Solar hot water

[SamKingfisher]

OK so about time I contributed something useful after finding so much helpful info on here.

 

I decided to stick a solar collector on the roof for summer hot water (don't laugh) as my only sources otherwise are engine and back boiler.

 

First I made a radiator in a box system. This wasn't much good in the cloudy conditions but would give a tank of hot water in the sun. I recently got rid of it in favour of an evacuated tube panel. Then I realised (can't believe I didn't spot it straight away) that any heat in the tank was just thermosyphoning back up to the panel at night. So perhaps my radiator in an insulated box with a glass lid was actually not so bad after all.

 

I use a differential thermometer from solarproject.co.uk (£20?) and a 6w pump (£25?) from same place. Panel cost me £250 nearly new.

 

So to deal with the thermosyphoning I bought a motorised valve from solarproject (starting to sound as if I have shares in him). This seemed like the best on market as it uses no power at all when off (it's just linked to the pump and opens when the pump runs) something like 2w when opening (takes about a second) and 0.2w or so - I forgot straight away cos it was such a low number - when open.

 

This has helped very much.

 

It shares the coil with the engine - I put in full bore valves to switch from one to the other. Obvs it also needs to share the same antifreeze coolant as some mixing will occur. Next time I would put in T valves if they exist, as an unwary person could empty the panel (not anywhere near enough water to worry about) into the bilge through the engine header tank (cheers gravity).

 

I am very proud of my new header tank. The last one was a golden syrup tin - don't bother kids, it rusts through in a year.

 

Yes it works. I would get a shower out of it even in this godawful weather. In the sun you get a nice hot tank of water.

 

Which brings me to . . . . can it boil the tank? Yes probably if I left the boat for 3 days of bright sun. You need a good PRV on the cylinder. I could rig up a thermostatic dump easily enough - a pipestat on the cylinder hw pipe linked to the pump on the back boiler - dump the heat to the radiators and woodburner. But for now I am going low tech and just covering the panel when I'm not around. Another option would be to just switch the motorised valve out of the loop so the HW becomes CW overnight each night. So far not an issue.

 

Edit for a spelling mistake

 

Edited May 15, 2013 by SamKingfisher

[BD3Bill]

Thanks for posting this. I am planning a similar system myself so it was very useful.

If I find a way of situating the header inside with any success I shall let you know, but congratulations on traditional looking one you have, tops itself up with rainwater?

Cheers

Bill

[Doodlebug]

Hi there, that looks really good, but I have a couple of questions.

 

The evacuated tubes, how are they positioned? At an angle or flat? Do you keep them facing the sun by turning it or is it stationary.

 

Also, how well does it heat your water in each season, I assume summer you have plenty but what about spring and autumn?

[SamKingfisher]

Hi. The header tank has a close - fitting lid, and an overflow / expansion hole drilled in the side.

 

The panel lies slightly tilted in two dimensions so that the highest point is the expansion tank, and the temp sensor. It would undoubtedly work better facing south at a more rakish angle but this way I don't need to keep messing with it when I move the boat. I certainly wouldn't bother turning it over the course of a day.

 

I think that because of the slow and steady way it heats the tank, the more insulation on the tank the better. I also feel that an upright calorifier would be more effecient.

 

This version of the system is new, but on a coldish cloudy day it will only just provide an acceptable shower. For me, if it's too cold for the panel, I probably already thought of lighting the fire anyway. This morning I could see my breath inside the boat.

 

Obvs a 10 tube collector would do better in spring & autumn but you'd need to slow it down somehow in summer.

[PhilR]

The header tank looks very impressive, but you might have bought shares in Brasso?

 

Are you on a permanent residential mooring? Or have you planned your cruising routes to avoid low bridges.

 

I admire ingenuity. Well done. Please let us know how the system performs this summer. And heres hoping we do have a proper summer this year.

[SamKingfisher]

The header looks high but it's just the photo. It's only about 10" above the roof and we don't have any chimney-off bridges oop north!

[Doodlebug]

Thanks for posting this, you've got me looking into it, and I think I can make something interesting.

 

I'm going to save some money by buying the empty tubes (I think) and then I will rig them up to a pipe takes water to one end, and then water then flows back around.

 

My main worry is overheating the water. Have you really not had any issues with water getting too hot? I was thinking I would run a pipe into the canal to dump excess heat.

 

Its still in the planning stage, but I figured by using the empty tubes they can stick straight upright absorbing sun at no matter what angle it is at.

[SamKingfisher]

I haven't had any issues overheating the water but then I haven't had two consecutive days of sun! The problem is that the differential between cloudy and sunny performance is very large.

 

I did think that photosensitive glass would be useful . .

 

But a day of full sun is easily absorbed by the calorifier so far.

[Doodlebug]

But the tubes you have pretty much cover your hot water needs right?

 

I'm trying to work out if its worth it or if I should focus my energy on the winter problems we have.

[SamKingfisher]

Right, but my needs might not be the same as yours . . You definitely couldn't rely on the collector alone in this country. However on dull days, when I do light the fire for extra hot water, the first x degrees have been heated by the "sun" and it's much easier to raise the temp for a shower.

 

IF you sorted out an automatic heat dump you could get a 10 tube collector which would be more use in cloudy conditions.

[Justme]

Couple of things to remember.

 

Not all tubes collectors can work at a very low angle. Some are specially spec'ed for it. Get the right ones.

 

For boats you can also get very short tubes that could be orientated the other way so gaining more header hight above the bottom of the tubes to increase efficiency of the internals.

 

and

 

You dont need to track the sun as much with tubes as you do flat plates & PV due to the curved surface of the tubes that always present the best profile to the sun that is possible in that inclination & direction.

[smileypete]

There's a linky to a small flat plate collector in this post:

 

http://www.canalworld.net/forums/index.php?showtopic=56104&page=2#entry1065768

 

cheers, Pete.

~smpt~