Re: Another turn your home into a mini power station thread...

[Bruno Prior <bruno@xxxxxxx>]

I thought this seemed like a nice idea, too, but apparently they may
have high NOx problems. Would be worth checking before purchasing.

British Gas have been promoting these for at least a year within the
industry (they had a big stand for it at last October's Sustainable
Energy Expo at Olympia), but I haven't heard any progress reports.

> Basically when the unit is producing heat, it will generate
electricity as
> well. If this is more than is currently be used by the house it can be
sold
> back to the grid. At present they need a grid connect to work, so
won't be
> any help in power cuts, however off grid systems are being looked at
as
> well.

How will they sell back to the grid? How will they meter how much you
are putting into the grid? The simplest way to do this is what is known
as "net metering", which is effectively your meter running
backwards
when you are exporting (so your exported electricity is worth what you
pay to buy it - although how you take account of varying prices at
different times of day is an interesting question). However, the
Distribution Network Operators (the people who own the electric cables)
have always been vehemently opposed to this, and, as far as I was aware,
had been successful (to date) in blocking any attempts to allow net
metering.

Has this restriction been removed, or would something like this require
its own Export Meter, and associated contracts with Meter Operators,
Data Collectors and Electricity Suppliers? I doubt, at under 1.5kW from
time to time, that the money to be made would be worth the cost of
installing and running the meter. In this case, you are more likely to
run this simply to supply your own demand as and when it coincides with
your heating demand, and discard the extra power when it isn't needed.

As for the philosophical point (in another message) - about it being a
nice model if everyone generates what they need and puts the extra into
the grid - there is certainly a diminimus argument while this is a
minority activity. But as soon as this became commonplace, it would
present enormous management problems. The electricity networks are
designed to support power flows in certain directions at certain
volumes. As soon as everyone starts dribbling small amounts of power
into the network in the oppposite direction to originally designed,
managing the network becomes a nightmare. Likewise for managing supply
and demand. Complex mechanisms exist to ensure that supply and demand
are closely matched. These mechanisms operate through a balancing market
where discrepancies can be compensated. But only significant generators
(supply) and electricity suppliers (demand) operate in the balancing
market. No one is going to get into half-hourly balancing of minuscule
loads such as from these Sterling engines (the equipment to provide the
necessary real-time metering would be prohibitively expensive, for one
thing), so such generation will remain outside the balancing calculations.

It would take a lot of Sterling engines (and PV arrays and private wind
turbines, etc.) to destabilise these arrangements, but nevertheless, one
should be careful about the practicalities before one starts envisaging
a world in which we all use what we want when we want it, generate what
we can when we can, and use the electricity network as a big dumping
ground to import from or export to as we see fit, without constraints.

For example, in the early days of the Balancing Mechanism (introduced in
April 2002), there were price extremes of plus and minus £10,000/MWh
(1000p/kWh). In other words, when there was a shortfall of generation or
excess of demand relative to predicted levels, the cost of the marginal
power to make up the difference was 1000p/kWh. When there was excess
generation or insufficient demand relative to predicted levels, it would
cost 1000p/kWh to dump any excess generation (yes, you had to pay to get
rid of power you had generated, if it wasn't contracted!).

Of course, this was only at the margins, but it did have an impact on
prices as a whole. Balancing mechanism prices became less volatile as
generators and suppliers became better at forecasting output and demand,
but I don't think any of them would like to see a market in which this
prediction became more difficult again. Which makes Powergen's
involvement so intriguing. I guess they are expecting this to be no more
than a niche market, that has little impact on their balancing
calculations.

What we really need are better mechanisms to encourage consumers to use
electricity in a manner that works best with the efficient generation of
electricity, better power storage mechanisms (difficult) and generation
capacity that is as flexible as possible. If you can have all that and
generate the power close to demand (to minimise transmission and
distribution losses), then you have the ideal system.

Cheers,

Bruno