Energy Systems and Technologies for the Coming Century ...

one hour to the next – corresponding to that their energy exchange can change from zeroto full or from full to zero within 3 hours. They can still regulate their power within thefull range for shorter periods.For larger wind farms this means that the up-regulating of the generation is restricted(this is easy to implement), and the down-regulation of the production must be controlled– either by reacting in due time before larger changes in wind energy are expected or byadding compensating power regulation capabilities, e.g. storage units.The customer’s active and reactive power exchange, E P i and E Q i , will be accounted at theactual prices, c p i and c Q i : Note, that these amounts can be positive or negative, depending on the direction of theenergy flow and if the prices are negative.In addition, the customer will pay a daily amount, C P E and C Q E , relative to the dailyenergy flow in both directions, E P d and E Q d : where || ||an amount relative to the maximum power exchange on daily basis: max max and finally a fixed amount, C S , for being connected to the power system, depending onthe rated power capacity of the connection. These cost elements, C E , C p and C S ,correspond to the customer’s use of the power system.The total daily amount to be accounted is thus: Note, that this amount can become positive or negative – negative means that thecustomer shall pay the amount to the power system operator and positive means that thepower system operator shall pay the amount to the customer – corresponding to the signof the power flow. All values will be recorded on hourly basis as basis and documentationfor the billing.3.3 Frequency responseAll power units must be designed to operate properly within a wider frequency range,45..55 Hz. The active power unit’s active power must automatically respond to (larger)deviations (from nominal, f 0 ) of the line frequency, f – see Figure 6.Risø International Energy Conference 2011 Proceedings Page 182