Jump to content


ebuild is sad to announce its closure - it has become too time and resource intensive to develop, manage and maintain.

However, ebuild will remain on-line in archive mode (ie no posting facilties) for several weeks so that users can use it as an information resource.

Is Solar Thermal More In Contention Now That 'fits' Is Virtually Zero


  • Please log in to reply
18 replies to this topic

#1 joe90

joe90

    Regular Member

  • Members
  • PipPipPip
  • 847 posts

Posted 22 September 2015 - 04:13 PM

My plans many moons ago was to have solar thermal ( maybe homemade flat plate drain back) installed in the top of a conservatory roof but this was discounted when most people thought that PV was more "useful", now that the FIT rate is likely to be very low does this mean that solar thermal to pre heat water in some way would be a good idea and cost effective?

#2 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 22 September 2015 - 04:34 PM

I'm not sure, but suspect that PV is still a better bet financially, even with a low FIT rate. Returns on PV, even with the low FIT rate, are likely to be around 8 to 10%, whilst returns on ST are (by the same measure) zero. Both can provide hot water, so you're really down to looking at the capital investment and ongoing maintenance and repair costs.

A home made ST system could be cheap, but absorb a lot of time and effort and need regular maintenance, but on a cost-only basis may be a better investment.

For those buying off-the-shelf systems, then PV almost certainly still offers more for the money, largely because the capital cost of PV has come down so much, whilst ST systems cost much the same today as they did a few years ago.

For me, I think that I'd still go for PV even without any FIT at all, really because of the versatility provided by electricity generation together with the "fit and forget" factor. I'd not want to have the bother of pipes, pumps, antifreeze, motorised valves etc when I could have some wires and a box of solid state electronics, with no moving parts.

Edited by jsharris, 22 September 2015 - 04:34 PM.


#3 Nickfromwales

Nickfromwales

    Short cuts take three times longer.....Fact

  • Moderators
  • 8,182 posts
  • LocationSouth Wales

Posted 22 September 2015 - 08:46 PM

Agreed. A lot of the st systems I have ever been called out to aren't working properly and the owners wouldn't know the difference as they cared not really. I only get called when it becomes an inconvenience, eg noise or leaks. Some are topping them up with cold mains water and not the recommended mix of antifreeze etc, so in essence are ticking winter time bombs.
I couldn't think of a more pita system to look after tbh, and it's still this one trick pony that's taking up time, effort and incurring ongoing costs plus service / maintenance etc.
I'd only ever recommend this if there's a pool tbh. I did one setup for a family with a huge outdoor pool, and I mean outdoor, and they never bothered having the panels installed ( as I fitted a 24kw backup,boiler dedicated to the pool phe only ) and just heat it with gas :huh:
Regards, nick.

#4 Auchlossen

Auchlossen

    Member

  • Members
  • PipPip
  • 26 posts

Posted 19 December 2015 - 01:12 PM

I installed a [too large?] solar thermal [12m2] in my last house ten years ago, flat plate down drain, and it never caused any problem - once I had reduced the cut off temperature which overheated and dried out the controlling valve - apart from producing too much hot water in the summer. Only used boiler for DHW in 3 winter months. Never needed topup, on the rare occasions that I checked it. Real fit and forget, I am pleased to say.
In new house to be built next year [since not in 2015!] I am debating still what sort of solar to employ.
I am less inclined to use solar thermal, mainly because it will require a thermal store, with space and heat loss issues, not good in passivhaus. Also best location for panels is on S bank below house, so drainback nbg, entailing antifreeze system = more complexity.
More inclined to use PV, even if I were not to connect to FIT, just to provide elec base load and DHW, but of course this will only be true for 9 months of year. And again I am disinclined to have a store of DHW, as above.

#5 Mackers

Mackers

    Regular Member

  • Members
  • PipPipPip
  • 233 posts
  • LocationBanbridge

Posted 19 December 2015 - 02:53 PM

The thing about solar thermal is you can build your own system very cheaply. If it's a drain back you don't have the problems associated with the anti freeze.

