Green Building Forum - Solar Panels (for heating water) - why do it?

Solar Panels (for heating water) - why do it?

cjard — Tue, 30 Sep 2014 17:16:46 +0100

In a nice little mini-heating guide that came with my recent copy of buildit! magazine, i find the nugget of imformation:

Solar thermal systems cost between Â£3000 and Â£5000 to install and can save around Â£55 per year if you heat your water via (fossil) and Â£80 a year if you use an immersion heater

Really? A fifty to hundred year payback? Who would buy such a system?

Solar Panels (for heating water) - why do it?

Gotanewlife — Tue, 30 Sep 2014 17:31:39 +0100

ME!!!! I have to use a 40 kW wood burner to heat my house but living where I do in Italy I only need to heat my house for around 6 months a year, for the rest of the time my over-sized solar panels (5x FPs) provide all the DHW (actually I use a tank-in-tank TS so the solar panels help a little bit all year). I do have to cover up 2 of the panels for the hottest 4 months or so but access to the roof is dead easy. Running a big log burner in the height of summer would be madness, as I am sure you can imagine! Around this time of year 2 full days of cloud leaves us with luke warm showers in the morning of the third day and me praying for sun! Have not had to burn this autumn...... yet.......

Solar Panels (for heating water) - why do it?

Ed Davies — Tue, 30 Sep 2014 17:43:09 +0100

Somebody who's paying considerably less than that. That might be a reasonable price for a one-off install on an existing property but if you're messing with the roof and plumbing anyway (new build or major refurb) then the incremental cost of solar thermal ought to be a lot less than that. Also a DIY install ought to be cheaper, too, particularly if your property is such that you can manage without scaffolding costs.

Solar Panels (for heating water) - why do it?

GarethC — Tue, 30 Sep 2014 19:55:34 +0100

I do think it's a valid point. Even if you manage to do it for Â£1.1k, the payback's 20 years. Basically you have to do it for tree hugging reasons (i.e. why that's why I would get one if I didn't share the roof).

And even that saving is predicated on average DHW use, when, if you're minded to, you can reduce your DHW needs a lot just by cutting wastage and changing a few habits. That's the problem we've got. With modern applicances and very short showers, our DHW use is already pretty low.

Solar Panels (for heating water) - why do it?

tony — Tue, 30 Sep 2014 22:34:47 +0100

Your 20 year payback does not seem to allow for energy price inflation.

Solar Panels (for heating water) - why do it?

SteamyTea — Tue, 30 Sep 2014 22:40:45 +0100

Posted By: GarethCWith modern applicances and very short showers, our DHW use is already pretty low.

Too true. It is really the key to DHW usage.

Solar Panels (for heating water) - why do it?

SteamyTea — Tue, 30 Sep 2014 22:56:53 +0100

Posted By: tonyYour 20 year payback does not seem to allow for energy price inflation.

That tends to even out with general inflation and saving rates.
High inflation periods erode your savings, but also reduce your borrowings in real terms
That is why we tend to get higher saving rates at times of high inflation, we want to take cash out of the economy to get inflation under control.
Admittedly we have had an odd few years, but it has kept spending levels higher than they would be, and the government has pumped billions into the economy (main reason why we have had house price inflation). The better than expected employment figures and VAT returns (which are a good indicator of the health of the economy) have kept us competitive in global terms.
Wage inflation is the thing that will cause commodities prices to inflate. But the odd thing is that you will still have to work X hours to pay your energy bills of Y. The ratio will not change hardly at all.

Solar Panels (for heating water) - why do it?

joe90 — Wed, 01 Oct 2014 10:40:39 +0100

From all the threads I have read I get the feeling that it is more sensible to install PV to heat the water?. Although I get this niggling feeling that not using the free heat from the sun is a wasted opportunity.

Solar Panels (for heating water) - why do it?

Ed Davies — Wed, 01 Oct 2014 11:28:27 +0100

Joe90, yes, I think so for values of â€œsensibleâ€ which involve basic physics and sustainability and also, though I'm less confident of this, when the effects of FiTs and RHI are taken into account. The exception, though, is if you don't have much roof space - for a given output power solar thermal takes up less space than PV; that is, ST is noticeably more efficient in using the photons it actually intercepts.

