Millions more homes should have solar panels on their roofs, the new energy secretary has suggested, vowing to "unleash a new solar revolution" across Britain.

Amber Rudd, the former climate change minister, was promoted to lead the energy department in this week's reshuffle, in a move that was welcomed by many green groups .

Ms Rudd indicated she would back the continued expansion of household solar panels , which are heavily subsidised by consumers through levies on energy bills.

"I want to unleash a new solar revolution - we have a million people living under roofs with solar panels and that number needs to increase," she told her local newspaper, the Hastings & St Leonards Observer .

The Coalition government introduced a generous subsidy scheme to encourage households to install solar panels, triggering a boom that far exceeded ministers' expectations and saw them embroiled in a High Court battle over attempts to rein in the payments.

In total about 640,000 homes now have panels installed. The annual cost of the scheme is now estimated to be in excess of £800 million a year - almost twice the level ministers originally anticipated, as a result of the early boom.

Critics say the scheme enables wealthy families to rake in subsidies paid for by many who are already struggling with their energy bills.

Amber Rudd MP becomes Secretary of State for Energy and Climate Change @DECCgovuk #reshuffle #Ministers2015 pic.twitter.com/uNdJITxUND — UK Prime Minister (@Number10gov) May 11, 2015

While the payments are less generous than they once were, a household can still expect to make thousands of pounds in profit by installing panels.

A typical solar panel installation of 16 panels on a large family home could cost in the region of £6,000 but an owner could expect to recoup that cash within 7 to 8 years and thereafter make profit, according to the Solar Trade Association.

Solar panels being installed on a roof

The homeowner is paid for every unit of electricity the panels generate – while also saving on cash by not having to buy energy from a supplier. If the panels produce more power than the home needs, the owner can get paid for selling it on to the National Grid.

Aside from solar, Ms Rudd told the newspaper that she wanted to "shout loud about the benefits of switching energy tariffs" and to improve home insulation.

"My ambition in my new role is quite simple: to keep the lights on and carbon emissions down, whilst saving consumers money on their energy bills," she said.

Among the key priorities for Ms Rudd will be implementing the Conservatives' manifesto pledge to "halt the spread of onshore windfarms" by ending subsidies for new projects, and awarding energy companies new exploration rights to frack to shale gas.

Boris Johnson, the Mayor of London, said the new Conservative government would "certainly" be the "greenest ever" – five years to the day since David Cameron pledged that of the Coalition.

He told BusinessGreen that "huskies are go", in a reference to Mr Cameron posing with huskies in 2006 on a Norwegian glacier as part of efforts to show the party cared about tackling global warming. Britain would be "crazy" not to extract shale gas, he said.

David Cameron with huskies in 2006