National Grid and surplus current

great unwashed

Can someone tell me how the Irish national grid works in terms of this:

there is x electricity demand from the population so we have to produce x+y electricity in case demand goes up suddenly. If our demand is 4 GW as a nation then we should try to produce 4.2 - 4.5 GW in case demand changes up or down.

What happens that extra electricity? Is there an overflow-pipe-like mechanism which earths the unused electricity? Or does the extra capacity stay in the grid like a battery?

corglass

There is no excess electricity produced (well not exactly).
There are numerous generators that run at partial capacity, and have the ability to wind up/down depending on the demand situation. The difference between the required (demand) and the supply results in the frequency variation, (from the desired 50Hz)

In reality, the system always has replacement generators 'on standby' to cover for increases in demand. The faster the response required (quick increase in loads) the more expensive the backup. E.g. Gas turbine power generation. As the load continues to increase, cheaper generators are added etc. The same can operate in reverse.

In extremes, pumped storage, tike at Turlough Hill Pumped Storage can be used to supply/use excess power.

Hope this helps!;)

great unwashed

corglass wrote: »

There is no excess electricity produced (well not exactly).
There are numerous generators that run at partial capacity, and have the ability to wind up/down depending on the demand situation. The difference between the required (demand) and the supply results in the frequency variation, (from the desired 50Hz)

Thanks for such a quick reply!
I'm more interested in falling demand - say like in the case of everyone using low energy bulbs or the like. Will it really have an effect on the grid? Is what you mean by frequency variation that if everyone stops drawing electricity like in the night time as everyone is switching off their lights, the current changes frequency to adapt? (that's difficult)

The generators you are talking about above - are they located in the likes of power stations like Moneypoint? i.e. the generators in that station can wind up or down as the demand changes? (but does the station still burn the same amount of fuel ??)

corglass

Falling demand works similarly, the generators ruduce their fuel, and reduce the steam feed to the turbines, this reduces the power input to the generators. This is the same with gas turbines.

If the generation is above whats required, the frequency is 50Hz + 0.XXX and vise versa.

Frequency is the same nationally, current demand varies at each node in the network, as demand varies with fixed voltage, so the variation occurs through currenct changes.

This is a complex balancing act that Eirgrid contols in Ireland.