Single-panel radiator as solar water heater...

I have obtained some single-panel radiators which I intend to use for solar water heating as mentioned regularly in this group.

They have a wavy fin pattern on one side, presumably to increase the surface area. (diagram)

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Would it be correct to state that the finned side should be painted (matt) black and face the sun?

Also should the other side be left white (before being insulated with rockwool etc.)

TIA for any help...

Reply to
Abdullah Eyles
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Maybe. It'll probably catch more light (less bounce off) when the sun is at a fairly steep angle to the panel (put the fins vertically). However, the thermal resistance of the thin fins will mean that the fins will be hotter than the radiator, so you'll lose a little bit of temperature. (if you post the fin thickness and lengths, this could be worked out).

You want to absorb all IR as well as visible rays. There may be significant differences between visibly identical matt blacks.

Glass will greatly raise the temperature.

Reply to
Ian Stirling

When I looked at this a bit back, I concluded that a reasonable idea might be to use clear twinwall glazing. Take a couple of sheets of it. Place the first with an air gap in front of the second. Now, feed dyed black water through the second.

Reply to
Ian Stirling

Huh... And I spent so long searching for the radiators... :-(

How would you ensure the dye stayed "in suspense" in the water? AND How could you seal the gap between the thinwall glazing and whatever pipe you use? Sounds worse the more I think of it..

As far as I can tell, the radiators have already been used with black water, due to the build-up inside them!!!

Reply to
Abdullah Eyles

In Britain, on a whole, it is usually only possible to increase the temperature of slow flowing water by just a couple of degrees, so thermal stores from solar power are still never efficient enough to be of any real use here. The use of solar power driven electrical devices is becoming more efficient than trying to capture the IR heat source to heat plain water with out any additives which help the water to transfer the temperature rise to storage unit. So you could buy loads of 12 volt cup heaters and wire them together inside a well insulated water storage tank and then use a car battery and solar charger to keep them running. :-))

Reply to
BigWallop

What a complete and utter load of old rubbish ! Troll alert !!

By FAR the most efficient way of collecting solar heat to heat water is using the Evacuated tubes with hi-tech interiors (heat pipes) but this is expensive in capital outlay.

Next is to DIY a solar collector - perhaps out of an old flat panel radiator housed in a well insulated glass-fronted box with its output going to a storage tank (insulation is very important on "high grade" heat) When using solar collectors in a "low grade" heat application such as heating a swimming pool where the water temp is only a few degrees above ambient, most don't even bother with any insulation - the heat differential is only a few degrees and the heat loss is minimal. Efficiencies of the above will be in the order of 50 to 90 % of incident energy collected.

The LEAST efficient will be to collect radiation, convert it to electricity (solar panel) store it (convert it to chemical energy, then back to electrical energy - battery) to run a heating element(s) - maybe a few percent efficient and costing a fortune !

The worrying thing is that you think you are correct because solar panels for producing electricity ARE getting more efficient (which is good) but they are way off direct collection of energy in efficiency for heating purposes. The only applications for solar panels for making electricity is where electricity is needed because there is no mains or unviable to lay mains, use a genny, use batteries, ie remote outposts for telemetry and control (space stations) and cellular phone boxes in Scandinavia. Or for keeping you car or boat battery topped up when you are away for a few weeks, or charging you satellite phone when you are walking across the Sahara... you get the picture.

Still I knew it was a troll..............

Nick

Reply to
nick smith

Well, it's nice and easy, and involves no challenging plumbing.

Dye is a small molecule that stays in suspension, like sugar. Pigment is a larger lump of stuff that is suspended in a liquid, and will settle out over time, like cocoa powder.

I haven't completely worked out how to fit pipes. Other than this, it's almost ideal. Cheap, no problems with freezing, low heat capacity, so that it can get hot with a short time of sun, ...

Reply to
Ian Stirling

panel)

I stand corrected then. :-))

Reply to
BigWallop

Hi,

Maybe a layer or two of twinwall in front of the radiator would trap the suns heat well. Some insulation on the back wouldn't go amiss either.

cheers, Pete.

Reply to
Pete C

In article , Ian Stirling writes

Would you pump the water around the system, or aim for convection circulation?

Reply to
Mike Tomlinson

The side receiving sun should have the sun directly hit the metal in contact with the water.

Colour is not important there, but white is the ideal.

The quickest dirtiest way to get such panels working is to cover them in polythene - might be ok if youve got easy access to the panels to replace the poly. A proper cover is much better of course.

There are 2 issues with rad panels:

  1. like most solar panels, feezing will break them, so you need to either a) use a drain down system, ensuring you empty the things before frost turns up, or b) use an indirect system with antifreeze.
  2. The rads hold a lot of water, so will take longer to provide hot water. I've never heard of anyone doing it, but I wonder if you can pour hollow beads into it to get round that?

One rad also makes a useful first warming panel: it is cheap and simple and adds a bit of warmth before your main solar panel, thus improving heat out/cost in ratio.

Water can be raised to above boiling with simple home made concentrating panels, to around 80C with well designed flat panels, or to about 60C with simple diy hosespipe panels.

Flat plate solar panels can achieve upto 50% heat collection efficiency with hot water: higher efficiencies should occur while the water is still cool.

Finally one thing makes a big difference: arrange reflectors to add extra sun to your panels. They will only add sun for part of the day, but this makes a big difference to amount of heat collected, final water temp, speed with which hot water is obtained, and extends the useful heat capture season.

Regards, NT

Reply to
N. Thornton

Pumped. More control, less uncertainty.

Reply to
Ian Stirling

Convection isnt really an option. Convection circulation only works when the heat source is near the bottom of the loop, with most solar installs its at the top.

2nd, convection is so slow it requires very large pipes: so large it would take hours for the HW to even warm up with solar.

While its not entirely impossible to use convection, its not a practical move.

Regards, NT

Reply to
N. Thornton

The fins will absorb heat convected from lower down on a roof if that is where it is going.

The biggest problem is finding a device that will shut it off in the evening and when it is cloudy and when it is raining and when the sun is shining but it is still cold.

Have fun.

Reply to
Michael Mcneil

Elektor Elektronics published a circuit having two LM334 sensors, one on the panel outlet, the other on the storage vessel. This activates the pump when the panel's temperature rises above the storage vessel.

The circuit was published in the book "305 Circuits", ISBN 0 905705 36 X, 1995.

I guess similar things can be found on the 'net...

Thanks! and you!

Reply to
Abdullah Eyles

OK here goes:

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has a guide book ref JEELEK3, "WATER PUMP CONTROL FOR SOLAR POWER SYSTEM" price

3pounds21p. (sorry no pound sign on my kbd.)
Reply to
Abdullah Eyles

The ideal thing is a diffrential thermostat and a small pump. Such a beast is fairly easy to make. The panels will work without that, but not as well. Many solar setups dont use a diff stat.

Regards, NT

Reply to
N. Thornton

The Centre for Alternative Technology in Wales have done some research into solar collectors, both commercial and DIY. They have several publications, see

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for example.

Reply to
John Weston

Hi,

Good idea, if you fill the rads with pieces of polystyrene or closed cell foam that would give the frozen water somewhere to expand when the radiator freezes too. Braided hose would be fairly frost proof too.

cheers, Pete.

Reply to
Pete C

I've got 3 double rads on the roof, they are pumped by a small 12v pump, powered by a large-ish solar panel. It works surprisingly well, the brighter the sun the faster the pump goes.

Reply to
Mark

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