A new solar farm in Swansea will help power the city's Morriston Hospital.
Electricity from the development, off Felindre Road, will be carried along a three-kilometre cable to the hospital.
The 10,000 solar panels are forecast to supply a quarter of the hospital's electricity and reduce the bill by £500,000 per year.
Swansea Bay University Health Board expects work to start on the £5.7 million project at Brynwhillach Farm, which also involves Vital Energi, early in 2021.
The health board spends around £6.9 million per year on energy, water, and sewage treatment. It has received £13.5 million from the Welsh Government for the solar farm and other energy-saving measures, repayable on an invest to save basis.
Health board assistant director of operations, Des Keighan, said the work was being delivered in two phases.
“The first phase was a range of energy conservation measures at Morriston and Singleton hospitals, and other health board premises," he said.
“These included changing the majority of light fittings, and improving the insulation, lagging and upgrading building management systems."
These measures should cut the energy bill by £1 million annually.
The second phase is the solar farm.
Mr Keighan said: “We will be the first health board in Wales to develop its own solar farm."
He added: “At peak production times this will meet the electricity demand for the entire hospital, whilst reducing our carbon emissions.
“This is in line with the Welsh Government’s commitment for the public sector to be carbon neutral by 2030.”
Emma Woollett, the health board's chairwoman, said: “Cutting our carbon footprint and cutting costs is a win-win for the health board, our patients and taxpayers.”
Funding for energy efficiency measures has also been given to Cardiff and Vale University Health Board and Hywel Dda University Health Board.
Lesley Griffiths, Minister for Environment, Energy and Rural Affairs, said: "I would like to thank each of the health boards for the work they have already undertaken in this respect; and would especially like to thank Swansea Bay University Health Board for their ambition, as they work towards creating a new solar farm, which will help power Morriston Hospital."
Vital Energi account director Phil Mottershead said: “Being able to deliver solar energy on this scale for an NHS site is an exciting opportunity."
