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The impacts of wind power in the electricity system depend to a large extent on the:
- level of wind power penetration;
- grid size;
- generation mix of electricity in the system.
Wind energy penetration at low to moderate levels is a matter of cost, as demonstrated by various national and regional integration studies. And the integration costs related to the impacts listed above are fairly modest.
For low penetration levels of wind power in a system, system operation will hardly be affected. Currently (in 2008) wind power supplies less than 4% of the overall EU electricity demand, but there are large regional and national differences in penetration, as shown in Figure 1.2.
The established control methods and system reserves available for dealing with variable demand and supply are more than adequate for dealing with the additional variability at wind energy penetration levels of up to around 20%, depending on the nature of a specific system. For higher penetration levels, some changes to systems and their method of operation may be required to accommodate the further integration of wind energy.
The impacts of wind power on the power system can be categorised into short and long-term effects. The short-term effects are caused by balancing the system at the operational timescale (minutes to hours), whereas the long-term effects are related to the contribution wind power can make to the adequacy of the system (that is its capability to reliably meet peak load situations).
Locally, wind power plants interact with the grid voltage, just like any other power station. In this context, steady state voltage deviations, power quality and voltage control at or near wind farm sites must all be taken into consideration. Wind power can provide voltage control and active power (frequency) control. Wind power plants can also reduce transmission and distribution losses when applied as embedded generation.
On the system-wide scale, there are other aspects to consider.
- Wind power plants affect voltage levels and power flows in the networks. These effects can be beneficial to the system, especially when wind power plants are located near load centres, and certainly at low penetration levels. For example, wind power plants can support the voltage in the system during fault (low voltage) situations. Also, wind plants that have a reactive power control system installed at the end of long radial lines benefit the system, since they support the voltage in (normally) low voltage quality parts of the grid.
- Wind power may need additional upgrades in transmission and distribution grid infrastructure, as is the case when any power plant is connected to a grid. In order to connect remote high resource sites, such as offshore or very large wind plants in remote mountainous areas, to the load centres, new lines need to be constructed (just as new build pipelines had to be built for oil and gas). In order to maximise the smoothing effects of geographically distributed wind, and to increase the level of firm power, additional cross-border transmission is necessary to reduce the challenges of managing a system with high levels of wind power.
- Wind power requires measures for regulating control, just as any other generation technology and, depending on the penetration level and local network characteristics, it affects the efficiency of other generators in the system (and vice versa).
- In the absence of sufficient intelligent and well managed power exchange between regions or countries, a combination of (non-manageable) system demands and generation may result in situations where wind generation has to be constrained.
- Finally wind power plays a role in maintaining system stability and contributes to the system adequacy and security of supply.
For an overview and categorisation of the power system effects of wind power, see the table below.
Table 2.1. Power system impacts of wind power, causing integration costs
Effect or impacted element Area Timescale Wind power contribution Short-term effects Voltage management Local/regional Seconds/ minutes Wind farms can provide (dynamic) voltage support (design dependent) Production efficiency of thermal and hydro System 1-24 hours Impact depends on how the system is operated and on the use of short-term forecasting Transmission and distribution efficiency System or local 1-24 hours Depending on penetration level, wind farms may create additional investment costs or benefits. Spatially distributed wind energy can reduce network losses. Regulating reserves System Several minutes to hours Wind power can partially contribute to primary and secondary control Discarded wind) energy System Hours Windpower may exceed the amount the system can absorb at very high penetrations Long-term effects System reliability (generation and transmission adequacy System Years Wind power can contribute (capacity credit) to power system adequacy
A graphical overview of the various impacts of wind power in the power system is given in Figure 2.7. It shows the local and system wide impacts, as well as the short and long-term impacts, for the various affected aspects of the power system, which include grid infrastructure, system reserves and system adequacy.
Fig. 2.7. System impacts of wind power (IEA Wind Task 25, Holtinnen 2007). Issues which are within the scope of Task 25 are circled in red.
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