Wind integration and research challenges

Phil Carson | Nov 01, 2011

 

Wind penetration is reaching 20 percent of total, annual energy demand and more than 50 percent in a given one-hour period in parts of the U.S., including Colorado and Texas, and Europe, according to a panel of experts from the Electric Power Research Institute (EPRI).

"These examples provide a picture of challenges that may be faced by operators and planners to ensure reliable operation and they point to areas where integration cost impacts can be reduced," Aidan Tuohy, a senior project engineer in the grid operations and planning group at, said during an EPRI conference call devoted to the subject yesterday.

Tuohy also leads an EPRI program task force on bulk system integration of variable generation and helped produce the April 2011 EPRI report titled "Impacts of Wind Generation Integration," available for download from the EPRI website.

"Integration is a leading candidate for cost reductions for wind," added Bryan Hannegan, EPRI vice president for environment and renewables. "Wind integration has not been mastered, particularly to the bulk power system at high penetration. Integrating wind involves other assets such as energy storage or transmission lines. And those drive costs in a big way."

"Integration challenges come from multiple aspects and impact costs in different ways, depending on different system factors, which include the generation mix, the penetration level of wind resources, system operating procedures—including the use of wind forecasting—the transmission system and other factors," Tuohy said.

All these factors interact with each other to impact the system and affect the cost of integrating wind, Tuohy said.

Challenges that can be mitigated by research include:

• Balancing wind's variability and, thus, uncertainty as a resource. The system needs "operational flexibility" to reliably and economically integrate wind. "Operational flexibility" means having the ability to use existing generation (gas turbines or other rapid resources) to ramp up to support ramp downs in wind.
• Transmission standards and technologies are needed to ensure that wind turbines, which have different electrical characteristics than conventional generation, do not cause issues as higher penetration is reached.
• Long-term system adequacy. Increased wind penetration brings greater variability and uncertainty, which will induce increased cycling of conventional generation, possibly affecting long-term sustainability of conventional generation.

 

The industry's response to these challenges will affect the cost of integrating wind, Tuohy said.

Studies have indicated that integration costs can range from zero dollars per megawatt hour for very flexible systems with sufficient transmission and low penetration of wind resources to as much as $6 per megawatt hour for systems with higher penetration and the need to increase transmission capacity and more flexible resources, according to Tuohy. These estimates depend on specific system characteristics and the methods used to derive integration costs, he added.

The research on integration is taking two basic tacks. One area of exploration is developing the tools and techniques to assist system planners in figuring out the proper mix of generation and transmission resources to handle wind, particularly when the wind resource is distant from load.

The other active area of research is developing tools to cope with wind's variability.

"I'm talking about advanced methods to capture the uncertainty of wind, so you can build day-ahead and week-ahead forecasts into system planning," Tuohy said. "Forecasting is one of the most important areas. That's a somewhat mature field, but it remains an active area of research. We need to know not just how the wind will behave, but we need to give system operators more situational awareness of wind's behavior over the next few hours."

Lessons learned from high penetration wind areas may serve other entities in other areas of the country, Tuohy said.

"Colorado has seen somewhere in the region of 15 percent to 17 percent of its total annual energy demand being met by wind," Tuohy said. "At certain hours, 53 percent to 54 percent of demand there is being met by wind power. In ERCOT, the Texas system, it's gotten to 10 percent and above of total annual energy demand.

"Other areas include the Midwest," he added. "The Midwest Independent System Operator there has 5 percent to 6 percent penetration. Hawaii and its islands are seeing significant penetration, above 10 percent. At certain hours of the year they get more than 40 percent of their energy needs from wind."

Generally speaking, penetration is measured at the ISO level, because the system operator is the party actually dealing with the variability and uncertainty challenges. So they're the ones determining the system needs to cope with variability.

No significant failures in terms of blackouts or brownouts due to wind integration.

"There haven't been any issues dealing with the variability and uncertainty as far as I know. Different systems have used different techniques to deal with large ramps. In some areas, it's using the transmission system to get as much wind energy as possible out of an area. Other areas will store the wind energy if they can, using pumped hydro storage, for example. Other areas may use quick-responding gas turbines. Or they may have some demand acting as a resource.

"Know or deciding what the right proportion of different technologies in your generation portfolio is a significant problem," concluded Revis James, an EPRI director for generation. "One research issue is the very question of how one does long-term planning effectively to ensure that you have an appropriate proportion of generation resources. And that's an active area of research as well."

Phil Carson
Editor-in-chief
Intelligent Utility Daily
pcarson@energycentral.com
303-228-4757