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Hello, and welcome to this week’s Fix the Planet, the weekly climate change newsletter that reminds you there are reasons for hope in science and technology around the world. To receive this free, monthly newsletter in your inbox, sign up here.

I had more or less written-off tidal power. For several years the technology has looked like it is in a cul-de-sac, eclipsed by wind and solar coming of age, and unlikely to make the jump from demonstration stage to commercial electricity supplies.

Yet in a surprising twist, , companies backing tidal as a key part of the clean energy puzzle will be able to bid for £20 million worth of UK government subsidies. That effectively fires the starting gun on a key decade for tidal-power developers to prove they can bring down the high costs for power stations operating in some of the harshest environments on Earth.

So why has tidal power come back into vogue? What difference will these incentives make? And are we finally going to harness the awesome power of the moon and seas in a serious way? This week’s Fix the Planet dips a toe into the waters.

Why tidal power?

It’s predictable and low carbon. Most places get two low tides and two high tides a day, and we know when they will happen. That makes it easy to know how much energy will be supplied on any given day or month. Tidal power is never going to outcompete wind and solar power on cost or scale, but it can marry nicely with the variable output of those two, something that came to the fore during the UK’s energy crisis in September, which saw a run of unusually still days. “It’s a complementary technology to wind and solar,” says Danny Coles at the University of Plymouth, UK. He that the UK has enough tidal resource around its coastline to generate 11 per cent of the country’s current electricity needs.

How does it work?

Either through the horizontal ebb and flow of the tides (tidal stream) or the vertical rise and fall (tidal range). For our purposes today I am talking about tidal stream, effectively the underwater equivalent of wind turbines. The designs come in a few different shapes and forms. There are some that attach to the seabed, made by the likes of Atlantis Energy and Nova Innovation, two firms based in Scotland. Some have two blades, some have three, like a wind turbine. Other designs hang from the underside of a floating platform, such as those by Orbital Tidal, another Scottish company. Those attached to the seabed have the attraction of being invisible from above and not affecting shipping, while floating ones sacrifice that for easier maintenance. Some are starting very small (Nova’s are 0.1 megawatts), others are much bigger (Atlantis’s are 1.5MW). Battery storage developments mean developers the occasional troughs in output that come from slack tides.

Why is the UK suddenly interested now?

The stars aligned. One of the UK government’s big ideas is to “level up” regions outside of London, which matches with the geography of tidal power resource and where the components might be manufactured. It’s also a chance for the UK to maintain its leadership on the technology, something it failed to do in the 1990s with wind power. There’s a neat fit with another government pitch, of “global Britain”. Canada, France and Indonesia are among the countries with a big tidal power resource that could be exploited with UK exports.

“Against the backdrop of ‘build back better’ and ‘levelling up’, tidal ticks a lot of boxes,” says Stephen Wyatt at the Offshore Renewable Energy Catapult, a government-funded research group. The amount of UK-made hardware in tidal power projects is also typically about 60 to 70 per cent, and even higher in some cases, compared with . “That’s really attractive,” says Wyatt.

“I think it also links into the higher ambition for net zero,” says Charles Hendry at the Energy Institute, who is a former UK energy minister. He says there is an increasing realisation that net-zero goals for energy cannot be met with wind and solar alone, and tidal power is one of the predictable technologies that could complement them, along with small nuclear plants.

What difference will the subsidies make?

“I think it’s a big moment,” says Tom Wills at Nova Innovation. “The UK was really running the risks of repeating the risks of the development of onshore and offshore wind where we had an early lead and failed to maintain it. It [the new subsidy pot] protects the UK’s leadership role.” In the past decade or so, tidal power in the UK has been hamstrung by its failure to compete in auctions for subsidies against wind and solar, which are mature and cheaper. Without that financial support, few companies could make final investment decisions, and few machines have been put in the water. “It’s a tremendous difference. It’s hard to overstate how important it is to have a route to market”, says Wyatt of the £20 million pot the government has ring-fenced for tidal power in the auction starting next week. The money is for schemes that can be operational in 2025-2026 and 2026-2027.

On a basic level, the money should add three times the UK’s current tidal power capacity. There is and globally there’s another 16MW. Wyatt thinks next week’s auction will buy another 34MW in the UK.

Tidal power’s advocates say the subsidies should mark the beginning of bringing prices down, like the falls that offshore wind has seen over the past decade. “I think we’re at the start of a key decade for tidal. It absolutely has to prove itself in terms of cost reduction,” says Wyatt. Tech from offshore wind could also help reduce costs, such as on cables taking projects’ power to the shore.

What’s going on internationally?

Australia, Canada, China and Denmark are among those deploying demonstration and small commercial tidal power projects. Nova has signed deals for turbines destined for Canada and Indonesia. Yet the International Energy Agency , saying tidal schemes “remain expensive because the economies of scale necessary for significant cost reductions have not yet been realised”.

Why might tidal still fail?

Most projects to date have been small scale. But if tidal is going to supply anywhere near 11 per cent of UK electricity, Hendry says companies will need to prove the hardware can withstand being crushed by the pressures that the most powerful tidal flows exert, as demonstrations have so far taken place in more modest waters.

Coles is more relaxed that the technology can prove itself. He says one issue will be that much of the tidal stream resource around the UK is in remote areas, relatively far from the cities that demand tidal’s low-carbon energy. New long distance power cables will be needed, or even discussions over whether to relocate energy-intensive industries closer to tidal projects, he says.

Like all power generation, tidal will have some environmental impact: . Some individual projects, as has happened with offshore windfarms, will not a green light from panning authorities after environmental surveys.

A more prosaic problem may be the economics of tidal power, and the risk of hoped-for cost reductions not materialising. If the industry fails this time, it won’t get another chance, says Wyatt. Yet observers think this is the decade tidal power will prove its mettle. “I think if we’re going to achieve the net-zero ambition, this is going to be an important part of the process,” says Hendry.

MORE FIXES

• A group behind a concept low-carbon plane using liquid hydrogen as fuel this week. Don’t expect to fly on it soon. But .
• Electric car sales in the UK last month , taking fully battery-powered cars to almost a fifth of market share.
• Green party MP Caroline Lucas if it could explain why its refusing to release a spreadsheet showing the emissions savings of individual measures in its flagship net zero strategy. Read �鶹��ý’s story about trying to obtain the document to find out more.

And finally, a little plug for , a hybrid online and in-person event taking place from 29 to 30 January 2022. Start by checking out .