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39

I made a passive solar heater using aluminum cans. The results are better than I expected.

submitted by totes_magotes to preppers 3.6 yearsNov 14, 2021 22:16:10 ago (+39/-0)     (preppers)

This is the heater

This is the general way to make one (Not my video) though I'll leave out for now largely useless details like whether or not to use glass or an acrylic pane ($76 for the size I needed but the price drops rapidly as you get smaller) and so on.

Mine has a little bit more and a bit more attention to detail. For example, silicone caulk and metal tape, reflective insulation board, two 12 volt solar panels to panel 2 12 volt CPU fans to push air a little more. $20 per panel, $12 for 4 fans though I only used two ($6 total).

Total cost was definitely less than $200 since I had most of the parts lying around anyway but I don't have a solid price on how much I spent since it's been a "back project" I piddled with for the last 4, maybe 5 years. This spring I kind of kicked it into higher gear - call it a gut instinct plust tired of it taking up so much space in the workshop - and now we're looking at a much higher cost for natural gas (at least) this winter which is what heats the main part of my house.

Using an extremely scientific and not-prone-to-errors meat thermometer, the temperature air I get out of it is between 150 and 160 degrees. The fans kicked on and provide a bit more push on the air than I initially expected and this doesn't seem to lower the temperatures any since it's still outputting about the same heat as smaller units you see people showing you how to make. The benefit I hope for with a larger unit is to still put out more heat in colder weather with less sunlight than smaller units can handle because I'm using this to heat living space and not a greenhouse or workshop.

The solar panels aren't as sensitive to light as I'd really like but I still get about 6 hours of push out of them and by the time the light is dim or not direct enough to power them, it's not really heating the cans inside either so that's fine. The fans kick on around 10 AM and cut off around 4.

I've had it up three days by this point and the day/night temps finally got to a point where I thought I could get you some good numbers. The part of the house it's heating is the first floor, somewhere around maybe 1500 square feet (seven rooms total). The house is "L" shaped so one part of the house (study, living room, dining room) benefit more than the rest (kicthen, foyer, bathroom, 2 bedrooms) but the difference between the two parts stays at just 1 degree.

This morning, at 7 am, it was 27 outside and the heater had already kicked on for the morning schedule to heat the house to 68. I turned off the heater and did periodic temp readings throughout the day.

7 AM -> 27 outside, 68 inside

9 AM -> 36/66

10 AM -> no reading but solar kicks on and the heater is still off.

11 AM -> 44/66

12 PM -> 48/66

2 PM -> 52/65

5 PM -> 51/66

It would seem that at least for early winter, late spring, this heater is going to be very useful for holding the house temperature high enough that I don't need to use the house heater. This does not indicate that it will be as useful when temperatures are sustained in the 30s or lower though I suspect that as long as I have enough sunlight that it will cut into how much I need to use the heater.

I plan to insulate the output hoses with corrugated plastic pipes, maybe wrap it in some thin insulation as I do this though I'm not sure about that part. It's not permanently mounted to the house and the hoses go to a window frame insert for a portable AC unit which is basically thin but stout plastic and that is a source of heat loss that I could stand to insulate.

In any case, the heater allowed me to go all day without using the house heater. With natural gas and other heating fuel costs predicted to hit sky high prices this winter, I should be cutting a lot off of my heating cost.

The bastard might be ugly and people driving by might wonder "WTF IS that??" but it works.







33 comments block


[ - ] SparklingWiggle 8 points 3.6 yearsNov 14, 2021 23:16:38 ago (+8/-0)

Your neighbors must love you. Just kidding. Something you might want to consider is running tubing through it or wrapping tubing with the aluminum and using a small 12V pump (connected to solar) to push the water through baseboard heating (if that is what your current natural gas systen heats.) Yyou can also make a fairly simple solar powered sun follower to keep it pointed all day.

You should also wrap the exposed tubing in foam insulation.

Congratulations on being self-sufficient and resourceful.

[ - ] totes_magotes [op] 1 point 3.6 yearsNov 15, 2021 07:34:11 ago (+1/-0)

Thanks!

This is an air system, no water at all. The sun heats the cans and convection (and the fans) move the air. I know it wouldn't seem like it would be all that efficient because the heating "tubes" are just... open. But it works. At 40 degrees, I was still getting hot enough air despite the hoses being uninsulated though, as I said, I expect that efficiency to drop at colder temps and for it to be a source of heat loss until that insulation is added.

[ - ] PotatoWhisperer 0 points 3.6 yearsNov 15, 2021 11:55:50 ago (+0/-0)

I think the extra push you get with the fans helps with the uninsulated hoses. It lets you move the hot air through them faster so that the air doesn't sit longer in the colder hoses and gets into the house faster.

