Tidal energy has long lurked at the back of the UK’s renewable energy arsenal, outshone by its wind and solar counterparts due in part to early issues with technology readiness and high costs.

Yet with recent research showing it could provide 11% of the UK’s electricity needs – and with significant government investment in the pipeline for UK projects – its future is looking ever brighter.

Tides are large movements of water around the Earth, powered by the gravitational pull of the Sun and Moon. In areas with particularly strong tides, we can harvest some of this power using turbines – similar to wind turbines, but underwater – that turn as water flows past them. This approach is more popular at present than previous ideas of using tidal barrages which are similar to dams, mostly because its environmental impacts are less severe.

In the last decade, the global tidal energy industry has demonstrated that siphoning energy from the sea works predictably and reliably. Around a dozen experimental turbine designs have been generating electricity in Scotland, Wales, Canada, China, France and Japan, many of them supplying power to homes and businesses.

The UK’s first “commercial” tidal energy projects, led by developers SIMEC Atlantis and Nova Innovation, both have multi-turbine arrays in the water in Scotland. The largest of these can currently produce six megawatts of power: that’s about the same as two or three onshore wind turbines, providing enough energy to run a few thousand homes. Expansion of the project is already underway. Over in the Faroe Islands, tidal developer Minesto has just announced plans for a 120 megawatt array which would supply 40% of the islands’ energy needs.

Tidal turbine designs tend to be divided by one big question: whether it’s best for them to float, or to be mounted on the seabed. Floating turbines are easier to access for maintenance, and they benefit from faster-flowing water near the surface. But those on the seabed are less affected by storms and – in deep enough water – could allow ships to sail freely above them. It’s not yet clear whether one approach will win out, or whether the choice will depend on the location.

Either way, now that it has working technology in its hands, the tidal power industry needs to demonstrate that it can bring costs down. Luckily, there’s precedent here in the story of offshore wind. With the help of government support in the UK and elsewhere, offshore wind developers around the world have cut costs by close to a third over the last decade, and further reductions are expected thanks to ongoing research and development.

Money Matters

The cost of tidal energy may never be as low as that of wind. That’s partly because tidal turbines can’t be scaled up in size in the same way as wind turbines (in a limited depth of water, you can only build so big), and partly because doing things under the sea is usually more expensive than doing them on the surface (it’s a harsher, less accessible environment). But matching costs may not even be necessary.

As critics are keen to point out, the wind does not always blow, the sun does not always shine, and the tide is not always flowing: so to build a resilient low-carbon electricity system, we’ll need to use a range of different energy sources rather than relying only on that which is cheapest.

Tidal power offers the unique advantage that while its output will vary over time, that variation is predictable years in advance by understanding the orbits of the Earth and Moon. This means that grid operators will be able to plan for the varying output of tidal turbines, and schedule other sources to fill in the gaps.

Fortunately, the UK government seems to be stepping up to help the tidal industry. The latest round of the UK’s “Contracts for Difference” renewable energy funding contains a “pot” for tidal energy, so that it doesn’t have to compete with cheaper technologies like offshore wind – for now. And the recently published British Energy Security Strategy promises rather fiercely to “aggressively explore” tidal and geothermal energy technology.

Tidal energy is never going to be a big player at the global scale in the same way as wind or solar, because only a few parts of the world have strong tides. And unfortunately, it won’t be ready in time to help with the energy price crisis that we face right now.

But for those places with strong tides, including the UK, it has significant prospects, with a global market estimated by some analysts at £130 billion. And there may be potential in developing turbine tech further to take advantage of slower, but more consistent, ocean currents like the Kuroshio current off the coast of Japan.

Tidal energy technology works, and it’s here to stay. Now, the most efficient way to get it powering our homes and businesses is to build more of it.

There are two main points that we’ve tried to get across:

• Firstly, that if we are to achieve the greatest possible energy yield for a given level of environmental impact, we’ll need to strategically plan tidal developments for a whole region – not do them piecemeal.
• Secondly, that tidal farms will interact. If they’re upstream and downstream of each other that interaction is detrimental, but if they’re side by side then they can have mutually beneficial effects. We think it’s a problem unique to tidal power that if one array stops working, its “rival” neighbor can lose power… and that raises a number of fun and interesting questions about management and liability.

