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Windstorm underscores need for energy diversification

Source: 
Belgrade News

The automatic shutdown of turbines during Montana's windstorm last week prove the need to maintain multiple energy sources to prevent consumers from experiencing "higher costs, lower reliability and grid instability," NorthWestern Energy officials say.

John Hines, the company's vice president of supply, said the Jan. 13 storm forced the automatic shutdown of many wind turbines in Montana. Those that generated close to their maximum capability of 430 megawatts on Tuesday afternoon, Jan. 12, completely shut down the next morning when wind speeds accelerated to around 70 miles per hour.

On Jan. 13, electricity generation fluctuated every 15 minutes from about 280 megawatts to less than 30 megawatts as the wind howled across the state, illustrating that "there is always the potential to be 450 megawatts long or 450 megawatts short when it comes to meeting our customers' demand with the wind resources in our Montana portfolio," Hines said.

Although it varies by turbine, the cut-out speed designed to prevent damage to equipment is generally 55 miles per hour, according to the U.S. Department of Energy. Last week's storm generated gusts ranging between 65 miles per hour to more than 90 miles per hour across the state.

According to a NorthWestern Energy news release, 67 percent of the company's energy portfolio comprises carbon-free sources, including wind, which it describes as a "good, clean energy resource, available 24/7." However, because it is a variable resource, it creates unique challenges to operating the energy grid reliably. Because of those challenges and built-in variability, the company does not rely on wind during times of critical energy demand, such as cold winter night and hot summer days.

The service outages experienced by some customers last week underscore the need for flexible capacity resources available on demand, such as hydro, storage and natural gas to keep the grid balanced and operating reliably at all times, the company asserts.

"NorthWestern Energy's redundant grid and energy generation resources located in Montana were critical to limiting customer outages," said Vice President of Transmission Mike Cashell. "This storm underscores the value flexible resources within NorthWestern Energy's service area contribute to maintaining reliability when conditions are good and when the weather turns and creates challenges."

Discussions

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Jim Stack's picture
Jim Stack on Jan 22, 2021

Most wind turbines have automatic furling in their design. The change the pitch of the blades to catch less wind and are almost straight with the wind to not spin. I wonder what type these were and it that feature worked properly. The output should be very steady with a good design. Even gale force winds can be adapted to. 

Roger Arnold's picture
Roger Arnold on Jan 25, 2021

I've wondered about that myself. I assume that the need to shut down results from the fixed twist in each blade. At high wind speeds, rotating the blades to furl them would result in the tips encountering the wind with a negative angle of attack, while sections further in had  positive angle of attack. That would place bending stresses on the blade above what it might be designed to handle. With the blade stopped together, the inner and outer parts still present to the wind with different angles of attack, but the wind speeds they see are much lower than if they were spinning.

Jim Stack's picture
Jim Stack on Jan 25, 2021

Yes South West wind in Northern Arizona had the auto furling in all of it's small wind turbines. They also used Carbon fiber since it was very strong. They went out of business a few years back but were pretty reliable for quite a while.

https://www.thebackshed.com/windmill/Docs/Furling.asp

Why do we use furling? Well it will save your windmill from destruction in high winds, effectively making it "safe", and it provides output power regulation. Manual furling systems, like those on the old Southern Cross windmills, use a manually operated lever or switch to turn the turbine out of the wind. This is done by changing the tail angle, instead of pointing straight out the back, its turned up to 90 degrees.The tail will always be down wind, so the wind against the tail will turn the front of the turbine away from the wind.

Automatic furling can be either electronic or mechanical. Electronic furling uses wind speed and direction sensors and a small computer to drive an electric motor, which turns the windmill in or out of the wind. This type of furling is used on the large wind farms.

Automatic mechanical furling uses a clever combination of gravity and wind force. Below is a simplified diagram of a windmill. The Tail Pivot is just a simple hinge that is angled back and to one side, usually with an angle of about 20 degrees. Because the pivot is angled back from the vertical, the weight of the tail will want to turn the tail down. Its a bit like a fridge door, if you tilt you fridge towards you, the door will open because the fridge door hinge it angled off from the vertical. There is a tail stop to stop the tail once it is pointing straight out the back of the windmill, at 90 degrees to the turbine. The windmill turbine is offset to one side from the tower/mast axis, so if you push against the turbine, it will want to swing around the mast axis.

 

 

Bob Meinetz's picture
Bob Meinetz on Jan 27, 2021

Demand-response could help that situation. For example, having businesses, schools, and public services shut down when the wind is blowing hard would prevent the need to resort to coal-fired power to maintain reliability.

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