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Perverse incentives

Everett True
Heard recently that the govt is going ahead with bringing in a subsidy for domestic solar hot water systems, whereby you get paid 18p or so per kWh of heat that you generate (as well as saving off your gas bill, of course).

It's estimated that a typical 20-tube installation on a south-facing roof will pull down somewhere around £400-500 for you per year through this subsidy: not bad.

There is a snag, though, which is that the subsidy isn't payable for installations on houses with combi boilers: only for those with the more traditional cylinder-plus-boiler setup. Not because there is any technical drawback to using solar-heated feed to a combi, or efficiency penalty, or anything like that: that's not an issue. It's simply a policy decision.

This is probably a bit galling for anyone who thought they were being nice and eco-friendly by installing a combi boiler, as previous govts persistently urged us all to do. But fair enough, maybe they are thinking that encouraging solar adaptation of older boiler systems is going to clean up more of the low-hanging carbon-emission fruit.

But this is where the title of this post comes in. It'll cost you about £3000 (say) to rip out your lovely efficient new combi boiler and replace it with a cylinder-plus-boiler system. With the subsidy guaranteed to rise with inflation for 20 years, you'd repay that and be quids in before too long.

Hmm.

Comments

( 12 comments — Leave a comment )
sea_of_flame
29th Sep, 2011 18:45 (UTC)
How much does the solar hot water system itself cost?

(We have a boiler+cylinder at present - although the boiler will probably need replacing in the next few years anyway)
undyingking
30th Sep, 2011 07:58 (UTC)
Depends on the height of your roof and so on (scaffolding is a major cost component), but probably somewhere around the 4-5K mark.
mr_malk
30th Sep, 2011 09:33 (UTC)
My boiler-man tells me that most or all combi boilers can equally be switched to operate as conventional boilers if you have a storage tank set up, which you'd need if you had solar-thermal installed, so I'm not quite clear on how that distinction works. Possibly if you have a tank for the solar-thermal, but still have the boiler set to heat water as it's used... but that doesn't make any sense... unless there's a thermostat on the combi-heater to switch it on if the piped water is below a certain temperature...

Hmmm. Anyway, thanks for mentioning the subsidy. My boiler's coming to the end of its useful lifem and I've been considering replacing it with a system that incorporates solar thermal in any case. Unfortunately my roof faces more NW-SE than N-S, so I might have to have panels both sides to make it worthwhile. Still, the subsidy will help the justification nicely.
undyingking
30th Sep, 2011 10:45 (UTC)
Yes, in practice if you want to use a combi boiler with solar thermal you have to add a storage cylinder for the solar-pre-heated water anyway, as a direct feed from the panels wouldn't provide hot enough water fast enough.

I suspect though that, as eg. combi boilers are specified in building regs for new houses, it is just that a list of certain boiler models are designated as officially combis and that's that, however you subsequently tinker with them.

There is some confusion over when the subsidy is going to come in. It was originally supposed to be this April, then it seemed like it was cancelled altogehter, now maybe next April or maybe sooner than that.
hatmandu
3rd Oct, 2011 08:17 (UTC)
My understanding was that the vast majority of combi boilers can't be used with solar thermal - IIRC something to do with modulating temperatures – but there are a couple of manufacturers who do make solar-friendly combis. (We're not on gas but I looked into it all before our renovation last summer; we ended up with a wood pellet stove with thermal store, and hope to plug solar thermal in when our finances recover.)
undyingking
3rd Oct, 2011 08:41 (UTC)
Hmm, I was told that any combi could, with a suitable adapter (essentially, an interposing pumped and switching cylinder). Well, I'll look into it more deeply if we ever get round to it…
undyingking
30th Sep, 2011 10:45 (UTC)
Oh, and: here's the relevant website: http://www.rhincentive.co.uk/
watervole
30th Sep, 2011 11:03 (UTC)
Sadly, my roof already has photovoltaic panels. I'd have prefered hot water ones in some ways.
mr_malk
30th Sep, 2011 11:14 (UTC)
The two are not mutually exclusive... unless you have a small roof of course...
watervole
30th Sep, 2011 12:31 (UTC)
We put on as many solar panels as would fit. The only empty roof faces north.
mr_malk
30th Sep, 2011 14:06 (UTC)
Fair point. I can see how that would pose a problem for future solar-powerd expansion!
undyingking
30th Sep, 2011 12:21 (UTC)
Solar hot water only needs a couple of square metres, so might you be able to squeeze them on at one end?
( 12 comments — Leave a comment )

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