5.2.4.5 GRID CONNECTED UNITS

For the immediate future it is safe to assume that the proportion of wind power in a national generating system will be small enough to allow option 1 to be chosen. It is not so clear how the energy mix will develop later in the century.

5.2.4.5.1 Control and prediction

Satisfactory AC frequency and voltage control requires that there is sufficient standby generating capacity in the overall power system. This standby plant can then be switched in whenever there is either a sudden demand surge or a sudden plant failure. At any one time therefore, a large grid system must have a substantial 'spinning reserve' of generators ready to deliver power, and others ready to be spun up to operating speed. But in Europe, demand often peaks on cold windy winter days - just when wind turbines can produce plenty of power. For these reasons, the proportion of wind power in a large system can rise to about 20% before any special control measures are needed. Beyond this amount, better prediction of power demand and supply may become necessary. The supply of wind power depends on the weather systems which traverse the nation or continent, some prediction of which may be possible within a 24 hour period. The economic viability of a system with a large proportion of wind power may depend on the accuracy of such predictions, because otherwise regular power stations must provide more spinning reserve. However for a country of reasonable size with wind farms distributed across its length and breadth, the wind is highly unlikely to drop simultaneously everywhere, and a gradual reduction can be easily accommodated.

5.2.4.5.2 Grid storage

Even hydro pumping systems are increasingly being used as general energy storage for financial return rather than specifically to meet peak demand. Specialised fuel cell systems are being developed to allow rapid conversion of electric power into chemical fluid energy (other than hydrogen) and vice versa. Increased grid storage capacities may therefore become economic in the future, in turn allowing greater wind power penetration.