Solar water heating

Oh great Oracle of STW, enlighten me….

After a great day out with the kids at CAT at Muck’n’Fluff, we are toying with the idea of getting some quotes for a solar water heating system – we have a south facing roof, intend staying in the house for another 15 years, so it seems worth investigating.

I’m guessing someone on here has already done this, so any expriences, advice, recommendations would be gratefully received, before I start wading through all the sales literature.

Before anyone mentions it, we don’t think going for a PV system instead would be worth it – the southerly aspect of the roof isn’t that big and the ConDem government is apparently cutting the guaranteed tariff

Cheers

As related on other threads I built my own system for about 1100e. I didn’t buy the commercial one and followed the advice on a French DIY forum instead. A plumber was especially helpful so I’ll pass on his advice:

Use two tanks. The first tank with a heat exchanger connected to the solar panel in it and a second one with a conventional electrical element or gas heating. Plumb it so that you can use the solar tank on its own, the solar tank as a pre-heater or the electrically heated tank on its own. I needed five valves to be able to do that which sounds complicated but my wife only has to turn two and flick a switch when she decides the solar tank isn’t hot enough on its own. If you only use one tank you’ll find the solar panel never gets hot enough to circulate in winter.

Use thermosyphon for the solar circuit if possible. This means having the solar panel below the tank and a panel which flows from bottom to top. It was just possible in my house with the panel low on the roof and the tank as high as possible. The advantage is you don’t need a pump or control system. The water circulates when the water in the panel is warmer than the tank and stops as soon as it isn’t. Make sure that there are no pipes or joints of a smaller diametre than the heat exchanger to restrict flow. 18mm in my case.

Run a hot pipe to your washing machine so you can fill it with solar heated water and then switch to cold for the rinse cycle.

I built the panel out of the biggest double-glazed Velux I could buy (not tinted or reflective glass)and about 20m of 18mm copper pipe. Water enters the lower feed rail and rises through vertical pipes to the top collect rail before flowing through very well insulated pipes to the tank. Yhe circuit is filled with car antifreeze and has a 50cl water bottle as a header tank. I’ve had to top up once in two years. Planning permission was no problem as it’s built into the roof (French laws). In theory it’s big enough for two people but does for three of us.

Some commercial systems are crazy, a colleage of my wife was horrified when he realised that there was no antifreeze in the system and the pump switched on when the temperature dropped below 0°C to prevent freezing. Electrically heated hot water was being used to prevent freezing!

I’ve just installed a complete system with 20 vacuum tubes for around £700. Here’s what I posted on DIYnot.com:

“The idea here is to pre-heat the water entering the main house cylinder, which is already 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 20 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 under 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 summer; the system bleeds itself pretty well as it fills.

Now in sunny May the panel is already achieving the target 60 degrees in the attic cylinder. The supplier near Bolton has sold me a super little 12v motorised T valve, which I’m going to use to divert the flow downstairs using the house cylinder as a heat dump. (Some people just dump into an old radiator in the attic) We have just had a new 160 litre main house cylinder installed in the airing cupboard, which has two coils, one for the boiler and another for the solar. The differential controller can take care of the switching, it’s pretty sophisticated.

We asked our local 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”. Planning permission is not needed.

Slideshow here:

http://s36.photobucket.com/albums/e49/C957/Solar%20project%202011/?albumview=slideshow

This is the bloke who supplied all the bits: http://www.solarproject.co.uk/

My neighbour is a retired plumber; he says I could charge £4000 to £5000 for this system, which took me two days to install. I think I’m in the wrong job.

Nice, Globaltic, you paid half what I did for the tank. More insulation on the pipes if you want it to work in December.

I didn’t mention the results so at 43°N in France:

From mid-October to March the solar system pre-heats with the water never hot enough for a shower but a gain of 10°C to 30°C compared with the mains. When there is snow on the roof I cut off the solar tank as the water comes out slightly colder than it goes in. In April, September and October we switch on the immersion heater at night after dull days. From May to mid September we only use the solar tank unless we have guests that live in the shower.

