UK GRID WATCH

Demand: This is the total demand of the entire country (but not plus exports) less any unmetered generating sources like wind but including an estimate for solar. The amber warning represents the demand level that cannot be reliably met by wood or fossil burning and nuclear generation, but must be augmented by imports, or unreliable intermittent ‘renewable’ energy.

Grid frequency is controlled to be exactly 50Hz on average, but varies slightly. A lower frequency corresponds to a higher potential demand than actual generating capacity; by allowing the frequency and voltage to go lower, the demand is reduced slightly to keep the balance, and vice versa.

Combined Cycle Gas Turbines are gas turbines whose hot exhausts are used to drive a boiler and steam turbine. This two stage process makes them very efficient in gas usage. They are also quite fast to get online – less than an hour in general, so they are used to cover (profitable) peak demand and to balance wind output.

Nuclear: Currently the UK has seven AGR designs and one relatively modern PWR. Nuclear power stations are run flat-out to maximise income. Since the cost of fuel is almost insignificant, it pays them to sell at any price they can get. Variations in output are generally signs that refuelling or maintenance is ongoing.

Wind: This is the total contributed by metered wind farms. Wind power contributes about another 30% from embedded (or unmetered) wind turbines that shows only as a drop in demand. Wind, like nuclear, will sell into any market price because turbines are expensive, wind is not and subsidies are always paid. The variability of wind leads to very high fluctuations in output.