You can rely on npower for your energy â weâre one of the UKâs biggest energy suppliers with the backing of one of Europeâs largest energy companies, the RWE group. We stand up for the community too. Weâre proud to have been a partner of Macmillan for 11 years raising over Â£3m.lease note that npower Fixed Energy June 2016 is no longer available. Those currently on this tariff may see their prices increase as of 30 June, 2016 as they will be automatically rolled onto 'Standard' tariff prices.