Solar Parabolic Trough Charcoal Oven

[Nitack]

Much much more. I have been running this down online all day. A 3'x3' (forgive the lack of metric, I am from the USA) Fresnel can heat a 1/2" area to over 2000 F.

 

Now reduce it down a bit, what if you lined up three smaller ones, capable of heating to 500+ at their focus point each... spread three or four of them along the length of the pipe, make sure to have a one way valve to release steam and gas but otherwise sealed... Now little heat is lost, and the thing is getting intense heat at multiple points. Use a cast iron pipe and you can get multiple sections up to 1000 degrees, the interior should easily get to 500+. The intense heat will cause all of the oxygen to be pushed out or burned up durring a few bouts of combustion and you will have a lot of charcoal. You could even use this method with something like a cast iron stove. I really think it could work, and have ordered a couple Frisnel lenses online to test. Can't find the damn things anywhere local or I would be experimenting with this as soon as I got off of work.

[Turtle]

.... I really think it could work, and have ordered a couple Frisnel lenses online to test. Can't find the damn things anywhere local or I would be experimenting with this as soon as I got off of work.

 

Sounds like a plan. You might try an RV (Recreational Vehicle) dealer for the Fresnels as they sell them for people to put on their RV backwindows for an enlarged view. :) B)

[Nitack]

When GAHD mentioned using AOL CDs, a fresnel reflector was my first thought.

 

The question becomes: Would a fresnel reflector dish at 48" produce more heat than Turtle's 48" parabolic trough?

 

Who says you would not be able to use the parabolic at the same time? If you mounted the Frisnel lenses correctly and angled the parabolics right you could use both...

 

Also, to be considered, they both should have the same energy output for both a 48"^2 parabolic and a 48" squared frisnel... they are both focusing the energy of the sun over that space into one point. Same space = same energy. Although in the end I think the Frisnel will actually have a higher energy output. With the parabolic the pipe shades the relecting mirrors. The parabolic mirrors may be 48"^2, but given the curve, are they actually reflecting 48"^2 of sunlight or less? All the geometry here is frying my brain.

[Nitack]

Sounds like a plan. You might try an RV (Recreational Vehicle) dealer for the Fresnels as they sell them for people to put on their RV backwindows for an enlarged view. :) B)

 

Wouldn't the RV ones be specially designed not to focus heat given the fact that they are out in the sun?

[Turtle]

Wouldn't the RV ones be specially designed not to focus heat given the fact that they are out in the sun?

 

It's worth going to check out. I wouldn't be surprised if they come with a warning to keep combustibles away on the interior. B)

 

PS I'll find a source. Meantime, check out solar forge. >> Solar forge - Wikipedia, the free encyclopedia

 

PPS I think you can adapt your system to whatever the focal length of the Fresnel you have. Here is a supplier & list of different sizes & focal lengths.

 

Edmund Optics - Fresnel Lenses

[Nitack]

So the next step in my little foray into being a Mad Scientist is I plan on using this process to produce a lot of charcoal. I have no intention I burning it, will probably use some of it in my garden, but I might just end up piling a bunch of it or burring it. I am trying to reduce carbon here.

 

The question is, would a fast growing plan like bamboo provide an ample source of organic material for this. It grows beyond fast, up to three feet a day, and can survive damn near anything. If I planted a lot of the stuff (I have half an acre to work with) would that be the most efficient use of land for the purposes of sequestering carbon. Figure I could cut it twice a week and cook it producing charcoal, and that could add up to a lot of biomass. Any ideas on another candidate plant?

[freeztar]

Who says you would not be able to use the parabolic at the same time? If you mounted the Frisnel lenses correctly and angled the parabolics right you could use both...

 

Actually, I was thinking of a fresnel parabolic reflector, not fresnel lenses per say. Something like this: Fresnel Solar Cooker Design.

But yes, you could use both.

Also, to be considered, they both should have the same energy output for both a 48"^2 parabolic and a 48" squared frisnel... they are both focusing the energy of the sun over that space into one point. Same space = same energy.

 

Makes sense...assuming both sources have the same focal intensity.

 

Although in the end I think the Frisnel will actually have a higher energy output. With the parabolic the pipe shades the relecting mirrors. The parabolic mirrors may be 48"^2, but given the curve, are they actually reflecting 48"^2 of sunlight or less? All the geometry here is frying my brain.

