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Wind Farms: Turbines break like match-sticks in medium waves, and their capacity is “overestimated”

Posted By Joanne Nova On March 1, 2013 @ 1:35 am In Global Warming | Comments Disabled

Not a good news week for wind power.

First windpower probably doesn’t produce as much electricity as people though it could. If the new estimates are right, humanity would need to cover 3 million square kilometers of the Earth to get just 10% of our electricity from wind. (And how many storms will that prevent do you think?) Could the “cure” be worse than the condition?

Second, it appears that wind turbines in the ocean might snap like matchsticks in particular conditions — conditions that are different for each turbine and at the moment, impossible to predict. The authors explain that it doesn’t have to be big waves or big storms — medium sized waves were the worst.

Windpower’s theoretical maximum isn’t what we thought it might have been

When we account for the wind shadows that large installations produce, at best, wind power may only give us 1 Watt per square meter (or 1 MW per square kilometer). According to this team our global energy needs are in the order of 30 terawatts, and one terawatt is one trillion (1012) watts. If that is the case, to to supply 10% of our global energy needs we’d have to cover…  3 trillion square meters or 3 million square kilometers.

…the latest research in mesoscale atmospheric modeling, published February 25 in the journal Environmental Research Letters, suggests that the generating capacity of large-scale wind farms has been overestimated.

Each wind turbine creates behind it a “wind shadow” in which the air has been slowed down by drag on the turbine’s blades. The ideal wind farm strikes a balance, packing as many turbines onto the land as possible, while also spacing them enough to reduce the impact of these wind shadows. But as wind farms grow larger, they start to interact, and the regional-scale wind patterns matter more.

Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter. Previous estimates, which ignored the turbines’ slowing effect on the wind, had put that figure at between 2 and 7 watts per square meter.

In short, we may not have access to as much wind power as scientists thought.

“If wind power’s going to make a contribution to global energy requirements that’s serious, 10 or 20 percent or more, then it really has to contribute on the scale of terawatts in the next half-century or less,” says Keith.

If we were to cover the entire Earth with wind farms, he notes, “the system could potentially generate enormous amounts of power, well in excess of 100 terawatts, but at that point my guess, based on our climate modeling, is that the effect of that on global winds, and therefore on climate, would be severe — perhaps bigger than the impact of doubling CO2.”

… Keith says, “It’s worth asking about the scalability of each potential energy source — whether it can supply, say, 3 terawatts, which would be 10 percent of our global energy need, or whether it’s more like 0.3 terawatts and 1 percent.” [Science Daily]

To go “100% renewable” with wind, we could convert, say, four countries to windfarms (pick four of these: US, Australia, China, Brazil or Canada).

Offshore wind towers have their own major problems

You would think the ocean is the obvious way to fill millions of spare square kilometers, but it is harder than it looks. This week one study suggests that offshore wind turbines may unpredictably break “like matches” when the right sized waves hit with the right pattern. It’s like the damage from resonance on a suspension bridge, and known as “ringing”. It is a problem that is hard to predict. It depends on how deep the water is, the solidity of the bottom, the slope, size of the tower, and the spacing of the waves. But no one is able yet to model that.

“The problem is, we still do not know exactly when the wind turbines may break,” says Professor John Grue from the Department of Mathematics at the University of Oslo, Norway. Grue is one of the world’s foremost experts on wave research. In 1989 he discovered an inexplicable wave phenomenon called ringing, which is a special type of vibration that occurs when choppy waves hit marine installations. The discovery was made in a 25-metre long wave laboratory located in the basement of the mathematics building at Blindern Campus.

So far scientists have studied ringing in small and large waves, but as it turns out, ringing is more common in medium-size waves. For wind turbines at sea with a cylinder diameter of eight metres, the worst waves are those that are more than 13 metres high and have an 11-second interval between them.

The good news is that this work is mostly based on models

The bad news is that the models don’t work yet. Nonetheless, researchers are still convinced there is a real problem. They allege the devastating cracks in one oil platform were caused by ringing.

Oil rig damaged

Ringing does not just harm wind turbines. Ringing has already been a great problem for the oil industry. The designers of the YME platform did not take ringing into account, and lost NOK 12 billion.

“It is possible to build your way out of the ringing problem by strengthening the oil rigs. However, it is not financially profitable to do the same with wind turbines,” says John Grue.

Financially — the word you are looking for is “ruin”.

If medium sized waves in average storms can knock over a tower, it makes offshore turbines just that much more expensive…

“If we do not take ringing into consideration, offshore wind turbine parks can lead to financial ruin,” warns John Grue to the research magazine Apollon at University of Oslo.

Shame they can’t predict which ones might fall over.

 

REFERENCES

Amanda S Adams, David W Keith. Are global wind power resource estimates overstated? Environmental Research Letters, 2013; 8 (1): 015021 DOI: 10.1088/1748-9326/8/1/015021

University of Oslo (2013, February 26). Windmills at sea can break like matches. ScienceDaily. Retrieved February 28, 2013, from

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