See my whisper

It appears that ETs installed to 'best practice' - ie sealed systems being allowed to stagnate - are failing long before they were expected to...see recent threads on the subject.

So my question, before telling you what I would fit, is: 'How are you intending to install the system?'

Otherwise, to draw an analogy, you are telling me you are setting off on an arduous vehicular journey across much of northern Africa. There is a high failure rate of vehicles, even expensive ones, if driven a certain route. It appears to me from your question that you are going this same route...and you want a cheap vehicle to do it? Am I missing something?

Agree that GOOD heatpipes are the way to go if you use ET. But both systems have been failing billt. And the tubes themselves - the glass - is also failing, not just heat pipes. I know this to be true as I am replacing them.

Moulesnfrites, in what way are they sufficiently superb to justify paying over twice the price?

That’s very interesting and i am curtain everyone would like to know, how about posting it up for all to see.

How has your oversized system worked?

What size cylinder to panel area?

Does it recharge quickly?

Posted By: moulesnfrites..........We use this company :-
<a href="http://www.barillasolar.co.uk/home/solar-thermal-wholesale-supplies" rel="nofollow">http://www.barillasolar.co.uk/home/solar-thermal-wholesale-supplies</a>
They are superb

I've had dealing with them too, and found them very helpful and knowledgeable, they seem to supply good quality equipment.

Posted By: owlmanI assume you mean me, 'cept it doesn't seem to work.

The solar system?

Posted By: an02ew
The solar system?

Ha! no that works better than me. Thicko me can't remove the whisper.

Posted By: an02ew

Posted By: crusoeSo my question, before telling you what I would fit, is: 'How are you intending to install the system?'

i am not installing myself, but have a very close friend that was in the ST business for many years(at the beginning) we have chewed the fat over which type of system drain down or pressurized, but are not really sold on either yet. So maybe give us your ideal system.

We have a drain back system and I don't think you can fault it. As it is not a pressurised system it can be drained and refilled easily. If the system gets too hot the pump is switched off and the fluid drains under gravity back into the drainback vessel, hence no possibility of stagnation/degradation of antifreeze mixture in the panels. I suppose strictly speaking there is no need for antifreeze but I am being ultracautious as usual! The only problem we had was having an annoying airlock when we tried to refill after we drained down to change the fluid (after 3 years) but this is mainly due to the design of our system which involves a very long horizontal run of pipework.

Interesting system Mike - if you had larger storage, it would mean less reliance still on the immersion heater. The problem with small storage, even at high temps like Gavin's, is simply not enough stored sunshine to last a few days. Crack that and you are nearer the magic 100% excepting winter (and recent summers, grrr). Oversize storage also allows almost no stagnation. I usually dump excess solar into pre-heating the central heating in separate thermal store.

Gavin-A, also interesting, but as you suspect, diminishing returns at high temps, better use of excess heat IMO to dump to 2nd tank and keep DHW at moderate temps across whole tank. Would also increase size of your cylinder, for reasons mentioned above - if it were mine, which it ain't - and I'm preaching to the converted I know

JeffB - yes, best way to go if you can.

Agree Barilla are good to deal with. Sound company and should survive recession as they are thinking long-term.

an02ew - I think terminology is getting in the way of a full discussion. If you are ideologically opposed to the idea of a thermal store, but like the idea of a buffer tank, somebody somewhere has confused you. A thermal store is always a buffer tank, but a buffer tank is not always a thermal store.

The latter allows you to do what you say you want to do, viz:

Some fixed parameters are.
1. The system will have to accommodate a wood stove with back boiler.
2. i am against thermal stores so a twin coil or thermal jacket and coil
3. roof pitch 33 degrees
4. roof area 60m2
5. we plan to over size tube area for a quick recharge of DHW yearound , then dump excess summer heat into buffer tank conected to AGS

I suspect the DHW element may be the eco-confusion here - ie you like the idea of storing sunshine, but want to keep the hot water separate? In which case you want hot water cylinder and separate thermal store, fully specced for the future when you can plug-n-play all the new renewable technologies into it (unlike a buffer tank) and thence, if you so desire, to your DHW too.

an02ew - Don't worry, you're not the first person to call a line-out a throw-in

OK, so as I suspected, you dismissed the thermal store because you sussed one of the disadvantages of a 'combined' thermal store - that next day, if the heating has been drawing on the store, there is no DHW of any temperature. I would agree - and am on record as saying so, many times, on this forum.