[ - ] WhiteCollarCriminal 4 points 3.6 yearsNov 15, 2021 01:32:14 ago (+4/-0)

Wow, I think I just found my next project, thanks! New found respect for magotes, seriously and thank you!

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 07:35:34 ago (+0/-0)

Dude, no problem at all. There are two ways to plan this out. One is to get your window or acrylic panel first and plan around that size or, two, just build it and buy the window or acrylic. The second way gives you more freedom at the cost of expense while the first way allows you to get the most expensive part whenever you find it cheap.

[ - ] beece 4 points 3.6 yearsNov 14, 2021 22:25:05 ago (+4/-0)

I'm in for an upvoat, thanks for sharing.

[ - ] 3Whuurs 3 points 3.6 yearsNov 14, 2021 23:33:14 ago (+3/-0)

That’s pretty cool! Thanks for the testing info.
I looked into making one of these a few years back and found a few guys claiming a design that just uses a few layers of aluminum screen painted black, with franell lenses instead of glass, and worked better the tin cans, and was WAY easier to make. With the franell lenses it looked like they made the box from sheet metal cause it was pumping WAY more heat then the house needed.
I was trying to design one for a cousin in the prairies for the -22° winters, and some guys had units utilizing the excess heat by blasting it at a cpl 45gal water drum (solar batteries), then recirculating that air at night with the latch closed to the solar heater outside.
It looked like a bunch of plumbing, but cheap enough to do, and it looked almost possible heat 24/7 in cold climate that way.

[ - ] PostWallHelena 1 point 3.6 yearsNov 15, 2021 10:06:26 ago (+1/-0)

https://www.builditsolar.com/Experimental/PopCanVsScreen/PopCanVsScreen.htm

Found this head to head comparison of screen v can. The screen is a little more efficient.

My question is, if the fresnel area covers the same area as the regular glass or acrylic and your absorbers take up the same area, how is the fresnel an improvment? They are collecting the same amount of solar energy right? Maybe if you did a convex curved array you might be more efficient at getting the sun from different angles. What am I missing?
@totes_magotes

[ - ] totes_magotes [op] 1 point 3.6 yearsNov 15, 2021 17:53:44 ago (+1/-0)

Well damn, that screen heater is pretty badass dead simple. Wish I'd known that before all this shit. Also makes me wonder what it would do if I popped the acrylic off and laid a screen over it. I bet not much. I don't think I've seen a unit go above 160.

Also interesting to note that he tested airflow and came up with about what I was just kind of "head experiment" figured... that the middle and ends would have more airflow. Hence, in the photo, you can see that my outlet hoses are in between, where he identified the slow spots. The block above it is just a kind of "empty baffle" to "connect" all the tubes into a common place to suck the air out (and hold the fan wiring).

But curving the lens is an interesting idea. Seems it would give you maybe an hour or two extra heat by allowing a wider field of sunlight to be collected and pointed to the cans.


I do have to wonder what would happen if I painted the sun-side of the cans with Black 2.0 - https://culturehustle.com/products/black-v1-0-beta-the-world-s-mattest-flattest-blackest-art-material

I have a bottle of it. I could mix it up, hit it with an airbrush.

[ - ] PostWallHelena 0 points 3.6 yearsNov 15, 2021 19:27:47 ago (+0/-0)

Yeah if you could replace the acrylic with a couple of domed acrylic skylights and line them with the right sort of fresnel lenses (smaller card size ones maybe) or a fresnel film using some sort of glass adhesive? you could get more morning and evening sun. Maybe. Anyway neat job.

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 19:37:04 ago (+0/-0)

Gotta be careful though. You want to collect more light, not focus it. If you focus it, you're just putting it in a small area which doesn't really help. The average heat will stay the same.

[ - ] PostWallHelena 0 points 3.6 yearsNov 15, 2021 20:18:44 ago (+0/-0)

What I am thinking is this— if you cover with a convex skylight cover lets say, will the skylight be able to refract light coming in at low angles to the collector plane? You need some sort lens to refract the light down to your absorbers which are being blocked from direct light by the sides of the box. Would a lot of small fresnel lenses refract the light down (without starting a fire lol ). I dont really want to focus, just redirect. Don’t worry about it.

[ - ] totes_magotes [op] 1 point 3.6 yearsNov 15, 2021 21:21:36 ago (+1/-0)

I think that's gonna be one of those things you practice and experiment with. I know you can get large fresnel lenses cheap if you can find some old large screen projector tv's. And you can get pocket fresnel lenses for fire starting.

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 07:36:49 ago (+0/-0)

That's an interesting possibility. It wouldn't take much to slap a fresnel lens on top of that and get benefits without removing the existing acrylic panel. That's a great idea, thanks for sharing that!