Solar Panels (for heating water) - why do it?

dimengineer — Wed, 01 Oct 2014 13:11:50 +0100

The numbers are wrong. On Gas, you save about Â£100 per year, on Electric it can be over Â£300. Depending on particular tariffs, how much solar you have....
So if you are on mains Gas, it makes no sense, financially, on Electric its much more viable

I did it for the warm fuzzy smug feeling it gives me

Solar Panels (for heating water) - why do it?

Ed Davies — Wed, 01 Oct 2014 14:32:07 +0100

It's a length of string question, isn't it? Depends so much on household size, water usage and so on. I think the saving figures cjard quotes are probably a little high for a single person who's frugal in the use of hot water but well short for a typical household.

Solar Panels (for heating water) - why do it?

billt — Wed, 01 Oct 2014 15:08:48 +0100

They're not that far wrong. I have measured the energy output from my 120 tube system for the last 4 years and it is just under 5MWh per year. At my electricity rates that would be about Â£500. However, this system is 4-6 times bigger than the average domestic installation and most of that energy is either wasted or not useful, so I think that you would be very lucky (or live in Spain) to save more than Â£100 pounds worth of electricity (< Â£50 worth of gas) with a typical UK installation.

Professionally installed solar thermal has never been financially sensible - it is pretty marginal with a DIY installation.

Disregarding subsidies, the costs don't add up any more - if you have space for a big array that is.

The (moderately inexpensive) thermal collectors that I used are now sold for Â£712 and have a peak output of 1500W (but a mere 297W with 400W/sq.m. insolation and 50C temp diff). I can get 1700 watts worth of PV panels for Â£900 which will perform better than the thermal system in less than ideal conditions (the ones that occur most of the time - about 700W under the conditions that the thermal system yields less than 300W).

They are much more versatile (you can use the energy for other things) and much easier to install. Yes, you need an inverter as well, but you can get one for rather less than all the ancillaries that are needed for a thermal installation.

Solar Panels (for heating water) - why do it?

Gotanewlife — Wed, 01 Oct 2014 15:19:18 +0100

I think you have summed it up nicely there billt - 4 years ago (when I installed PV, Log Burner and FPs), the cost of PV was much higher - sadly, sadly, sadly at the time I said no don't bother fitting an immersion coil at the top of my tank-in-tank TS. When the FPs finally go, rather than replace them I think I might just stick in more PV and install a DHW tank in line, but after, my TS.

Solar Panels (for heating water) - why do it?

jamesingram — Wed, 01 Oct 2014 19:03:27 +0100

About Â£6k now for a 4kWp PV system with a immersion dump device such as a iboost. PV sys. Will generate just 4000kwh per year @ 15p kwh ( 'no standing charge' grid price electric?)= Â£500-600 worth of usable energy.
Thats about 8-10% of cost. Without FITS
I'll have a look at my summer usage and see if i can tell what my iboost saving this summer brb

Solar Panels (for heating water) - why do it?

dimengineer — Wed, 01 Oct 2014 22:08:16 +0100

James - to be pedantic, you probably aren't getting 4000kWh of useable energy - unless you go to heroic lenghts. A fair amount of electricity use - several hundred kWh per year is lighting - so PV isn't going to cover that. On a hot sunny day you just are not going to use the 15 - 20kWh you generate, some will go into the grid. Even if you divert into hot water, it'll be hot well before the end of the day.
I'm geussing that its pretty well impossible (without the heroics) to directly use more that 60 - 70% of those 4000kWh. So its more like Â£400 per year. Still useful, but...

Solar Panels (for heating water) - why do it?

SteamyTea — Wed, 01 Oct 2014 22:21:23 +0100

One thing when comparing energy prices for DHW. If you heated all your water with electrical resistance then you would probably change to E7 at about 7p/kWh. For me on my own it is a marginal case, probably better off with an electric mains pressure shower and an instantaneous heater for the rest of the hot water. But then I have heating to pay for as well.

