Wind power need not be backed up by an equal amount of reserve power

The production of wind power varies and is harder to forecast than the fluctuations in electricity demand. Adding large quantities of wind power to power systems is therefore challenging. The power system impacts of wind power were studied in international collaboration coordinated by VTT Technical Research Centre of Finland. The results indicate that the frequently stated claim of wind power requiring an equal amount of reserve power for back-up is not correct. A substantial adjustment tolerance is already built in to our power network, and the impacts of wind power fluctuations can be further balanced through a variety of measures.

The collaboration within the International Energy Agency (IEA) Implementing Agreement for Wind Energy, coordinated by VTT, has resulted in the publication of the first state-of-the-art report assessing the international experience gained on the system impacts of wind power.

The impact of a large share of wind power can be controlled by appropriate grid connection requirements, extension and enforcement of transmission networks as well as integration of wind power production and production forecasts into system and market operation. The state-of-the-art report presents the assessments of the impact of wind power on the reliability and costs of the power system conducted in different countries.

The assessments performed in different countries are often based on substantially different assumptions. Comparison of the studies showed that in particular the assumptions concerning the use of international transmission connections and the time scale of updating wind power forecasts had a major impact on the results.

The aggregation benefits of a power system covering a large area help in reducing wind power fluctuations and improve predictability. A large power system also has a larger amount of generation reserves available, and the increased regulation effort can be implemented cost-effectively. The transmission capacity between areas is crucial for the utilisation of the benefits arising from large production areas. An electricity market in which production forecasts can be updated a few hours ahead also helps in keeping down the forecast errors and thereby the costs of balance power.

The report contains a summary of the wind power impact assessments performed in 11 countries. The assessments are divided into three categories:
1. Additional costs arising from the balancing of wind power fluctuations
2. Grid reinforcement needs due to wind power
3. Capacity of wind power to replace other power plant capacity
With wind power penetrations amounting to 10–20% of the gross electricity demand, the additional costs (per MWh of wind power) arising from the balancing of wind power fluctuations are estimated to range between1–4 €/MWh. This is less than 10% of the long-term market value of electricity.

Current wind power technology makes it possible for wind power plants to support the grid in the event of faults such as significant voltage drops and to participate in voltage regulation. Wind power plants are also able to limit their production fluctuations. The grid reinforcement needs due to wind power vary in different countries depending on how far from the consumption centres the wind power plants are constructed and how strong the existing national grid is.

Even though wind power is mainly an energy resource that replaces fossil power generation, it can also be used for replacing existing power plant capacity. In areas where wind power production is high during peak demand, wind power can replace other capacity by up to 40% of the installed wind power capacity. However, when a larger share, more than 30%, of electricity is produced by wind power and in areas where the wind power production is low during peak demand, wind power can only replace other capacity by 5–10% of the wind power capacity.

Publication: Design and operation of power systems with large amounts of wind power. State-of-the-art report:
http://www.vtt.fi/inf/pdf/workingpapers/2007/W82.pdf
http://www.vtt.fi/vtt_show_record.jsp?target=julk&form=sdefe&search=58120