By Clare Davidson
Business reporter, BBC News, Didcot power station, Oxfordshire
The cooling towers are crucial to the production of electricity
The vast cooling towers in Didcot dominate the Oxfordshire landscape as they belch out plumes into a clear sky.
The cooling towers are a vital part of energy production
It evokes an image of cigarette smoke on an industrial scale.
But the association is misleading. As the Department for Environment, Food and Rural Affairs (Defra) says: "While existing coal plants are a contributing factor to climate change, the damaging emissions are invisible."
"People associate cooling towers with pollution," bemoans Steve Waygood, regulation manager at Npower. But what you see is water vapour, he explains.
"Water is fundamental to the energy process, by creating steam," says Mr Waygood, a chemist who has worked for the firm for more than two decades.
Cooling towers help remove heat into the atmosphere.
Producing energy, whether in coal or gas stations, needs water. Water is also used in refining oil and gas and for running nuclear power stations.
Nevertheless, people often forget how essential it is, he explains.
The cooling towers - totalling six - are deceptive in size.
Only when you are standing next to them, looking skyward, does their true scale become apparent. At 300ft in diameter and more than 370ft high, they appear even larger than anticipated.
The cooling towers are largely empty inside
Water spraying into a shallow pool, below the tower, creates a constant rushing sound.
Climbing up an outside staircase to the entrance is enough to make anyone feel quite dizzy, as the top of the towers looms overhead.
"There is always a wind around the towers," says station chemist Tom Cracknell, urging us to hold on tight to the railing as we are buffeted by the air.
As we step inside one of the Didcot A towers, temporarily taken out of service, there is an eerie calmness.
You expect to find activity inside, but it's quite the opposite.
There are no moving parts or motors or fans, simply a central walkway with boards on either side.
Thick mist prevents us from seeing beyond a few metres. Only Mr Cracknell's high-visibility jacket proves his presence.
The water used by Npower, explains Mr Waygood, comes from the same source that everyone else uses locally: the river Thames.
DIDCOT POWER STATION
Didcot A, a coal fired power station, generates 2000 MW, enough electricity to supply two million homes
Didcot B, a combined cycle gas station, generates 1360 MW
The most significant loss route for water is through evaporation
Npower pays £1m yearly for town mains water, including treatment costs
The licence fee for the river costs about £300,000 a year
What is different is the scale.
Didcot B took 11 million cubic metres from the river in 2007, and returned about 5.5 million cubic metres of that after using it for cooling.
Meanwhile, Didcot A used 24 million cubic metres, while returning 17 million cubic metres to the river.
This comes on top of more than one million cubic metres of Thames-treated mains water needed to top up the boiler water circuits.
"This works out at 3,000 to 3,500 cubic metres a day in town mains water," says Mr Waygood. "To put this into perspective, an individual is estimated to use 160 litres daily."
Mr Waygood looks quizzical and does a quick mental calculation: "We use in a day what 50 people use in a year [in mains water]".
Access to water
A trip to the pump house, about a mile up the road from Npower's plant, shows where the water comes in.
You can't talk about energy or water in isolation
Philippe Rohner, investment manager, Pictet
It is hard to grasp that this small building, set adjacent to a pretty riverbank, is so crucial in ensuring that hundreds of homes have reliable access to electricity.
There is a low hum as a device draws water from the river, but nothing grandiose to see.
As we arrive, technicians Dave Belcher and Alan Hawkins are checking one of the pumps.
"River availability is a key issue. It has natural changes in flow during the year," says Mr Waygood.
"We know that there will be times when we won't be able to take enough to allow for all the units at Didcot A and B to run."
While Npower attempts to return as much water as possible to the river, without access to it, energy production would be impossible.
The dependency goes both ways. Just as water is essential to produce energy, it takes a lot of energy to treat and distribute water.
The pumphouse brings in water from the river Thames
Philippe Rohner, an investment manager at Swiss investment firm Pictet, known for its water fund, puts it bluntly: "You can't talk about energy or water in isolation."
But there is a significant difference in the amount different types of energy require.
Debates about the environmental impact of energy often concentrate on greenhouse gas emissions. But factoring in water usage can paint quite a different picture.
Nuclear energy, for example, requires access to vast amounts of water.
A report by JP Morgan, entitled Watching Water, said there was increasing anecdotal evidence about the material impact of water on the power industry.
Claudia Kruse, an analyst at JP Morgan, said one of the main challenges for firms, including in the power generation industry, was reliability of water supplies.
"The impact of climate change on water quality and availability should not be underestimated," she said.
This point was underlined in 2003, when France, which relies heavily on nuclear energy, had exceptionally high temperatures and low river levels. Energy firm EDF had to close a quarter of its 58 nuclear power plants, the JP Morgan report said.
The average electricity price soared by 1,300% and the firm lost 300m euros by having to import power.
So low water levels could mean yet higher energy prices.
Uncertainty about our future energy supplies persists. But one thing is clear - access to water and how much it costs will be a crucial part of the debate.
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