 

So you think the fresnel will perform better because of less shade? That sounds reasonable.

 

I can't seem to find it now, but I remember seeing a dish on the internet that was a simple parabolic dish which had hundreds of tiny square mirrors (1 inch) glued onto the surface of the parabola. That's what I was thinking of with the AOL CDs. But if they degrade so rapidly, it's more of a fun project than a serious one.

 

A friend of mine is obssessed with parabolic solar collectors, especially cheap and easy to construct models that can be used in the third world. He wants to build one from scratch and incorporate a stirling engine to produce electricity. He thought of one idea that I liked. He suggested lashing together 4 pvc pipes in a square fashion and attaching ropes on a winch that can be used to pull down the pipes from the centers. Doing this to one parrallel pair would create a parabolic trough while doing it on both parrallel pairs should create a 'square' parabolic dish. We haven't tried it yet, and I'm not sure we ever will, but it seems like it could work.

[freeztar]

Any ideas on another candidate plant?

 

Depending on your climate...Kudzu.

[Nitack]

Depending on your climate...Kudzu.

 

I thought about Kudzu, although not sure which would be better. I know Kudzu is hardy as all bloody hell and does grow fast, but not sure which of the two produce the most biomass. Another consideration, if it is close between the two I would go with bamboo just because growing straight up the stuff is easier to harvest for this purpose.

[freeztar]

I thought about Kudzu, although not sure which would be better. I know Kudzu is hardy as all bloody hell and does grow fast, but not sure which of the two produce the most biomass. Another consideration, if it is close between the two I would go with bamboo just because growing straight up the stuff is easier to harvest for this purpose.

 

 

Yeah, I would imagine that bamboo would produce more mass in less time since it is woody. Also, kudzu dies off in the winter months whereas bamboo continues to grow a little.

I'll try to think of another good candidate, but it seems that bamboo is best.

 

I'd also recommend charring your lawn waste (grass clippings, leaves, pinecones, fallen branches, etc.).

[Nitack]

I'd also recommend charring your lawn waste (grass clippings, leaves, pinecones, fallen branches, etc.).

 

Hehe, yeah I was definately planning on the yard waste. Grass clippings are plentiful and can fill in space between larger bamboo stalks or the like. Plus it will take up space meaning less oxygen to start out with. I am so into making this idea work.

 

I was also thinking this could be a very good method for dealing with fall leaves. I can sequester all of it as char.

[freeztar]

I was also thinking this could be a very good method for dealing with fall leaves. I can sequester all of it as char.

 

That's my plan as well this fall.

While all the neighbors are burning their leaves, I will be charring them. :)

 

Of course, in order to do this in fall, we need to figure out this solar charring idea pronto!

[Nitack]

That's my plan as well this fall. :warped:

While all the neighbors are burning their leaves, I will be charring them.

 

Of course, in order to do this in fall, we need to figure out this solar charring idea pronto!

 

Well we don't burn here, it is illegal. as for figuring this thing out, we are going to make this work. If I have to buy one of the ebay MEGA fresnel lenses I will. I have seen videos of those melting glass and even steel when you get to the larger ones. We will make this work.

 

Fear the massive array I am picturing in my head...:)

[Turtle]

That's my plan as well this fall. ;)

While all the neighbors are burning their leaves, I will be charring them. :)

 

Of course, in order to do this in fall, we need to figure out this solar charring idea pronto!

 

Some observations. :cup: For charcoal making applications I think the parabolic trough is the better choice because the receiver pipe is spread out & can hold more material per 'load', wheras with the Fresnel or parabolic dish any increase in size of the 'roundish' shaped receiver just puts it outside the focus and so requires multiple load/process/extract cycles. The offset is it has to be large. (remember my 4 foot trough only reached 200F)

 

In any case, I think a practical home/farm solar furnace ought to at least have interchangeable receivers so one can make char, heat water, or make electricty. While there would be more losses, the ideal seems to me to just make electrity, store it, and use it to heat water, make char, light lights, pump pumps etc. The losses in conversion are offset by the decrease in labor to change receiver setups. That's all i got. :warped: :cup: :)

[Nitack]

My thoughts on the parabolic mirror are thus...

