[Closed] National Electricity Grid.....generation at times of low relative demand?

Various things- you can dial down other production, run pump storage, etc.

Pretty much, yes. Some attempt is made to 'store' power by such things as pumping water back up to the top reservoir of hydro-electric power stations like Dinorwic.

I think there are some industries that try to use most electricity when it is at its cheapest, too??

Rachel

http://en.wikipedia.org/wiki/Cruachan_Dam

I may be talking utter bollocks (it is standard on here, afterall) but I was under the impression that it was emitted as heat from the power lines. Like I said, I'm probably wrong.

With wind farms they can just adjust the blade pitch to reduce the power. There isn't a lot you can do with excess electricity - there are only so many pump storage sites and their capacity, as a percentage of the total grid, is pretty tiny. Hence the enthusiasm for Gas generation - very easy to control, can spin up a turbine to 500 MW in a matter of minutes and likewise spin it down to idle.

EDIT: I suspect they'd spin down the gas first if they had excess wind power to manage. All the suppliers have different supply contract terms stating what they have to provide and what they can chose to supply and the suppliers look at the spot price for electricity and adjust their capacity to maximise profit. Eg a gas turbine power station might just pump the gas to Transco rather than run turbines if the gas price exceeds the spot price for electricity (Eon do this with some of their sites).

There is a lot of research into grid-scale energy storage - large batteries - that could be built into the grid of the future. The idea of distributed generation needs to be balanced, especially with renewables in the mix, with distributed storage.
When I say batteries, think of things the size of ISO containers that store that energy. Different chemistries are being pushed to come up with something plentiful and stable enough for this.

The daily demand fluctuates between rough 30GW and 50GW so the daily variation is currently far in excess of the amount of wind power in the system at the moment. Wind generates anything from near zero to around 4GW.

One problem with wind is that as it sometimes generates almost nothing it needs near 100% backup from other sources so the public is paying for two power generation systems. Once for the wind turbines and again for the backup.

As can be seen from the charts at the link below predictable daily demand fluctuation is met in the main by increasing or decreasing gas generation and to a lesser extent coal.

http://www.gridwatch.templar.co.uk/

[i]So, imagine all these lovely wind turbines spinning happily overnight...

What happens when generation output exceeds demand?
[/i]

You'd need millions of the things to have this problem, and they'd still just phone our house as usual to ask me not to switch all the lights off after the family leaves them on 😉

Wind turbines don't really generate any "real" electricity. It's all a big scam/pr stunt, so you really don't need to worry about them producing any excess.

The simple answer is generators respond to demand, the demand being the load on the grid, as demand receeds the generators back off, generating sites with multiple generators will shut down and standby machines not required. Wind powered generation will always be able to export their maximum output to the grid as they produce such a small amount of power.

Heavy bulk users can be offered pricing deals to encourage use when other demand is low or to reduce use at high demand times, think steel works or big land drainage pumps etc, anything with big loads where you can choose when to switch.

@getonyourbike they do that in some places (really cold places for example) to stop ice forming on the power lines over night as this could pull the power lines down.

what we need is a self contained gsm-immersion unit* installed in every home with a hot water storage tank that can be remotely turned on to dump surplus generated electricity for use by the public at a knock down price....

* not my idea, obviously, I'm not that bright...

So, imagine all these lovely wind turbines spinning happily overnight...

What happens when generation output exceeds demand?

Is it so simple that generation is simply curtailed?

Apparently no such thing as a silly question......

The retailers and generators have scores of people employed to study the impact of weather and other trends to forecast what the demands of the grid are. This is layered up from a 3 year basis, with fine tuning done at nearer intervals up to intraday, and of course some installations can be switched on and off quite quickly, like gas, whilst others, like nukes, can not.

djg - you seem to know this stuff, I think igm does too, what's the short term tolerance in the system (in terms of demand spikes and troughs) 1, 2, 3%?

The whole idea of Economy 7 was to encourage users to make more use of off peak electricity. Certain power stations where never designed to change load to respond to demand and are classed as "base load generators" e.g. Nuclear Stations. Gas fired plant on the other hand can respond to changes in demand much quicker.

good question! I work firmly in the retail end, so not sure, but the spikes will be much much smaller than the grid can actually cope with which is +/- 5% I think

So, why don't we build a gigantic van de graaff generator, and use all this excess power to shoot lightning bolts at France?

We already import electricity from France via the cross channel link, it'd be a waste to fire it back (unless you have some very good targets in mind 😉

Leave France out of it. It gives us Alps, cheese, wine and saucisson sec.

As many people have pointed out, most renewables can just be left to not generate quite easily (adjust blade angles in wind turbines, be allowed to bob or spin freely in hydro). Most fossil and nuclear plants cannot, they must operate at a minimum (about 40% output), or turn off totally (they don't like this). This is because of process limits within the cycles (minimum temps etc otherwise you end up with wet steam, instead of dry, in the turbines and issues in the boilers). They cannot just disconnect their load as they have no way of controlling the generators (you might be looking at 200+ MW needing to go somewhere even when throttled, leave your generator to spin with no load and see how long that lasts!).

These do indeed get dumped into pumped storage, burned in constant loads like industrial processes and of course exported.

They just run the wind turbines backwards and make wind. That's why you always have a headwind when cycling.

One of the reasons Scotland has decided to extend the life of Hunterston B nuclear plant until 2023 is because over reliance on wind would mean in imbalance that could mean selling cheap off-peak power to England and then having to buy back expensive [peak-time] power.
The Danes effectively subsidise the Germans by having to do this

Wind farms are occasionally "bid off" during the night, for which NG pay handsomely.

"With wind farms they can just adjust the blade pitch to reduce the power. "

Turbines can do that, but they don't in this context (that I've seen).