It has been fascinating to follow system operators’ ways of managing increasing shares of wind and solar energy. From initial reactions of “we will reach a limit of wind energy in our system at less than 10 percent share,” the bold and the brave are now preparing operational practices to deal with close to 100 percent instantaneous shares of wind and solar.
Wind energy did pose some serious challenges when first encountered by system operators in the 1990s, and system operators were challenged to investigate some of their rules of thumb in planning and operating the system. Initial wind integration studies set out to check that the balancing impacts and costs could be kept at a moderate level. The first real experience shared by system operators proved that they could.
Sharing a joy will double it—and sharing a sorrow will make it only half the size. -Finnish proverb
Sharing lessons learned is an important way forward to make sure that countries and power systems in earlier stages of wind and solar integration can proceed without undue delays caused by issues with system operation, and even leapfrog to best practices.
System operators need to have very good confidence in their operating practices to make sure that grid reliability stays at the high level demanded by society. The organization that would eventually become ESIG, the Utility Wind Integration Group (UWIG), was one of the first platforms that enabled discussion of all concerns. It became obvious from the first discussions that time was needed for the terminology used and the actual operational practices of the different power systems to develop. Early on it was not always straightforward to apply the experience, or study results, from one system operator to another.
The European Network of Transmission System Operators for Electricity (ENTSO-E) enabled both sharing lessons learned and more practical collaboration. After the UK, the Netherlands, and Germany struggled to manage the power system during a major storm that struck one country after the other in 2013, it became obvious that sharing real-time information between control rooms has a high value for neighboring countries. As Europe moved toward a more common internal electricity market, a long process of harmonizing the operating practices and grid codes took place in order to enable more concrete collaboration. Ireland has introduced a new faster frequency control service, which is also being implemented in other countries, to support the system in times of low inertia.
One of the Most Important Lessons Learned: Sharing Resources
Sharing the balancing task is a powerful step toward mitigating the increased variability and uncertainty that wind and solar pose to the power systems. German experience showed that sharing the balancing task with neighboring areas was enough to tackle the rising balancing costs from day-ahead forecast errors of wind. In fact, the use of operating reserve declined despite increasing wind and solar generation, as sharing real-time balancing is highly beneficial for power systems even without wind and solar. The Nordic power system has had a common real-time balancing market since 2002. This has helped one of the countries, Denmark, increase its wind share to close to 50 percent on average—coping with periods of wind energy production surpassing 100 percent of demand through export, but also by turning off all large conventional power plants and relying on grid support (ancillary) services from the high voltage DC (HVDC) interconnection lines and smaller power plants. Many of these lessons are documented in the IEA Wind Task 25 collaboration.
Another Powerful Lesson Learned: Use Wind and Solar Power Plants for Grid Support
This is beneficial at higher shares of wind and solar, when there are hours and days of surplus generation where it is cost-efficient to use a small part of that for providing grid support. Xcel Energy and the Electric Reliability Council of Texas (ERCOT) in the United States, Hydro Quebec in Canada, and the power systems of Denmark and Spain in Europe have all proved that wind power plants comply well with instructions and show consistent, fast response. Grid codes can require online data and basic frequency and voltage support capabilities from wind and solar power plants, even if they are not needed immediately. An understanding of how to best remunerate these power plants for services provided is evolving, and we are continuing to glean the lessons learned from that experience.
Some Challenges Remain
Transmission build out is an important enabler of sharing resources. Transmission bottlenecks were shown to limit the deployment of wind potential and cause delays in building out the resource as early as the 90s. Larger area planning, like the ENTSO-E 10-year network development plan (TYNDP) process, and proactive investments like ERCOT competitive renewable energy (CREZ) zones provided valuable experience. However, even as it became clear that time delays of transmission build-out can cause years of high curtailments of wind energy, this problem has not always been easy to tackle in practice. The German example from past years shows that permitting a large transmission line can take more than a decade. Ways to improve utilization of existing infrastructure with dynamic line rating and Flexible AC Transmission System (FACTS) solutions are good examples, but even they cannot totally defer build out of new infrastructure.
As new countries from outside Europe and the United States hear the experience and success stories of system operators, one more challenge in sharing lessons learned emerges: a need for tools for control room operations and simulations to enable the system operator to make sure that reliability is maintained with no surprises. It is easy to see that with flexible operational practices, faster dispatch decisions, and larger balancing areas or more exchange with neighbors, more wind and solar generation can be absorbed by the system. But if the capabilities of control rooms are not quite there, the balancing task and stability challenge may seem too much to tackle. It is good to remind any new system operators that the sophistication of system operation seen in more advanced systems today was not there at the beginning of wind and solar build out. There is time to prepare the system operation—and all developments needed will benefit the system even with smaller shares of wind and solar. The trend toward open source models and data will be a welcomed help.
The new international collaboration Global Power System Transformation Consortium (G-PST) has just been launched to tackle the challenges and share the experience with all others. In addition to working groups and task forces of the Institute of Electrical and Electronics Engineers (IEEE), the International Council on Large Electric Systems (CIGRE), and the International Energy Agency (IEA). It is very welcome to see collaboration led by concrete system operator needs for operating their systems with higher and higher instantaneous shares of wind, solar, and other inverter-based resources. The long record of sharing lessons learned has shown both successes and challenges in applying the best practices. All efforts to introduce concrete possibilities for new countries to adopt for the new challenges they face deserve applause!
International Energy Agency Technology Collaboration Program (IEA TCP) Wind Task 25/ Recognis Oy