Six of the pioneering powerstations are to be built in locations across Britain, with at least one already in the planning stage.

Four of them will be located in Wales — in Swansea, Cardiff, Newport and Colwyn Bay — and there’ll be one each in Bridgewater in Somerset and West Cumbria.

Tidal Lagoon Power, the firm behind the project, eventually believes that six lagoons could generate eight percent of the UK’s electricity for a cost of £12 billion.

The plan is backed by energy secretary Ed Davey.

Here’s how it’ll work in the first location, Swansea Bay.

A sea wall eight kilometres long will be built to encircle a large area of water three kilometres out from the coast, isolating it from the sea like a lagoon. Turbines will be set in the wall, which will then generate energy from the difference in water height four times a day as the tide rises and falls.

One of the benefits of tidal power, compared to solar or wind, is that it’s totally predictable. We know how much energy such a scheme would generate decades into the future, making it much easier to integrate with existing electrical infrastructure. It’ll also last a long time — the firm estimates about 120 years.

But getting started isn’t cheap. The first lagoon is expected to carry an extremely high price tag — at least £1 billion — which taxpayers will front. That’ll provide energy for 155,000 homes alone and serve as a test bed for the technology, making subsequent plants of the same type less pricey. “It’s a little bit expensive to start off with, then very cheap for a very long time,” Mark Shorrock, the CEO of Tidal Lagoon Power, told BBC News.

Previous plans for a tidal barrage on the Severn river were cancelled due to environmental concerns, but this project does not affect the mud flats crucial for wading birds. As such, it’s been cautiously welcomed by environmental groups placing the clean energy it will generate over the limited disruption to the ecosystems of the bay from the delayed tides.

However, anglers have expressed fears over the effect of the turbines on fish migrating to spawn in local rivers. The company factors that the numbers of fish caught in the turbines will be small, and the new sea wall will create a reef habitat that benefits fish.

Right now, Tidal Lagoon Power is negotiating with the government over how much it can charge for the electricity. It’s hoping for £168 per megawatt-hour the Swansea lagoon, falling to £90-£95 for a second lagoon in Cardiff. That compares well to the planned Hinkley Point nuclear plant, which will generate power at £92.50 per megawatt hour.

“The Swansea Bay Tidal Lagoon provides the key to unlock large quantities of reliable, low cost, low carbon electricity for the next 120 years,” said Shorrock. “Backing the Swansea Bay Tidal Lagoon also means backing a catalyst for British industry and exports, a new option for strategic flood defences, an opportunity to regenerate coastal communities and a vision for national energy infrastructure that can work hand-in-hand with nature.”

You can explore an interactive 3D model of the lagoon here.