Cheap and simple evacuated tube solar hot water.

The idea here is to pre-heat the water entering the main house cylinder, which is heated by the gas boiler. A 20 tube panel (£350) fed by a small 12v DC pump £28 and a 12v differential controller (£95) supplies a 160 litre cylinder (£125 unused off Eblag) which is plumbed in tandem with the main house cylinder below. The weight of the cylinder bears on the studwork around the airing cupboard, which is directly below. The panel is directly above the cylinder with around 20m of 10mm copper tube taking the liquid, which is water with car anti-freeze. There is only about 25 litres of liquid in the tank and system.

Set up was pretty easy, the hardest part was getting the frame for the tubes onto the roof and I realise now that I made it difficult for myself by trying to slip the SS straps through the tiles; I should have just removed the tiles at the four corners and punched cleanly through the felt. The tiles are concave underneath so it was simple to grind away channels for the 10mm pipes to pass under the lower edges. All pipework is sloped uphill and the radiator bleed cap on the manifold has turned out to be unnecessary so I will remove it in the Spring. The system bleeds itself pretty well as it fills.

Even on a freezing December day with frozen snow on the tubes, they are picking up solar radiation and the pump is kicking in for a few minutes at a time. When we see how it performs this summer, we will consider adding a second panel. If we end up with excess heat the differential controller has a function that powers a motorised valve via a relay and once the top cylinder is up to 60 C can divert the flow downstairs using the house cylinder as a heat dump. We plan to have a bigger, faster, twin coil house cylinder installed in February.

We asked Ribble Valley BC if Building Regs approval was needed and they didn't know so they came anyway, the inspector took one look and said "Fine, I'll send the approval next week".

Pics here: Can you see them? http://s36.photobucket.com/albums/e49/C957/Solar project 2011/?albumview=slideshow

hats off fella.

hope to hear how it works over the next 6 months or so.

OMG.

Tell me more. I have a wet UFH. This may save me a fortune. Ive thinking about a diy pre heat system form ages.

I really don't know how appropriate solar is for underfloor heating; it is sporadic in summer and almost non-existent in winter when you need it most.

I'd have thought my neighbour's arrangement with a ground source heat pump much better for heating; it works all year round no matter what the weather is doing. His cottage is kept at a steady 20 degrees of lovely even warmth radiating out of the stone floors. Mind you it has all cost a fortune and he doesn't expect to see the payback in his lifetime.

Postscript: now at the end of March the panel is heating the water up from incoming mains temp of 8 degrees C to around 40 C, well on course for the target of 60 degrees. By June we will be receiving 2.5 times the solar radiation we are now so I'm anticipating having some excess heat to dump, hence my Q on the plumbing forum about a 12v motorised valve.

Thats brilliant, I thinks Im gonna make me one of them. Have you got a parts list and cost per part?

Parts list is as above and here's the supplier: http://www.solarproject.co.uk/

There's even an Excel spread sheet on there with all the parts and costs.

Very impressive - now I need to convince the wife we need one!

Just a little confused as to how the solar heated cylinder is connected into the normal one. You say "in tandem", so I assume it's something like header tank into 'solar' cylinder, then from top of there to the input of the normal cylinder. Am I right?

Actually, whilst typing the question, it has become clearer to me that must be how it works - do you need any sort of check valve to prevent hot water from the normal cylinder rising back up to the solar one?

Any reports on how it has performed over the last couple of months in the much warmer weather?

Cheers!

Hi Foggy,

Sorry, I don't look at this forum very often so missed your post.

Yes, the header tank only supplies the primary circuit, which is just a few litres of water with 25% car antifreeze whizzing around between the panel and the coil.

The cylinder in the attic receives cold water from the cold water F&E tank. The panel heats that cylinder and the contents then flow out of the top and down into the bottom of the house cylinder, which we have recently enlarged to 160 litres. Hence they are in tandem.

