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At high penetrations, the expected peak production of wind-generated electricity may be more important; while there is no generally accepted measure of the relevant proportion, measures may include expected peak wind output minus firm export capacity over minimum demand levels (and possibly corrected for minimum base-load generation that cannot be economically shut down, such as nuclear). All of these figures should be treated and used with caution, as the relevance or significance (or any implied limits) will be highly dependent on local factors, grid structure and management, and existing generation capacity.
* As the fraction of energy produced by wind ("penetration") increases, different technical and economic factors affect the need for [[grid energy storage]] facilities, [[Energy demand management|demand side management]], grid import/export, and/or other management of system load. Large networks, connected to multiple wind plants at widely separated geographic locations, may accept a higher penetration of wind than small networks or those without storage systems or economical methods of compensating for the variability of wind. In systems with significant amounts of existing [[Pumped-storage hydroelectricity|pumped storage]], [[hydropower]] or other [[
* In jurisdictions where the price paid to producers for electricity is based on market mechanisms, revenue for all producers per unit is higher when they produce when prices are higher. The profitability of wind farms will therefore be higher if their production schedule coincides with these periods (generally, high demand / low supply situations). If wind represents a significant portion of supply and wind farm output is highly correlated, overall revenues would be lower. In economic terms, the [[marginal revenue]] of the wind sector as penetration increases may diminish.
* Depending on the profile of other generation, strong wind generation at times of low demand may result in an excess of supply, which can harm grid stability, as certain generation types are not maneuverable. If mechanisms to export, store or otherwise divert this energy do not exist or are insufficient, wind turbines may have to curtail their output (for example, by changing the pitch of the turbine blades). This is a normal operating procedure that can be handled by turbine operators and control software. It reduces, however, the revenue generated by the wind plant and will affect the economic viability of wind production. Some jurisdictions - notably Germany - require grid operators to purchase from renewable sources first. In other cases, grid pricing procedures may allow for nil or negative prices, providing incentives to market participants to curtail production or increase load (for example, for storage). Excess supply events which may require curtailment can be expected to increase with wind penetration, which may also encourage the development of storage solutions.
* Although penetration is generally stated in terms of nameplate capacity (peak output) over peak demand, at higher penetrations of wind generation, penetration may be better measured as peak wind output over low demand plus export and storage.<ref>http://www.uwig.org/OklahomaCity/Soder.pdf Presentation on maximum wind penetration in Nordic grid</ref>
* On most large power systems a moderate proportion of wind generation can be connected without the need for storage. For larger proportions, storage may be economically attractive or even technically necessary. The profile of other generation facilities in the system (nuclear, coal, natural gas, hydro, etc.) will also influence the potential need for storage. At present, there are few large systems (for example, at the national or regional level) with sufficiently high wind generation to drive demand for storage (or other solutions, such as export, have been more economical), and discussion of the issue and potential upper limits for wind penetration remain largely hypothetical.
* Electricity demand is variable but generally very predictable on larger grids; errors in demand forecasting are typically no more than 2% in the minutes-hours-day ahead timeframe. Depending on the demand profile and ___location, local weather conditions - particularly temperature - may be the primary driver of demand, and the sensitivity of demand to prediction errors may be well understood. Wind energy production can also be [[Wind Power Forecasting|forecast]], but there is considerably less experience predicting wind speeds, and the time frame of forecasts and sensitivity factors less well understood. At present, error rates for predicting wind production at important timeframes for grid operators (hours and day-ahead) are significantly higher than for predicting demand.
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* Long-term storage of electrical energy involves substantial capital costs, space for storage facilities, and some portion of the stored power will be lost during conversion and transmission. The percentage retrievable from stored power is called the "efficiency of storage." The cost of compensating for the variability of wind has been studied extensively at low to medium penetrations, but would be expected to rise with higher penetration levels; the increase in costs with significantly higher penetration may be non-linear as the variability becomes more significant at higher levels, and particularly if storage needs to be purpose-built for wind.''See: [[Grid energy storage]]''
* In energy schemes with a high penetration of wind energy, secondary loads, such as desalination plants and electric boilers, may be encouraged because their output (water and heat) can be stored. The utilization of "burst electricity", where excess electricity is used on windy days for opportunistic purposes greatly improves the economic efficiency of wind turbine schemes. An ice storage device has been invented which allows cooling energy to be consumed during resource availability, and dispatched as air conditioning during peak hours. Various other potential applications are being considered, such as charging plug-in electric vehicles during periods of low demand and high production; at present, the scale at which such technologies are employed is relatively low.
* In [[Colorado]], a test facility financed with the cooperation of the National Renewable Energy Laboratory will produce hydrogen from wind power that will be used for electricity production during peak hours. This hydrogen could also be used in [[hydrogen vehicle]]s. Production costs are estimated at $8 per kilogram (roughly the equivalent of one U.S. gallon of gasoline), or approximately "three times as expensive as using gasoline".<ref>http://www.mercurynews.com/mld/mercurynews/business/16260527.htm Mercury News article on Wind/Hydrogen study</ref>
* One solution currently being piloted on wind farms and in other applications, is the use of rechargeable [[flow battery|flow batteries]] as a rapid-response storage medium [http://www.memagazine.org/backissues/membersonly/oct05/features/rerere/rerere.html]. [[Vanadium redox battery|Vanadium redox flow batteries]] are currently installed at [[Huxley Hill Wind Farm, Tasmania|Huxley Hill wind farm]] ([[Australia]]), [[Tomari Wind Hills]] at [[Hokkaido]] ([[Japan]]). A further 12 MWh flow battery is to be installed at the [[Sorne Hill wind farm]] ([[Republic of Ireland|Ireland]]) [http://www.leonardo-energy.org/drupal/node/959]. The supplier concerned is commissioning a production line to meet other anticipated orders.
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1. Power generation for periods of little or no wind generation can be provided by retaining the existing power stations. The cost of using existing power stations for this purpose may be low since fuel costs dominate the operating costs. The actual cost of paying to keep a power station idle, but usable at short notice, may be estimated from published [[spark spread]]s and [[dark spread]]s. As existing traditional plant ages, the cost of replacing or refurbishing these facilities will become part of the cost of high-penetration wind if they are used only to provide operational reserve.
2. The aggregate maximum rate of change of generation from a close to 100% wind scenario may be lower than the existing rate of change of total generation due to unscheduled power station outages (for example, in the UK).{{
3. Automatic load shedding of large industrial loads and its subsequent automatic reconnection is established technology and used in the UK and US, and known as [[Reserve service|Frequency Service contractors]] in the UK. Several GW are switched off and on each month in the UK in this way. Reserve Service contractors offer [[Peaking power plant|fast reponse gas turbines]] and even faster diesels in the UK, France and US to control grid stability.
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