Thames Water has signed a deal to install photovoltaic systems large enough to cover 15 football pitches at three key sites in London.
The water firm is aiming to become Britain's biggest on-site solar power producer and industrial user after signing with Ennoviga Solar, a specialist photovoltaic developer.
Under a £7m, 25-year contract, Ennoviga Solar, has created an investment company that will own and maintain the solar arrays, repaying the investment by selling all the clean electricity produced to the water company at a market-competitive price.
Dr Piers Clark, commercial director at Thames Water, said: 'With the price of energy forecast to increase above inflation, the way we've structured this agreement will give us cheaper, renewable source of power from a secure source over the long term. We think this is the right thing to for our 14m customers and to help move Britain that little bit closer to becoming a low-carbon economy.'
When fully completed, the three sites will provide an annual output of more than 4,500 megawatt hours (MWh) of electricity - enough to run around 970 average-size homes.
The scheme will shave £100,000 a year off Thames Water's electricity bill, providing 0.5 per cent of its 1,180 Gigawatt hours (GWh), £80m annual energy requirement - for processing and pumping 2.6bn litres of water a day and 2.8bn litres of sewage a day - in addition to the 16 per cent already generated from anaerobic digestion of sewage.
After the installations are completed at the three sites, Thames Water plans to fit more photovoltaic systems at up to 100 of its smaller locations, delivering a further 0.5% of the firm's annual energy requirement.
The solar arrays are being fitted in otherwise unusable places at three operational sites in the capital: on the roof of the Beckton desalination plant in Newham, on the top of vast storm tanks built in the 1800s at Crossness sewage works in Bexley, and on redundant sand filters at Walton water treatment works in Sunbury.
Stefano Gambro, director at Ennoviga, said: 'The UK is running late on building new power generation to replace its ageing power stations. The feed-in tariff scheme was launched in April 2010 to provide a stable investment climate so private investors would build this new capacity, and at the same time make Britain's electricity cleaner.
'By working with us, Thames Water has led the industry in exploiting otherwise unusable space to generate clean electricity. When energy prices rise and carbon charging starts, the impact on Thames Water customers' bills will now be that little bit less.'
A 450kW array of solar panels, commissioned last week at Beckton, will generate 385 MWh a year on average, while 150kW arrays installed at Crossness and Walton will each generate 133 MWh a year on average, enough to power 140 average-sized homes.
Once the Crossness array is expanded to its full potential of 1,700 kW, it will generate an additional 1,400 MWh a year on average. And once the Walton array is expanded to its full potential of 3,000 kW, it will generate an additional 2,500 MWh per year.
Thames Water has set a voluntary target of reducing its greenhouse emissions by 20 per cent in real-terms on 1990 levels by 2015.
