Texas Reliably Integrates Growing Wind Resource

If you have been paying attention to renewable energy growth in the U.S. during the past decade, you likely know that Texas leads the nation in wind power development.

In fact, the portion of the state that is served by the Electric Reliability Council of Texas (ERCOT)—about 75% of land area and about 90% of the electric load—ended 2014 with nearly 12,500 MW of installed wind generation capacity. Interconnection agreements and studies indicate installed capacity could surpass 18,000 MW by the end of this year, potentially topping 21,000 MW by the end of 2016.

At 14% of total generation capacity in 2014, wind provided about 10.6% of the energy used on the ERCOT grid last year, and instantaneous output reached a record 11,154 MW this past February.

Although our competitive energy-only market does not favor one fuel over another, ERCOT, as the independent system operator, has worked to understand the unique aspects of wind resources so we can integrate them effectively, efficiently, and reliably into grid and market operations.

Managing Rapid Growth in the Nation’s Leading Wind Power State

The growth in wind capacity occurred rather quickly, from 116 MW in 2000 to more than 10,000 MW by the end of 2012, surpassing the Renewable Portfolio Standard set forth in 2005 by the Texas Legislature—10,000 MW by 2025—more than a dozen years early.

At first, most wind capacity in the ERCOT region was concentrated in West Texas, where there was little demand at the time and few paths to move the power to load centers within the ERCOT grid.

By the end of 2013, transmission providers had completed about 3,600 miles of new 345-kV transmission facilities, with capacity of 18,500 MW, to move power from the West Texas and Panhandle areas to other parts of the grid. This $6.9 billion Competitive Renewable Energy Zones project was directed by the Texas Legislature and the Public Utility Commission of Texas.

Using Future Forecasts to Support Real-Time Success

As a result of rapid growth, ERCOT planners and operators have learned a great deal in a short period of time about how wind farms perform and what to expect under a variety of conditions.

The forecasts that help ERCOT manage this dynamic resource in its nodal market must be as accurate as possible. In daily operations, ERCOT experts evaluate wind forecasts—which consider location, technology, and weather patterns—to prepare for likely outcomes and position the system to maintain reliability. ERCOT also takes wind generation variability into account when determining ancillary services requirements.

For planning purposes, a combination of experience, improved data, and wind generation technology has led ERCOT to change how we model the capacity contribution from wind generation resources, based on expected performance during peak demand, for both its seasonal and longer-term resource adequacy assessments.

Before we had significant historical data, ERCOT counted wind resources at 10% of installed nameplate capacity. In 2007, we began to count wind capacity at 8.7%, based on a probabilistic assessment of reliability compared to a dispatchable resource. This “effective load carrying capability” remained in place until 2014.

After studies in 2010 indicated ERCOT could expect a higher percentage of installed capacity over peak, we tested these assessments and ultimately changed our practice. The passage of a new market rule in October 2014 established a mechanism that enables ERCOT to predict more accurately in our planning process the wind resources upon which we can expect to rely as these resources continue to increase and change.

The new method uses historical data from the top 20 peak hours each year over a six-year period to project summer and winter wind availability on peak. So, rather than applying a set percentage to the entire portfolio, the formula accounts for performance improvements and the location of facilities. In recent years, development has increased along the Gulf Coast, where coastal breezes are more likely to produce higher outputs during hot summer afternoons, when power demands in the ERCOT region are greatest.

Based on the new rules, ERCOT’s 2014 Peak Average Wind Capacity Percentage for facilities along the Gulf Coast is 56% during the summer and 36% during the winter. We expect facilities in other parts of the ERCOT region will provide 12% of nameplate capacity during the summer and 19% during winter.

Continuing to Adapt and Look Ahead

Currently, it appears wind generation will continue to grow in the ERCOT region. As we integrate more of this growing resource, as well as emerging utility-scale solar power resources, we will continue to learn and apply more understanding of our diverse generation mix to provide a reliable grid and efficient market.

— H.B. “Trip” Doggett is president and CEO, Electric Reliability Council of Texas Inc.