All 14 Asda stores in Northern Ireland are now powered by electricity derived from 100% green sources, the company announced.
Asda said it was closer to its target of buying 100% of its energy requirements from renewable sources for its 376 stores across the UK after signing up with Airtricity, a company based in the Republic which has now expanded into Northern Ireland.
US parent company Walmart has set an energy efficiency savings targets of 20% by 2010 across all existing stores.
It takes around 34 gigawatt hours of electricity per year to power Asda's Northern Ireland stores. The company said the switch to Airtricity would enable the company to consume around 30% less energy, significantly reducing its carbon footprint.
The company said it has also pioneered cleaner, smarter, energy efficient ways of working throughout its business - from the shop-floor to office, distribution and warehousing.
David Olivivant, Asda energy procurement manager, said: "This is another major milestone for Asda in Northern Ireland and is proof that we are living up to our green credentials and aspirations.
"Everyone knows that running supermarkets requires significant energy usage, but our goal is to do so effectively and efficiently, saving costs where we can."