After looking at the physics and the resulting policy issues, we discuss some ways of dealing with them. We argue that if we want to get the most that we can out of our seas we will need some form of interventionist, centrally planned, approach to managing tidal power; the free market will not deliver. The arrangements that we have at the moment are just fine while we’re only putting a few turbines in the water. But as we scale up – and we must scale up, if tidal energy is going to be significant at grid level – this stuff will start to matter, and it’d be really nice if the necessary policy frameworks were in place before they’re needed.

I’m proud of this one, for two reasons: Firstly that I think it’s important, in that it asks some questions that I don’t think anybody in the marine spatial planning, policy or governance spaces has been thinking about much as yet (although I gather they have been grappling with similar issues around wind). Secondly because it’s been a genuine multidisciplinary, collaborative, process. I had the original idea for the paper a couple of years ago, and after discussion with one of the other authors we tried to flesh it out, but we realised that we needed people with policy expertise. We brought them on board – including Steph Weir, a former PhD officemate of mine who wrote major chunks and taught me about unitization – and the result is a pleasingly short paper that really couldn’t have existed without all five of its authors.

If you want to read the whole thing yourself – it’s only five pages long, and it’s written for a non-specialist audience – then you can get the official version here with a subscription to Marine Policy, or the unformatted, post-review, version here for free.

I couldn’t immediately understand why the code wasn’t working for this student, so I asked him to send his files to me… and I found a bug in my code. With a growing sense of dread, I realised that this bug would have affected results that were already published. I notified my co-authors on the paper and in haste, on evenings and weekends (because this was not my full-time job at the time), I corrected the code, reran a hydrodyanamic model, redid the analysis… and found to my relief that the overall conclusions of the paper were not affected and so there would be no need for a retraction. It did, however, feel as though the record should be corrected, so I got in touch with the editor, and… long story short, a “corrigendum” to the original paper appeared online today. For those without a subscription to Ocean & Coastal Management, I’m also hosting it here for now.

I was already an advocate for good software development practices in science, in order to reduce the liklihood of exactly this sort of thing, and now my feeling on this matter is strengthened…

If you have been using my code for inserting tidal turbines into Delft3D you should make sure that you are using the current version, which had this error fixed in December 2017.

The majority of the research here is about the effects that renewable energy extraction will have on the environment, which is certainly an important topic. A few, including my own poster, look at “environmental interactions” in the other direction, in my case asking “how will the wave power arriving at the west coast of Orkney change, as the planet warms in the future?”

It’s only a short, preliminary look at the problem, and it has a high level of uncertainty attached. However, it looks as though the change between now and 2100 will be small. That’s good news for wave energy developers.

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It’s the first time in many years – since returning to university for my masters – that I’ve tried to write something journalistic. I used to do such articles long ago for the trade press in my old industry, but I never felt very good at it; the writing seemed stilted to me. I wondered whether having trained myself in academic writing would make this more difficult – but to my surprise, the opposite was true.

Communication? (Photo: Flickr user mindaugasdanys, licensed CC-BY-2.0)

I did have to consciously avoid some of the usual turns of phrase from journal articles, and try to write more as people speak, but it was much smoother than past experience. I attribute this to three things: part of it is simply that I’ve had more writing experience now. Part will be because this was shorter, so I was concentrating on optimising rather than writing lots. The biggest part was probably the input of the editor.

Unlike the trade magazines that I’ve written for before, which simply use your text verbatim, The Conversation (hereafter TC) assigns a professional editor to each article, as a newspaper might do. However, wheras for a newspaper you’d submit your copy and then be at the editor’s mercy, for TC it’s a two-way process where the researcher gets final approval of everything, including pictures and the headline. We did go back and forth a couple of times where the editor made things a bit too hyperbolic, claiming things that weren’t supported by the study – but she was willing to roll them back when I explained, and she did wonders for improving the readability of the article for the public. It’s a good way of working.

TC provides analytics, and I spent some of last week glued to that page. So far, three days after it appeared, it’s had 1450 readers. This is gratifying, and vastly surpasses both the audience that anything of mine has had before, and the audience that the vast majority of journal articles ever get. For a while I had a response of “eek. So many people. What if it’s controversial, or wrong?”, and I had to remind myself that I do have confidence in my results, and so does a peer reviewer or two.

