‘The tide is nature’s battery’: How tidal power can help replace gas and oil

The need for Ireland to move, as a nation, to renewable electricity generation has probably never been more apparent. Quite apart from the looming spectre of climate catastrophe, there’s now the sudden realisation that around half of our electricity comes from gas, and gas is a resource that can be politically controlled, and its price artificially inflated.

There was justifiable applause in February this year, when Ireland set a new record of generating 53 per cent of its electricity demand from wind power. That is impressive, but it does disguise a salient fact. The wind doesn’t always blow, so what happens to that 53 per cent on a calm day? Or indeed, what happens when the sun isn’t sufficiently sunny for solar power to generate much power. There is a constant baseline demand for power which cannot reliably be met by wind nor solar, never mind what happens when demand peaks – generally between 5pm and 7pm in the evening.

There is, though, a potential solution. Tidal power. The concept of tidal power is nothing new – tidal flows can be exceptionally powerful and generating electricity from large volumes of moving water is technology that’s well understood. A tidal energy generator is, in very simplistic terms, rather like turning a hydro-power station inside out – turbines on the inside, water on the outside.

To date, Ireland has not made much of the fact that we are a nation of coasts, but that could be about to change. Stuart Murphy – yes of course there are Irish family connections with that name – grew up in The Wirral, in Liverpool, and watched the river Dee flowing in and out of the vast estuary there. It’s that memory of vast movements of water that have inspired him to create TPGen24, which has plans for vast numbers of tidal power generators up and down the coast of both Britain and Ireland.

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Murphy says: “Putin has done more for tidal energy in the last two weeks than we’ve done ourselves for the last 20 years. Because it’s become apparent to everyone that we have to become self sufficient in power. To be truly renewable energy, you have to have no human interaction in the system. The wind blows, the sun shines, and the tide goes in and out.”

Murphy’s obsession is the baseline power demand – that constant background need for energy which, in Ireland, is currently being met by natural gas-burning power plants. It’s not that wind can’t provide the necessary energy to meet baseline demand, it’s more that it can’t reliably do so, day-in, day-out. While there have been proposals for huge battery storage systems to store excess wind power for later use, even using the growing ranks of electric cars as storage, such ideas raise at least as many – expensive – questions as they provide answers.

“Once you understand that wind and solar are intermittent, you realise that they can never provide baseline power,” says Murphy. “You’re left with only one solution and that’s tidal. The whole idea of battery storage for wind or solar just isn’t going to work. Imagine it’s six o’clock in the evening and everyone in Dublin, or Limerick, or Cork has just come home and they’re all putting the kettle on and cooking dinner. Can you imagine the size of the batteries we’d need to provide all that power at peak demand? The tide is nature’s battery.”

At this point you might be thinking that there’s a flaw in Murphy’s tidal power plans, which is that there are four tides a day and they have large gaps between, so while a tide is more or less faultlessly predictable, it isn’t actually constant. Murphy has an answer for that, though.

“We can manipulate the sea water so that we can produce power 24/7,” he says. TPGen24’s plan is for a series of “islands” – man-made structures that sit about 1km out to sea. They’re big – 15km long by 7.5km wide – but they’re low-lying, so many of the usual complaints about wind-turbines being eyesores or solar panels dazzling passersby don’t, at least in theory, apply. Within these islands are a series of tanks, or lagoons, which are sequentially filled by the incoming tide. That tidal force generates power itself, but when the tide has passed, and the sea is at “slack water” the lagoons come into play. The water that’s filled them up can be drained back out, tank by tank, driving the same impellers that generate power from the tide itself. By the time the tanks are drained, the tide is on the move again and the cycle restarts. “You can put 50 turbines in there and you can fill the thing to the top in two hours with the high tide and I’ll give you more power – nine gigawatts of power – for over an hour. They’ll give you more power than a nuclear power station for that one hour,” says Murphy.

His plan is to line up a series of these power-producing islands off the west coast of the UK, from Cumbria down to Aberystwyth in Wales, where the height of the tides can exceed 10m, opening up vast potential for power generation. Ireland’s potential is rather less – our tides usually run up to about 5m – but TPGen24 is working on a second design of tidal barrage that can generate power from a 5m tide, and Murphy has had discussions with the Sustainable Energy Authority of Ireland about using them off the west coast.

You know where we are right now? We are where Edison was with light bulbs

The next question, of course, is how much will all this cost? Presumably a man-made power-generating island doesn’t come cheap. “It costs around £5 billion,” says Murphy. “You have to compare that with nuclear power, though, which is currently generating baseline in the UK, 10 gigawatts of power each day. The new nuclear station being built at Hinkley is costing some £30 billion, and that’s going to provide enough power for six million homes. So if we can get between a million and two million homes out of each raft, well it’s going to be more cost-effective. But the thing is, unlike nuclear, rocket scientists need not apply. This technology is swimming pools with water wheels attached to turbines.”

Inevitable questions will be raised about the impact on marine life, but Murphy has a riposte for that, too. “Maybe the environmentalists say: ‘well, we don’t want that outside our window.’ Hang on though, because you’ve got 3,000 wind farms now. In Liverpool Bay, there’s not much but lugworms. The real thing to remember is that if we don’t generate this power, the fish aren’t going to generate it either . . .”

Murphy thinks, and clearly hopes given the time and money he’s invested in the idea, that tidal power’s time has come and he’s in no mood to listen to naysayer. “You know where we are right now? We are where Edison was with light bulbs. And you can imagine someone saying to him; ‘Excuse me, Mr Edison. We’ve had candles for thousands of years. They work great. Yes, the occasional man comes home a bit worse for wear, knocks the candle, burns the house down but just the way things are.’ It’s a moment in time where we are, in the Edison eureka moment. Sometimes humans, it takes a disaster to make us realise that we need to do something. We didn’t put enough boats on the Titanic, we will do in future, but it’s too late for those people. You wouldn’t think that the tides would be connected to a conflict, but in this instance, unfortunately, they are.”