NREL study shows eastern grid can handle greater growth of renewables

The power grid in the eastern part of the United States could accommodate up to 30 percent annual penetration of wind and solar generation without technical problems, according to a recent study from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).

NREL’s Eastern Renewable Generation Integration Study (ERGIS) analyzed a year of operations at five-minute intervals – the same real-time interval used by regional transmission organizations for scheduling resources.

NREL developed new modeling and analytical approaches using the lab’s supercomputer, which helped reduce the processing time for the ERGIS calculations from 19 months to 19 days. NREL modeled more than 5,600 electricity generators and more than 60,000 transmission lines in a power system that spans from Florida to Maine and portions of Canada and as far west as New Mexico.

The results showed the Eastern Interconnection, which covers two-thirds of the United States, could reliably balance the variability of wind and solar energy at 30 percent annual penetration levels.

The grid can likely accommodate even greater than 30 percent renewables, Aaron Bloom, ENREL project manager and lead author of the ERGIS study, recently told Daily Energy Insider.

“It is still all within the realm of feasibility,” Bloom said. “Five years ago, people couldn’t even comprehend five percent, and now five percent is happening all over the place. “

Some energy analysts have argued there is an approximate 15 to 20 percent limit to the level of variable energy resource generation possible on the grid.

The concern with higher levels of renewables was that managing the grid would become difficult due to the uncertainty about when the generation would occur, as well as challenges in ramping up and down dispatchable generation to offset the fluctuations in variable energy resource generation, according to a June report from the White House on incorporating renewables into the electric grid.

There are many countries around the world and some U.S. states, however, that are already experiencing very high levels of penetration with renewable energy resources. Portugal was 100 percent run on wind, solar and hydropower for four days straight in May, while Texas hit a record level of 45 percent instantaneous penetration from wind generation during one evening in February, the White House report said.

The benefits of adding more wind and solar and other renewables to the grid was reflected in the ERGIS study in the form of lower costs and emissions.

In the study, when analyzing the 30 percent penetration scenario, operating costs also dropped by 30 percent.

“When you add renewables to the power system, fuel costs drop considerably because you are displacing thermal generation and you are no longer burning fuel,” Bloom said.

Future CO2 emissions also declined by approximately 30 percent annually under the high wind and solar scenarios.

Bloom said that one of the challenges of incorporating more wind and solar into the grid could involve the uncertainty around extreme weather conditions.

“I think we need to look at the extreme conditions more. I’m not as concerned about 30 percent, but I would be more concerned with looking at the 50 percent number, and trying to understand what happens with contingencies and extreme weather,” Bloom said.

The ERGIS study opens the door for discussions about the potential for new technology, demand response, energy storage and electric vehicles, Bloom said.

“The president has outlined some pretty aggressive clean energy targets for the nation, so we are going to continue looking at much higher penetration levels of clean energy technologies in the U.S.,” Bloom said.

Some of that grid-related research is being conducted as part of the Grid Modernization Laboratory Consortium that involves 14 Department of Energy national laboratories and dozens of industry and state and local government partners.

One project under that umbrella focuses on extreme weather events, Bloom said, while another study is looking at coordinating the operations of the three interconnections in the U.S. power grid.