Wind records across the U.S. were broken in November, providing a real-world demonstration of how grid operators are reliably integrating large amounts of wind energy. These new heights are possible because of technological advances that now enable wind plants to meet or exceed the reliability contributions of conventional generators.
Technological advances were also a driving factor behind a recent North American Electric Reliability Corporation (NERC) report that discusses how improving reliability services capabilities enable renewable resources to play a greater role in our nation’s energy mix.
Record levels of output show wind is being reliably integrated
November’s wind output records are summarized in the map below. Highlights include:
-The Midwest grid operator (MISO) set its record for the most megawatts (MW) of power from wind, at 12,614 on November 19.
-The main Texas grid operator, ERCOT, followed up by setting the U.S. record of 12,971 MW of wind output on November 25. At one point the next day, ERCOT set its own record for wind’s contribution to electricity use, with wind meeting 43.55 percent of demand. Wind generated more than 40 percent of ERCOT’s power for 11 hours from November 24-26, and more than 30 percent for most of that three-day period. For the month of November, wind provided 18.4 percent of the electricity on the main Texas grid, and so far this year wind generation in ERCOT is about equal to the state’s nuclear output, with each providing 11.3 percent of ERCOT’s electricity.
-The Southwest Power Pool, which operates the grid for the region just north of Texas, set its own record with 9,564 MW of wind output on November 23.
-On November 1, the grid operator for the Mid-Atlantic and Great Lakes states, PJM, set a record with wind providing 5,648 MW and 9.1 percent of electricity demand.
-The main grid operator in Colorado set a U.S. record for the largest share of electricity use from wind, averaging 66.4 percent for one hour on November 11. Between mid-September and mid-November, Xcel’s Colorado power system had 20 hours in which over 60 percent of its demand was met with wind generation, and 100 hours in which wind served over 50 percent of demand.
Technology advances enable wind plants to provide all essential reliability services, in many cases better than conventional power plants
All modern wind turbines contain advanced power electronics that condition the electrical output to ensure it precisely meets system needs for voltage and frequency. Advanced controls also allow faster and more accurate control of power output than is possible with conventional generators.
Xcel Colorado has noted that in some hours it uses wind plants’ advanced controls to keep system frequency stable. ERCOT requires wind plants to provide the full range of grid reliability services. All of the large grid operators discussed above now fully integrate wind energy into their electricity markets, with wind governed by the same rules as other energy sources.
NERC’s report outlines how improving reliability services capabilities allow renewables to be an increasingly important part our nation’s energy mix. While the recommendations in the report for renewable resources to provide greater reliability services are reasonable and are already being pro-actively implemented by the wind industry, some of the discussion in NERC’s report needs to be put into perspective to make sure it is not misinterpreted.
Half of NERC’s recommendations deal with the power system’s ability to maintain reliability following a voltage or frequency disturbance. As NERC notes, those disturbances are typically caused by “the sudden loss of a major resource,” e.g. a large power plant.
This reliability threat is almost always the instantaneous loss of a large fossil or nuclear power plant. While individual wind plants do sometimes experience abrupt failures, they are not large enough to be the single largest contingency that the power system must be designed to withstand. Changes in wind energy output also occur gradually over many minutes or hours, and are predictable using advanced weather forecasting. Data from the Texas grid operator demonstrate how accommodating the abrupt failures of large conventional power plants imposes a far larger cost on the power system than integrating wind energy.
Once a disturbance begins, another way in which wind generators are superior to conventional generators is their ability to “ride-through” the voltage and frequency disturbance, while other conventional power plants often trip offline and make the disturbance worse.
Wind plants far exceed conventional generators in their ability to remain online following a frequency and voltage disturbance, and meet a far more stringent standard. In fact, some owners of conventional generators blocked efforts at NERC to enact a standard that would bring conventional generators up to the same ride-through requirements as wind generators.
This capability is important, as the failure of conventional generators to ride-through grid disturbances can lead to a cascading failure and has been a significant contributing factor in several recent blackouts. For example, many critical customers in the Washington DC area lost power when a transmission line failure caused a voltage disturbance and nearby fossil and nuclear power plants tripped offline earlier this year. While not a reliability event, last week wind energy remained online and helped to moderate price spikes in New York after half of a large nuclear plant went offline following an electrical disturbance.
NERC’s report overlooks another way in which conventional generators fail to support grid reliability following a disturbance.
