How to heat water by sunlight

[horizon]

This isn't really a cycling query but I was in Spain recently and looking at how to heat water using sunlight. I know that there are numerous configurations from simple camping shop showers to major roof installations but none quite fitted my requirements. I was looking for a non-mobile (i.e. I don't need to carry it around) arrangement that involved simple, preferably free, materials that would heat enough water for washing clothes and a shower but not a full family-sized facility. What I had to hand were various water containers, some thick black and clear plastic sheeting, some wood, gaffa tape and nails. Possibly a sheet of glass as well. One requirement (and I think this rules out the hose pipe idea) was that the system had to be filled by bucket and not by water pipe/tap. Welding and such like would be beyond my capacity.

Then I realised that I didn't really understand the principles on which all these systems were based, what works and what doesn't, what needs to be black etc etc. Some quick Googling got me stuck in a myriad of, mainly commercial, possibilities.

(I'm also interested in water heating for wild camping in Spain but that is a separate issue.)

Any thoughts gratefully received. I'm happy to refine the materials/resources list further if need be.

[james01]

The simplest crude starter kit is to get hold of an old single-panel central heating radiator (free from most skips), paint one surface matt black, and make a well-insulated case for it with a clear plastic or glass panel facing the sun. Get an old water tank (copper cylinder or loft top-up tank), place on platform higher than radiator and plumb in the pipework (link top of rad to top of tank, bottom of rad to bottom of tank to give simple thermo-siphon circulation, no pumps required). Fill tank above level of highest pipe entry point. Tank will get warm in a surprisingly short time on a sunny day. Ladle water as needed or fit a nice drain-cock if you want to feel sophisticated

[Audax67]

One DIY effort I saw somewhere used soft drink cans. They removed top & bottom then soldered them together to make tubes about 3' long and sprayed them black. They then mounted a dozen such side by side to a drilled pipe at each end, mounted the whole kit in a flat glass case and stood it in the sun. Water entered cold at the bottom and came out at 60°C at the top. You'd need a hell of a lot of cans & ditto patience with leaks, though.

[mig]

my (now retired father) was plumber and central heating engineer. one of the summers in the late seventies he had me help him cut an aluminium beer barrel in half with a hacksaw and help bend many lengths of 15mm copper tube so that cold water entered at the bottom then meandered up the half barrel to exit at the top to re-enter the hotwater system of the house. a sheet of plain glass covered the front of the barrel. positioning meant that it caught the summer sun for maybe 10 hours or more per day. the effect on the water temperature was incredible and it could churn out a fair amount too!!
never sure if he copyrighted it though

[horizon]

So what role does the colour black play in all this? Why don't I just paint my water container black (matt?)?

[cycleruk]

So what role does the colour black play in all this? Why don't I just paint my water container black (matt?)?

Black easily accepts heat whereas white reflects.
Matt black better than gloss black.

[james01]

A black object absorbs all wavelengths of light and converts them into heat, so the object gets warm. A white object reflects all wavelengths of light, so the light is not converted into heat and the temperature of the object does not increase noticeably.

Above is copied from a science website. Probably a bit simplistic but you get the idea.
Painting the container black would help, but heat would be lost through convection etc. The radiator method offers a more efficient collection of solar heat. A very simple water heater would actually be a black plastic dustbin full of water with a large clear plastic bag over it to stop air moment.

[al_yrpal]

Dead easy, you get the Sun, screw it up into twists and light it under a can of water. Works with the Daily Fascist, Torygraph and Sunday Sport too.

Seriously, big a solar shower. Basically a thick black plastic bag with a pipe on it. Black absorbs heat, white reflects it.

Al

[horizon]

Looking at the solar camping showers, it seems the only requirement is that the bag or container is black. I am presuming that the flatter the container the better. I think I might be over egging the pudding on this - it's simpler than I think .

[horizon]

It looks like these would follow all the rules:

http://www.amazon.co.uk/Litre-Black-Pla ... jerry+cans

[Stewart H]

I have owned a few of the black plastic bag with shower rose type, they work just about okay in the best British weather on deck of a boat, perhaps a little tepid, I would imagine they ought to go great guns ashore in a Spanish summer.

[DaveP]

It looks like these would follow all the rules:

http://www.amazon.co.uk/Litre-Black-Pla ... jerry+cans

If you fill one of these with water and leave it out in the sun I'm sure the contents would get warm. Don't forget to leave the top loose to allow for expansion.

Could be a bit clearer about what you want to accomplish?

From my reading the basic idea for DIY solar water heating is to allow water to flow slowly through multiple channels in the full glare. You could set up a sheet or two of corrugated iron at a convenient height, the precise slope to be established by experiment. You would need a reservoir (large bucket?) slightly above the high end, connected to a length of hosepipe fixed across the sheets with a small (expt. again!) hole over each trough.Possibly some sort of tap for fine control. A length of guttering under the bottom edge to collect the hopefully steaming product. Painting the iron black would make the system more efficient but it's not essential - you will have heard about cats on hot tin roofs?
Thinking about it, and reviewing your list of materials, you could always try creating your own corrugated surface by draping black plastic over closely spaced battens. However the iron would be more effective because the entire surface would heat up and conduction would make all that energy available to the trickling water.
A sheet of plastic over the top to keep things clean, possibly an insulated container for your product, but that's about it. The rest is down to your bucketing skills
That sort of installation has been done successfully as school science projects in the UK. If you have Spanish sun to play with... use gloves?

[AaronR]

+1 for black plastic jerry can

Spent long hours waiting for a cool, refreshing water in the middle of many training areas and places the army sent me, and year round you can rely on water coming out of a black jerry can to be warm at best