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Author Topic: And yet, another Solar Kiln thread ...  (Read 1323 times)

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Offline 50 Acre Jim

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And yet, another Solar Kiln thread ...
« on: December 08, 2017, 03:48:59 PM »
Been planning my solar kiln build for some time now.  Ive read all the threads and watched other members build theirs, so now I should be an expert, right?   But of course, Im not.  About the only things Im sure of is I want my kiln to be completely solar powered, handle larger/longer boards, and to convert from an air-drying structure into a solar kiln when the lumber has air-dried to the proper MC.   Heres what Ive got so far, complete with (not to scale) images.

As mentioned, the kiln will be completely solar with the fans running on 24-volt DC directly from the solar panels.  I plan on having 2 fans but will adjust that number accordingly as the project matures and I start to get an understanding of what is actually happening in the kiln vs what I think will happen.  The fans I am looking at are called Solar Direct DC Super Fans, are 16 in diameter and capable of moving between 1,000 cuft/min on the low setting to 1,900 cuft/min on the high setting.   I plan to let the sun turn the fans on/off simply by when it raises or sets.  If I need to run an exhaust fan after sunset I will run a smaller fan off of a battery bank.  I hope that wont be necessary as I want to keep this system simple and minimize my daily intervention as much as possible. 

Image 1 is a side view of the kiln.  It will be 16 wide, 8 deep and 8 tall.  The solar heater sits above the main structure and is 4 tall on the back side and tapers down until it connects with the front of the kiln.    The solar windows on top will be made of Sunlite 24 in. x 96 in. Polycarbonate Clear Twinwall Roof Panel.  (Unless someone has a better suggestion.) 




There will be 4 doors on the kiln, 2 on the front and 2 on the back.  Image 2 and 3 show the kiln without and with doors.    With all 4 doors open, the building becomes a 16X8 shelter for lumber to air-dry in.  The location I have chosen has a Southern exposure and sits on the side of a hill with an almost constant breeze that will speed the air-drying process.   When the doors are closed and the solar fans are turned on, the building becomes a solar kiln capable of drying lumber up to 16 long. 


 


The next images shows the kiln with the movable wall slid into the center of the kiln.  This center wall parks against the far-left wall but can be moved accordingly to make 2 separate drying stalls of equal or different sizes.   



Using the movable wall allows both chambers to simultaneously dry different types of lumber or two batches that are started at different times, say a couple of weeks apart from each other.   It also allows for lumber to be air-dried on one side will kiln drying lumber on the other. 





I spent the last couple of days cutting a pad, driveway and turnaround for the kiln.  Wanted to finish it off and start construction today but 6+ inches of snows says otherwise.   

So there it is guys.  Look it over and give my you ideas, criticisms, suggestions, etc.    Thanks in advance,

Note: Since I made these drawings I have decided to put the solar panel(s) on a separate, free standing support and not take up space on the kiln itself.   No sense in wasting all that solar exposure, right? 

Jim






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Offline CharlieP

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Re: And yet, another Solar Kiln thread ...
« Reply #1 on: December 08, 2017, 07:42:38 PM »
Hey neighbor, we are over in Stecoah, off 28, I built a solar kiln this fall based on VA Tech plans, you are welcome to come over and check it out , I would be glad to go over some things I have run into.
  Charlie

Offline WLC

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Re: And yet, another Solar Kiln thread ...
« Reply #2 on: December 09, 2017, 01:23:19 AM »
IF you are gonna dry 16' lumber your kiln will need to be longer.  I'll be watching as you build this.  Very interested in how it turns out!
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Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #3 on: December 09, 2017, 07:18:03 AM »
Maybe I can find a market for 1511 lumber?  :D   Or better, Ill probably end up with a 2X4 on each side to increase the width a bit.     

I think the greater problem here is that the solar collector is not at 45*.  Is that serious enough that I need to raise the back wall of the collector from 4 to 8 or will I catch sufficient sun at the current angle?
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Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #4 on: December 09, 2017, 10:10:01 AM »
The angle is a big issue, with a big effect from September through March.  You will recover as much as 15% less energy.  The best angle is your latitude, so 45 degrees is too steep for your location.

Are the walls 6 thick? Doors too?  Floor insulated also?

I am not sure why there is so much space from the top of the pile to the horizontal baffle.

Will the fans blow downward?  Will the vents have adjustable covers?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #5 on: December 09, 2017, 12:05:24 PM »
The angle is a big issue, with a big effect from September through March.  You will recover as much as 15% less energy.  The best angle is your latitude, so 45 degrees is too steep for your location.