 

Think of it this way. the solar heat transfered to the kiln via use of the fresnel is based on the size of the lens, not on the size of the kiln. This means that if you used one of the massive lenses available at roughly 43" by 33"(for sale on ebay now) that would equate to 1419 square inches of sunlight. Obviously you would not want it at the exact focal point as it would melt your kiln in all likelihood. You could also use secondary lenses and use a mirror to reflect the light at your kiln as well. Lets say you use two more, and they have a focal point at 24". You place the mirrors so that the light hits the mirror at about 2/3 the way to the focal point so that the heat will not crack the mirror (most mirrors will not be reflective enough not to absorb some of the heat). That ads another 2838 square inches of sunlight. Using Mirrors your kilns heat absorption is no longer limited by the surface area behind it. At this point you could have a kiln that is absorbing the light from 4257 square inches of sunlight, or roughly 355'^2. The parabolic mirror on the four foot pipe is offering roughly 96'^2. You could get a little over 3.6 times the solar energy out of the Fresnel rig. Rotation could be a problem, but if you re-aligned it every hour or so you could be done in two or three hours with the kinds of temperatures we could get. And, if you mounted the whole thing on a lazy suzan or furniture dolly type set up, rotating could be all of a five second process.

 

I am not trying to knock the parabolic system, it is a much less hands on system and probably easier from a set up and leave it standpoint, but I think the Fresnel system could work and be much faster. I also think you could be afforded a higher kiln capacity as well. With this rig you would not be limited to a cylindrical shape and therefore could take advantage of the infinitely more space efficient sphere. The shadow that the kiln casts is no longer a concern. Think of how much more organic material you could cram into something the size of a steel oil barrel (only for example, too thin to support this kind of high temp kiln) than a 4x1/2 pipe.

 

Don't quote my calculations, those are very rough and don't account for energy loss. I think the theory is sound though

[freeztar]

with the Fresnel or parabolic dish any increase in size of the 'roundish' shaped receiver just puts it outside the focus and so requires multiple load/process/extract cycles.

 

I'm not sure I understand you here. :shrug:

In any case, I think a practical home/farm solar furnace ought to at least have interchangeable receivers so one can make char, heat water, or make electricty.

 

This is not necessary with a dish or fresnel, but would definitely be useful for a trough.

 

While there would be more losses, the ideal seems to me to just make electrity, store it, and use it to heat water, make char, light lights, pump pumps etc.

 

That's a very valid argument. One problem I see though is batteries. They would not last forever and are potentially caustic to the environment. Also, the manufacturing of the batteries would tip the carbon scale back the other way. I'm not saying it's unethical, but that battery storage is probably not the best method.

 

Of course there are other ways to store the energy. The same friend I mentioned before came up with a clever idea (it's what we do for fun, he comes up with ideas and I try my hardest to make them unfeasible :)). He suggested using the electricity produced by the dish to run a pump that would pump water from a lower elevation pond into an upper elevation pond. His reasoning is that you could have a water wheel between the two ponds and by releasing water from the elevated pond, you could have energy on demand, night or day, rain or shine. I'm sure you can come up with some of the arguments I made against the system he proposed ;), but it's still a pretty novel idea.

 

The losses in conversion are offset by the decrease in labor to change receiver setups. That's all i got. :cup:

 

Again, the "labor to change receiver setups" (:hihi:) is only a big deal if you are using a trough. Keep in mind that the "losses in conversion" are higher when you compare a parabolic trough versus a 'Stirling dish', and I imagine a fresnel as well.

The overall efficiency from collector to grid, i.e. (Electrical Output Power)/(Total Impinging Solar Power) is about 15%, similar to PV(Photovoltaic Cells) and less than Stirling dish concentrators.[1]

Parabolic trough - Wikipedia, the free encyclopedia

[Turtle]

...

Of course there are other ways to store the energy. The same friend I mentioned before came up with a clever idea (it's what we do for fun, he comes up with ideas and I try my hardest to make them unfeasible :shrug:). He suggested using the electricity produced by the dish to run a pump that would pump water from a lower elevation pond into an upper elevation pond. His reasoning is that you could have a water wheel between the two ponds and by releasing water from the elevated pond, you could have energy on demand, night or day, rain or shine. I'm sure you can come up with some of the arguments I made against the system he proposed , but it's still a pretty novel idea.

 

I'll go just with this one as I have some chores. In short, good idea. :)This is in fact what all city water departments do and why we have/need water towers. The pumps only pump into the tower when the level in the tank drops. The supply pressure to users is entirely a result of the hydraulic head in the tower. gotta run.