A method of controlling operation of a component connected to an electricity supply network, the component being either a generator or load of a type that is able to store energy within and is operable at a range of power levels between zero and a maximum power C D, the method comprising the steps of: (a) Operating the component over a time period such that, within the time period, adjustments are made to a rate at which energy is transferred between the component and the supply network in accordance with a baseline power function B(t); and (b) Simultaneously operating the component over the time period such that adjustments are, in addition, made to the rate at which energy is transferred between the component and the supply network in accordance with a fast-moving power function F(t), such that the fast-moving power function F(t) is superimposed on the baseline power function; wherein the baseline power function B(t) is derived from a slow-moving power function D(t), such that for δ « 1: B t = δ C D, if D t < δ C D, B t = D t, if δ C D ≤ D t ≤ 1 − δ C D, and B t = 1 − δ C D, if D t > 1 − δ C D; wherein if adjustments are made to the rate at which energy is transferred between the component and the supply network in accordance with the slow-moving power function D(t), the component would benefit economically from a variation in a prevailing price of electricity on the network or a variation in a value that can be derived, directly or indirectly, from the supply of electricity on the network; and adjustments made to the rate at which energy is transferred between the component and the supply network in accordance with the fast-moving power function F(t) are adjustments that are responsive to and such as to counter imbalances between power generation and power consumption over the electricity supply network, these adjustments having a high probability of being much less than the maximum power C D. (a) Operating the component over a time period such that, within the time period, adjustments are made to a rate at which energy is transferred between the component and the supply network in accordance with a baseline power function B(t); and (b) Simultaneously operating the component over the time period such that adjustments are, in addition, made to the rate at which energy is transferred between the component and the supply network in accordance with a fast-moving power function F(t), such that the fast-moving power function F(t) is superimposed on the baseline power function; wherein the baseline power function B(t) is derived from a slow-moving power function D(t), such that for δ « 1: B t = δ C D, if D t < δ C D, B t = D t, if δ C D ≤ D t ≤ 1 − δ C D, and B t = 1 − δ C D, if D t > 1 − δ C D; wherein if adjustments are made to the rate at which energy is transferred between the component and the supply network in accordance with the slow-moving power function D(t), the component would benefit economically from a variation in a prevailing price of electricity on the network or a variation in a value that can be derived, directly or indirectly, from the supply of electricity on the network; and adjustments made to the rate at which energy is transferred between the component and the supply network in accordance with the fast-moving power function F(t) are adjustments that are responsive to and such as to counter imbalances between power generation and power consumption over the electricity supply network, these adjustments having a high probability of being much less than the maximum power C D. the baseline power function B(t) is derived from a slow-moving power function D(t), such that for δ « 1: B t = δ C D, if D t < δ C D, B t = D t, if δ C D ≤ D t ≤ 1 − δ C D, and B t = 1 − δ C D, if D t > 1 − δ C D; wherein if adjustments are made to the rate at which energy is transferred between the component and the supply network in accordance with the slow-moving power function D(t), the component would benefit economically from a variation in a prevailing price of electricity on the network or a variation in a value that can be derived, directly or indirectly, from the supply of electricity on the network; and adjustments made to the rate at which energy is transferred between the component and the supply network in accordance with the fast-moving power function F(t) are adjustments that are responsive to and such as to counter imbalances between power generation and power consumption over the electricity supply network, these adjustments having a high probability of being much less than the maximum power C D.