Are the walls 6 thick? Doors too?  Floor insulated also?

I am not sure why there is so much space from the top of the pile to the horizontal baffle.

Will the fans blow downward?  Will the vents have adjustable covers?

Latitude/Slope of panels: Latitude for Franklin NC (I'm 15 miles West of Franklin) is 35.1823 N and the slope on the collector is currently at 23*.   I can change the degree of slope by making the back of the collector a little higher.  It's 4' now, raising it to 5', or possibly 6', should help considerably.

Wall thickness: Walls will be true 2X6 construction as I am cutting the lumber myself.   

Floors: Floors will sit on 4X6 beams that rest on pier blocks.  I will insulate the area between the beams and cover that with a couple layers of 30lb felt.  Then cover that with 1/2" plywood. 

Baffle: The drawing is to not to scale.  It's only purpose is to provide a mental projection of what the design looks like.  Anything and everything is subject to (and most likely will) change.  With that in mind, the positioning of the baffels in the diagram is there only for you to see that there is a baffle and the approximate location. 

Fans: Currently I plan on 2 fans, one on each side of the kiln.  And yes, they point down as they pull the hot air from the top of the kiln and direct it down into the drying chamber.  These are very powerfull fans, I don't expect there will be an issue with too little air movement.  If anything, there may be too much, if that is possible. 

Vents: Yes, all the vents will have adjustbable covers. 

Thank you for your input/questions Gene.  Any suggestions are appreciated. 
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Offline scsmith42

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Re: And yet, another Solar Kiln thread ...
« Reply #6 on: December 09, 2017, 12:27:33 PM »
Jim, if you're headed to Raleigh any time soon you're welcome to stop by and look at my 4 solar kilns.  One is the traditional design and three are modified to better fit my standard kiln stacks.
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Offline Savannahdan

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Re: And yet, another Solar Kiln thread ...
« Reply #7 on: December 09, 2017, 01:37:18 PM »
I notice that your vents are in the sides of the front chamber.  Wouldn't it be better to have them in the back so that the air flow through the stacks is constant and you're pulling fresh air in.  I do like your 2 chamber system.
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Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #8 on: December 09, 2017, 02:09:39 PM »
I notice that your vents are in the sides of the front chamber.  Wouldn't it be better to have them in the back so that the air flow through the stacks is constant and you're pulling fresh air in.
I'm pulling a regulated supply of fresh air in from the front so that it is introduced into the lowest part of the heating chamber, where it is warmed as it rises.   I'm hoping this will ensure that the hottest air possible is being pulled out by the fan and forced down through the stack.       



If the vent were in the back the forced hot air would be exiting prior to going through the stack.  By putting the vent in the bottom front, I am allowing wet (heaver) air to vent that has already been forced through the stack. 

I do like your 2 chamber system.
Thank you!
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Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #9 on: December 09, 2017, 05:14:46 PM »
I do,believe the vents are ok, but if you could move the two front ones closer to the center, this would help air movement side to side.
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Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #10 on: December 09, 2017, 05:42:55 PM »
I do,believe the vents are ok, but if you could move the two front ones closer to the center, this would help air movement side to side.
I'll make those changes in the final build.  Thank you!

Edit:  Sorry Gene, I just saw what you meant about the baffle being so far back in the picture on the stack.  Fixed it!  Also moved vents from side to front and extended the back of the solar collector to 5', which should bring the pitch of the collector to 32*.  Optimum is 35*.  Jim

Edit #2 - 12/12/2017: Although it is not noted in the image below, I have changed the back wall to be 5'6" high, which will make the pitch of the solar collectors exactly 35*.  Life is good...




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Offline Savannahdan

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Re: And yet, another Solar Kiln thread ...
« Reply #11 on: December 09, 2017, 08:51:00 PM »
Ok, the airflow diagram helps. 
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Re: And yet, another Solar Kiln thread ...
« Reply #12 on: December 13, 2017, 07:08:41 PM »
Im about 99% finished cutting out the pad that the kiln will sit on.  I made it 50 X 95 which will give me plenty of room to add another kiln if this design works out well.  I wanted to be sure I have enough room to load/unload lumber as well as being able to turn a truck or tractor around without running into anything.  It was 15* this morning with a steady wind that made it hard to see through the tears!  I have a little bit of grading to do to insure the water drains in the right direction and then Ill be ready to start laying out the blocks for the kiln to sit on.



