It is interesting to speculate how Grid Control might handle
large amounts of varying power generated by large wind farms at
relatively short notice but which cannot be relied upon to last for a specified period of time.
Grid Control Staff know the typical load requirements for the day based upon their experience; for example, day of the week, the season, whether or not it is a holiday, what the weather is like, and so on.
They know the generating costs per unit of electricity from each power station, and they arrange that those delivering the cheapest power (ie the nuclear power stations) take the base load first.
When the load increases above about 20% of total capacity then they progressively bring onto line the coal fired and the oil and gas fired stations, chosen in relation to their generating costs.
Large power stations, which are the most efficient, cannot be started from cold and put under load immediately.They require to have their temperature raised slowly over a significant number of hours before having the load imposed upon them.
To cater for small variations in demand, Grid Control arrange for a “spinning reserve”
to be available to deal with relatively small short term increases in demand. “Spinning reserve” means a steam turbine or a gas turbine that is kept in an immediate state of readiness (at operating temperature) but not taking any load. This is obviously very inefficient and therefore the spinning reserve is maintained at the minimum level consistent with the load-following requirement.
Picture the situation on a Sunday evening when the base load on the grid is quite low and it is being fed by the most cost efficient power stations.
A stiff breeze springs up. The local wind farm now has the potential to supply electrical energy at a rate of up to 240 mega-watts, but with no guarantee of being able to maintain the level of supply for a fixed period of time.
What does Grid Control do?
Nigel Deacon / Habitat21 website /2006
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