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 10:26:11 +0100

just looking at what iboost potentially saved this summer on gas, relative to last years usage
March to October ( heating off, cooking included )
2013 1247 kWh
2014 834 kWh
just over 400kwh
Â£20 , that's just for the summer,
well paid for my beer last night

Solar Panels (for heating water) - why do it?

SteamyTea — Sat, 04 Oct 2014 10:58:37 +0100

Posted By: jamesingramÂ£20 , that's just for the summer,
well paid for my beer last night

Put energy price into perspective that does

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 11:01:48 +0100

Fitted it about 10 month ago. Display is showing 980kwh saved.

Solar Panels (for heating water) - why do it?

SteamyTea — Sat, 04 Oct 2014 11:32:33 +0100

How does the display work?
I can see that it could show the energy generated, not so sure how it shows what has been saved.

100 kWh is about Â£7 on E7, and is about what I use for hot water.
This is my problem, it is just not worth me getting a system.

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 11:39:43 +0100

iboost is an pv immersion dump box (wireless just fit inline with immersion feed) display just shows kWhs dumped or 'saved'

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 11:48:35 +0100

My 4kWh ish PV sys has generated 11,800kWh in 33 months about 978 days

Solar Panels (for heating water) - why do it?

SteamyTea — Sat, 04 Oct 2014 11:57:22 +0100

Sorry James.
Thought you had a ST system with a heat meter.

So you system is doing about 4.3 MWh/year. Or about my target for usage in the next year (assuming I don't get a lodger again).
Shame I can only get about 3 kWp on the roof, and half that would be facing North East.

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 12:02:15 +0100

They do 330W panels now 1.6/1m . Might change things a bit for you ( of course they're expensive)

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 12:09:01 +0100

They do 330W panels now 1.6/1m . Might change things a bit for you ( of course they're expensive)

Solar Panels (for heating water) - why do it?

SteamyTea — Sat, 04 Oct 2014 13:38:18 +0100

Yes, I have looked into them. Think there was only one make at the time and they were insisting that they could only be fitted by 'specially trained fitters'. Was just an excuse to keep the price up.
I am rather hoping the the FITs scheme fades away and that smart metering can take control of the import/export problem.
Then DIY it and claim ROCs.
I think smart metering my cause a few problem in the market.

What is odd is I know a lot of people locally that have studies or taught Renewable Energy, also know many people that are, or have been involved in it. Very few actually have PV fitted. Half of those I know do it for the interest more than anything else. The other half do it for the financial return, but that will back fire when saving rates go up. There was only a marginal difference over an ISA anyway.

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 14:49:15 +0100

checkout the BenQ Sunforte 327W or 330W , available via wholesaler to all comers

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 15:05:16 +0100

I'm an installer so lucky , got the high tariff 3 years ago and have already covered my Â£6500 material costs at the time for the install via FITs .
Irrespective of that I'd fit them on any house I lived in. At first I was sceptical , but after monitoring them for the last few years , I'd fit them without subsides .
Energy efficiency improvement of the existing housing stock to me seems a sensible priority. Once the simple cheap easy things are done you hit a bit of a brick wall in respect to costs and benefits.
PV is simple and it works and I think should be considered as the first, next thing to do, once the low hanging fruit have been plucked. As for listed and hard to treat properties , they're perfect.
As for new builds , high occupancy/use buildings and all public state owned building they should be fitted by law

Solar Panels (for heating water) - why do it?

renewablejohn — Sat, 04 Oct 2014 15:29:52 +0100

James

Have you had any experience of using solarwall PVT.

http://solarwall.com/en/home.php

Supposed to keep the PV panels cooler in summer plus additional hot air which we want to use for drying woodchip.

Will be a 30kw system on a new agri building.

Solar Panels (for heating water) - why do it?

jamesingram — Sat, 04 Oct 2014 15:49:23 +0100

Sorry John no. I'm sure some PV wall solution with rear heat flow channel could be ridged up though .
Like a trombe (thermosiphon) wall ?