On Twitter I was gratified to see it retweeted by such accounts as @NERCscience and @BGSScotland, in addition to my own institution. Most of those reads were in the first two days, while it was at the top of the feeds and making its way around social media, and it’s leveled off now; it probably won’t ever get many more. 28% of readers were in the US, which surprised me, 26% in the UK, which didn’t, and 31% in Other, which I wish was broken down more. I hope that a lot of that is Japan, since the article is about the energy situation there.

Readers. (Photo:
Jean Beaufort. Public domain (CC0))

TC also provides analytics that compare your reader numbers to articles published by others from your own institution, and I found myself feeling surprisingly competitive as I watched mine climb from the bottom to… well, quite near the bottom still. The high-flyers there are timely articles that tie in with a news story, or social science based ones that resonate with the zeitgeist and get picked up and republished by The Guardian. That’s fair enough. But having more readers than the articles by two of my former bosses is strangely gratifying!

This wasn’t a major time investment. It probably took two hours to write – which would be less with practice – and maybe an hour after that for editing and correspondence. When considered in the context of the number of hours that go into performing research and getting it into journals, it’s nothing – and it’s a nothing that brings the research to more than a thousand eyes. Good experience, would do again

The most recent is my second journal article as lead author, and one that I’m quite proud of. It covers the work that I did in Japan last year, and in the months after returning, on the tidal energy resource of the Goto Islands of Nagasaki Prefecture. We produced estimates of the amount of power that could be obtained – which is mostly of interest for the people planning tidal development in that archipelago – but of more general interest are the findings about inter-channel interactions. The Goto Islands have several parallel channels that could contain turbines.  When this arrangement has been studied in other places, it has usually been found that putting tidal turbines in one channel causes flow to divert into the others, and hence that to reach the full potential for power we would have to put turbines in every channel. Goto doesn’t behave like that – instead, the channels have very little effect on each other – and in the paper we looked a little into why that is. My thanks are due, of course, to my co-authors on this work, both in Scotland and Japan.

Plot showing the mean power available from various numbers of turbines in the channels of the Goto Islands, using simplified M2 tides.

Just a few weeks ago I attended the EWTEC conference in Cork and presented this paper on Lashy Sound, which is a channel with strong tides in the Northern part of Orkney. In this work, I used very similar methods to those that were developed in Japan to look at the tidal resource – in this case, not for realistic turbine developments but in terms of the theoretical maximum available power if we didn’t care about things like environmental impact, or allowing ships through. Unsurprisingly, it looks like achieving this maximum yield would have some significant impacts. I also considered the more plausible scenario of a smaller tidal farm, similar to the 30MW one that has been planned for the area, and was able to show that its effects would be small and confined to Lashy Sound itself – something that’s important when other potential tidal energy sites are just a few km away in neighbouring channels.

Both of these papers are available for free at the links above, or at the publications page on this site.

It’s called “Implementation of tidal turbines in MIKE 3 and Delft3D models of Pentland Firth & Orkney Waters”, and it describes work that myself and two groups at Heriot-Watt and Edinburgh Universities did a few years ago, near the start of my PhD. Lots of people have represented tidal turbines in regional-scale flow models, but most of them have used academic codes that industry and investors won’t trust, or have modified trusted code – which itself tends to undermine that trust. Our aim for this work was to look at how tidal energy extraction can best be represented in two widely-used commerical modelling suites, without modifying their code. We also did some actual modelling, by way of example, and the results of that have been passed on to others in the project to use for ecological work.

In a small way this was perhaps a baptism by fire, in that I had to pull together work and writing done by people far senior to myself, add my own work on top of each, and try to construct a single coherent publication. Perhaps partly for this reason, coupled with my own inexperience, it had a long journey through review… but it’s out there now, and I’m glad it’s done!

If you have a subscription to Ocean & Coastal Management you can read the published version here; otherwise the “accepted version” (without journal formatting) is available at this finely crafted link.

One is a summary paper covering the TeraWatt project, and drawing out conclusions from a number of primary publications (including one of mine which, while cited in this one, is actually still in review!).

The other is an updated review of the wave and tidal energy resource of Scotland. Contributors are from multiple universities across Scotland, including myself, skilfully corralled by Simon Neill.

Keen eyes may also notice a new paper listed as “in review”, based on the work that I did in Japan last summer. More on that if and when it is published.