It's therefore a quicker payback than PV.

#6 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 19 December 2015 - 03:29 PM

Mackers

You got some figures to back that up.
A lot of it depends what you are starting with I think.

Its hard to beat the payback when compared to a gas combi set up.

Edited by SteamyTea, 19 December 2015 - 03:30 PM.


#7 Mackers

Mackers

    Regular Member

  • Members
  • PipPipPip
  • 233 posts
  • LocationBanbridge

Posted 19 December 2015 - 03:42 PM

I don't but if you build the whole lot yourself, and I mean the collector, thermal store and plumb it yourself it's a few hundred quid compared to thousands.

I like both technologies and they have their pro's and con's but it all depends on how hands on you are and your knowledge.

#8 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 19 December 2015 - 03:50 PM

The way I see it is that putting pipework though roofs is pretty hard compared to a couple of cables, attaching PV or ST to a roof is almost identical. A pump and controller, plus antifreeze every year is probably about the same price as a cheap inverter.

You may also find that ST on the roof is notifiable to BC these days (not sure, not checked, PV is). So that has to be costed in.

I am not sure how cheap you can make a few m2 of ST collector, not going to be 50 quid.

#9 joe90

joe90

    Regular Member

  • Members
  • PipPipPip
  • 847 posts

Posted 19 December 2015 - 03:53 PM

Mackers, like you I wanted to build my own solar thermal system but someone mentioned the possibility of very hot water escaping if a fault developed, just another thought in the mix.

#10 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 19 December 2015 - 03:54 PM

View PostMackers, on 19 December 2015 - 03:42 PM, said:

I don't but if you build the whole lot yourself, and I mean the collector, thermal store and plumb it yourself it's a few hundred quid compared to thousands.

I like both technologies and they have their pro's and con's but it all depends on how hands on you are and your knowledge.

The same goes for PV, though. Years ago I bought a load of wafers, some ribbon and flux very, very cheaply and made up some DIY PV panels. The cost was tiny compared to buying panels at the time. The downside was all the labour involved and the dubious reliability of anything DIY'd under less than perfect conditions, but then the same applies to anything DIY.

If you compare factory made components, then PV is a fraction of the cost per kWh produced to ST, just because PV costs have come down a great deal as a consequence of the volume market. There's no equivalent volume market for ST, so costs have stayed high.

Edited by jsharris, 19 December 2015 - 03:55 PM.


#11 Mackers

Mackers

    Regular Member

  • Members
  • PipPipPip
  • 233 posts
  • LocationBanbridge

Posted 19 December 2015 - 05:40 PM

Joe90, I don't see the likelihood of hot water escaping being anymore dangerous than a heating system in any normal building. I regularly design heating systems using high temperature hot water or steam in pipework above ceilings.

Im going to be doing a diy solar thermal install on my father's house linked to a radiant heat source, it'll be significantly cheaper than PV.

#12 joe90

joe90

    Regular Member

  • Members
  • PipPipPip
  • 847 posts

Posted 21 December 2015 - 09:55 AM

Mackers, I would be very interested in the design of your system, and I am sure a few others on here would so please let us know what you do and keep us updated. I am planning a sun space across the south side of our house and had planned the top bit of roof as not glass to shade the house from too much sun and creating this as solar thermal panels seems perfect!.

#13 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 21 December 2015 - 10:26 AM

Trouble with making your own flat panel ST is that you need to insulate the back of the collector. This generally means you get a very thick box unless you go for something like aerogel. PU and EXP tend to melt.
Why, and as much as I hate the looks of them, evacuated tubes are so much better.