NERC has previously documented how around 90 percent of conventional generators fail to provide sustained frequency response, which involves increasing power output to return system frequency to normal in the seconds following the loss of a generator. In many cases, conventional generators do not provide sustained frequency response because the generator “governor” is not operating, while in other cases plant controls override that governor response. Thus, NERC’s latest report overstates the reliability contributions of most conventional generators when it claims, “Conventional units such as coal plants provide frequency support services as a function of their large spinning generators and governor control settings….”
Wind plants are capable of providing fast frequency response, though like conventional generators they typically do not because there is no financial incentive to do so. AWEA has consistently advocated for a market-based solution to obtain frequency response service from the resources that can provide it at the lowest cost.
In summary, readers should understand that the reliability of wind plants is superior to that of conventional power plants in not causing large voltage and frequency disturbances to begin with, and then remaining online and not causing a cascading failure once a disturbance begins.
Most of the remainder of NERC’s recommendations address the power system need for voltage and reactive power control, reliability services that are provided by both conventional generators and wind plants. The sophisticated power electronics that are standard in all wind turbines now being installed in the U.S. allow precise control of voltage and reactive power. AWEA supported PJM in its recent move to require reactive power service from wind plants. More recently, FERC noted these technological advances in wind plant power electronics when proposing that wind plants meet the same reactive power requirement as conventional resources. That proposal would result in wind plants nationwide meeting the same or greater requirements as conventional power plants for all reliability services.
The following table summarizes how wind plants’ provision of essential reliability services compares favorably to that of other resources, with links providing citations to previous NERC reports and other documents:
|Reliability service||Wind||Conventional generation|
|Ride-through||– Excellent voltage and frequency ride-through, meeting FERC Order 661A requirements– Power electronics electrically separate wind turbine generators from grid disturbances, providing them with much greater ability to remain online through disturbances||– Many cannot match wind’s capabilities or meet Order 661A ride-through requirements|
|Reactive and voltage control||– Wind turbine power electronics provide reactive and voltage control equivalent to that of conventional generators– Power electronics can provide reactive power and voltage control even when the wind plant is not producing power||-Conventional generation provides this service.|
|Active power control||– Can provide extremely fast response in seconds, far faster than conventional generation– Like other generators, wind will provide this response when it is economic to do so- Xcel Energy sometimes uses its wind plants to provide some or all of its frequency-responsive automatic generation control
|– Like wind, many baseload generators do not provide active power control for economic reasons, though they technically can|
|Frequency response||–Adding wind can help system frequency response by causing conventional generation to be dispatched down-Wind can provide frequency response, but it is typically more costly for it to do so than for other resources as it requires curtailing wind generation in advance||– Changes in conventional generator operating procedures have greatly reduced frequency response– Only 70-75 percent of generators have governors that are capable of sustaining frequency response for more than one minute, and about half of conventional generators have controls that may withdraw sustained frequency response for economic reasons– “Only 30 percent of the units on-line provide primary frequency response. Two-thirds of the units that did respond exhibit withdrawal of primary frequency response.” So, “Only 10 percent of units on-line sustain primary frequency response.”|
|Inertial response||–Can provide with no lost production by using power electronics and the inertia of the wind turbine rotor; this capability is commercially available but not widely deployed because there is no payment for any resource to provide this service||-Conventional generation provides this service.|
|Increases need for operating reserves, integration cost||– Very small impact on total reserve need and integration cost||-Contingency reserve needs and costs are quite large|
Further documentation of wind’s reliability services contributions is available from the following NERC reports:
- NERC recently noted, “This issue does not exist for utility-scale wind energy, which offers ride-through capabilities and other essential reliability services.”
- NERC stated “Modern wind turbine generators can meet equivalent technical performance requirements provided by conventional generation technologies with proper control strategies, system design, and implementation.”
- Regarding voltage and reactive power control, NERC has noted “As variable resources, such as wind power facilities, constitute a larger proportion of the total generation on a system, these resources may provide voltage regulation and reactive power control capabilities comparable to that of conventional generation. Further, wind plants may provide dynamic and static reactive power support as well as voltage control in order to contribute to power system reliability.”
- NERC also recently noted that “… by causing conventional generators to have their output dispatched down, wind and solar generation can increase generator headroom and, therefore, the amount of total frequency response being provided.” The National Renewable Energy Laboratory also documented that “Wind power can act in an equal or superior manner to conventional generation when providing active power control, supporting the system frequency response and improving reliability.”