Solar Hot Water heating

[RogerM]

We spend about £900 per annum on heating and hot water. I've been thinking about solar hot water heating for some time as I don't reckon oil will get cheaper in the long haul, and I reckon conservatively we could save about £200 min per year. Our house faces due south so ideally situated. But I've never been able to understand why it is so expensive - about £4,000 for a hot water system from most providers which makes the payback time about 20 yrs at current fuel prices - equivalent to a 5% return on capital.

So I was interested to read in the book of the tv series " it isn't easy being green" that Dick Strawbridge used this system and really rated it

http://www.navitron.org.uk/solar_collector_panel.htm

Looks like you can install a complete system for around £1,000, giving a 5 year payback time, or a 20% return on capital. Normally I'd be sceptical, but given that Dick Strawbridge was enthusiatic about it I'm inclined to take it seriously. Anyone any thoughts?

 

[houtslager]

here you go , 2 more links for you to browse on solar heating

http://www.itsnoteasybeinggreen.org/forum/viewtopic.php?t=706

http://www.itsnoteasybeinggreen.org/forum/

2nd is the forum link and you can do a better search then me.
hope this helps, after speaking to the peeps at Navitron I give them a 9/10 rating and they are damn good tubes too

 

[devonwoody]

I have no experience of this product myself but no doubt the price comes about because of the marketing manner.
Advertising most probably 16%
Salesman " " 20%
Sales management 10%
So there is 46% to start with.

Should have started a ding dong 3 days before I depart forum

 

[Nick W]

I just had a quick scan of the link, and what they don't seem too keen to point out is that you need a hot water cylinder with two coils, though it is shown in the diagram. This will mean at least some re-working of the plumbing in your airing cupboard (or wherever) before you even start to install the solar part.

The Solar Panel is connected to the lower coil, and serves to pre-heat the water, before is is bought up to full temperature by your boiler using the upper coil. Because not all the water in your cylinder is at full temperature you will need to fit a cylinder that is bigger than what you might otherwise have.

 

[Anonymous]

Apparently the time to make back your money is longer than the lifetime of the tubes. That's why the solar companies are so reluctant to tell you about the real savings.

We've just had a new oil boiler fitted which claims to be around 92% efficient. Given the price of oil you may find you can save more money here than you can with solar.

Other options are having a wood burner fitted to save on heating costs.(I can normally find cheap/free logs)

I'm sure solar will become more of a reality in the future but for now I think it's just a buzzword.

Dave

 

[devonwoody]

Whilst on green subject etc.
Bio fuel what happens if you get a massive crop failure one year, no bio diesel?

Wave created energy, There is an exceptional gale, above hurrican force like New Orleans and power producing equipment is damaged and out of action 12 months= no energy from that source.

And both those things happen in one year.

So the greens haven't got it all right.

 

[ike]

Roger,

Thanks for that very interesting link. I'm very interested in the idea and am going to do the sums on it. My father has a similar installation now for 3 years. He's very pleased with the performance of it. It provides 100% of HW requirement for roughly 6-8 months of the year. He had to get planning approval as it is a listed building. In my case, because the collectors would have to be on the road-facing side of the roof I contacted the planning dept. They were very helpful and have simply asked for an explanatory letter with some further information and if posible pictures of the proposal but don't anticipate formal planning permission being required.

Apparently the time to make back your money is longer than the lifetime of the tubes.

.

The tubes are guaranteed for 5 yrs. They may well last a lot longer. In the event they can be replaced individually.

Ike

 

[ike]

BTW,

I'm considering a system with thermal storage cylinder to pre-heat mains pressure cold feed to the on-demand multipoint gas boiler for HW(no central heating in my house). With a 2-panel collector I could also tee-off the same storage cylinder to warm a couple of radiators - just for background space heat. Could be just enough for many of the spring/autumn mornings/evenings, but I'm speculating as I need to go and do all the thermal calcs for the house.

Spoke to the manufacturer of my boiler W.Bosch). They only guarantee boiler operation with a maximum 25°C feed temp. :roll: It will operate with higher feed temperatures but as to the longer term effect they don't know.

