page_title: Wind power
section_title: Variability
hierarchical_section_title: Wind power / Wind power capacity and production / Variability
caption_attribution_description: English: Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. For wind and PV an equal distribution over Europe has been assumed and a modern wind energy turbine and PV module has been assumed. Details of the methodology are described in Kaspar et al. 2019; https://doi.org/10.5194/asr-16-119-2019
context_page_description: Wind power or wind energy is the use of wind to provide the mechanical power through wind turbines to turn electric generators and traditionally to do other work, like milling or pumping. Wind power is a sustainable and renewable energy, and has a much smaller impact on the environment compared to burning fossil fuels.
  Wind farms consist of many individual wind turbines, which are connected to the electric power transmission network. Onshore wind is an inexpensive source of electric power, competitive with or in many places cheaper than coal or gas plants. Onshore wind farms also have an impact on the landscape, as typically they need to be spread over more land than other power stations and need to be built in wild and rural areas, which can lead to "industrialization of the countryside" and habitat loss. Offshore wind is steadier and stronger than on land and offshore farms have less visual impact, but construction and maintenance costs are higher. Small onshore wind farms can feed some energy into the grid or provide electric power to isolated off-grid locations.
  The wind is an intermittent energy source, which cannot make electricity nor be dispatched on demand.
context_section_description: Electric power generated from wind power can be highly variable at several different timescales: hourly, daily, or seasonally. Annual variation also exists, but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. Intermittency and the non-dispatchable nature of wind energy production can raise costs for regulation, incremental operating reserve, and (at high penetration levels) could require an increase in the already existing energy demand management, load shedding, storage solutions or system interconnection with HVDC cables.
  Fluctuations in load and allowance for failure of large fossil-fuel generating units require operating reserve capacity, which can be increased to compensate for the variability of wind generation.
  Wind power is variable, and during low wind periods, it must be replaced by other power sources. Transmission networks presently cope with outages of other generation plants and daily changes in electrical demand, but the variability of intermittent power sources such as wind power, is more frequent than those of conventional power generation plants which, when scheduled to be operating, may be able to deliver their nameplate capacity around 95% of the time.
  Presently, grid systems with large wind penetration require a small increase in the frequency of usage of natural gas spinning reserve power plants to prevent a loss of electric power if there is no wind. At low wind power penetration, this is less of an issue.
  GE has installed a prototype wind turbine with an onboard battery similar to that of an electric car, equivalent to 60 seconds of production. Despite the small capacity, it is enough to guarantee that power output complies with forecast for 15 minutes, as the battery is used to eliminate the difference rather than provide full output. In certain cases, the increased predictability can be used to take wind power penetration from 20 to 30 or 40 percent. The battery cost can be retrieved by selling burst power on demand and reducing backup needs from gas plants.
  In the UK there were 124 separate occasions from 2008 to 2010 when the nation's wind output fell to less than 2% of installed capacity. A report on Denmark's wind power noted that their wind power network provided less than 1% of average demand on 54 days during the year 2002. Wind power advocates argue that these periods of low wind can be dealt with by simply restarting existing power stations that have been held in readiness, or interlinking with HVDC. Electrical grids with slow-responding thermal power plants and without ties to networks with hydroelectric generation may have to limit the use of wind power. According to a 2007 Stanford University study published in the Journal of Applied Meteorology and Climatology, interconnecting ten or more wind farms can allow an average of 33% of the total energy produced (i.e. about 8% of total nameplate capacity) to be used as reliable, baseload electric power which can be relied on to handle peak loads, as long as minimum criteria are met for wind speed and turbine height.
  Conversely, on particularly windy days, even with penetration levels of 16%, wind power generation can surpass all other electric power sources in a country. In Spain, in the early hours of 16 April 2012 wind power production reached the highest percentage of electric power production till then, at 60.5% of the total demand. In Denmark, which had power market penetration of 30% in 2013, over 90  hours, wind power generated 100% of the country's power, peaking at 122% of the country's demand at 2  am on 28 October.
  A 2006 International Energy Agency forum presented costs for managing intermittency as a function of wind energy's share of total capacity for several countries, as shown in the table on the right. Three reports on the wind variability in the UK issued in 2009, generally agree that variability of wind needs to be taken
caption: Seasonal cycle of capacity factors for wind and photovoltaics in Europe under idealized assumptions. The figure illustrates the balancing effects of wind and solar energy at the seasonal scale (Kaspar et al., 2019).[131]
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