Written elsewhere

Here’s why UK tides are soon going to play a much bigger part in powering your home

I wrote this article at the request of an editor from The Conversation, who wanted to know about the current state of, and future prospects for, tidal energy. It was published there on 14th April 2022, and is licensed CC BY-NC 4.0.

The Conversation

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.

A ship's crane lifting a turbine from a quay
Green Energy Futures/Flickr, CC BY-NC-SA

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.

A ship lowing a turbine into the water
Glen Wallace/Flickr, CC BY-ND

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.

Posted by simon in Publications, Written elsewhere

After the tsunami: how tidal energy could help Japan with its nuclear power problem

This article originally appeared in The Conversation. It is licensed CC-BY-ND. Click here for original.

Japan was the third-largest producer of nuclear power in the world in 2011. Then, on March 11 of that year, an earthquake of magnitude 9 was followed by a catastrophic tsunami, resulting in the first nuclear disaster of the 21st century – at the Fukushima Daiichi power station. The country’s nuclear plants were shut down, and within a year Japan had become the world’s second biggest importer of fossil fuels.

Before the tsunami, nuclear power provided 25% of Japan’s electricity, and a strategic plan was in place to expand this to 50%. Japan has few fossil-fuel resources of its own, so most of the resulting shortfall in electricity was made up by burning imported coal, oil and gas – an unsustainable solution from both environmental and economic perspectives.

But on a group of islands to the west, tidal power may offer part of the solution to the country’s energy needs.

A renewable future

By 2030, the Japanese government plans once more for nuclear power to provide around 21% of the nation’s electricity – which is highly controversial – but also stipulates (see page 8) that 22-24% should be delivered by renewable energy sources. At a local scale, two prefectural governments, Fukushima and Nagano, have pledged that all of their electricity will come from renewables by 2050.

Most of the new renewable energy available in 2030 is likely to be solar and wind, along with existing hydropower, but some contribution from the tides is possible. To this end, a zone in the Goto Islands of Nagasaki Prefecture has been designated for tidal energy development, and a cluster of companies plans to install the first turbine in 2019. This project will be of the tidal stream type, where underwater turbines are placed in the free flow without any dam or barrage, similar to the MeyGen project in Scotland.

Installing a tidal stream turbine base at the MeyGen project off the coast of Caithness in northeast Scotland.
MeyGen/Atlantis Resources

When tidal turbines are placed in a channel, they remove energy from the flow. This causes it to slow, and represents a partial blockage of that channel. In turn, that means that the behaviour of the tides in an area after turbines are installed can be different to how it was before. Understanding and predicting this change is important for estimating both how much energy is available and the impacts of removing it; if there are too many turbines, the flow could slow too much and much less power would be generated.

Going with the flow

My recent work, in collaboration with researchers in Scotland and Japan, involved using a computer simulation of tidal flow around the Goto Islands to investigate the effects of installing large numbers of turbines.

We estimated that between 24 and 79 MW of power could be generated from the designated area. The reason for this range is because the number of turbines that are used will ultimately depend on economic considerations. The first few will offer the most benefit, while later ones will suffer from diminishing returns. Tens of megawatts represents a very small contribution to Japan’s overall electricity needs, but a very large chunk of the local demand in these islands.

A number of parallel channels run through the Goto archipelago, of which two are within the tidal energy zone. In situations like this, it is common to find that adding turbines to one channel simply causes the water to flow by a different route. That means that to harvest energy efficiently we need to collect it from all the channels at once – an expensive proposition for a new technology.

In the Goto Islands, all the channels run parallel but separate to each other, never merging or meeting, so they can each be exploited without affecting the others.
Elsevier, Author provided

However, our modelling shows (see sections 4 and 7.2) that the parallel channels in Goto do not behave this way; instead, they are independent of each other. The reason for this unusual behaviour lies in the geometry of the islands.

Partially blocking a channel causes water levels to rise a little behind the blockage. The interactions that we see elsewhere in the world are a result of this extra water “spilling” into other channels. In Goto, because all of the channels run separately from one end to the other without meeting or merging, and because their mouths are spaced well apart, there is no way for this “overspill” to occur. Consequently, any or all of the channels can be exploited without affecting the others, which should make the area more attractive for commercial development.

If the relatively small-scale development in Goto is a success, it could act as a proving ground and a springboard, leading to the use of tidal energy in other locations all over Japan. And for a country ambivalent about its return to dependence on nuclear power, additional contributions from renewable energy will be welcome.

The Conversation

Posted by simon in Working in Japan, Written elsewhere

“My favourite tool”

Software Carpentry are running a series of short blog posts where they ask their supporters what their favourite tools are. Most have been software, although a few people have gone for things like “asking for help”. QGIS probably isn’t my favourite tool, but my first few choices had already been mentioned by others…

This post originally appeared at https://software-carpentry.org/blog/2018/01/waldman-fave.html

QGIS (formerly Quantum GIS) is an open source Geographic Information System.

QGIS is capable of advanced analysis and cartography, but I don’t use it for that.

In my research in hydrodynamic modelling, I deal with a lot of spatial data – coastlines, bathymetry, and the like – and this will eventually be processed and plotted using R, MATLAB or Python.

But if I’ve received a file and simply want to take a quick look at it, or if I want to quickly compare two files that use different coordinate systems and see if things line up, most of the time I can throw the file at QGIS and it will show it to me with a few clicks. This approach lacks the reproducibility of a coded solution, but it’s an awful lot quicker for a throwaway visualisation.

Posted by simon in Written elsewhere