half the weight of oak, the numbers would double...about 3% MC loss per day average.

Anything we can do to reduce building energy loss is extremely helpful.  That is why good insulation for walls and floor, two layers of glazing, etc. is strongly encouraged.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more


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