Got a partial cut list made.  I will have to buy the plywood, but I have enough stock to cut everything else.  Also got my solar fans ordered.  Depending on the amount of sunlight hitting the panel at any given time each fan will move between 1,000 - 2,000 cuft/min.  If that isn't adequate I'll add a third fan but I think with the amount of sun that hits this area I will see them turning at the 2,000 cuft/min speed more than not.   Pricey little rascals at $239.00 apiece, but anything "solar" seems to cost twice as much. 

 

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Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #13 on: December 14, 2017, 04:10:10 PM »
Cheap fans are not as efficient and use brass bushings or worse.  Your fans will last forever and the cost of running them will be good.

Sometimes, using this area to air dry is good, plus if you had a pole shed with only a roof, no walls, you can work in any weather...put that on your Christmas wish list.
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Re: And yet, another Solar Kiln thread ...
« Reply #14 on: December 14, 2017, 04:55:32 PM »
I am so in for this build. Me likey so far.
I knew what I thought I meant.

Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #15 on: December 14, 2017, 07:03:51 PM »
Cheap fans are not as efficient and use brass bushings or worse.  Your fans will last forever and the cost of running them will be good.
 
Good to know!  I feel a little better about the purchase now. 

The good news: Got all 19 of my 2x6x12 rafters cut today.  :) They sure are purdy!
The bad news: Got 80 more 2x6x8 to go! 
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Re: And yet, another Solar Kiln thread ...
« Reply #16 on: December 15, 2017, 09:12:51 AM »
I like your design - it has a lot of flexibility.

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Re: And yet, another Solar Kiln thread ...
« Reply #17 on: December 18, 2017, 06:58:14 PM »
In spite of snow, ice, and rain I managed to cut 30 - 2x6x8 today.  Only 50 more to go and I will have enough framing lumber for the walls.  Then I'll move on to the 4x6's for the floor and the single 4x12x18 that will span the front, hold the walls together and support the 2x6x12 rafters that the polycarbonate panels will rest on.  And then, I will visit Lowes to buy some 3/4" plywood for the floors and walls.   My plan is to use plywood on the walls and then cover the outside with lap siding that I make from White Oak. 

Lot's more to do but so far I'm having a good time!   
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Re: And yet, another Solar Kiln thread ...
« Reply #18 on: December 18, 2017, 07:43:38 PM »
Off topic of your kiln, which I am definitely excited to follow, but had a question.  Ever still find any chestnut logs in the creeks around your parts?  Been 25 years ago, but helped pull a couple of logs out of a creek down towards Franklin.  Made some nice wormy lumber.  Still have a picture frame out of it.
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Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #19 on: December 19, 2017, 10:28:10 PM »
The original Virginia Tech design used CD-X plywood.  You might have to replace a sheet or two in a year or two, but the cost is good.
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Offline jaciausa

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Re: And yet, another Solar Kiln thread ...
« Reply #20 on: December 20, 2017, 08:16:10 AM »
Hi Jim,
 I believe you have the start of a good plan except the slope of the 6/12 pitch roof (rise/ run ) that would make it only 26 + degrees.

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Re: And yet, another Solar Kiln thread ...
« Reply #21 on: December 20, 2017, 08:25:24 AM »
For your area cutting a 7/pitch roof would give you 35 + degrees. Hope this is helpful.

Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #22 on: December 20, 2017, 12:48:29 PM »
Off topic of your kiln, which I am definitely excited to follow, but had a question.  Ever still find any chestnut logs in the creeks around your parts?  Been 25 years ago, but helped pull a couple of logs out of a creek down towards Franklin.  Made some nice wormy lumber.  Still have a picture frame out of it.
This is the first I've heard of finding/pulling Chestnut out of the creeks.  That would be wonderful to find such a treasure!


The original Virginia Tech design used CD-X plywood.  You might have to replace a sheet or two in a year or two, but the cost is good.
I think CD-X plywood will be fine, especially if it gets a coat of waterproofing somewhere along the line.  :-) 


For your area cutting a 7/pitch roof would give you 35 + degrees. Hope this is helpful.
Although not reflected in any of the previous drawings I have raised the back wall to a height of 5' 6" which I believe will give me a 35* angle.  Let me know if there is a difference in what your saying and my height calculations.   I used the following calculator to get my measurements.     https://myrooff.com/roof-pitch-calculator/
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Offline jaciausa

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Re: And yet, another Solar Kiln thread ...
« Reply #23 on: December 20, 2017, 01:28:14 PM »
Your fine with how you are doing it. i was just stating what the framing square or the speed square shows. That would give a true 7/12 cut for the tails or a birds mouth.  The exact degree is 30.26.

