Generating electricity from water

Which marine renewable technologies are out there...
31 May 2022

Interview with 

Simon Waldman, University of Hull




Now, last week, solar power was in the spotlight, but we've waved that goodbye, and this week it is the turn of tidal energy to be subject to our scrutiny. We're going to see how marine renewable technologies can contribute. The UK makes for a great case study, of course, because being an island nation, there's no shortage of water all around us just waiting to be farmed. Oh boy, it looks like Harry has nipped out of the studio. Where's he got to?

Harry - I'm down in Milford on Sea, it's on the South coast of the United Kingdom. On a day like today, when it's sunny, it almost looks like the Isle of Wight is within spitting district. We have an estimated 18,000 kilometres of coastline, and, on top of that, territorial waters that stretch 22 kilometres out to sea. It seems almost nonsensical that we are not making the most of this marine environment, this resource as an energy source that's on our doorstep. With that in mind, I'm hoping that we're going to be able to find out why we don't have the technology in the marine environment to compete against something like wind in the UK. And, also, what the future of marine renewables looks like.

Chris - So how do we currently extract energy from water. Well, Simon Wardman is a lecturer in renewable energy at the University of Hull.

Simon - Last year, 43% of the UK's electricity came from renewable energy. About 30% of that was offshore wind about a quarter of it was onshore wind. And then there's some solar and some hydro and some other things.

Harry - That's got to be better than expected, isn't it? That's got to be breaking the targets that we've set?

Simon - Well, we're hoping that by 2050 we'll be entirely zero carbon, which means renewables plus nuclear. So, we're not quite there yet, but we're doing well at it. And that's up considerably, it was only 37% in 2019. Back in 2010, it was 5%. So, it's been a remarkable shift in that time.

Harry - Wow. I didn't realise that. How do we go about generating electricity from bodies of water? What are the different methods?

Simon - Hydro, at present, is about 5% of our renewable electricity generation. That's significant. The other two big ones, potentially, are tidal energy and wave power. Tidal is working. There are early machines in the North of Scotland that are generating onto the grid right now. So, a tiny fraction of what goes into the lights that you and I are sitting under is coming from the tides. There was a recent scientific publication that estimated that, if we develop it, we could get about 10% of the country's current electricity needs just from tidal stream energy. Wave is not at that stage yet. Wave is still very experimental and is a bit further off.

Harry - Hydroelectricity in the UK is really running at full capacity, leaving us with three marine environments left to exploit on a major scale. As Simon said, that's wave energy, and we can actually split tidal energy into two different factions: stream and range. After much deliberation, I think the best way of demonstrating how these three potentially big players can work is to run a bath. That should probably do it. Let's turn of the taps. Ok, so, first up we've got wave energy. That's going to require a little bit of chop.

Harry - There are a few ways that we can make the most out of this environment and take energy from it. But the most effective method so far has been to place a long line of cylinders on the surface right here. That's been demonstrated by a massive, 120 metre prototype called Pelamis off the shores of Portugal. The name is actually derived from a sea snake, so it sort of looks like one of those toy snakes that can move, or a toy train with all its carriages. As the cylinders bob up and down, two hydraulic rams on either side are pulled and pushed alternatively, and that in turn drives a turbine. In the other two cases, we're drawing on energy from the tide. Let's start by trying to make a large swell in the bath, back and forth. Here we go. If we want to exploit the large tidal ranges we have in the UK, we need to wait until the tide is in and then try and trap it somehow, try and trap some of that water. I'm going to use a storage lid, but it's more likely companies would build a damn like structure or wall.

Harry - Here we go. Let's try and get some then. All right, it's not a great seal, but I think I've got some. What you can do is you store it, and then eventually when you'd like to, and when the tide is out, you can release this energy which will in turn drive turbines much like a hydroelectric down. So, all that energy is stored up and we just release it. Finally, we have tidal stream renewables. Now, the currents that are produced by the swell of the tide are scarily strong, so if we could place a simple device in the water capable of surviving these extreme conditions, it could be relatively simple to drive a turbine. For this, obviously our device would need to sit under the surface of the water.

Simon - At the moment, we are favouring tidal stream, mostly because tidal range is very tempting in terms of the amount of power that's available, but it has very large environmental impacts and has a very high upfront cost. Whereas, tidal stream is a bit easier to get into.

Harry - We're still at the start of testing these prototypes. Why is it that we are stuck in the Stone Ages - maybe that's a bit harsh - of marine renewables.

Simon - I think it is a bit harsh to say we're stuck in the Stone Ages. Some people would say that, at the moment, tide is in a similar place to where wind energy was in maybe the 1990s. In the last decade, the industry has demonstrated that tidal energy works. The task now is to deploy it at greater scale, to learn by doing, and bring the costs down.

Harry - You said that this could make up 10% of the UK's electricity needs. Whereabouts would these machines be employed?
Simon - For tidal stream, you have to put the machines where the fast flows are. In the UK, that means various places around the North and the West of Scotland, also around Anglesey, and some of the West Wales headlands, and possibly some other sites like the south coast of the Isle of Wight.

Harry - If you haven't got wind and you haven't got any sunshine, you know you're going to have a consistent source of energy.

Simon - Exactly. Tide isn't available all the time, but we know when it will be available. Because the wind doesn't blow all the time and the sun doesn't shine all the time, we don't want all our eggs in one basket. We want to have a range of technologies to help us out.

Harry - In terms of bodies that we actually have in the water, what do we actually have that's generating electricity around the UK coastline.

Simon - There are quite a number of individual single machine prototypes, including at test centres in Scotland and Wales. But there are also two companies who have got early arrays, what they call the first commercial arrays. One of them is a company called MeyGen, and they've got six turbines at present just off the North coast of Scotland. And there's another company called Nova Innovation who have, I think, three or four turbines in the Shetland islands.


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