Micro-CHP

[Anonymous]

I'm still a sinner…so I can't post on the thread.

But, there's a review of micro-CHP in Building for a Future Vol. 13 No. 3, which mentions the Whisper machine.

I can find a link if you need it,

Peter.

[Andy Mitchell]

Oh, and I have no special knowledge of this topic so can't contribute in either forum!!

[Anonymous]

I have no special knowledge either, and can really only summarize bits of the article alluded to (link:

http://www.newbuilder.co.uk/bffmag/winter03/13_3%20Cover_story.pdf

-there are other bits on mCHP in the same issue as well).

The idea of mCHP is that people have their own units which generate both heat and electricity. One difficulty is in balancing the two, and with the current size of units proposed, you seem to need an additional boiler (which the units incorporat, but they're not 95% efficient condensing boilers, but only 75% efficient ones).

A second difficulty is involved with selling any excess electricity back to the grid (or at least getting paid for doing so).

A third problem might be expected lifetime. I don't think that there's really much experience to go on here, but the calculations were something like 3 – 7 years, which doesn't sound great to me.

A 4th problem might be EMF fields in the home (from the stirling engine generating your electricity). Is there a way of shielding this?

A 5th problem, is that they run off natural gas (the mCHP ones, not the larger ones). Calculations suggest that there should be a saving on the amount of gas used, but it's still non-renewable gas which you're using, not, say, woodchip. Still, perhaps after 7 years when your current model has conked out they'll be a biomass one.

I think at the end, the authors hint that a district-sized CHP unit might be better, with a corresponding local grid, which could also take power from other sources such as wind and solar. Though would I be right in saying that managing such a small grid (admittedly with a link into a national grid) with very variable supplies and demands might be quite an effort? Also, is there a lot of effort in converting, say, a street to having all their hot water supplied from a single unit?

I like the idea of local, but you want simple and reliable as well, I think. I don't know quite how this sort of technology fits in with this. I guess that there must be an optimum(-ish) scale which balances out capital cost, reliability, efficiency, etc.

Peter.

[Anonymous]

An expected life of 3-7 years sounds abysmal. These things went into trial last year I believe, someone out there must know more.

[Anonymous]

I spoke to Powergen in some little detail about the Whisper Gen mCHP unit. They have successfully completed their trials, and are now offering it as a commercial product.
They send a trained installer to assess an existing property for suitability (or review a proposed building). The current unit is only suitable for small to medium properties in terms of heat output, but they are bringing in a larger model late summer 05.
My main concerns were that the efficiency quoted was roughly similar to that of a good condensing boiler (something around 90%), including the electricity generated, with a greater cost and a greater risk attendant on installing relatively untried technology, being dependant on a relatively small number of trained people to do maintenance. (For instance they have no approved installers in London at present – BTW has anyone else noticed that London always seems to be a black hole interms of sutainability tradespeople / support? If we can't make some headway in London/SE, then we're not going to make much progress -1/4 of the population)
One thought I had was using the electricity to provide underfloor heating via an electric system in the case when the heat demand was higher than the unit's capacity.
Of course, in a low energy home the small unit should be more than enough…

[Anonymous]

Did they say what the price and installation costs are likely to be?

Peter.

[Author]

Posts