 

[Jake]

If you are using a thermal store anyway, all you need is another heat exchanger primary circuit for a boiler, so the solar has first bash and then the boiler kicks in whatever else is required into the store rather than into the hot water directly.

edit: oh sorry, misread your post I think - if you already have a water heater rather than a boiler, you are bit more stuffed.

 

[ike]

Sorry if I didn't describe things very well.

I don't have hot storage at all - just a simple pressure-fed, flow-demand hot water heater (WB call it a 'multipoint' boiler as opposed to a 'combi'). So in theory I can reroute the mains cold feed via the coil in a 170-200 litre capacity solar thermal storage tank. But as the storage temperature can reach 60°, this may or may not affect the boiler operation.

WB say it operates from a flow-demand valve - (open tap -pressure drops, boiler fires). In theory then as I perceive it, with solar pre-heated feed, the flow demand valve works as normal except boiler won't fire up as often/to same degree.

Only problem I can think off is that water is very hard here so it might be a good idea to have a water softener in mains supply (probably cost neutral to maintain given the current annual expenditure on bathroom cleaners and descaler - not to mention the time spent cleaning the shower, bath etc!).

Ike

 

[ike]

In fact looking at the guff it appears the solar thermal storage tank is pressurised to directly heat the cold feed. In this case I would need a pressure-reducing valve going into the tank as we have v.high mains pressure (>3bar).

Ike

 

[Jake]

No you described it fine, I just misread it as a planned new system rather than an adaptation of what you already have.

The difficulty with your plan is that, as Bosch are saying, they aren't going to guarantee that the multipoint will cope with a hot input - probably bits of plastic stuff in the cold feed because it is expected to be cold.

With a combi you could use the CH circuit to heat the store rather the water as I was suggesting. With a multipoint that isn't an option.

You could switch with valves, so that if the store is hot enough, the hot is taken from there, and if not the cold feed water is diverted through the multipoint instead, but that increases the costs and reduces the efficiency savings to the point where I can't imagine it being worth it.

 

[ike]

Hhmm, thanks for the input Jake. Replacing the existing heat system just to incorporate solar source certainly wouldn't make any financial sense.

So my idea would be still be feasible except for unknown effects on boiler components. Did notice that WB now make solar compatible boilers but as mentioned a new boiler is finacially out of the question.

cheers anyway,

Ike

 

[dedee]

I just had a quick scan of the link, and what they don't seem too keen to point out is that you need a hot water cylinder with two coils, though it is shown in the diagram. This will mean at least some re-working of the plumbing in your airing cupboard (or wherever) before you even start to install the solar part.

It was the "new tank" requirement that scuppered my plans when I last investigated this. We currently have a very narrow torpedo shaped tank in a similarly narrow airing cupboard in an already small bedroom. At the time the thinnest tank available would have added an unacceptable 12" to our cupboard.

Andy

 

[Waka]

Roger

I had a system put in at the beginning of the summer, with the available grant (£400) you can get a system put in for about £3000.

Like you my gas bills were going sky high and this was before the recent 25% rise.

I've not used any gas for heating the hot water since it was installed and was amazed at the amount of hot water is produces. With the new lagged tanks they do nowadays there is plenty left for the morning, that still requires adding a dash of cold. Even with the overcast weather we have been having of late, it still gives us plenty of the hot stuff.

I've not really calcualated the pay back time yet, I'll need to run the system for a full year to see what the savings are, but I'm sure it will be less that 20 years.

 

[nickson71]

I just can't see me staying in the same house for long enought to see solar paying for it's self

 

[RogerM]

Guys - thanks for all your input.

here you go , 2 more links for you to browse on solar heating

http://www.itsnoteasybeinggreen.org/forum/viewtopic.php?t=706

http://www.itsnoteasybeinggreen.org/forum/

2nd is the forum link and you can do a better search then me.
hope this helps, after speaking to the peeps at Navitron I give them a 9/10 rating and they are damn good tubes too

Thanks for the links houtslager - lots to read there.

