Announcing annual results Hargreaves said pressure on power plants to cut emissions and the high cost of renewable energy are likely to push up prices for households and businesses.
The group, which recently closed Maltby deep mine in South Yorkshire, said price hikes and a power generation squeeze could force politicians to reconsider coal as an alternative fuel, with new nuclear, gas and renewable plants slow to replace ageing coal power stations.
Chief executive Gordon Banham said: "Our own view is that coal fired generation will remain an important element of the UK energy mix well into the second half of the 2020s and probably even beyond."
The group plunged to £50 million annual losses after closing Maltby earlier this year, but has since been scooping up surface mines in Scotland.
It bought the rights to surface mines in Scotland from failed mining groups ATH and Scottish Coal to consolidate its position as a "key UK coal producer and distributor", leaving it with more than 24 million tonnes of provable reserves.
Revenues surged by more than a third to £843.3m as it supplied much more coal to power stations and steel producers.