Bloomberg and other news outlets, including the Washington Post, reported on the leaked staff report in mid-July.
"The power system is more reliable today due to better planning, market discipline and better operating rules and standards," the draft said. "The grid is in good shape. System resiliency continues to improve." The final version of the report is likely to be politically massaged.
Some renewables proponents have warned that the document — by the pro-fossil-fuel Trump administration — may fault wind and solar as unreliable, an outdated point of view. The study was led by Travis Fisher, a former economist at the right-of-centre Institute for Energy Research.
Fisher previously criticised the existence of federal tax credits for renewables, according to US political website The Hill.
Within days of the leak, the excerpts reported in the news had been changed, according to the DOE. The report's release date was unclear as Windpower Monthly went to press.
"I've asked the staff of the Department of Energy to undertake a critical review of regulatory burdens placed by the previous administration on baseload generators," energy secretary Rick Perry said in June. Barack Obama's administration had championed renewables.
The US's multi-state regional transmission operators (RTOs) and independent system operators (ISOs) are used to working with wind's variability.
Ercot, the RTO that oversees the grid in most of Texas, set up a reliability risk desk in January to oversee the state's renewables — mainly wind — as well as inertia and ancillary services, such as extra reserves in case a plant suddenly goes offline. Based in Taylor, Texas, the reliability risk desk operates 24/7.
Ercot now has 19GW of wind plants on its system. Icing of wind turbine blades, for example, poses a risk to output. "Our biggest wind forecast errors are because of that," said Dan Woodfin, senior director of system operations. "But we have not seen anything we cannot handle."
Dealing with swings
The Southwest Power Pool (SPP), whose territory includes windy Oklahoma and Kansas, has experienced a 10GW swing of wind power in a 24-hour period, and a 3GW swing within an hour.
A decade ago, the SSP used to assume that wind could never serve more than 20-30% of its load, according to the RTO's 2016 annual report.
During the second quarter, SPP saw wind penetration ranging from 1% to 54%, said Bruce Rew, vice president of operations.
Icing is again the main reason for wide swings in wind output, because most of the projects in SPP's territory do not have cold weather packages as such conditions are not common enough to justify the additional costs.
SPP's total power plant capacity is now 84GW, including more than 16GW of wind. Some 30GW of wind is in its interconnection queue, and more than 17GW is projected to be built by the end of 2017, said CJ Brown, director of system operations.
"We have grown with the wind industry and gained a lot of experience," added Rew.