EDP Top100 firm Roys of Wroxham has so far invested £750,000 in solar panels for its stores in a programme that began last December.

More than 2,700 panels have been fitted to the roofs of five branches across East Anglia - Dereham, Sudbury, Bowthorpe and two in Wroxham - and Roys' Thetford store will be having them installed in the next two weeks.

Mike Kett, the company's risk and facilities manager, said: 'The panels can't be seen from the ground. They enable us to create our own energy instead of taking it from the national grid.

'The amount generated depends on the type of day - the sunnier the more productive - but overall we are saving 9pc of the total energy we pull from the national grid.'

Mr Kett said that so far the panels had saved them £40,000 with another £40,000 coming on top of that from the government's feed-in tariff designed to encourage green energy use.

He said: 'We are still looking at installing them on a further two stores. We should recoup all the costs in six years and we have a guaranteed feed-in tariff for 20 years.'

Mr Kett said Roys had started its green energy drive in 2005 when the company joined the Carbon Trust.

He said: 'They gave us some ideas and by implementing them our overall energy savings have been 29pc on a like-for-like store.'

Measures ranged from installing more modern plant, such as refrigerators, to changing store lights to energy efficient tubes.

'We have installed power optimiser units in our bigger stores which save energy by turning the power down to the level you need for your equipment,' he said. Mr Kett said the green drive had been led by energy champions nominated at each store to pinpoint cases of energy being wasted.

He said: 'Saving energy helps each store as they are individual cost centres.'