Researchers Paving Way for Renewables With New Technologies
No. 1465, November 1, 2010

As California pushes forward on a gubernatorial commitment to serve 33 percent of electric load with renewable energy by 2020, the rush is on to find ways to ensure the state's energy system is equipped to accommodate this major shift to green power.

Numerous research projects funded by the California Energy Commission's Public Interest Energy Research (PIER) program aim to deal with challenges from the influx of intermittent sources of power such as wind and solar. Researchers highlighted the results of their PIER-supported work at a "Paving the Way for Renewables" symposium at the CEC on Oct. 25.

"It's a challenge today operating the grid that we have with the amount of renewables we have," said Jeff Dagle, a scientist with Pacific Northwest National Laboratory's Advanced Power and Energy Systems group. "It's just going to continue to get more challenging."

With technical support from BPA and the California Independent System Operator, PNNL has been testing the viability of a "wide-area energy and storage-management system" to address intermittency and fast ramps associated with higher levels of wind and solar power feeding into the grid in California and the Northwest.

The proposed management system uses an aggregate of flywheel energy-storage devices and hydroelectric power to provide balancing authorities with a real-time source of regulation service, according to Dagle.

Hydro and thermal power plants incur wear and tear and lose efficiency providing continuous regulation services. Under this proposed concept, an array of flywheels, which can discharge very quickly, could be used to augment fast regulation, while hydroelectric facilities would still be tapped for slower regulation services.

Plants with slow regulation can develop ramps of about 1 to 3 percent of their capacity per minute. Fast regulation can develop ramps of 100 percent of capacity per minute. While some hydropower plants can provide fast regulation, their maneuverability is frequently limited by multiple constraints, including environmental, PNNL scientist Yuri Makarov told Clearing Up.

"The flywheels can change their output from [minus] 100 percent to 100 percent and back on an intra-minute basis," he said.

Makarov stated BPA's concern "is whether, in view of multiple operational constraints, the existing predominantly hydropower generation fleet will be able to meet the increasing balancing-reserve needs."

PNNL has conducted simulations using 20 MW of flywheel capacity and 20 MW of hydro capacity. According to flywheel developer Beacon Power and PNNL, the flywheels minimize wear and tear on hydro units, compensating for the inaccuracies caused by the response delay, dead zone and deviation characteristics of hydropower.

Moreover, according to PNNL, an integrated service between Cal-ISO and BPA could reduce the regulation requirement by 30 percent in their control areas, compared to the traditional treatment. In essence, this means a regulation resource could provide 30 percent more regulation capacity if it sells it to two balancing authorities (BAs).

"The reason is the regulation signals from these BAs do not coincide, so we could hardly expect them peaking at the same time," Makarov said.

"We believe that with this concept we can efficiently provide regulation reserve, and it's an effective and scalable technology," Dagle said.

As for other promising technologies highlighted at the symposium, researchers said synchrophasors could also play a prominent role in helping the grid operate with higher levels of renewables.

While they may sound like the stuff of science fiction, synchrophasor measurement technologies are actually devices that can be installed at various places on the grid to measure current, voltage and other things grid operators love to get reads on, and they can do so 30 times a second--far faster than current devices, which take measurements every two to four seconds.

Joe Eto, manager of Lawrence Berkeley National Laboratory's Consortium for Electric Reliability Technology Solutions, said synchrophasors can give grid operators "MRI-like visibility" of power systems.

Eto and other researchers have been working with Cal-ISO to test how synchrophasor technology can be used to support real-time system operations, and also to boost use of existing transmission for renewables integration.

"If we can use the asset base more intelligently," Eto said, "we'll be able to flow more renewables and more reliably."

Researchers are also finding ways to use synchrophasor data to "develop advanced protection systems that can detect changed system conditions in real time, 'supervise' the operation of protective equipment to improve system security and provide improved visualization of relay system information," noted Lloyd Cibulka of the California Institute for Energy and Environment at University of California, Berkeley.

The reason these advanced protection systems are needed is that undesirable relay operations, or "false trips," can be an important contributing factor in the sequence of events leading to a cascading outage, according to Cibulka. Current protection systems, he explained, are calibrated for normal system conditions, and can't automatically compensate for events that weaken or stress the transmission system, or even for normal changes such as the addition of new lines and generators, especially renewables.

Another way researchers are helping grid managers plan for renewables is through the development of dynamic wind-generator models.

"You can't emphasize enough the need for good models," said Charlie Smith, of the Utility Wind Integration Group. "You can't do high-penetration renewables without them."

Smith said that while turbine manufacturers have developed dynamic models for use in grid-interconnection studies, the models are often proprietary and don't lend themselves to more general grid-planning activities involving multiple stakeholders.

The CEC, along with the Western Electricity Coordinating Council, supported the development of generic, non-proprietary dynamic models that planners and grid operators can use to study the stability of the bulk electricity system, so stability would be maintained with a significant amount of wind energy.

These models, according to Smith, have been used by Cal-ISO to study integration of renewables into the grid, and to answer numerous questions related to power-system dynamic behavior. He said solar-photovoltaic plant models are also being developed for transmission planning and interconnection studies [Leora Broydo Vestel].

This article is excerpted from Energy NewsData's Clearing Up publication. If you aren't a current subscriber, see for yourself how NewsData reporters put events in an accurate and meaningful context -- request a sample of Clearing Up.

Please contact webmaster@newsdata.com with questions or comments about this site.