Supermarket giant Coles has signed a long-term contract to get electricity from three new solar farms, the latest in a series of companies that have turned to renewable energy to lower power bills.

It comes as a group of 41 retailers and businesses including Bunnings, Harvey Norman, Ikea and JB Hi-Fi plan an unprecedented joint electricity purchase in a bid to reduce costs. Coles announced a 10-year deal to buy most of the electricity generated at three new solar farms to be built outside Wagga Wagga, Corowa and Junee in NSW.

Steven Cain, Coles Group’s chief executive, said the company was committed to being the most sustainable supermarket in Australia. It had spent more than $40m on energy efficiency over two years and installed solar panels on 30 stores, with another 38 to follow this financial year.

The supermarket agreement follows a similar announcement on Monday by Molycop, a manufacturer for mining and rail companies, that it had signed an 11-year-deal to take electricity from a separate solar farm near Wagga and the Sapphire wind farm in northern NSW to help it limit the impact of rising power prices.