Tidal Lagoon Power has secured the grid connection for its project in Wales.
It has reached an agreement with National Grid over plans to build the £8 billion project, which is expected to power every home in Wales.
Located between Cardiff and Newport, it would be the first tidal lagoon power plant at full-scale.
The company said the Swansea Bay project would cost £89.90/MWh of electricity delivered to the grid for its 90-year lifespan while the Cardiff follow-up project would total £60-£70/MWh due to lower supply chain costs.
The UK Government is still considering the findings of its Hendry review, which backed the plans.
Chief Executive Mark Shorrock said: “Our offer to the UK Government is to contract Swansea Bay Tidal Lagoon for a lower subsidy per megawatt hour than Hinkley Point C.
“What’s more, by leveraging the commanding position taken by UK industry preparing for Swansea Bay Tidal Lagoon, the supply chain contracts awarded for Cardiff Tidal Lagoon will be worth more than £6 billion to UK companies.”
Guaranteed prices for new offshore wind projects are lower than new nuclear power plants for the first time in the UK under the government’s latest Contracts for Difference (CfD) scheme.