The NHS spends around £400m (NZ$1 billion) on energy and emits one million tonnes of carbon each year.
However, statistics on NHS action on sustainability are hard to come by and the information available presents a very mixed picture.
Roughly half of English trusts, 207, have signed up to the Sustainable Development Commission 'good corporate citizen' scheme, which includes sustainability.
Six Welsh, five Scottish and four Northern Irish trusts have also joined.
Regional variations are striking: in the northwest, 84 percent of trusts have registered; but in London it is just 32 percent.
Acute trusts with large estates are leading the way, with 67 signed up. There are 65 primary care trusts and 40 foundation trusts taking part, as well as mental health trusts, care trusts and ambulance trusts.
Only five out of the 10 strategic health authorities are on board.
With just 20 percent of the NHS carbon footprint stemming from energy (60 percent is from procurement and 20 percent from travel), trusts are faced with a set of challenges wider than simply investing in a token amount of renewable technology.