A review commissioned by the government into the potential for tidal lagoon energy in the UK is to be published.
If the independent review, conducted by former energy minister Charles Hendry, backs the technology, it could provide a boost to a "world first" project to harness the power of the tides in the Severn Estuary.
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The assessment, commissioned last year amid negotiations on the project, has looked into whether the lagoons represent value for money and how they could contribute to the UK's energy mix in the most effective way.
Renewable energy firm Tidal Lagoon Power wants to secure subsidies for a £1.3 billion scheme to build the world's first lagoon power plant in Swansea Bay.
The lagoon would involve a U-shaped breakwater built out from the coast, with a bank of turbines turned by water which would harness the rise and fall of the tides to generate renewable electricity.
While the Government has expressed backing for lagoons, former prime minister David Cameron said his enthusiasm had been "reduced" by the costs, with much higher subsidies than nuclear or offshore wind mooted at one stage.
Tidal Lagoon Power now says the Swansea Bay scheme would require only the rate of bill-payer support currently offered to nuclear, and because the project was small it would cost households as little as 20p to 30p on average.
It would also generate thousands of jobs and boost the Welsh economy, while supplying predictable, clean electricity for 155,000 homes.
The company claims the Swansea Bay lagoon would be a proof-of-concept project opening the way for a series of lagoons around the coast, costing less due to economies of scale and meeting 8% of the country's power needs for 120 years.
But conservation groups have raised concerns about going ahead with a series of lagoons before the impacts of the Swansea scheme are assessed.
Mr Hendry said lagoons offer a "completely predictable" source of power.
He told BBC Radio 4's Today programme: "We know it absolutely works. One of the great advantages is it is completely predictable for all time to come.
"We know exactly when the spring tides and neap tides are going to be every single day for the rest of time and so, in terms of meeting security of supply, lagoons can play an important role."
Mr Hendry said he had assessed how expensive the project was by spreading the cost of the subsidies over the lifetime of the project.
"If you look at it over the cost of that 120 years then you get a very much lower figure than almost any other source of power generation."