Energy bills at a row of Swansea Valley bungalows which have been re-fitted with solar panels and a Tesla battery have dropped to just a pound a week.
The six council-owned properties in Craigcefnparc have undergone a wholesale transformation in a pilot project which is expected to be rolled out across Swansea and south west Wales.
Speaking at a cabinet meeting on May 7, Cllr Andrea Lewis said the energy bills were £71 per property in January but just £3 for the first 21 days in April.
By the summer, she said, the bungalows could be "in positive territory" energy-wise and exporting surplus power to the grid.
Although April was remarkably sunny and perfect for anyone with solar panels, people were also at home using their computers and other gadgets due to the coronavirus lockdown.
Cllr Lewis, cabinet member for homes, energy and service transformation, mentioned the retrofit scheme as colleagues approved a £505 million homes as power stations project for the Swansea Bay region.
The idea is that 7,000 properties will be retrofitted across Swansea, Neath Port Talbot, Carmarthenshire and Pembrokeshire over five years, with a further 3,000 energy-efficient houses built.
The bungalows at Ffordd Ellen, Craigcefnparc, have new roofs, triple-glazed windows, insulated wall rendering and solar panels. Warm water comes from ground source heat pumps, while air is circulated via ceiling vents, which helps retain warmth.
Funding came from the Welsh Government and the Welsh School of Architecture, which also provided expertise. Around £55,000 has been spent on each property.
Cllr Lewis said she would work with housing associations and look to roll out more of these projects.
More about renewable energy:
"I appreciate it will take some funding and resource," she said.
But she expected costs to come down, and added: "That could effectively mean we eliminate fuel poverty."
Cllr Francis-Davies said the £3 bills for most of April were "absolutely staggering".
Meanwhile, tenants are due to move into a new-build council housing scheme at Parc-Yr-Helig, Birchgrove, next month, where energy bills should also be very low.
The homes as power stations initiative is one of 11 Swansea Bay city deal projects and will need to be approved by all four participating councils, regional leaders and the UK and Welsh Governments.
A 140-page project business case included in the cabinet papers said there were risks, and that it would not directly lead to the development of "a stand-alone private sector house building programme".
The report said it expected average retrofit costs of £25,000 per property to drop to below £20,000 through economies of scale.
Cllr Stewart said: "People should not be faced with a heat or eat decision in their homes.
"What we are building are a better standard than the private sector, and why should it not be that way?"
