Andrew Crossland, energy storage specialist and blogger at MyGrid, says we should invest in tidal lagoons to increase the diversity of our energy supplies and reduce our carbon emissions

The UK is committed to carbon reduction in all sectors of the economy, be that electricity, heating, transport, agriculture or industry. The recently announced project to build a 320MW tidal power station at Swansea Bay has drawn much attention in the media and is lauded by the government as a “mega-project” to help generate sustainable local energy and assist with climate goals.
The indications are that the power station will be a provider of low-carbon electricity. The Intergovernmental Panel on Climate Change lists carbon emissions for different sources of electricity but doesn’t list tidal generation. It estimates that equivalent sources such as hydroelectric dams (whose emissions stem from construction) have carbon emissions 20 times lower than gas or 34 times lower than coal. Swansea Bay is projected to run for 120 years, so will have plenty of time to offset emissions from construction.
How much can it reduce our annual carbon emissions? I believe I can answer that. Through my MyGridGB platform, I track electricity generation in GB in terms of the volume of electricity produced and the carbon emissions from the sector. I have proposed an alternative generation mix – the MyGrid Manifesto, with more nuclear, solar, wind and storage to meet our climate goals – that is simulated in real time.
A tidal array will produce a reliable and predictable amount of energy over the year and do so in tune with the tides. As a relatively small power station – a tenth of Hinkley Point C – it is unlikely to be curtailed during times of low demand.
It is impossible to predict how much wind, solar, nuclear and biomass will be connected to our electricity system by the time Swansea Bay opens. Similarly, it is difficult to predict demand: how many electric cars will be online by then is a mystery to me. So to assess the impact on carbon emissions, I propose that we look at what would have happened if Swansea Bay was opened in January 2016 and at the same time all coal power stations had closed.
Had coal been replaced by gas, the chart shows our electricity mix. This is a frightening chart for anyone outside the gas industry. Gas dominates our electricity system and our domestic heating market. Gas is king in Great Britain.
My chart represents 298TWh of electricity generation in 2016, releasing 92MT of CO2. It is reasonable to predict that the tidal array will offset energy generated by gas power stations, because coal stations will have closed. Gas is flexible enough to meet the peaks and troughs in tidal generation and it is nonsensical to switch off nuclear, wind or solar.
Swansea Bay is projected to produce 530GWh of energy a year. In our 2016 scenario with no coal, Swansea Bay means 530GWh less gas-generated electricity. CCGTs emit a median of 490gCO2/kWh, according to the IPCC, so the station alone will reduce carbon emissions by 0.25MT or 0.27% of what was released in our 2016 scenario (assuming our tidal plant has the same embedded carbon emissions as a hydroelectric plant at 24gCO2/kWh).
That isn’t much on its own. However, let’s not forget that Swansea Bay is part of a fleet of proposed stations around the country at a decreasing strike price. The prices of solar and wind power have plummeted and both are now reaching grid parity. If the government is strong and continues to support the industry with clever price signals, then the same should be expected of tidal arrays.
Should Cardiff and Newport be added to Swansea, the three tidal arrays would reduce GB carbon emissions by 4.3% and gas consumption for electricity by 5.6%. The company behind Swansea Bay also proposes other projects for Colwyn Bay, West Cumbria and Bridgewater Bay. If built, these would make further inroads into GB gas consumption and carbon emissions.
Is that a good thing? I think it is. Anything that diversifies our electricity mix and supports locally produced electricity for a reducing price has to be good for consumers and good for industry. Our country risks being dangerously exposed to the whims of foreign gas cartels that could raise prices or reduce supply at any moment. Swansea Bay could be the start of a revolutionary reliable and new (for GB) source of power and we would be mad to let it slip away.

Further reading:

From the archive: Swansea’s tidal lagoon – how does it work and where are the costs?