They are a familiar sight in the war and disaster zones of the Third World.

Floating power plants - essentially giant barges or ships with diesel generators on them - have saved lives and propped up economies from Gaza to Panama.

Now, sources have revealed, the emergency technology is being mooted as stop-gap solution for Scotland's electricity needs.

Power transmission giant National Grid is considering three contract proposals to maintain voltage in the power network north of the border for the next two years.

Two are known: the existing conventional stations at Longannet, in Fife, and Peterhead.

Without this contract Longannet will have to close, says its owner, Scottish Power.

National Grid has not revealed the third but The Herald understands it is power barges. Energy industry sources say they are not convinced by the proposal.

One said: "These floating power stations are used around the world, just not the first world.

"This is an untested solution being considered by a London-centric organisation.

"You can float anything up the Clyde, but this untried technology would remain a risk to the Scottish economy that would never even be considered in London."

Scotland has considerable expertise in temporary power generation systems - for major outdoor events or emergencies - with Dumbarton-based Aggreko a market leader in the technology.

However, energy sources, who do not wish to be named, said they were sceptical that such technology could maintain voltage in the way a fixed thermal plant can.

When asked about power barges, National Grid declined to comment on what its third option was.

A spokesman said: "All am I able to say is that we have received three proposals, which are currently being assessed."

Mike Calviou, director of transmission network service at the National Grid, this week told Holyrood Economy, Energy and Tourism Committee that a decision would be made within weeks.

Scottish Power told the same committee that it would have to shut Longannet within the year if they did not win the contract as transmission fees rose because of the Fife plant's Scottish location.

SSE, which runs Peterhead, admits its plant was also facing economic challenges.

The National Grid contract is a short-term fix until a major new power link between Scotland and Wales opens in 2017, allowing alternative energy to go south and conventional power to come north.

Floating power plants, unlike Longannet, could be relocated after the contract were up. They would also have to pay transmission fees.

Environmentalists have long campaigned against power ships outside emergency situations.

Richard Dixon, director, Friends of the Earth Scotland, said: "Any way you look at this, floating power plants are a stupid option.

"This is supposed to guarantee the security of the electricity supply in Scotland but power plants on ships are vulnerable to storms.

"Both the Clyde and the Forth have serious flood risks and diesel generators are just about the worst possible option when it comes to climate emissions.

"We should stick with what we know and rule out this last-resort option straight away."

There are scores of power barges currently operating around the world, almost all using diesel generators and almost all in the Third World.

A large one is currently anchored off Beirut to keep lights on in the once war-torn country as its economy grows.

Russia is currently developing floating nuclear power stations - the first scheduled to be launched next year - despite major green concerns.

There are also a handful of power ships, most made in Turkey. One has been offered to help Gaza rebuild after much of its electricity infrastructure was destroyed by Israeli bombing.