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Challenges Remain For Integrating Large Amounts Of Wind

Published at: Dec 20, 2011
source: Renew Grid Magazine
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Wind generation is rapidly increasing worldwide, and this trend is expected to continue. But wind power is intermittent, and integrating large amounts of the resource onto current and future grids remains an issue for the electric utility industry.

In order to find a solution, the U.S. Department of Energy (DOE) collaborated with researchers at Alstom Grid Inc. to investigate the most effective methods to guide strategies, business practices and control-room tools in order to reach the U.S. goal of 20% wind power by 2030.

The research was a global effort and involved 33 electric grid operators in 18 countries. Grid operators in geographically diverse areas - including the U.S., Europe, Asia and Africa - were surveyed by researchers at Alstom Grid on best practices, lessons learned and decision support tools currently in place. The combined amount of wind power represented in the report is 141 GW, or 72% of the total installed capacity around the world.

Wind power forecasts, especially the accuracy of such reports, are extremely important to integrating wind power, according to the report. Furthermore, grid operators say that centralized forecasts are currently the best method for reliably and effectively integrating wind resources.

Centralized forecasting systems, in which a single system provides the forecast for all of the wind generators connected to a power system, can be maintained by the grid operator or outsourced. A single system combines the different forecasts and produces a single forecast.

Ninety percent of respondents have implemented or are in the process of incorporating centralized forecasts. Since the survey was completed, one U.S. grid operator has suggested utilizing a hybrid method consisting of both centralized and decentralized forecasts, according to the report.

Although wind forecasts are important to successful integration, there are limitations, including the lack of accurate ramp-event forecasting and intra-hourly forecasts, limited resolution of National Oceanic and Atmospheric Administration weather prediction models, and infrequent updates of the forecast, according to the report.

Larger penetrations of wind power can introduce new patterns and affect the flow of power in the transmission and distribution networks and cause disruptions. Congestion management is one of the most important functions of a control room, according to the report.

Approximately 55% of respondents have integrated wind forecasts into software tools in order to manage congestion. Most of the respondents were worried about the operational risk of not fully understanding the potential impacts that wind variability and forecasting errors could have on identifying transmission bottlenecks.

Congestion can be managed in several ways, according to the report; however, there is still no consensus on the best method of doing so. These approaches continue to evolve, and the report recommends more research on dealing with congestion.

When integrating larger amounts of wind, flexibility is vital to maintaining reliability. Examples of operational measures that can be used to gain more flexibility include better forecasting, larger balancing areas, efficient ancillary-service markets and faster electricity market operations.

Adding more wind also means altering the operational process. These steps include visualization of system conditions, automated decision support tools, and faster, more accurate ramping. The three most important changes that are required are more accurate wind forecasting, more flexible traditional generation and more transmission.

Some of these changes will require new regulation and market protocol, while others may need local or national policies, which could take longer to implement.

Smart grid

The smart grid is another way that grid operators can increase flexibility. A smarter grid is expected to increase the use of controllable power-electronics-based devices in transmission and distribution networks, thereby making the grid more flexible to incorporate more wind power.

For the purpose of increasing wind penetration, the following smart grid applications should be considered: demand response (DR), dynamic line rating, energy storage, plug-in electric hybrid vehicles (PHEVs) and transformer load management.

DR, PHEVs and energy storage could help grid operators balance ramps resulting from wind integration, because these applications can provide quick responses to system changes. But in order to be effective, these applications will have to be modeled and implemented in - and then controlled from within - the energy-management system.

The impact of energy storage on wind integration was ranked high among respondents, even though no studies have concluded that energy storage is absolutely essential to integrating large amounts of wind power, the report says.

The report concludes by offering recommendations and possible changes that are necessary if the U.S. wants to achieve its goal of 20% wind by 2030. Short-term recommendations for grid operators include utilizing centralized forecasts with multiple forecasting providers, making control-room improvements, changing management processes and improving overall training.

Longer-term recommendations include faster electricity markets, more transmission capacity and dashboards in control rooms.

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