[ - ] toobaditworks 2 points 3.6 yearsNov 15, 2021 06:26:13 ago (+2/-0)

nice work now work on learning to post a link correctly

https://pic8.co/sh/VI3npG.jpg

[ - ] JudyStroyer 2 points 3.6 yearsNov 15, 2021 05:56:03 ago (+2/-0)

Very nice, i may try this for a little workshop out in the yard that i normally use a little propane heater for.

[ - ] TheSimulacra 2 points 3.6 yearsNov 15, 2021 03:53:27 ago (+2/-0)

You could pipe that heat into a large box with some layers of netting for a solar powered dehydrator as well.

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 07:38:02 ago (+0/-0)

Eh, I could. But I have solar power as well and an air fryer that does a killer job dehydrating so I don't have a whole lot of incentive to make the system more complicated.

[ - ] deleted 2 points 3.6 yearsNov 14, 2021 22:50:59 ago (+2/-0)

deleted

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 14, 2021 23:05:40 ago (+0/-0)

Thanks.

[ - ] PostWallHelena 2 points 3.6 yearsNov 14, 2021 22:49:14 ago (+2/-0)

Nice job. Can you adjust the angle? I guess if you keep it at the steep angle you get more heat at the colder parts of the day but it will crank out the most heat if you point it towards the noon sun.

I did a little research into passive heating. We are really just building our houses stupidly and we’ll have to change our designs to absorb more heat from southern exposures and retain it in thermal masses—since our energy market is now totally jewed. Thanks jews. My southern exposure is blocked by the neighbor’s house. :(

[ - ] totes_magotes [op] 2 points 3.6 yearsNov 14, 2021 23:04:34 ago (+2/-0)

I did a shit job making a stand for it. I suppose I could but I just slapped some 2x4s on there and braced it. In theory, I could make it adjustable but I didn't think it was worth it.

[ - ] paul_neri 2 points 3.6 yearsNov 14, 2021 22:46:25 ago (+2/-0)

"The bastard might be ugly" - is that why there's no pic?

[ - ] totes_magotes [op] 2 points 3.6 yearsNov 14, 2021 23:05:19 ago (+2/-0)

Yeah, I guess standard markdown doesn't work here yet. First line:

[ - ] paul_neri 2 points 3.6 yearsNov 14, 2021 23:09:59 ago (+2/-0)

no, my mistake. I didn't read the post 'cos I'm not a tech head.

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 07:30:20 ago (+0/-0)

lol, fair enough. My eyes glaze over on a lot of stuff. If you can use a hand saw, paint, something to drill or grind, and a screw driver, it's pretty simple.

[ - ] PostWallHelena 1 point 3.6 yearsNov 14, 2021 22:54:50 ago (+1/-0)

[ - ] thebearfromstartrack4 1 point 3.6 yearsNov 15, 2021 03:07:09 ago (+1/-0)

WHY didn't you use poly carbonate instead of acrylic you daft fag? WHY would you do that to a horse?

[ - ] totes_magotes [op] 1 point 3.6 yearsNov 15, 2021 07:40:23 ago (+1/-0)

Because it was a mean horse :)

[ - ] germ22 1 point 3.6 yearsNov 14, 2021 23:30:10 ago (+1/-0)

Good job.
I've build one myself last winter but ran into a few issues. I had massive heat loss from the pipes that ran from the heater into my house. Then at some point my little fan and solar panel stoped working. It got so hot in the solar heater it melted the insulation.
since then i have had not enough time to tinker with it again.

[ - ] totes_magotes [op] 1 point 3.6 yearsNov 15, 2021 07:39:58 ago (+1/-0)

I'm expecting the same heat loss problem and I'm considering wrapping the 2.5 inch air hose tubing with some insulation sheets and shoving the whole thing in a corrugated pipe. At least going to put it in pipes though maybe not the insulation bit. As long as there's sun to heat the unit, it should heat the tubing as well.

[ - ] Kung_Flu 0 points 3.6 yearsNov 15, 2021 20:45:23 ago (+0/-0)

What if you put this through an insulated tub? Or maybe wouldn't have to insulate a sand pit. Something with thermal mass so it would continue to provide heat a few hours after the sun goes down.

Only getting heat during daylight seems less than ideal.

[ - ] totes_magotes [op] 0 points 3.6 yearsNov 15, 2021 21:24:39 ago (+0/-0)

Can you explain a little more? Tub? Sand pit? It works by heating the aluminum cans by sunlight so I'm not sure how a tub or sand is going to help?

[ - ] Kung_Flu 0 points 3.6 yearsNov 16, 2021 02:58:47 ago (+0/-0)

I mean insulated tub of water. Or a tub of sand. The idea is to add some thermal mass. This thing heats up your thermal mass and it will still be warm after the sun goes down.

Probably wouldn't be worth the effort as the specific heat of a small tub of water isn't comparable to the whole home but just an odd thought.