Overall I reckon it provides about 2/3 of our hot water needs.

you ‘ve made a more than decent job of that well done. As a heating engineer i am extremely sceptical of anyone who says they have an economically viable alternative heat source however this seems to fit the bill.
raising my hand though.. as the manufacturer states it is only suitable for vented systems ie non combi boilers, what are you going to do when your boiler needs replacing?

totalshell – Member
as the manufacturer states it is only suitable for vented systems ie non combi boilers, what are you going to do when your boiler needs replacing?

Umm, ive not read it all, but, the vented system will surely refer to the cylinder and not the boiler. The solar will be used to heat a coil in a vented cylinder.

What gain would there be by piping your heating circs through a solar panel?

Edukator: the amazing thing about these vacuum tubes is that even when they were covered in frozen-on snow on sunny days in December they were still picking up usable solar radiation and the pump was kicking in. The debit from that big coil in my Ebay cylinder is so high that the pump would only run for a few minutes before the manifold got cooled back down but it was still raising the incoming water temp from 8 to around 15 degrees. Even when the tubes are heating the water vigorously they feel cold to the touch on the outsides thanks to the vacuum in the twin wall.

My pipe runs are extremely short, just a few feet, the liquid runs fast through the 10mm piping and slow through the 22mm manifold and coil and it’s insulated with the stuff they use for AC systems so I reckon the loss is pretty low.

Totalshell: the boiler is a standard condensing boiler running in a vented system. We replaced it about a year ago and that has saved about 40% off our gas bill. I did add another 100mm of glasswool in the attic at about the same time so it’s probably a lot of the boiler and a little of the insulation. As you can see my solar circuit is vented as well, though the seller does supply pressure vessels etc. for a closed system.

Paulosoxo: You wouldn’t gain much by running solar heat through your heating because the need for heating mostly comes in winter. You would need a massive heat store (many tons of warm water under the house) from which to draw during cold weather.

Paulosoxo: You wouldn’t gain much by running solar heat through your heating because the need for heating mostly comes in winter. You would need a massive heat store (many tons of warm water under the house) from which to draw during cold weather.

I understand this, I was asking the previous poster why they thought you would connect a heating system to a panel.

Your views on solar electricity panels.

My brother in law is fitting loads in more afluent areas of London and is quoting an 8% return on their investment.
iI have (a sort of sleeping partner) who is about to install two systems to become fully acredited. So I’m wondering if it’s a bandwagon to jump onto?

It does depend also on where you live postcode solar radiation index web thingy. You need to base your calculations of pay back upon proper data. I live in Lancaster and the pay back time is considerably longer than were I to be at say my parents house in Eastbourne.

Micro climate also effects how much solar radiation you get. Eastbourne gets loads of sunshine hours and is one of the sunniest places in the country. Scilly Isles are also great!

I agree the vacuum tubes are more efficent, Globalti. When I looked into the pros and cons they were the obvious choice in a pumped system.

Guys – just about to specify a thermal solar system to plug into my thermal store.

Its going to be an active indirect sealed system as I have an indirect coil at the bottom of my 700L thermal store to plumb it into.

Just so I can get some ideas in my head, am I right in thinking that I need:
1) a non-return valve from the store to the array?
2) a relay switched 240v CH pump
3) a drain cock in the return
4) an expansion vessel (suitably sized) in the return

and finally a controller that turns the pump on based on differential T? Since Im happy for the solar panel to be heating my Store ALL the time there’s a positive differential, I guess Im going to be better off getting a v v low energy pump like the £150 grundfos 5W?

I dont think I’ll be able to thermosyphon as Im using ground mounted panels but my tank is also on the ground. The coil being maybe just 12″ lower than the panel bottom with the pipework connecting the two over 10m in an underground duct 600mm down.

Can I attach the controller thermostat to the outside of the indirect pipe just as it enters the thermal store? As I dont have a thermostat port in the tank at the bottom.

Stoner, why does it have to be 240 volt? Have a good look around that website I linked above and ring the owner, Peter, for a chat. Apart from anything else he will be interested to hear about your project. He’s a former brewer so he’s on my wavelength!

Thanks for all the pointers and links guys

certainly a positive system the only issue i would have is how can i be certian that the water circulating in the tubes will not freeze when this year i had minus 12.5 centigrade?
if i can be persuaded on that issue i’d certainly go ahead.. as for PV loads of money to spend for limited return an investment not a means of reducing your energy bills, which the first system ofers.

globalti – going 240v simply because I dont have a 12v source in my boiler house ATM and the solar array is over 10m away. Like the site, will have a nosy.