#14 Nickfromwales

Nickfromwales

    Short cuts take three times longer.....Fact

  • Moderators
  • 8,182 posts
  • LocationSouth Wales

Posted 21 December 2015 - 10:43 AM

Agreed. ST arrays need to be efficient to get useable energy ( at least slightly in excess of demand ) and need their location / orientation to match, more so than Pv as you need that daily high temp 'spike' to get your dhw up to temp rather than long and low like Pv can get away with.
With that space available I'd definitely go with Pv, then your excess can go towards offsetting the running costs of your white goods etc ( after providing dhw) whereas ST will just sit there doing zero.
:unsure:

#15 alexphd1

alexphd1

    Regular Member

  • Members
  • PipPipPip
  • 133 posts

Posted 21 December 2015 - 11:55 AM

My parents have had two in roof flat plate panels for approx. 10 years and have had no problems apart from topping it up twice over that period. I have pulled together most of the material off ebay apart from the roof flashings (which where the dearest part) for my new build, saved a lot of money and no hassle of a diy. panels £90 each, pump station £100, controller £50. Think the panels could match in with a ashp and a sunamp store pretty well.

#16 jsharris

jsharris

    Please ignore all posts by me, some are erroneous

  • Member Blogger
  • PipPipPipPip
  • 11,461 posts
  • LocationWiltshire/Dorset border

Posted 21 December 2015 - 12:32 PM

Interesting discussion. I'm just having a quick tea break from working in our service room. The weather here is light rain, 8 okta cloud, 10 deg C OAT. Every four or five seconds I can see that I'm charging up the Sunamp PV to store spare energy as heat for hot water.

My next door neighbour has 20 evacuated tube ST panels on their roof, same orientation as my PV, and I know from talking to them that they get near-zero hot water out of their system from November through to March. Not really surprising, as the chance of even an evacuated tube getting hotter than about 40 deg C to start transferring sensible heat on a day like today is zero. A flat panel system would be a fair bit worse, because of the inherently greater heat losses.

This is the main issue with ST, it can only ever transfer heat when the collector is hotter than the hot water storage system, which means that, in winter, there is only a very narrow part of the middle of the day when the system could have possibly got hot enough to start working, and on most days this won't happen.

With PV my system had already put around 0.5 kWh into the Sunamp PV by 10:00 this morning. This is the only means of getting hot water at the moment (the ASHP is off as is the electric boost heater) and I'm pleased to say that there is loads of it, all from the PV system.

Edited by jsharris, 21 December 2015 - 12:33 PM.


#17 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 21 December 2015 - 04:01 PM

Got the urge to try and model what would be expected to happen.
So here is some nice charts (charts are always good).
Thing to note is the expected temperature rise in the water, the right hand side scale, and the time it starts to heat on the x axis.

Attached Files

  • Attached File  Jan.jpg   31.64K   1 downloads
  • Attached File  Mar.jpg   32.53K   2 downloads
  • Attached File  May.jpg   33.18K   1 downloads
  • Attached File  Jul.jpg   33.12K   1 downloads
  • Attached File  Oct.jpg   32.57K   1 downloads
  • Attached File  Nov.jpg   31.68K   1 downloads


#18 joe90

joe90

    Regular Member

  • Members
  • PipPipPip
  • 847 posts

Posted 21 December 2015 - 04:10 PM

I confess I started this thread as I planned my new build years ago before PV was so cheap. At the top of the conservatory I want a shade of about 800mm wide and 8 meters long to stop overheating within the house and thought this the perfect place to put homemade solar thermal panels under the glass, all up hill to the tank. Job done. It might help to pre warm the water before the ASHP etc. My current plan is to put PV on my large garage anyway as I don't want panels to detract from the cottage look I am trying to create ( if I ever get planning!!!)

#19 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 21 December 2015 - 04:24 PM

If you could make it 1m by 8m then you can use 5 PV modules.
That will give you about 1.45 kWp which could heat 200 lt of water for half the year (depending on shading blah, blah, blah).
Or just stick the wires into the mains and reduce your overall usage.

5 PV modules will probably cost about £900, micro-inverters about £140 each.

Edited by SteamyTea, 21 December 2015 - 04:26 PM.