I just had a quick scan of the link, and what they don't seem too keen to point out is that you need a hot water cylinder with two coils, though it is shown in the diagram. This will mean at least some re-working of the plumbing in your airing cupboard (or wherever) before you even start to install the solar part.

Nick - in fairness they do point this out and is pretty much standard with these installations. They also point out that in soft water areas you can have a direct heating system where you actually heat the water you are going to use rather than put it thru a heat exchanger. this saves on the cost of a new tank and associated plumbing - must save several 100 £'s. Incidentally, "Solartwin" also uses a direct system

http://www.solartwin.com/easy_to_plumb_in.htm

.... and we are lucky enough to have VERY soft water. Not a hint of scale ever.

We've just had a new oil boiler fitted which claims to be around 92% efficient. Given the price of oil you may find you can save more money here than you can with solar.

Other options are having a wood burner fitted to save on heating costs.(I can normally find cheap/free logs)

Dave

This was our first thought. However, our existing boiler, although quite old now, is burning with 88% (tested!!) efficiency. I don't think a new boiler would make a huge difference. And yep - I agree 100% - We've already got a woodburner with clear view glass - magic!

My father has a similar installation now for 3 years. He's very pleased with the performance of it. It provides 100% of HW requirement for roughly 6-8 months of the year.
Ike

Thanks Ike. Do you know which system your father uses?

Roger

I had a system put in at the beginning of the summer, with the available grant (£400) you can get a system put in for about £3000.

Like you my gas bills were going sky high and this was before the recent 25% rise.

I've not used any gas for heating the hot water since it was installed and was amazed at the amount of hot water is produces. With the new lagged tanks they do nowadays there is plenty left for the morning, that still requires adding a dash of cold. Even with the overcast weather we have been having of late, it still gives us plenty of the hot stuff.

I've not really calcualated the pay back time yet, I'll need to run the system for a full year to see what the savings are, but I'm sure it will be less that 20 years.

Waka - very encouraging! Which system did you use?

I'm very tempted to go down the direct feed route due to simplicity and low cost and the fact that our water is virtually lime free - never any scale. I can always retro fit a new cylinder and swap to an indirect system later if it proves to be necessary. Just need to work out how you overcome the overheat problem if you go away for a week during hot weather. Whilst you can have a thermostatic valve diverting water to the bathroom radiator in an indirect system I'm not sure what the solution is for a direct system, although I guess if the water boiled it will just go up into the header tank in the loft - no sealed system to worry about.

 

[RogerM]

This is the direct system I envisage.

Key to Diagrams:

1. Navitron Solar manifold with 20 Vacuum Solar Heater Tubes
2. Pressure Gauge
3. Automatic Air Bleed
4. Drain Cock
5. Expansion Tank
6. Gate Valve
7. Single Check Valve
8. Double Check Valve
9. Filling Loop
10. Circulating Pump
11. Pressure Relief Valve
12. Overflow

 

[Waka]

Roger

I got the tube system as opposed to the plate system becasue it tends to be more efficient.

regarding the going away bit, I have spent a fair bit of the summer away and during the hot spell I have to admit I was a little concerned, so I had my duaghter check on itperiodically.

The hottest the water in the tank got was 83 oC with the collector temp at 100. My system , should the water get to boiling will expand into the small pressure relief vessel. You have to remember that the whole system only holds about 8 litres of water.

I'm very pleased with the system and unlike some of the members I will not be moving again, so hopefully by the time I'm 65 I could see some payback.

 

[Les Mahon]

Roger,

I'm slightly confused by the logic in your direct system, Am I right in assuming that you are intending running the hot water supply via the solar collector? If that is the case surely you will only get 8-10 litres of hot water at a time.

Also from the research I've done one of the problems is preventing the water freezing in the solar collector in winter.

I've spent the last 6 months looking at these things, for me the current front runner is:
http://www.energycabin.com
which comes in at €25,000 installed (I will get a grant of 6000 off this) and a payback of 6 years approximatly (assuming all sorts of things obviously)

The situation may well be different over here but these guys have an interesting selection of systems:
http://www.rvr.ie

Les