Wind power does not need 100% back-up capacity

A detailed analysis by the Technical Research Centre of Finland

One of the major drawbacks of wind energy is that it requires extra reserve capacity to compensate for the intermittency of its power output. Opponents of wind energy even contend that it requires a 100% back up: they claim each megawatt of wind power would require a megawatt from a combined cycle power plant as a standby. A study by the Technical Research Centre of Finland has now demonstrated this last claim to be incorrect.

Size matters

The study 'Design and operation of power systems with large amounts of wind power' was commissioned by the International Energy Agency (IEA) for its Wind Implementing Agreement, and resulted in a state-of-the-art report. It shows that the amount of back up needed for wind energy varies greatly according to the systems’ characteristics. The size of the system and the correlation of wind production with peak demand are two major and decisive factors.

In systems that cover a large area, wind-forces vary from region to region, leading to an aggregation benefit. Large systems are also more stable, making it easier to compensate the intermittency of wind power. Moreover, the increased regulation efforts associated with wind energy are implemented more cost-effectively in large systems.

Limiting the impact of intermittency

The impact of intermittency and the need for back-up capacity can be controlled and limited. Useful actions are:

• Creating appropriate grid connection requirements
• Extending and enforcing transmission networks
• Integrating wind power production and production forecasts into system and market operations

60% back up

The conclusion of this study is clear. Though a large part of wind capacity does indeed require another plant to be on stand-by, this back-up requirement never reaches 100%. In areas where wind production is high during peak demand and the share of wind is no more than 30% of production, a mere 60% back up would be sufficient. In other cases, larger back-up capacities might be required, up to 95% at worst.

Finally, the influence of wind power on the systems management does not need to be purely negative. Recent wind power technology makes it possible for wind power plants to participate in voltage regulation and to support the grid in the event of faults such as significant voltage drops.