The £4.2m grant-funded installation at Castle Hill Hospital in Cottingham, East Yorkshire, covers 7.7 hectacres, around the size of 14 football pitches.
Hull University Teaching Hospitals Trust, which runs the hospital, said the scheme meant the trust was currently saving about £250,000 a month.
Work, which began in September amid plans to generate a third of the total energy requirements of the hospital, was completed in February.
And due to the start of British Summer Time, the panels are generating about 26MWh per day, the equivalent to the average daily energy needs of 3,250 UK households.
The Trust said this is enough to meet the daytime running needs of the entire hospital, with output expected to almost double during the peak summer months.
The trust, which also runs Hull Royal Infirmary, is replacing 20,000 lights across both sites with LED bulbs and is to insulate buildings and install pumps to cut heating costs.
Alex Best, head of Capital for the trust, said: “Our aim has always been to generate enough electricity to make the hospital site self-sufficient in the summer months when the days are longer.
"And now that the clocks have gone forward, the panels are generating around 26MWh per day so far in May, and are anticipated to rise to a peak summer load of 50 MWh per day.
“Not only does this represent a significant contribution towards our plan to become carbon neutral by 2030, but the project is also saving us a significant amount of money on hospital energy bills; approximately £250,000 to 300,000 every month."
The project, dubbed the ‘Field of Dreams’, is part of the trust’s campaign to tackle the NHS’s impact on climate change by achieving net zero carbon emissions by 2030.
Mr Best added: “The team which has worked on the solar field has done a fantastic job and we’re really pleased to be leading the way in this respect.
"We hope our patients and visitors will also see the value in what we’re doing for them, and for generations to come.”
Marc Beaumont, head of Sustainability for the trust, said: "Castle Hill Hospital is a specialist regional centre for cardiology, oncology and haematology for example, and it boasts one of just a handful of specialist infectious diseases units around the country.
"When you consider the size of the Castle Hill Hospital site and the amount of activity that goes on here, that’s a huge amount of power that’s required to keep it running.
“Now if you stop to consider what the solar panel project is actually contributing, it’s incredible to think that the power used to deliver patients’ radiotherapy treatment sessions, to support many life-saving surgical procedures, and to keep our intensive care unit running right now is all completely self-generated, green electricity.”
Work has also started 12-hectare solar farm which is being developed on a former landfill site next to New Cross Hospital in Wolverhampton.