The new house cylinder in the airing cupboard has two coils, a standard half hour coil for the gas boiler and beneath that, a smaller finned coil for the solar. Some people dump excess heat into an old radiator in the attic but I have recently connected the smaller coil to the solar panel via a nifty little 12v valve, which is actuated by the differential controller when the bottom of the attic cylinder reaches 60c. So far this is theory only because we haven't seen the cylinder reach 60 since fitting the "dump" circuit; it did one afternoon in late April when we were out; we came home to find that the pump had switched off and the manifold was up to 115c, nothing seemed to have happened and the system returned to normal function as soon as it all cooled down that night.

Performance-wise I still don't have any figures but in June and July sunshine we are achieving 58 degrees C at the top of the attic cylinder and since the boiler 'stat on the airing cupboard cylinder is set at 60 we seldom hear the boiler firing up. We have set the timer so that the boiler doesn't come on until 7 pm. If it does, it fires then quickly ramps down again.

Hot water from the house cylinder couldn't siphon back into the attic cylinder because there's no circuit. I experimented with a one-way valve to stop heated water from the coil from siphoning back up into the manifold but this made it impossible for air to self-bleed out of the pipework so I removed it. The manifold is so well insulated that any small amount of thermal energy that we lose isn't really going anywhere anyway.

I have to say I'm very impressed. I checked all the links out that you memtioned and they are all printed. I'm putting up a front extension and I think it's worth investing in a little project like this. It will easily fit in a budget of less than a grand.

I mentioned on a previous (new) subject that I was looking for amybody who had done a similar DIY project using compost/ manure. But from my earlier readings I could only get upto 57 degrees from the compost heap. Your temperatures are fantastic.

Certainly got something to think about now.

Well done and thanks.

This is a really easy system to retro-fit and so flexible in the way you can do it. Any DIYer ought to be capable and there's lots of help and advice from the seller of the equipment. I had a little trouble with a small leak from the spindle on the 12v motorised valve and within a few weeks his Chinese supplier had improved the O rings and sent FOC replacements, which sorted the problem.

The only people who won't help are the professional plumbers who will suck their teeth and mutter darkly about Legionella, but that's understandable when you are spending £500 for a system they would have charged you £5000 to install. My neighbour is a retired plumber who ran his own business employing several blokes and he told me I could be charging £3500 to £5000 for the installation I had just done. One of those a week would be a good living!

A great system. I installed a similar system in 2009 but my solar hot water is stored in an un-vented cylinder and feeds my combi boiler through a thermostatic mixer valve set to 30'C. If the tank temperature hits 60'C, a 3 port valve diverts the hot water straight through to the domestic hot water line, by-passing the combi. The pump is solar PV powered and no mains is used on the system. Own build differential controller and modified 3 port valve (12v).

Also 20 tubes and self install. It saves gas, as the combi never has to see mains cold water whilst the tank is below 60'C.

Best regards

This has been a very interesting read.

Where I live we have a lot of sun, and average outside day temps are 30C or higher. But the water arrives underground so is pretty nippy in the morning.

I've toyed with ideas of running a hot water tank up on our roof garden, with a tube panel that directly circulates the water in the tank, through thermosiphoning, rather than as enclosed system. I'm not sure how efficient it will be.

My tube panel will probably be copper pipe, painted black, and maybe sealed in a glass fronted box to contain heat better.

I can't really justify buying a proper evacuated tube device from England, as it'd never arrive on one piece, though there may well be some local source.

I'll start gradually, and see what temperatures I can create. On a really sunny day we can see ambient temps of 45C in the shade, so I don't want to produce steam.....

I have just finished installing a larger solar PV panel and using a linear drive, it now tracks east to west which improves the PV efficiency by 15%. Problem with the static panel was cloudy weather which allowed the main 12v gel cell to run too low by not being fully charged.
The linear drive only uses 300mA when driving and the battery gets fully charged even in cloudy weather. The panel resets to the east after dark, ready for the rising sun the next morning.

Best regards

The summer has been so bad the contribution has been very poor. The system would have switched over to dump once only and that was one hot day at the end of April when we had a boil.