This has been done before but…..

Solar Thermal: Good for hot water in UK, not good for heating – there isnt enough heat in the months you need central heating for it to be viable or even worth the extra cost of integrating it into a heating system. A solar thermal system will deliver 50-70% of your annual hot water spread mainly over the summer months. the further south you are, the nearer 70% of hot water you can get. Anyone claiming more than 70% has oversized the system or is bullshitting!

In terms of hard cash that hot water costs a typical household…

a 210 litre DHW cylinder(typically sized for a 4 person property) heated from 12-65deg C requires 12.72kWh of energy. mains Gas costs 3.9p/kWh, oil 6.5p, LPG 6.9 and electric immersion heater approx 13p. take mains gas – 12.72 x 3.9p x 365 x 70% = £126 annual saving assuming you can get 70% of hot water. even a DIY system costing £1000 would need 8 years to break even.

October 2012 – Renewable Heat Incentive (RHI)is due to come into play – an additional payment from the Govt to incentivise us to ‘go green’ and reduce the countries carbon footprint (dont hijack the thread and start the whole climate change debate again). This is LIKELY to mean an annual payment of approx £250 to the householder but only if you use an aproved contractor and aproved kit – DIY will not qualify. We would be charging £4500-£5000 for an fully installed 210L unvented cylinder with an appropriately sized collector. same cost saving as the DIY kit, but taking the RHI into account a 12 year payback against gas. IMHO there is no financial argument for fitting solar thermal when connected to Mains Gas. Other fuels get a better payback.

Word of warning about combi boilers – most manufactiurers do not now warrant their boilers for anything above a 25deg C incoming supply so be careful with any diy install with a combi!

Solar PV:

Feed in Tarrif is in place and you can get a 13% return on a PV system costing £13500 (7.5 year payback), guarenteed 25 years and index linked. Given that you have the cash and dont need to borrow, its as good a deal as you can get IMO.

That 13% is based on being able to use the majority of energy produce, which means having a high background load during daytime in the summer. If you dont, then a lower return is likely – round about the 10-12% depending on the background load. Energy saving of £100-£300 depending on the daytime summer usage in a property. certainly as good a saving as a solar thermal system replacing mains gas.

Not sure if that helps, but the claims made by some solar themal installation companies about the potential savings are difficult to reconcile with physics.

That said, the thermal store mentioned above (given that it is already installed and is solar ready) will make use of the solar gain all year round, just dont expect it to heat the house..

ps. in response to the question above, you should fill the indirect side of the solar system with a 30-40% mix of glycol – we fill ours such that its good to -18deg C – think that is 40% or so but cant be certain without checking.

pp. Condems confirmed the FIT in the spending review in October, confirmed they wouldnt act retospectively and have only announced a limit to large commercial jobs so the OP is wromng on that score. FIT will reduce March 2012 (IMO) but only to new entrants then, current FIT is not going to be changed for domestic installs.

Totalshell – my panel circuit is filled with 5 litres of car antifreeze and 15 litres of water. This has protected it through the winter. In fact it’s all so well insulated that the manifold temperature never matched the outside temperature.

The more ethylene glycol you add the less efficient the liquid becomes at transferring heat.

Stoner – look at my slideshow linked in my post above. The entire system is powered by a 12v cellphone charger plugged into the mains. Going 12v avoids the need for Building Regs approval. A 10m pipe run isn’t a problem with 10mm pipes, the liquid whizzes through so fast it has little opportunity to lose heat and the pipes will be well insulated if you use the AC insulation stuff I used.

That said, the thermal store mentioned above (given that it is already installed and is solar ready) will make use of the solar gain all year round, just dont expect it to heat the house..

Indeed solar thermal is for all year round contribution while the pellet/biomass boiler does call for heat.

Gti – I will look at the slides. I was planning on using the chunky insulated steel coiled piping – its going in 2x 50mm corrugated ducts in the ground. What pipes do you use?

oooh woodpellet boiler – shiny!

I like it and its very compact compared to some I’ve seen. What make and how is the cleaning?