Sometimes there is no space for a second tank, so a combined TS is better than nothing. But where possible, go for a separate DHW tank. This also allows you to drain the heating TS of all useful heat rather than switch it off artificially early to safeguard the DHW temp - but it sounds like DHW is def your priority anyway. Having established your ground rules, the rest is detail, and site-specific. In principle, therefore, one option is as follows:

1. Twin (or triple, you can't have too many) coil hot water cylinder, vented type (or small TS with DHW exchanger just for DHW) if you will be lighting the WS cooker regularly and want to heat it straight from that source. Bottom coil heated by solar, third (top) coil, if you have it, heated by the large TS itself, which will, if you size it right, have several days worth of sunshine for DHW stored in it (esp in Summer when there is no back-up if WS cooker not lit)

2. Oversize array of 10m2 minimum, on drainback, allows safe oversizing and will give you masses of DHW on even modest days. Controller will send excess heat to TS of 1000 litres plus rather than wasting the solar. This allows an adequate heat dump for most times. And if that gets hot too the system drains so cannot stagnate anyway.

Make hot water while the sun shines, and store it, cos we don't get that much sunshine!

Firstly just to check, evac tubes have a smaller collector area than physical area - right? If so then per m2 of roof they are less efficient? Or have I got that completely back to front.....

I'm currently looking for a system that gives a good amount of DHW plus some energy for UFH. Space heat demand should be low (if everything goes to plan). The Akvaterm Solar Plus tank seems to be an ideal solution to me but I am getting conflicting advice on size of collector v size of tank. Firms seem to throw figures into their software but cannot then explain the results! One says Solar Yield of 254.6 kWh/m²/Year the next 450!! Is there any reasonable formula?

On the backup heat source front, I'm pretty sold on an Andrews Fastflow instant water heater for DHW as it will take pre-heated water and modulate right down. I suspect I will need a small gas boiler to occasionally heat the body of the tank for the UFH, but this would only be to a lowish temperature. I do not think I can connect the fastflow without another heat exchanger.

I am also sold on the drain back system. Why have a complicated pressurised system when gravity will do the job for you?

My real question is tank size v panel size. Evac tubes seem the way to go, and I do have a fair bit of space to put them (SE facing though). However, 3 off 30x58mm arrays takes a huge amount of space. Flat Panels would be far more compact.

So back to the OP's question. A 30 tube x 58mm array from Eco-nomical is £594, from Navitron £782 and Barilla £1440. So is the Barilla one really 3x better?

Posted By: Ed DaviesPosted By: borpin: “I am also sold on the drain back system. Why have a complicated pressurised system when gravity will do the job for you?”

This paragraph seems to be conflating a number of distinct issues but I'm not sure which. Gravity doing what job? - thermosyphon or frost protection?

Well both if the pump controller is set up correctly and the position of the drainback is within the warm envelope. I could be wrong though....

Posted By: borpinYes but if you need a 6M2 collector and do not have the space for the ETs then that has to be a factor as well does it not?

Are you saying that when calculating the size of ET i should use the gross collector area, the aperture area or the absorber area? There is a huge difference between them. Especially when I am looking to buy around 10m2

Posted By: an02ewAre you saying that when calculating the size of ET i should use the gross collector area, the aperture area or the absorber area? There is a huge difference between them.

Obviously from the point of view of the roof space you need to use the actual dimensions of the panels. For calculating output I don't think it really matters as long as you are consistent as the n0, a1, a2 parameters are given for each of the areas in the test results.