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Re: And yet, another Solar Kiln thread ...
« Reply #24 on: December 20, 2017, 01:37:34 PM »
Are the top of your walls level? or cut on angle so you do not need a birdsmouth cut top or bottom? Possibly you are blocking them without using a cut.

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Re: And yet, another Solar Kiln thread ...
« Reply #25 on: December 20, 2017, 02:06:01 PM »
Are the top of your walls level? or cut on angle so you do not need a birdsmouth cut top or bottom? Possibly you are blocking them without using a cut.
At this time I intend to use a birdsmouth cut on each end.  But in retrospect, I can't think of a project I've done that started and ended as planned.  Why should this be any different?  ;D
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Offline jaciausa

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Re: And yet, another Solar Kiln thread ...
« Reply #26 on: December 20, 2017, 08:37:05 PM »
Sixty six inches or 5 ft 6 inch total rise would be an 8.25 inch rise per foot and exactly 35 degree slope as you have planned.

Offline btulloh

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Re: And yet, another Solar Kiln thread ...
« Reply #27 on: December 21, 2017, 09:21:07 AM »
I think the collector angle deserves a bit more study before you commit to the 35 degree slope.  I went through this with solar panels as well as with my kiln build.  There are a number of solar angle calculators on the web you can play with and the exercise could be useful.

One rule I'd seen for the kiln collector was to use your latitude plus 10 degrees.  There are some other things worth considering.  The ideal angle changes of course with the seasons, so any fixed angle is a compromise.  In the summer, with a high sun angle and high ambient temperatures the kiln gets enough plenty of energy to operate well.  Around the spring and fall equinox, the angle is lower but there seems to be enough energy falling on the collector to produce good results in the kiln.  This angle corresponds roughly to the latitude plus ten degree rule, so that is about optimum for the collector angles we tend to build into these kilns.  As the winter solstice approaches, the sun angle drops and the energy decreases, plus the days are shorter. 

It may be worthwhile to go with a steeper collector angle to help with the winter months where it is harder to get enough energy to run the kiln.  The long days and higher temps in the summer can run the kiln even when the collector is steeper and optimized for a lower sun angle.  From what I've observed with my kiln, I think I would compromise further toward the lower angle (steeper collector) than the 45 degrees I chose.  Of course that complicates the build a bit.

Or you could build a collector that can be adjusted for the season.  Fun.

Another thought on the collector angle thing:  Even though we talk about the pitch of the panels as the collector angle, the real story is not the roof pitch but the black thermal absorptive surfaces inside the the kiln.  The angle of the panels is not the determining factor in energy collection.  The amount of surface area inside the kiln that is struck by the sunlight determines the thermal gain.  The panels just allow the sunlight to get to the black surfaces.  That means that we need to take into account both the panel area admitting the sunlight and the area inside the kiln that is collecting the energy.

I'm starting to ramble a bit, but that's my two cents worth.

Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #28 on: December 21, 2017, 10:51:46 AM »
The best overall single unadjustable angle is your latitude. You can add 10 degrees for slightly better performance in late fall and winter, but poorer in the summer, and that means the rear wall is higher and that may be undesirable. As we go further north, then we suggest 45 degrees as it is easy to make that angle.  So, 35 is good for you. A collector that you can tilt from time to time is neat, but it is a lot of work and you might shorten drying time by a day.

As mentioned, the area of the roof measured perpendicular to the sun at noon (or the shadow at noon) controls the amount of energy entering the kiln. Once in the kiln, the light energy must be absorbed and converted to heat energy. We use black surfaces in the kiln- -walls, baffles. Their area is not important.  A few people put the black absorber near the clear roof, but it seems easier to use the walls and baffles rather than make a separate absorber.  Either method will absorb about 100% of the incoming energy, which is the clear area perpendicular to the sun at noon. This is about 1000 BTU per square foot per day, which will evaporate about one pound of water per square foot per day on the average.

Hope this is clear.
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Re: And yet, another Solar Kiln thread ...
« Reply #29 on: December 21, 2017, 12:51:25 PM »
The latitude here in SE Iowa is around 40 degrees. Being colder the 45 degree will be better choice for me. The best reason for me to use 45 degree is cutting all the rafters using a speed square at 6/12.

