Texas weather: Are frozen wind turbines to blame for power cuts?
image copyrightGetty ImagesAs freezing temperatures grip the southern United States, there have been major power failures across Texas as increased demand for heating has overwhelmed the energy grid.
Supplies of both electricity and gas have been intermittent, with the authorities saying they need to "safely manage the balance of supply and demand on the grid" to avoid another major power cut.
Republican representatives and media commentators have blamed green energy policies, in particular the increased use of wind turbines.
"So it was all working great until the day it got cold outside," Fox News's Tucker Carlson said.
"The windmills failed like the silly fashion accessories they are, and people in Texas died."
What went wrong?
The bitingly cold temperatures have caused major problems across the energy sector in Texas.
Wind turbines froze, as well as vital equipment at gas wells and in the nuclear industry.
But because gas and other non-renewable energies contribute far more to the grid than wind power, particularly in winter, these shortages had a far greater impact on the system.
So when critics pointed to a loss of nearly half of Texas's wind-energy capacity as a result of frozen turbines, they failed to point out double that amount was being lost from gas and other non-renewable supplies such as coal and nuclear.
image copyrightGetty ImagesTexas has promoted the development of wind energy over the past 15 years.
And on average, renewable energy sources - mostly wind - account for about 20% of its energy supply.
But the largest proportion comes from fossil fuels, as well as 10% from nuclear.
On Tuesday, the state's principal energy supplier, the Electricity Reliability Council of Texas (Ercot), said the freezing conditions had led to:
- 30GW being taken offline from gas, coal and nuclear sources
- a 16GW loss in capacity in wind and other renewable energy supplies
And this, it said, had severely curtailed its ability to satisfy a peak demand of 69GW over the past few days - a surge even greater than anticipated.
In its plan for an extreme winter weather event, Ercot says it expects only 7% to be provided by wind energy.
The company's Dan Woodfin said: "It appears that a lot of the generation that has gone offline today has been primarily due to issues on the natural gas system."
The cold weather also affected a water system needed to run the South Texas Nuclear Power Station, causing one reactor to shut down.
Dr Joshua Rhodes, at the University of Texas at Austin, tweeted: "There is no single resource to blame for this.
"We usually think of peak events happening over a couple of hours. This one is lasting days.
"Wind has been below expected output. But so have other sources."
image copyrightGetty ImagesCould Texas source energy from elsewhere?
Texas is the only state in the US with an independent power grid, meaning it is largely dependent on its own resources.
In normal times, this works fine because Texas is a large producer of energy, both fossil and renewable, and can provide enough for its population and export to other states.
But when its infrastructure is under strain, for example during a cold-weather event, most of the state cannot link up with other grids around the US to make up the shortfall.
Texas officials have now called for a hearing into the state's grid's ability to cope with extreme weather events.
Misleading claims on social media
The debate about renewable energy and the blackouts in Texas has also prompted the sharing of misleading claims online.
One image widely circulating on Twitter and Facebook shows a helicopter de-icing a wind turbine, with some comments suggesting it is in Texas.
"In Texas today... a helicopter, using fossil fuels, spraying de-icer, made with fossil fuels, to de-ice a wind turbine, manufactured using fossil fuels, that is supposed to produce clean energy without using fossil fuels," one Facebook post says.
But the picture actually shows ice being removed from a wind turbine in Sweden, using hot water.
BBC News traced the image back to a 2016 report published by Swedish company Alpine Helicopter, demonstrating "airborne de-icing solutions" for wind turbines.
Reporting by Christopher Giles, Jake Horton and Olga Robinson.
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