As Twin Cities residents awoke on Jan. 29, the first of three straight days of sub-zero temperatures, about half of the area's electricity was coming from wind farms located in the Upper Midwest.
Wind power across the northern region of the independently operated Midcontinent System, which stretches from Minnesota to Iowa, peaked that morning between 9 and 10 a.m. at 11,445 megawatts. Wind farms produced about half of the region's total electricity output, according to hourly data from the grid operator.
At the time, it was minus 8 degrees Fahrenheit in the Minneapolis-St. Paul International Airport. Gusty winds made it feel like minus 19F.
But grid operators would watch as wind power steadily declines over the next day and a half.
As of the afternoon of Jan. 30, there was less than 550 MW on the MISO North grid, providing just 2.5 percent of the region's power. The temperature, which had bottomed out an hour earlier, had dropped to minus 21F with a chill of minus 31F.
That drop in wind output during last month's freeze is now fueling the debate about the nation's embrace of renewable energy. The polar vortex arrived as calls grew on the left for a “Green New Deal” to transition to renewable energy and address the threat of climate change, while various state-level proposals to increase renewable energy penetration floated across the country. country.
It was also fresh ammunition for a minerals industry and other critics of renewable energy mandates that have long cast doubt on the ability to maintain reliability in a grid increasingly dependent on intermittent energy sources.
But what exactly happened to the Midwestern trail?
Read more: 7 pointers on how grid operator PJM dealt with the polar vortex
Part of the reason for the decline in wind output was the normal daily variation in output. In fact, the grid operator expected less wind power to be available throughout Jan. 30, according to MISO's next-day forecast.
Other turbines in the Upper Midwest shut down due to the drop in temperatures.
Output from wind farms — a technology billed as the new baseload power in the Upper Midwest — fell even faster than expected starting last night as temperatures dipped below minus 20 F, the cutoff point below which the turbines automatically stop working.
A MISO presentation released ahead of today's commission meeting shows that when the grid operator declared a “peak generation event” just before 3am. on January 30, only about half of the nearly 14,000 MW forecast for wind generation was available. which produces energy.
Brian Draxten, director of resource planning for Otter Tail Power Co., said wind turbines across North Dakota were shut down because of the extreme temperatures. In fact, he said wind farms went from being a power producer to a 2 megawatt load on his system because they required heat to avoid damage.
Xcel Energy Inc., which also gets nearly 20 percent of its power from wind, said wind farms in Minnesota and North Dakota automatically shut down when the temperature reaches minus 20 F.
Utility spokesman Randy Fordice said the timing of the shutdowns varies, but they generally shut down overnight on Jan. 29 and 30. Some operated on the day of January 30th and normal operation resumed on January 31st.
A representative of MidAmerican Energy Co. of Iowa also said extreme temperatures affected wind generation, though the utility was not specific about the temperature limit or how long wind generation was curtailed.
Freezing temperatures, wind speeds
Jakob Skjoeth, chief engineer at Siemens Gamesa Renewable Energy SA, the world's second-largest turbine maker, said the company has many turbine configurations. But even equipped with so-called cold weather packages, the turbines can operate down to minus 22 F (minus 30 degrees Celsius).
Extreme cold affects various parts of a turbine, from the electrical cabinets to the gearbox, generator, oils and steel components, which can become brittle if the temperature drops enough, Skjoeth said.
While turbines can be equipped with deicing systems to help operate through snow and ice, that's not the problem seen in extreme cold like what the Upper Midwest saw during the polar vortex, he said.
Meanwhile, Skjoeth said the industry has little focus on developing turbines that will operate below minus 20 F because the economics of generating power in such extreme conditions would not justify the additional cost.
“Historically, very cold weather is accompanied by a decrease in wind speed,” he said. “When you get that low, you don't have that much air, usually.”
Even in Minnesota and the Dakotas, cold temperatures recorded in the last three days of January are rare. But the polar vortex is still a key data point in the region's energy transition debate.
Minnesota, in fact, is among the states where clean energy advocates are pushing a bill to establish 80 percent renewable energy standards by 2035 with a goal of 100 percent clean energy by mid-century (EnergywireFebruary 6).
Read more: Polar vortex offers utility customers a lesson in demand response
Days after the polar vortex, a lobbyist for Dairyland Power Cooperative, a generation and transmission cooperative, told a Minnesota legislative committee hearing on the bill that wind power didn't show up when it was needed.
The lights stayed on “only because of fossil fuel power plants that could be called in and dispatched,” he said.
However, MISO data shows that coal-fired and natural gas-fired power plants across the region also failed in the extreme cold. In fact, the grid operator's report shows 15,000 MW of coal and natural gas generation suffered forced outages on January 30 and January 31.
MISO officials were not available to discuss the grid's performance during the polar vortex. However, the network manager is set to cover the issue at the Reliability Subcommittee meeting this afternoon.
The MISO report is consistent with similar data from PJM Interconnection LLC, which also showed coal and natural gas plants dominated forced outages in the Mid-Atlantic region.
Renewable energy sources are increasing
With or without legislation to accelerate the energy transition in Minnesota and elsewhere, states will continue to rely more on renewable energy, especially wind and solar, to keep the lights on.
There are currently 163 wind projects on the MISO grid Tailrepresenting more than 31,000 MW of power.
Otter Tail, based in Ferguson Falls, Minn., is among the Upper Midwest Utilities adding more wind power to its portfolio — a 150-megawatt wind farm to be completed next year that will help replace a coal plant in Minnesota. The wind project will be complemented by a 248 megawatt natural gas peaking plant being built in neighboring South Dakota.
Draxten, the utility's resource planner, said the wind is counted for power while the gas turbine provides the required capacity. “We see this combination as the new base load,” he said.
“Can we have greater penetration of renewables? Absolutely,” said Draxten. “The question is how far can we go and how fast can we go? I just always think we're always going to need some kind of thermal generation.”
Michael Goggin, vice president of Grid Strategies LLC, a clean energy consulting firm, said the grid can accommodate significantly more wind and solar power as long as power can be transferred between different regions via high-voltage transmission.
“What really matters is the eastern link,” he said. “A bigger grid helps a lot in this type of event.”
In a suspension for the American Wind Energy Association, Goggin argued for the value of transmission during the polar vortex as PJM Interconnection exported more than 5,000 MW of power to MISO, a reversal of the typical west-to-east power flow.
In fact, MISO North data shows that while coal and natural gas power plants in the region have increased output as wind power has declined, energy imports have played a leading role in filling the gap.
Clean energy advocates believe that the shutdown of renewables is not a problem for grid reliability until penetration reaches about 75 percent.
Wade Schauer, research director for US energy and renewables research at Wood Mackenzie, noted that it is becoming “exponentially” more difficult economically to justify renewable energy penetration beyond 50%, including hydropower, because of increasing cuts during periods of overproduction and due to necessity. for extractable power.
“You can keep building more, but you still need more backup to be there on days like this during the polar vortex,” he said.
MISO also released a renewable energy integration impact assessment last fall that found that exceeding 40 percent renewable energy penetration will be increasingly difficult and could require additional transmission.
Ultimately, Schauer said significantly higher penetration of renewables will depend on better long-term wind forecast accuracy, more transmission and longer-lasting battery storage than is available today.
Until then, MISO has identified steps it can take, including maintaining data on temperature cutoff limits for wind turbines, so that it is not caught off guard by the loss of wind generation on the grid in extreme conditions.
