Solar water heating and combi boilers

[Steve Firth]

Yes but that proponent also believes in imaginary friends so I think I'll give it the credibility it so obviously deserves.

[John Rumm]

Many combis have a maximum input temp in the low 20's, hence with the solar water at say 30 to 40 degrees, and the selected blended output at

60, the combi will still be required to do half the lifting.

[John Rumm]

Yes it would, if you collect the heat in a thermal store, you can have a mains pressure feed to the combi heated by the (unpressurised) store. Also we were talking about blending the the store heated mains flow with the output of the combi - not necessarily its input.

Some are, some aren't. Not really the point though is it.

[David Hansen]

On Wed, 17 May 2006 15:47:44 +0100 someone who may be Steve Firth wrote this:-

Which proponent is that?

[John Stumbles]

I did, above. I said that it would make more sense to replace an inefficient boiler with a high-efficiency one than install solar water heating and keep the dinosaur. Do you agree?

Of course if resources permit one can go for both. I don't think I was implying that one couldn't.

[Mary Fisher]

Why argue about it?

You're not going to prove anything

[John Stumbles]

I haven't looked at the specs of combis with this in mind but I'm curious to know what they'd do when given water warmer than this. Except maybe invalidate your warranty :-)

Still, whether the combi gets its input from the cold mains or the store is of secondary importance compared to being able to combine the two in this way (assuming it works).

[David Hansen]

On Wed, 17 May 2006 20:05:09 GMT someone who may be John Stumbles wrote this:-

That depends on the situation. For example, if someone was able to run an old boiler for a few more years and then install a micro CHP unit I suspect that would be better for the environment.

[John Stumbles]

OK, but that would be an extremely unusual situation and, dare I say?, a rather contrived example.

I was (and am) trying to establish a rule of thumb that you don't put in solar water heating before you've addressed draughtproofing, insulation and heating efficiency. This isn't an academic exercise: I know someone who's just signed up for a (very expensive) solar system. His rambling old

5-bedroom house has draughty external doors, many draughty single-glazed windows, at best 50mm loft insulation, probably no insulation in the cavity walls, and a standard efficiency boiler with a programmer + room thermostat as controls (single zone). He coukld have spent 1/10th the money and resources and saved vastly more energy than the solar system is going to produce.

Now this guy isn't your average SUV driver who thinks he's green because his wife buys Ecover but an economist working for a radical economic/ecological think-tank FFS! If he doesn't know better what hope is there of getting Joe/Jo public to make ecologically-sensible decisions?

Don't get me wrong I'm all for renewables, and have no objection to people with the money putting in solar systems (after they've got the other factors right) even though it may not pay back economically. Likewise the (proposed?) local regs in London requiring renewables in new developments. As with condensing boilers as the technology becomes more widespread the costs should come down furthering deployment of the technology, which is IMHO A Good Thing.

BTW picking up on your mention of microCHP I looked into the MicroGen and WhisperGen but they didn't seem to be available at the moment. There are also issues of what to do with surplus electricity produced (I think this came up here or on uk.environment recently?). Do you know of any domestic-scale installations in the UK?

[David Hansen]

On Fri, 19 May 2006 20:47:42 GMT someone who may be John Stumbles wrote this:-

I don't think so.

It is an example of a situation I am familiar with in a few places.

All these things need to be done, but within limits. These limits are not precise, but depend on individual priorities.

Certainly insulation of pipes and cylinders is a priority. However, the best way of insulating a cylinder may be to replace it with a solar cylinder. If doing so it may make sense to use it properly. I don'y think there are any hard and fast rules, it is a matter for the art of engineering.

They have been installed in a few trial areas IIRC.

In the UK the electricity output will largely tie up with maximum demand, for example lighting demand is highest on winter nights when central heating is also turned on.

[Peter Parry]

Does this qualify for the finest non-answer to a question of the year so far?

[David Hansen]

On Sat, 20 May 2006 00:08:06 +0100 someone who may be Peter Parry wrote this:-

It is an answer to the question that was posed. It may not be the answer that you wanted to hear, it is not a complete answer, but that does not make it a non-answer.

[Mary Fisher]

No, you have that crown :-)

[AJH]

About a year or so ago I did a search and came up with a guy in a remote cottage in Derby that had fitted a DC version from a boat, I cannot find him now. Victron seem to suggest they have sold a number for boats. Manchester council were supposed to be trialing a load in a housing scheme. I did at one time get a "quote" for a whispergen at GBP3500.

AJH

[John Stumbles]

IIRC the electrical output of a microCHP rig is in the order of kilowatts. That's a lot of lighting, even without using low-energy lamps.

[Andrew Gabriel]

In many areas of the country, summer aircon demand has outstripped winter heating/lighting demand for a few years now.

[AJH]

^ by electricity??

AJH

[Mary Fisher]

Which areas are those?

Assuming you're talking about UK that is ...

Mary

[David Hansen]

On Sun, 21 May 2006 08:51:20 GMT someone who may be John Stumbles wrote this:-

Indeed, which is why it was an example. However, unless every building is to have such a plant I doubt if all the plants will produce more than the total lighting load. Every street light will not have such a unit.

[John Stumbles]

My original question was what to do with the surplus electricity. Indeed I'm not sure what the regs are, currently, wrt to connecting microCHP into a mains installation. I understand suppliers are concerned about the risk of their engineers getting fried by power fed back from a CHP generator into what would otherwise be a dead part of the system under fault conditions.

Apart from that are there ways of selling surplus power (I recall someone talking about trading RECs)? Or does one just give it away?