DIY Solar panels - air heaters made of pop cans

It is really simple and cheap to build DIY solar panels for supplemental home heating, and it heats the air directly.
The most interesting is the fact that collector is almost entirely constructed out of empty aluminum cans!

Housing for solar collector is made of wood (plywood 15mm), while its front is 3 mm (0.12 inches) Plexiglas/polycarbonate (you can use tempered glass as well). The back of the case set is made of 20mm rock wool (or styrodur) as insulation.

Solar absorber is made out of beer and soda aluminum cans, painted in matte-black paint resistant to high temperature. The upper part (cover) of cans is specifically designed to provide more efficiency in heat exchange between the cans and the passing air.

details on : http://solar.freeonplate.com/solar_panel_DIY.htm

Comments

[sandybrown097]

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Solution: Using Surplus Solar Cells You can get pay back in 1-2 years
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[Triole666]

You get what you pay for unfortunately. These individual PV cells you can find for sale are the ones that were rejected by the manufacturers. The variances in output between cells as well as manufacturing issues (sealing, soldering, ...) will have these home-made PV panels perform rather poorly, with performance losses far greater than the 20% in 25 years warranted by (most) manufacturers .

[treehouse24]

just a hint/ question, would it be a benifit to have a one way air check on the inlet side to the heat chamber, so at night the air does not reverse flow and cool the room.you have inspired me to try to build one of my own

[kirkb150]

Some one may have already mentioned this, if so sorry...

Brick would only be the right choice in situation where you wanted to STORE the heat of the day and release it after the Sun is no longer warming the "system". I think this is awesome... If I didn't have side hinged windows I'd like to try this. Might be interesting to replace an entire window with one of these...

[calskin]

This is a great idea.

I have a couple questions though.

I live in Canada, and we get temps down to -40. Would this still put out "hot" air?

I was also thinking if you put a reflective surface like a mirror or space blanket on the back of the inside of the box, you could push the temp up even further. Is there any reason you wouldn't do that?

I would be interested in knowing if you were to slow down air movement in the cans by using smaller holes so the air had more contact (wrong term I know) with the sun to make the air hotter, could you push the performance even further...

[hellgas00]

The greater the difference in temperature, the faster both states want to reach equilibrium. So if you slow the rate of air flow, it will result in a less efficient system. You want to keep air moving, because as the temperature of the air and the cans gets closer, the rate of heat transfer slows. You are probably thinking of temperature vs heat. Think of it this way, you would rather transfer 20 cubic meters of air 2 degrees hotter than the air in the house over 5 cubic meters of air at 4 degrees hotter than the air in the house, as the former has a greater caloric content.

[calskin]

Interesting.

[johnny3h]

@ calskin.  What you are describing is called "contact time," and it does affect how much heat [the "real" goal, versus actual "temperature" of the air] is transferred from the heated can tube wall to the air passing through.  This can add a few degrees [and more heat (measured in Calories)] to the air, but there is a point of "diminishing return" where slowing the flow rate down too far will cause inefficiency in the transfer of as much heat as possible to the room, which is the real goal.

Yes, the faster the air flows through the can tubes, the less time there is to transfer that heat.  And, as someone else mentioned there is only just so much total heat available [limited by the size of the collector], so "throttling" the air flow is sort of a trade-off on the amount of heat transfered to the room versus temperature of the air going into the room.  The greatest AMOUNT of heat [not temperature] transfered from the collector to the room results in the greatest efficiency.

There are a couple of advantages of not using a too slow air flow rate:

1.  If the flow rate is way too slow it may allow enough heat build up in the collector to damage the insulation, OR even cause a fire!. 

Years ago [back in the 1970s] I read an article where this type of solar collector, in new houses somewhere in Colorado, that were vacant and waiting to be sold, and had the air circulating blowers turned off, allowed the "stagnated" air in the collectors to get so hot that the polyurethane insulation in the collectors caught on fire, resulting in roof fires on those houses.

2.  IF the air flow rate is TOO slow, then you will only get the amount of heat that that air can carry, whereas a higher rate will allow the collection of more heat and adequate airflow will be able to carry all the heat collected.

Also, "tseay" [prior comment] made a good point about prevention of heat loss from the heat INSIDE the collector by creating a "dead" airspace at the glass interface. 

This is commonly referred to as "double glazing" which creates a layer of non-circulating air which acts as an insulating  blanket to reduce heat transfer "back" through the glass to the atmosphere.

Double, or even triple, glazing is a great efficiency improvement for any thermal type collector.