The orientation along the other axis to solar noon is just as important if you can still change it. This site can help you with that calculation-https://www.esrl.noaa.gov/gmd/grad/solcalc/-
 I thought my kiln was off a little, but turns out calculating it with solar noon here in Iowa it was correct.
Hope this helped some.
Also Iyou said you were using 8 foot panels for collector and if you are you will need to downsize the width for the total run of rafter.

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Re: And yet, another Solar Kiln thread ...
« Reply #30 on: December 21, 2017, 12:56:01 PM »
i meant 12/12, just not thinking to clear.

Offline GeneWengert-WoodDoc

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Re: And yet, another Solar Kiln thread ...
« Reply #31 on: December 22, 2017, 08:33:11 AM »
A solar kiln in SE Iowa is really tough...it has to withstand hail storms, strong thunderstorm winds and nearby tornadoes, heavy snow fall, and maybe a few baseballs if you are close to the Field of Dreams.  The steeper roof will help drain or remove rain and snow.

In general, as you move further north, the summer sun rises in the NE, so with a 45 degree steep roof, it is several hours after sunrise before direct sunlight gets onto a kiln and the interior humidity drops.  Likewise, the south-facing collector at 45 degrees will see the last of direct sunlight several hours before sunset in the NW.  what this means is that until the kiln is about 20 degrees hotter than the morning low temperature, it will not have a very low humidity...it will not dry wood very fast.  So, this is why we suggest turning on the fans several hours after sunrise and off well before sunset.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #32 on: December 26, 2017, 01:51:54 PM »
My solar fans arrived a few days ago but the weather wouldnt permit me testing them.  But I got a chance today and they seem to run just fine.  I plan to use 4-24 volt panels (like the one in the test today) strung together in a parallel configuration.   This may seem like a little overkill but I want the fans to be well supplied even in the earlier hours of the day. 

Also posted a couple of pictures of the location where the solar kiln will sit.   It really is a great location and even in the Winter its getting sun from 9:00 until about 4:00.  If the weather holds I hope to get the pier blocks down and the 4X6's laid out this weekend.







Constantly reinventing the wheel...

Offline btulloh

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Re: And yet, another Solar Kiln thread ...
« Reply #33 on: December 26, 2017, 05:30:01 PM »
You must be on a first name basis with the Kubota dealer.  :D
HM126

Offline 50 Acre Jim

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Re: And yet, another Solar Kiln thread ...
« Reply #34 on: December 26, 2017, 05:51:17 PM »
You must be on a first name basis with the Kubota dealer. 
lol And that's just what you see.  I have a barn full of mowers, bush hogs and accessories as well.  But a few years ago Dave retired and the guy that took his place acts like he doesn't even know who I am.  I got tired of being treated like second-hand trash and quit supporting them.  Unfortunately, that seems to be the norm more than the exception these days. 

But hey, what did you think about that fan?  Little rascal really moves the air for a fan that plugs into a solar panel!
Constantly reinventing the wheel...

Offline btulloh

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Re: And yet, another Solar Kiln thread ...
« Reply #35 on: December 26, 2017, 07:18:41 PM »
Fans look great.  Four 24 volt panels and 4 fans.  Spare no expense!  That's a great way to do it if you're willing to lay out the dough.

Are you using batteries or just running the fans right off the panels?  Voltage regulation?  Low-voltage conditions?   

It's going to be fun watching all this.  You are jumping right in to the deep end of the pool.  Right on!

Too bad about the dealership.  It does seem to be the way things go these days.  Aggravating.  Customer service seems to be a lost art.  It's almost like to you have to work real hard to spend your money these days.  And nobody ever says "thanks for your business" anymore.
HM126

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Re: And yet, another Solar Kiln thread ...
« Reply #36 on: December 26, 2017, 07:28:50 PM »
No batteries, fans run straight off the panels.  I am using fan thermostats that will turn the fans on when the solar is adequate.  And of course, they will shut down accordingly when the sun starts to depart.   

Im big on the alternative energy thing which is similar to buying organic vegetables.  Everything looks the same, you just get to spend 5 times more to get the same result.  But hey, if North Korea ever lobs an EMP on us Ill still be able to produce quality dried lumber for people to make bowls out of.
Constantly reinventing the wheel...

Offline slaghunter

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Re: And yet, another Solar Kiln thread ...
« Reply #37 on: January 16, 2018, 07:03:29 AM »
.  But hey, if North Korea ever lobs an EMP on us Ill still be able to produce quality dried lumber for people to make bowls out of.


 :D :D :D

 


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