Wind, wave and tidal energy projects are projected to create up to 3500 jobs in the area by 2030, but they are dependent on a new transmission interconnector cable to carry the extra power.
Scottish Hydro Electric Transmission, part of SSE, now estimates it will be 2019 at the earliest before it is laid between Lewis and Wester Ross. Previous targets had been 2015 and 2017.
But Niall Stuart, chief executive of industry body Scottish Renewables, said: "I am afraid it is getting harder and harder to see the new interconnector to the Western Isles ever happening. If there is no connection, there are no major projects and the dreams of green energy heralding a new economic dawn will be shattered."
He said that for SSE to lay the interconnector across the Minch at a cost of £750 million it must obtain permission from regulator Ofgem, which will only agree if the energy firm has a cast-iron business case. Mr Stuart added: "It is impossible for SSE to submit such a business case because none of the developers know what the transmission charges are going to be. Also none of them know what their income is going to be."
He said the developers first had to win a Contract for Difference - a deal signed with the National Grid but following rules set out by the Department of Energy and Climate Change (DECC). It is the new mechanism for subsidising nuclear and renewable energy.
He added: "They are caught in a never ending circle because they can't get a Contract for Difference because they can't get a grid connection before 2019, and SSE can't sign off on the grid connection because developers can't guarantee that they will ever get a Contract for Difference."
However, others are not so pessimistic. A DECC spokeswoman said a meeting in London on Thursday between Energy and Climate Change Secretary Ed Davey and his Scottish counterpart Fergus Ewing "re-iterated our shared commitment to tackling the complex issues involved".
A spokesman for the Western Isles Council said: "The process for getting an interconnector to the islands has certainly been frustrating, however we are not giving up the fight."
He also said the council did not agree with all Mr Stuart's analysis, particularly on the respective roles of SSE and Ofgem.