I heard some bad things about the quality of UK manufactured pellets – high silica content leading to buildu on the burner plate – any issues?
(not scaremongering, just checking on something a manufacturer said when they ut back launch of their new boiler – blamed the current fuel supliers!)

this is the mineral deposit in the burner cylinder after about 1000 hrs

My man from Jaspi says thats not bad at all.

Been burning 4 tons of Balcas Brites since October (Oirish wood). Theyve been OK, but Ive just moved to Verdo for a change (English wood). I keep logs of everything (natch 🙄 ) so will see how they do – the balcas have been fine expect for screwing up some deliveries, But theyve been cheapest.

The boiler is a Jaspi biotriplex (pellets on the right, log furnace on the left). The burner is an Ulma 2000 (20kW)

a clean and a service takes me about an hour or so.

this s my consumption chart.

Blue line is bags per day (1 ag = 50Kw) dotted is rolling average
Colour area is mean temp from local weather station

This for a 3,000 sq ft house.

Obviously this is without the solar thermal installed yet which I expect to make a significant impact from March onwards

stoner. blown away. good work.

maybe…..remember the 12.72kWh/day(or thereabouts) in summer from a 4msq flat plate or a 20 tube evacuated system. maybe 10-20% of that in winter – how big is your thermal system to be?

Speak to these guys: http://navitron.org.uk/category.php?catID=71

AN get on the Navitron forum: http://www.navitron.org.uk/forum/

going for 12m2 to match the tank.

in that case, ignore what i said about the heat contribution – 12m2 is way more than the normal domestic setup. you could be looking at 4000-5000kWh/annum of contribution!

If I can get some 70mm tubes say, at 2.32 KWh/m2/day (at say 1000 W/m2 iraddiance) then thats a good chunk of summer hot water.

I dont have any stratifiers in my tank so Id just end up with a mushy luke warm water in there even in summer unless I packed the energy in. I also want to stop my boiler from firing for most of summer if possible.

do you think hat 12v pump and 10mm pipe could handle 60 tubes and 20m of run?

Yup. and yes, you can put the stat at the TS but it would be more accurate if you can clear a way to fix the thermistor onto the inner shell of the TS – remove some of the insulation then fix it to the shell with some thermal paste and sealant.

TBH accuracy of the thermistor is not going to be that important as I can always fiddle the settings to compensate if Im getting iffy temperature diffs.

ok, just make sure its a positive difference – wouldnt want to heat the sky! 😉

Im going outside to check on the solar panels love

Stoner, you’d need to talk to Peter the seller about pump capacity. It comes in two or three sizes; mine handles 20 tubes with ease and can create a 2m head, have a look at the video on the site I linked. Since I bought 20m of 10mm tube and used it all up there must be 20m in my system though I don’t know where it all went because the panel is just above the cylinder on the roof.

The little pump is so vigorous that I was thinking of restricting the flow or setting the controller to reduce its speed because it is debiting heat from the panel too fast.

cheers gti. WIll give him a shout.

My specifier is coming round tonight. It will be a fine line to walk between keeping this close to DIY because I want to do the lions share of the work, but also have him make sure my capacities are adequate (expansion vessels, pipe diameters, pump heads) without paying too much by buying loads of retail stuff thorugh him or wasting his time by just getting the tubes from him and doing the install myself.

I also need to check MCS certification requirements for RHI. Im pretty certain that unless its installed by an MCS installer I cant get at the RHIs will be quite a lot with the scale of my install.

Stoner

sorry,I think i answered yup to the question before the pump question……..

I think this is right – better get my next statement checked though….

Heating pipes can deliver 18kW/hr at a spead of 1.5m/s – this is a ‘rule of thumb’ used to size pipes in heating circuit – 1.5m/s being the max speed that manufacturers recommend to avoid excessive system noise. If you are looking at (2.72 x 12) kW/day (say 8 hours) then I THINK 10mm should do, but would recommend 15mm. Not sure about the pump though.

cheers smudger. will report back tonight once hes been.

Stoner Just checked with a heating designer…

3kW is the max he would put through a 10mm pipe, with a 7m run.

He recommends 15mm for your system.

where are you? There may be something I can do for you in temrs of MCS.

see profile for website – we are MCS accredited.