Re: Renewables in power cuts

On Mon, 03 Oct 2005 06:48:31 +0100 someone who may be Andy Baxter
<news4@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote this:-

>The point being that daytime and nighttime loads are different,

The loads are in fact varying all the time. For example a dark cloud
passing over an area will mean increased lighting.

>so it makes sense to have a buffer somewhere in the system.

The system already has buffers.

>Otherwise the
>remaining coal fired capacity ends up being the buffer by running at
>reduced loads when the wind is blowing.

Wind can be forecast fairly accurately a few hours ahead. Hydro
schemes running in standby can supply electricity in a few seconds,
yet emit no greenhouse gases while waiting. From a standing start a
hydro scheme will take a little over a minute to supply electricity
[1]. Gas turbine plants can start in two minutes.

These times are much less than wind speeds can be forecast over.
Thus there is no need to have coal fired plants running
inefficiently at part loads. They would be better modified to
co-fire biomass and left running continuously. That would mean that
the gas turbine plants could be moved to standby uses, except where
they provide CHP.

>Or else more plants like dinorwic
>in wales, which isn't a bad thing,

Dinorwig (the name was changed some time ago as part of a general
renaming exercise to remove some of the Anglicisation) was largely
justified as a way of soaking up the excess electricity produced by
nuclear power stations, which are essentially on or off devices,
overnight. It was expensive, but has a great future in a sustainable
electricity system. The landscape lobby have stopped a number of
large scale hydro schemes, but recently one gained approval.

>but it might make more sense to design
>each micro-generator with a micro-buffer built in.

The buffer is the surrounding electricity system. Adding a buffer at
each device adds cost, but not much capability to the supply.

The first wind farm in the UK (at Delabole) was studied in great
detail. It reduced dramatically the number of times the automatic
tap changers operated at the 33/11kV substation, because it
stabilised the local voltage. This is good for the local electricity
company as maintaining tap changers costs money.

[1] the hydro figures are for relatively modern plant. Some older
plant can take longer, but all that I have heard of can supply
within five minutes.


--
David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
I will always explain revoked keys, unless the UK government
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