By - Jim Vess

Growth of distributed renewable generation poses challenges for bulk electricity market

Energize Weekly, March 29,2017

The growth in renewable energy resources—particularly ones distributed across the grid—provide both an opportunity and a management challenge for the wholesale bulk-power market, according to a report from the ISO/RTO Council or IRC.

The report by IRC’s Emerging Technologies Task Force identifies three key areas that operators of these regional power systems must deal with: integrating renewable resources, enhancing data management and controlling an increasingly distributed system.

The IRC is composed of nine independent system operators (ISO) and regional transmission organizations (RTO) in North America, which run wholesale markets serving two-thirds of electricity consumers in the United States and more than half in Canada.

“IRC member organizations have devoted an extensive effort to capitalize on emergent technologies to integrate renewable energy resources like wind and solar over the past several years,” the report notes.

The role of the wholesale markets is seen as key to enabling increased renewable generation. Regional grids can balance the intermittency of some sources—if the sun isn’t shining or the wind blowing in one place, it will be sunny or windy someplace else—and they can absorb and move excess renewable electricity.

This last function lets utilities avoid curtailment where wind turbines or solar plants are taken offline at their peak periods because there is no place to send the electricity. Curtailment ends up making renewable resources more expensive.

The IRC report notes that while the U.S. Department of Energy’s SunShot initiative aimed at reducing the cost of photovoltaic electricity to 6 cents a kilowatt-hour is about 70 percent of the way to its goal, solar curtailment could push it up back up to 11 cents a kilowatt-hour in some cases.

The size of large regional markets makes it possible to absorb larger quantities of renewable energy. This past Saturday around midday, for example, the California ISO (CAISO) was serving 57 percent of its demand with renewable resources, primarily solar.

More than 80 percent of all wind capacity and 81 percent of all solar capacity is situated in the CAISO and the other regions served by IRC members, according to the report.

While breakthroughs are being made technologies, including renewable generation, gird-scale energy storage and microgrids, the IRC task force questions whether there is “enough activity happening cohesively to integrate all these disparate components into an overall electricity system?”

To help answer that question, the task force supports policies looking to accommodate large-scale amounts of renewables, remaining agnostic on the technologies used, and avoiding “early technological lock-in.”

“Several IRC member organizations are already piloting various “outlier” technologies that may someday overtake present day mechanisms if their effectiveness can be proven,” the report says.

The task force also calls for discussions to “achieve a continent-wide consensus of the extent to which renewable integration will be achieved through regional or interregional trade.”

An electricity system with more distributed energy resources (DER) becomes less predictable, and requires more data and better management at the ISO/RTO level, the report says. It calls this increased “situational awareness.”

“The situational awareness of IRC members has largely centered on the bulk electricity system,” the report says. “This is changing, however, both in terms of data sources and the intensity of the data itself.”

“The IRC recognizes that the traditional monitoring and forecasting framework established in the 1990s may not accommodate the changing demands of an evolving electricity sector.”

The approach toward data and data management has been evolving since the period of market deregulation in the 1990s when supervisory control and data acquisition (SCADA) systems became widespread.

While SCADA typically provides data at the two-per-second resolution, the addition of phasor measurement unit (PMU) data offers data at a time-synchronized sampling rate of many times per second. While PMU has been deployed by most IRC members, the way it is used in the future could change dramatically, the report says.

Changing distribution sector load is another factor for which the bulk electricity market will have to account. For as more distributed generation sources are added to the distribution system, traditionally a consumer has the potential to be a “net injector” into the bulk electricity system.

“Data is a common theme running through the DER issue,” according to the report.

The ultimate challenge is controlling an increasingly distributed electricity system. “Emerging technologies form part of the solution to providing a system capable of enabling a future with a high penetration of DERs, but often these technologies need policies to enable their full potential,” the report says. “Perhaps the most pressing part of this discussion has been the governance of the interface between the transmission and distribution systems.”

The IRC task force laid out a number of policies and actions it says are needed to assure coordination and stability in the system.

For example, the council says there has to be some type of “coordinating influence” in a high-DER future to ensure reliability.

IRC says it also supports policies to ensure that if variability at the distribution level results in a risk to system reliability, ISO/RTOs have appropriate authority over DERs—or otherwise isolate their impact from the bulk electricity system.

The council said it will also continue to facilitate a continent-wide dialogue on the appropriate means by which mass DERs and the bulk electricity system can mutually benefit each other.

This dialogue should focus on effective transfer of data across the transmission/distribution system interface, the report says, while allowing maximum flexibility for the development of local policies and market mechanisms.

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