Winds of Change
More Renewables Mean Different Grid
For most of us it has not been customary to think very hard about when to flip a light switch or how the electrons get there. Now, the people responsible for the reliable operation of the electricity grid say they’re facing special, new challenges and their published remarks seem to indicate consumers can expect to notice a difference.
Adjustments that will be needed to integrate the vast additions of new wind-energy capacity anticipated in response to state and federal policy mandates “have the potential to fundamentally change the way the system is planned, operated, and used—from the grid operator to the average residential customer,” according to the North American Electric Reliability Corporation (NERC) in a report published in April.
Titled “Accommodating High Levels of Variable Generation,” the report weighs in with an examination of how wind development over the coming decade—because of wind power’s intermittent availability—will fundamentally alter the way the grid is planned and operated.
Unprecedented Expansion
The NERC is a non-governmental regulatory body that’s had the job of setting electric reliability standards and monitoring industry performance in the U.S. and Canada since 1968. Four years after the great Northeast blackout of 2003, the federal government put teeth into NERC standards, giving the organization authority to make them mandatory and enforce them for all users, owners, and operators of the bulk power system.
That task is getting bigger thanks to the unprecedented expansion of renewable generation now underway. Solar energy and other combustion-free technologies play a part, but wind is really where the action is. According to the American Wind Energy Association (AWEA), wind accounted for 42 percent of all new generation capacity added last year. More than two dozen states, up from just 10 in 2003, have renewable energy mandates and it’s generally assumed Congress will soon adopt one nationwide. In various states, percentages of electric generation that must be obtained from renewables range from 10 percent to as much as 30 percent over a time frame of five to 15 years.
In other words, to comply with state and probable federal laws, power providers will have to participate, either with their own generation or as wholesale customers of other generation owners and operators, in more than doubling renewable energy capacity over approximately the same period of time it now takes to obtain regulatory permits and build one new, conventional power plant.
Within the territory of the Roseville, Minnesota-based Midwest Reliability Organization (MRO), the NERC says an installed capacity of 45,000 megawatts of wind generation is expected by 2017. That means nine-fold growth over the less than 5,000 megawatts installed as of last year.
Operating under NERC and federal authority, the MRO serves Wisconsin, Upper Michigan, Minnesota, Iowa, the Dakotas, Nebraska, and parts of Manitoba and Saskatchewan.
Overall, the NERC’s 2008 Long-Term Reliability Assessment estimates more than 145 gigawatts of wind generation either planned or proposed by 2017 in North America. To tie that number to something more tangible, visualize building roughly 141 new Point Beach nuclear plants, or just shy of 97,000 wind turbines at 1.5 megawatts each.
If only half of the expected renewable capacity were to be built and connected over the next 10 years, it would still represent a 350-percent increase in variable generation compared with last year, the NERC says.
That’s a lot of intermittent generation spread over a broad geographic area sure to be experiencing a wide range of wind conditions at any given moment. And since the grid needs to be kept in balance—power usage matching power production at all times—the NERC and every operation it supervises will necessarily be looking for engineering and infrastructure solutions to cope with sizeable numbers of generation sources going off-line and maybe others coming on, a few or a few hundred miles away.
If alternative renewable sources aren’t available at the opportune moment, more conventional sources will need to be accessed. Figuring out how to make the grid able, on a moment’s notice, to tap whatever sources are available in an increasingly changeable supply situation is the challenge for the coming decade.
Flexible Forecasts
Planning and forecasting for grid operation will confront new challenges, the report says, noting, “The output of variable resources is characterized by steep ‘ramps’ as opposed to the controlled, gradual ‘ramp’ up or down of electricity demand and the output of conventional generation. Managing these ramps can be challenging for system operators, particularly if ‘down’ ramps occur as demand increases and vice versa.”
Errors in forecasting electricity demand are typically small, but errors in forecasting wind availability can be large, the NERC says. A 12-hour demand forecast for a system with 10 megawatts of peak demand would typically be subject to an error of about 3 percent, while a 12-hour forecast of wind availability for the same system could “readily” be subject to error of 20 percent to 100 percent, “And forecast errors grow appreciably with time horizon,” the report says.
That’s one reason why the NERC and just about everyone else in the business of moving electricity from one place to another are talking about lots of new transmission lines, especially across the upper Midwest, as discussed last month in Wisconsin Energy Cooperative News. (See “Lining Up,” WEC News, May 2009.) Those lines will provide what Wisconsin Public Service Commission Chairman Eric Callisto has described as “optionality,” the ability to reach out to many sources of power.
Another reason for new lines is that the best renewable resources are typically a long way from the greatest concentrations of customers.
“Many new variable generation plants interconnecting to the bulk power system will be located in areas remote from demand centers and existing transmission infrastructure due to fuel [meaning wind and sunshine] availability,” the April NERC report says, noting that just 7 percent of the U.S. population lives in the top 10 states for wind potential.
This is not an unexpected challenge. In February 2008, NERC President Rick Sergel said the organization had seen “a lot of public support for wind and renewables development over the past year, but in order to realize the value of these resources, we need the same kind of support for the transmission lines that will link them to population centers.”
Variabile, Viable
As the national trade association for the wind energy industry, the AWEA said it welcomed the NERC findings, calling the report “an excellent roadmap for the grid planning and operations changes needed for America’s future electricity generation portfolio.”
AWEA CEO Denise Bode said the recommendations “open the way to upgrading grid planning and operations in ways that will make our aging electric utility system more efficient and reliable while saving consumers money.”
Today’s grid already copes with variability in generation and can similarly handle variability from renewable resources, the AWEA said.—Dave Hoopman |