[calskin]

Thanks for your comments. That helps a lot! Especially the bit about the fire :)

[Mladen_solar]

1. Hot air is result of Sun's light and not outside temp. You just have to be sure, there is no heat leaks, or looses in pipes (if present). I had same doubt when my interest in this started, but heat is transferred via Sun's rays, in component of light spectrum (not distributed around the Sun all the way to the Earth. This way, empty space would be hot, and not cold...right?)

2. There is no space between cans for light to pass, so mirror in the back of the cans has no purpose (there would be no light to reflect from behind...). If you have spare mirror and open space around solar panel (and if it is low mounted), you can position mirror near it and reflect additional volume of light on panel. There is video on Youtube where some guy test this, and it have couple of degrees temp. increase...

3. "could you push the performance even further" - this is true in terms of max temp., but not in quantity of heat collected from device and added to living space. Yes, by slowing air flow, you will gain higher temperature, but less air to transfer it. There is calculation of volume of heat (energy) received from this kind device on net, where air temp, and air volume are included. Your goal is not to have small volume of air with max temp, but to heat the room as much as you can during sunny hours. Your goal is to transfer as much collected heat using max air-flow, into the room as possible. All heat (energy) which remains in collector and not transferred into the room is NO GOOD. :-)

I apologize for long sentences and bad English...

[calskin]

Thank you for commenting. Your English was perfect!

I didn't realize there was no space between the cans. That makes sense now.

[efahrenholz]

Solar thermal systems do not rely on the visible light to conduct the heat. They use the infrared spectrum coming off the sun. Visible light does not convert to much heat at all. To give you an appropriate example, look at LED lights. They produce lots of visible light, but hardly any infrared light unless specifically tuned for it. Even tuned, they don't produce long-mid wave infrared associated with heat.

[tuns]

Could you do this but with bricks (the ones with 3 holes through the middle) painted black?

Double/triple glaze and well insulate it and have a vents at the top and bottom to restrict air flow during the day and open them up at night/when required, like an electric storage heater?

Mike

[hellgas00]

You wouldn't want to use brick because ceramics have very high thermal capacity, it would take far too long for the heat to penetrate the brick and transfer it to the air. Most of the energy would be transferred back to the surrounding air. That's why aluminum works so well, the heat is almost instantaneously transferred to the air flowing through the can. So I would definitely shy away from using brick.

[njmalhq]

I do wonder if this is any more efficient than a double glazed window of the same size. Since each has the same square footage, it is exposed to the same amount of solar energy. So the difference is just how much heat the furniture etc. behind the window retains heat, vs. how much the cans do. It may actually be a toss up. Because from a distance a window with no inner light looks black. It may in effect be as much of a black body as a bunch of black painted cans. Of course the heater above can be placed where windows aren't feasible, for whatever reason.

[njmalhq]

... and ... I may be wrong. No offense.

[mrfoltz]

Great ideal!!!
I live w-a--ay up north in Winnipeg, Canada and it gets down to -40c as well...

But I noticed my insulated, metal back door, with a outside storm door is warm, sometimes hot, to the touch even at real low temperatures.... [it faces South/west and is painted dark for that purpose]..

I wonder if I can rig something to attach to the door? This way I'm not drilling trough insulated walls etc..... and can just replace the door if it doesn't work as well???

[wndwalker]

just a suggestion, try Mylar in place of mirrors cheaper and a more powerful reflective surface, plus it will conform to most any surface...

[gnjurac78]

Mladene
Koliko je vremena potrebno da se zagrije prostorija od npr 30 m2 na nekih 25°C i da li može da se odžava ta temperatura ako je pretežno suncano, kuća je termo izolovana.
Unaprijed hvala

[tseay]

This is really clever. There are a lot of possible improvements. For very cold climates, try using a vapor (air) lock layer in the front the box temp will be better and boast performance. You just want a layer of air that doesnt move, but let the sun shine through it. Insulating the ends and sides will help too.

[flyingpuppy]

What's the output on a clear day? I agree, it looks good too.

[Mladen_solar]

Air temp goes over 70 degrees Celsius on a clear day

[flyingpuppy]

Regardless of incoming temp? Or is that assuming 0 degrees celcius? Regardless, I love this idea. Am trying to figure out how I can add some panels to keep our garden warm in early spring.

[Mladen_solar]

I had output temp over 70 deg Celsius, while intake was outdoor air at 2 deg.celsius. When you have incoming air from room instead of outdoor air, results must be better (at least couple of degrees).

[l8nite]

it looks good but this would have been better as a full "ible" not just a slide show

[Mladen_solar]

Sorry for this short manual with just few pics. I had no time to make better. You have detailed one in link shown

[smirnoff04]

Nice design and the results in the link look pretty good too.