wonny j, I'm intrigued. I've just re-read my thread and can't find any specific mention of payback although I suppose you could argue that it is implied where I stated that PhotoVoltaic is more expensive and less efficient solar thermal.

I'm also feeling a bit dim this morning as I have no idea what "FIT's" is

feed-in-tarrif.

Bear, basically my problem my problem with ASHPs is the lack of any independently published data on the performance. There are lots of manufacturers claims, like coefficient of performance of >4.5 However, in practice because the poor performance in winter this would seem to drop significantly, and if it gets near 3 then you might as well stick with an efficient gas boiler.

Some of my colleagues have looked into this and it would seem that attempts to publish proper performance data have actually been pulled by manufacturers.

Anyway, the people I've spoken to who have had extremely high bills for this winter, aren't too happy with their ASHPs performance.

I suppose the renewable heat incentive might change this, but who knows at this point?

What about a GSHP then? much better heat reservoir for the winter?

Some people here seems a bit confused abvout the difference between PV and solar thermal.

I think the jury is still out on PV, but…

When you consider solar thermal it is not just about the current payback, but also about insulating (no pun intended) yourself from future price shocks. Gas may not always be as cheap (or even available at all) as it is now.

Another option you could consider is a thermal store – I've got one from these people although other makes are available.

They are expensive, but the advantage is that they will accept inputs from just about any heat source you want. Currently mine is powered by immersion heaters on Economy 7 (I'm intend to add solar thermal but am in a conservation area so there are planning issues) – but it also has tappings to add a boiler or a feed from my wooburner if I want. Similarly it currently only supplies hot water but could also act as the heat source for central heating.

One other advantage of this system is that is is open vented, which means no annual maintenance (unlike an unvented system) and no risk of explosion when you start adding different heat sources.

My main advice would be do plenty of research before you buy – there are lots of options and they are all expensive, so make sure you are very comfortable with your decision before you spend money.

photovoltaic
Go on keep me in a job 😆

ASHP's aren't the most efficient things despite manufacturers claims, CoP's closer to 2 seem more the norm. Didn't they used to be called air assisted electric heaters? There should be some independent heat pump data coming out in a few months or so. Insulation and air tightness, as unsexy as they are, are the really important things to get right.

Going back to the OP, I reckon (evacuated tube) solar thermal to heat water is a good idea particularly for green rather than financial motives. Although the renewable heat incentive due next year covers it, at least in the consultation I think, so there could be an additional income from that depending how the scheme is implemented. Vented or unvented? – if the Navitron and builders forum don't help then find some local installers and have a chat.

Forgot an important point about the thermal store. It is vented BUT you still get your hot water at mains pressure.

Dont be fooled into thinking that an ASHP will be great for heating your house. You need to heat your house when its cold outside, exactly the time when ASHP will be at their least (roughly 1 to 1) efficient. You might as well have night storage heaters and only pay e7 prices.

GSHP are a much better idea, BUT only if you can install underfloor heating. If you having full on refurb, this may be an option.

Solar hot water, will reduce the domestic hot water cost to some degree. Generally works out to be about 20% reduction.

Solar electric (PV) not too sure on this.

Interestingly I just went to a talk on this the other night. The expert, was an archetect designing low energy buildings. His view was that any renewable energy (on a single house) was just eco-bling. His advice was spend the money on more draft proofing, better insulation, triple glazing, highest efficiency boilers/appliances etc. All of which can be very very expensive to do really well. GSHP was a good choice if the house was suitable.

Having said all that, I know how emotive these issues can be, and peoples very different attitudes to things!

His advice was spend the money on more draft proofing, better insulation, triple glazing, highest efficiency boilers/appliances etc

And what about when you've done all that?

When you've done that really really well there's no cost imperative to do anything else. Apart from hook up to a district heating scheme.

Yep, all part of the energy hierarchy. Reduce demand –> improve efficiency –> generate from renewables, in that order.

And what about when you've done all that?

Once you've done all that, there is very little else to do. Job done!

I don't mean to sound glib with that comment, just that once you have done all that, you'll be using very little energy. Any savings will therefore be minimal. Going the extra mile with solar hot water would save some energy during the summer months, if your not interested in payback then this would be the next/last step…

…Really though I wouldn't bother, if you have money left over (lucky thing) then start looking at greening other areas of your lifestyle. The house is done. Now work on transport, food etc. That will save much more energy than domestic hot water heating.

We are renovation a house at the mo and doing a similar thing. We have a mixture uf UFH & rads for heating. We will be fitting a condensing system boiler which then feeds into a thermal store. This is for 2 reasons, condensing boilers generally achieve their efficiency when running at full tilt, not when you are just using enough water to wash your hands. The thermal store has coils for heating & dwh. So the boiler runs flat out every so often to keep the store warm. Also the store has other sets of coils that will allow us to fit solar and or ASHP at a later date.

FYI the store is about £2k from these guys:-

http://www.chelmerheating.co.uk/thermalstores.html

We have also gutted the house and added about £5K work of insulation to the walls floor & roof.

Good work mos. Sounds like you have the right ideas, and the right approach ie doing it all at once during a refurb.

I've never heard of the heat store idea before, but it sounds like a potentially viable idea. Would be interested to know how it works out in practice.

Fair point – our new build house uses very little heating energy anyway, and there are still places I reckon I could insulate it further. So if I were to invest in anything it'd be PV I reckon.

Although surely – the more your total heating bill goes down, the greater percentage of your usage could be achieved with solar? I mean if solar hot water cuts 50% of your gas usage, then you save 25% of your gas usage via insulation, you'd still get the same amount of energy from solar – so your percentage from solar would go up to 66% right?

Yes but it would be a greater percentage of a much smaller total.

Hang on tho. If solar gets you X watts of power, and your house needs Y watts, then you'll spend Y-X on the equivalent mains gas. If you insulate loads to the point where Y = X, then you need no gas at all.

I don't understand where people are getting the idea from that you can get enough solar energy (of any form) to contribute to heating a house.

If my understanding is correct (might well not be) there just isn't the energy to do it during the winter months, when your heating is on.

Far enough during the summer there is generally plenty to heat domestic water (ie baths/showers/taps), but this will be a small fraction of you total yearly energy use.

All the stuff I've seen says that there IS enough solar energy to make a difference to your bills. And if your bills are super low to begin with, it'll make more of a difference in percentage terms.

What the others on here are saying is that the initial cost of the system might not be worth it against the savings.

heat store = thermal store

I gave a link to DPS who are another manufacturer earlier.

I don't understand where people are getting the idea from that you can get enough solar energy (of any form) to contribute to heating a house.

Well you can, easily, but it does mean building a completely different kind of house.

or a passivhaus

(scroll down a bit)

Wow, ecohouses that look good and also perform well.