Mackers

Hone Solar Thermal

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Any particular reason why you are looking at ST as opposed to Solar PV?

ST would be great if you had a swimming pool, but after that I'll take some real convening to lay money on that instead of PV.

 

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Looks like a bog standard evacuated tube solar thermal system, with a huge number of very questionable buzzwords thrown in and a lot of what look like apples-to-oranges comparisons to me (e.g. metered data against a SAP model - the difference between the two proves that they had unusually sunny weather, not that their system was wonderful).

Solar thermal is also one of those technologies that look like they ought to be a great idea, but when you start studying them in detail it all falls over. PV tends to give more usable energy in winter (no losses, making up for the higher efficiency of ST) while not suffering from the overheating problems of ST in summer and needing far less maintenance. If designing a system for new build, PV + heat pump works much better than ST + heating system.

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The ascendancy of PV over solar thermal is a very recent phenomenon. Before about 2014 the idea of using PV to heat water was economic nonsense; the FIT subsidies distorted the solar thermal market.

 

There is still a case to be made for solar thermal if you have a small area available for collectors and your priority is heating water. If you have an enormous PV array, of course there is no case for solar thermal.

Edited by billt

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18 minutes ago, billt said:

If you have an enormous PV array, of course there is no case for solar thermal.

Does a PV array have to be enormous to compete? Given ST is just a one-trick-pony I done see there being that much argument in favour of ST, unless as I said youve got a swimming pool or a hot tub etc eg a large mid temp heat requirement. ST won't ever charge your EV or keep your beer cold in the fridge ;) 

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28 minutes ago, Nickfromwales said:

Does a PV array have to be enormous to compete? Given ST is just a one-trick-pony I done see there being that much argument in favour of ST, unless as I said youve got a swimming pool or a hot tub etc eg a large mid temp heat requirement. ST won't ever charge your EV or keep your beer cold in the fridge ;) 

So much depends on how big your heat demand is, how it varies throughout the year, how you're producing the heat at the moment, etc. To give an example for my current thinking in my case:

  • We're thinking of building a passivhaus or similar - that means low demand for heat, possibly some requirement for cooling and of the heat a large fraction will be for water heating. the use of solar gain to provide a significant chunk of the heating means that there is little opportunity to use ST for additional heat - the windows will be doing the same thing at the same time anyway.
  • This being the case, it becomes quite hard to justify keeping the existing gas connection - the desire to have active cooling pushes you towards a heat pump solution, and in any case given the low demand gas becomes quite an expensive form of heat due to the standing charge and servicing requirements.
  • Solar thermal can't guarantee heat year-round, so a back-up hot water system is also required. If a heat pump is fitted anyway, this is the obvious source of that heat.
    • COP for an air source heat pump providing hot water in summer (when solar thermal works best) is surprisingly good - very roughly the amount of heat delivered to hot water from solar thermal and solar PV per square metre of roof is the same in both cases.
    • We'd ideally like solar PV anyway to tackle plug loads - so the cost comparison is for a standalone ST system about 2m x 2m, or adding the same amount of area to a PV system - the latter being much cheaper in both initial and ongoing costs. We would have a large south or south-east facing roof (TBC) so both are practicable.

There are any number of points in there where ST starts to look viable again - for instance, if we decided that we didn't need cooling then resistance heat starts to look very attractive. That being the case, ST would give much more heat per unit area of roof and would probably help a little more than PV were we to make getting certified a priority.

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In a PH ( or similar ) the argument to go all-electric is very strong. Simple, clean, "elegant" and near zero inspection / maintatence etc. Fortify that with solar PV and its game, set and match. 

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We have installed ST but on the cheap with a system that it will work very well with. If you go down the RHI route then it also makes financial sense but if I was paying the goin rate for a installed system with no RHI then it's a no starter.

 

I have seen good brand PV panels as low as 27p the watt.... had to argue with that prices! 

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2 hours ago, Nickfromwales said:

Does a PV array have to be enormous to compete?

 

It needs to be about 4 times the area to harvest similar amounts of power. If you want to use the electricity as well as heat water it needs to be bigger than that, so enormous is a reasonable comment.

 

Of course neither of them produce much heat energy when you really need it, in the winter!

 

No, I wouldn't install solar thermal now either.

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36 minutes ago, billt said:

No, I wouldn't install solar thermal now either.

 

I have ST despite it not being the best choice now, but it was installed in 2010 when it seemed ok as an option to heat water. One of the big minuses to installing ST is that if if goes wrong as mine has there just isn't anyone who can service it. The company who installed it said 'we don't do that now', and I've contacted 5 other companies with no joy so far. One of them did come out to give me a quote but then ran for the hills when he realised it was a 2 storey roof even though I told him that on the phone. So I've got not just a poorer performing option (when it works) but one that has become a white elephant because I can't get anyone to maintain it. Wonder if that is an issue in other areas too?  

 

Having said that I can't get anyone to come and quote me to install an ASHP either ... 

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28 minutes ago, newhome said:

Having said that I can't get anyone to come and quote me to install an ASHP either ... 

Try looking up local air conditioning companies - most of the ones around me say on their websites that they install ASHPs, but never turn up in google searches for ASHP installers for some reason.

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1 minute ago, pdf27 said:

Try looking up local air conditioning companies - most of the ones around me say on their websites that they install ASHPs, but never turn up in google searches for ASHP installers for some reason.

