Variability of Wind and Wind Power

The installed capacity for wind power is increasing substantially in response to the worldwide interest in low-emissions power sources and a desire to decrease the dependence on petroleum. The European Union directive 2009/28/EC enforces the mandatory target of a 20 % share of energy from renewable sources in overall Community energy consumption by 2020 and a mandatory 10 % minimum target to be achieved by all Member States for the share of biofuels in transport petrol and diesel consumption by 2020. These targets may require between 30 and 40 % of the electricity in the European Union to come from renewable energy sources by 2020. In the U.S., the world's top wind producer (The Guardian, 2008), wind currently makes up just one percent of the energy supply. Wind power generation share is expected to grow up to 20% in the USA by 2030 (EnerNex, 2006; U.S. D.O.E., 2008). Moreover, many U.S. states have legislated similarly ambitious renewable energy portfolio standards. These goals were set without regard for the fact that many in the scientific community have concluded a theoretical wind penetration limit of only 20% due to the degradation of system reliability (DeCarolis et al., 2005). The Department of Energy states that there is no fundamental technical reason why 20 percent of wind energy cannot be assimilated into the grid by 2030. To help make its point, the agency debunks the reliability myth in its fact sheet on Wind Energy Myths (U.S. D.O.E. 2005). According to (Feldman, 2009), the renewable output could leap to 40 percent of the Irish electricity share; in Denmark to 33 percent; in Portugal to 28 percent; and in Germany and Greece to 25 percent. After 2020, a higher proportion may be needed. A significant amount of this renewable electricity is likely to come from wind, and the variability of this power needs to be managed. With this amount of wind generation, the future electricity markets could be very different to those of today: instead of thermal power stations dominating the system, the market could be dominated by large amounts of price-insensitive nuclear and wind power, combined with highly intermittent output from the wind farms (Pöyry PLC, 2009). The extent of uncertainty and variability in wind generation makes this resource different from the traditional, dispatchable generation resources, with the result that wind power generation cannot be readily integrated into standard system operating procedures (IEA, 2009). At relatively low levels of installed capacity, wind turbines and the output from large wind farms can essentially be absorbed into traditional system operations without