A £42m wave energy project off the Cornish coast has yet to produce any electricity despite being up and running for eight years.
Wave Hub, an undersea "socket" installed to test wave energy machines, has hosted just one device since 2010.
But it was not connected to the shore and one of the project's two remaining potential customers has now pulled out.
Wave Hub said it was "disappointed" that energy firm Carnegie had decided to test its device in Australia.
Carnegie - an Australian company - was given £9.6m from the European Regional Development Fund to test its device.
Wave Hub, based at Hayle in west Cornwall, said the wave energy business was "unfortunately taking longer to develop" than anticipated so it was "diversifying" and exploring options for testing floating wind turbines.
The scheme was financed by the South West of England Regional Development Agency (£12.5m), the European Regional Development Fund Convergence Programme (£20m) and the UK Government (£9.5m).
The authorities said at the time that it could generate £76m over 25 years for the regional economy.
MP for the area, George Eustice, said: "This is obviously disappointing news. Cornwall has a wave resource that is second to none, however the development of technologies to successfully harness wave energy has taken longer than hoped."
A total of four developers can connect a number of devices into the Wave Hub via the seabed socket, which then supply energy to the national grid.
Johnny Gowdy, from Regen South West, which promotes renewable energy systems, said floating wind turbines were a "great way of using the asset" and there was more money going into that technology than into wave power.
In 2006, three companies were signed on for initial development but all pulled out.
Michael Ottaviano, chief executive of Carnegie, said that grant support and the feed-in tariff support for wave energy had been removed over the last two years "and that has led to the situation we have today where we have a world-class piece of infrastructure in Cornwall and no wave technologies like Carnegie operating".
He said wave energy resources were "exceptional" in the UK and local expertise was "world leading" but "the better support we can get is in our home country".
He did not rule out returning to the UK "when the policy settings move again".
Seatricity, the firm behind the only device to have been hosted at Wave Hub, said it was funded by the company and received no public subsidy.