 

Thanks. Would they be MCS? Need that as I want to apply for the RHI payments. 

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Unlikely. Do you have a special reason for wanting to claim RHI? The vast majority of MCS-registered installers essentially tack on the value of the payments to their bill so the financial benefit of going down that route is very minimal unless you're in some fairly unusual circumstances.

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1 minute ago, pdf27 said:

Unlikely. Do you have a special reason for wanting to claim RHI? The vast majority of MCS-registered installers essentially tack on the value of the payments to their bill so the financial benefit of going down that route is very minimal unless you're in some fairly unusual circumstances.

 

Have taken a punt on the costs as I haven't managed to get a quote back yet but someone at work has a quote for one of a similar size to what I will need so I had thought that the MCS option would cost circa 9k and I would get that back in RHI payments over 7 years and I could get an interest free loan for the kit. If I go down the non MCS route I reckon it's about 3k plus for the unit and another 2k ish to install, so 5k and no return on that. Does that sound reasonable or have I done the maths wrong? 

 

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@newhome funny i was playing on the rhi calculator just now and was coming to the same figures! 

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How big? Monobloc or bi-block? A Chinese ASHP can be had as a 10kW monobloc for less than £2k, which only needs a small amount of plumbing and electrical to install. If you're getting £1,300 per year in RHI then you might want to look at insulation levels and the like first since that works out at something like 15 MWh of heat provided.

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I think I am looking at monobloc as I'm not sure I have room for an indoor unit although with the electric boiler gone that will be needed for RHI there's an outside chance there may be space I guess dependent on size. Is one type better than the other? I was basing it on a 16kw ASHP. I don't think I can do much about the insulation levels TBH. The walls aren't bad, the floor is fixed and has UFH so can't be altered, and the loft has 3 layers of Rockwool in most places. When I use the RHI calculator the payments are a lot less until I put the floor area in. As soon as I put 350 m2 in it shoots up and says I exceed the cap so it's 9.1k over 7 years. I have also been advised that it might be good to link it up with the ST (assuming it can be got working again). 

 

 

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I think £9k is very optimistic for a 16kW ASHP - you're looking at £5k just for a monobloc unit from someone like Samsung, maybe a little less on eBay. Installation should be pretty easy, but will still cost a bit. Having said that, if you're on an electric boiler at the moment then shifting over to an ASHP is pretty much a no-brainer financially whether or not you get RHI.

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On the topic of ST versus PV and the relative cost and energy production, Ed Davies did some useful work on this in his blog.  It's a bit out of date now, but Ed's work is still valid, in my view, and well worth a read for anyone contemplating ST or PV.  It's interesting to see how his views changed slightly over time, too:

 

https://edavies.me.uk/2011/12/pv-heating/

 

https://edavies.me.uk/2012/01/solar-per-area/

 

https://edavies.me.uk/2012/01/pv-et-flat/

 

https://edavies.me.uk/2012/11/pv-dhw/

 

https://edavies.me.uk/2012/11/pv-immersion-gotchas/

 

https://edavies.me.uk/2016/07/mp-pv-heater/

 

https://edavies.me.uk/2014/12/dead-solar-thermal/

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17 minutes ago, pdf27 said:

I think £9k is very optimistic for a 16kW ASHP - you're looking at £5k just for a monobloc unit from someone like Samsung, maybe a little less on eBay. Installation should be pretty easy, but will still cost a bit. Having said that, if you're on an electric boiler at the moment then shifting over to an ASHP is pretty much a no-brainer financially whether or not you get RHI.

 

The guy at work has paid that much for a 16kw bi-block with MCS install so I am basing it on that. He has paid but not had it installed yet. If I can't get it done for around that figure I won't bother as it's just me here and I don't heat at least half the house if there is no one else here as I never use all the rooms. 

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I think more like 3k for a 16kw samsung ashp. I don't know if you would need to change your thermal store aswell to qualify, shame if you do but maybe trade in for a sunamp? 

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11 minutes ago, Alexphd1 said:

I think more like 3k for a 16kw samsung ashp. I don't know if you would need to change your thermal store aswell to qualify, shame if you do but maybe trade in for a sunamp? 

 

I was hoping not to get rid of the TS TBH but yes I could look at Sunamp I guess but that would push the cost up quite a lot. 

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3 hours ago, JSHarris said:

On the topic of ST versus PV and the relative cost and energy production, Ed Davies did some useful work on this in his blog.  It's a bit out of date now, but Ed's work is still valid, in my view, and well worth a read for anyone contemplating ST or PV.  It's interesting to see how his views changed slightly over time, too:

 

https://edavies.me.uk/2011/12/pv-heating/

 

https://edavies.me.uk/2012/01/solar-per-area/

 

https://edavies.me.uk/2012/01/pv-et-flat/

 

https://edavies.me.uk/2012/11/pv-dhw/

 

https://edavies.me.uk/2012/11/pv-immersion-gotchas/

 

https://edavies.me.uk/2016/07/mp-pv-heater/

 

https://edavies.me.uk/2014/12/dead-solar-thermal/

This is why I started this post, thanks. Just looking at various options to save energy on an Industrial Laundry. Initial ideas are preheat for boilers, energy recovery from the steam system. Very early days but open to suggestions.

 

Perhaps recovery of energy from high level warm air somehow.

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