Grid operators in Texas and Colorado have figured out how to successfully integrate renewable penetration levels of up to 50%, showing that growing concerns about reliability issues stemming from increases in variable generation may be overblown, according to a new study.
Concerns that higher levels of renewables under the EPA's proposed Clean Power Plan, especially those raised by recent reports from the North American Reliability Corporation (NERC), fail to credit the capabilities of modern operations, reports a new study from the Brattle Group.
“The success to date of [the Electric Reliability Council of Texas (ERCOT)] and Xcel Energy Colorado shows that integrating variable renewable energy at penetration levels of 10% to 20% on average and at times above 50% – i.e., high relative to the current levels in most of the United States – is possible,” the consulting and research firm writes in "Integrating Renewable Energy into the Electricity Grid,' its report released this week.
The study was provoked by one of several conclusions in recent NERC reports on the feasibility of the EPA Clean Power Plan (CPP), according to Matt Stanberry, Marketing and Development VP for Advanced Energy Economy Institute, which commissioned the study.
NERC identifies possible reliability problems
NERC raises three key questions about renewable energy integration in its assessment of the CPP building blocks for emissions reductions, Stanberry explained:
- With the many expected coal plant closures, will there be enough basic capacity?
- With increased reliance on natural gas, will there be an adequate supply to meet both heating and electricity generation needs?
- With increased reliance on renewables, can grid operators across the country reliably manage the increased variability?
Both AEE and Brattle found NERC’s concerns “overstated,” Stanberry said. But this Brattle study only addresses the question of whether the current ability to integrate variable renewables will create reliability challenges. It leaves aside issues such as the time necessary for construction of new generation and transmission assets, which NERC found to be too long to comply with the EPA's proposed 2020 start date for emissions compliance.
“It is about the technological and operational techniques grid operators are using to integrate high levels of renewables," Stanberry said.
Integration challenges will vary regionally depending on the generation mix and grid status, the study reports. But using operations and technologies developed and planned by ERCOT and Xcel Colorado, ISOs, RTOs and utilities across the country can reliably integrate increasing shares of variable renewables with only “modest operational challenges.”
One threat to reliability raised by NERC last year was whether reserves to support renewables would be adequate. A conventional grid built around fossil fuel and nuclear generation historically responded automatically to frequency changes with essential support services, it explained.
But “as variable resources increase, system planners must ensure the future generation and transmission system can maintain essential services [including frequency and voltage support, operating reserves, ramping capability, and disturbance performance] that are needed for reliability.”
Because the CPP gives developers incentives to expand to displace existing coal generation, wind and solar capacity could grow 5% per year, NERC found. That would “significantly increase the demand for reactive power and ramping flexibility.”
It would also necessitate more frequent ramping and, therefore, increased cycling of conventional generation. The result would be more maintenance and/or more outages, and either would necessitate more reserves. “Additional assessments, including interconnection-wide studies, will be needed as the resource plans unfold to better understand the impacts," NERC reported.
Additional renewables “will not only increase the need for ancillary services (e.g., frequency response and reserves) but also create additional planning and operational needs,” a newer NERC study reported.
“To accommodate the higher penetration of [variable energy resources]," it added, "operators need to adjust their practices and rely on more flexible resources to ensure voltage and frequency support are maintained within acceptable margins while maintaining frequency."
Brattle gets in the discussion
In fact, Brattle reports, the studies NERC calls for would be redundant because the adjustments are already being made in real time by real grid operators in Texas and Colorado.
“The generation mix is undergoing a transformative change and the Clean Power Plan is expected to accelerate it,” NERC vice president of reliability assessment and performance analysis Tom Burgess recently explained. “The goal of [the NERC] assessment was to identify threats to reliability.”
The Brattle study should be part of that discussion because, Stanberry said, it is vital to recognize ERCOT and Xcel Colorado are already successfully integrating high levels of renewables into reliable electricity systems.
“The thing that stood out,” he said, “was the variety of operational and technological techniques that grid operators are already using and the amount of continued innovation they are working on that will allow even higher levels of renewables penetration going forward.”
Colorado and Texas
The Xcel Energy Colorado balancing area’s peak load in 2013 was 6,646 MW. Wind accounted for 18.7%, even though Xcel Colorado is not part of a regional system and has no day-ahead or real-time energy market on which to rely, Brattle explains. The result is “challenges that make Xcel Energy Colorado a good case study for integrating variable renewable energy sources.”
It has been successfully addressing the system operational issues associated greater renewables penetration by using “changes in ancillary service requirements, improved wind forecasting, and increases in generation flexibility.”
The Texas installed wind capacity, which is twice that of any other state, provided 10% of ERCOT’s total demand in 2014. During some hours, it was almost 40% of total demand. And ERCOT expects penetration on its isolated system could almost double again by 2017.
ERCOT is therefore a study in renewables integration without the option to mitigate imbalances with geographic distribution of resources, Brattle explains. Instead, it has:
- moved to a dynamic, five-minute market,
- identified competitive renewable energy zones (CREZ) for streamlined transmission development to maximize delivery of the available resource
- improved calculation of wind’s capacity value to stimulate market forces in providing peak demand support
- incorporated advanced wind forecasting
- supported turbine technology that minimizes the need for grid support
- redesigned its ancillary services market for greater efficiency
- stepped up its demand response programs
The Clean Power Plan
The levels of wind incorporated into the Xcel Colorado and ERCOT systems “are much higher than those envisioned by EPA in its proposed state emissions targets under the Clean Power Plan,” American Wind Energy Association Research Director Michael Goggin wrote in his review of the Brattle study. “EPA could significantly strengthen those targets without any electric reliability concerns.”
Costs for renewables integration on the systems studied “have generally been small to modest,” Brattle adds. “ERCOT estimated the cost of integrating its first 10,000 MW of wind, approximately the capacity currently deployed, to be about $0.50 per MWh of wind generation.”
The ability to integrate renewables will continue to improve, according to Brattle. Renewables technology such as smarter inverters and more cost effective batteries will make reliability easier to maintain.
Technology unrelated to renewables will also continue to advance. That includes the collation of historical weather data and forecasting and smarter customer-sited infrastructure to streamline demand management.
Stakeholders, including NERC planners as well as the public, policymakers, and other grid operators, need to be aware of what is possible, Stanberry said.
“Integration of variable renewable energy at levels of penetration as high as those reliably managed by ERCOT and Xcel Energy Colorado, if not higher, should not be seen as a significant technical obstacle to compliance with EPA’s proposed Clean Power Plan,” Brattle reports.
Lessons learned in these case studies, it adds, “should help ISOs and utilities ensure that significantly larger amounts of variable renewable energy can be integrated at small to modest costs while maintaining high levels of reliability.”
