Wave and Tidal Power

There is a lot of energy in the seas, as we remember each Winter when storms do major damage. We are learning how to harvest some of it. Wave and tidal power are often grouped together, although they are based on very different energy sources. Waves are created by the motion of winds over the seas, so waves are really stored wind energy, whereas tides are due to the gravitational pull of the moon and the lesser pull of the more remote sun on the sea. 

Wave and tidal power have both been seen as promising sources of renewable energy, but so far progress has been limited, especially in the case of wave energy. It has proved hard to extract power form the sometimes very chaotic interface between air and water.  There have been some spectacular prototype wave system failures during storms and the technology is still struggling to get to scale around the world.  

However, there is still much enthusiasm and hope for the future, as well as some success, especially with small to medium scale wave projects like Ecowave’s on-shore system at Gibraltar, the Wave roller off Portugal and the Danish wavepiston to be tested in Gran Canaria.  In the UK there is a Cor-Power Ocean ‘wave boost’ review, seeking to upgrade plant efficiency, and a £1.4 m Apollo scheme in Aberdeen.  The Blue Star project is also getting going in Edinburgh. And there is continued scope for progress beyond the initial prototype stage, with clever new ideas like Bombora’s £17m 1.5 MW sea bed mounted mWave system, a version of which is being built at Pembroke Dock in Wales. 

Tidal power though is generally doing better. There are two medium-scale tidal barrages (around 250 MW each, one in France, one in South Korea) and much work is underway on smaller tidal stream devices, which work like underwater wind turbines on the relatively clam tidal ebbs and flow beneath the surface. Following on from the very successful MCT project in Strangford Loch, Northern Ireland, the UK-French Tiger consortium is backing a range of projects, like the Mygen/Atlantis project in Pentland Firth, with 6 MW installed so far, Orbital’s 2MW floating unit with turbines mounted underneath and Minesto’s Deep Green Tidal kite being tested off Wales. 

Each of these three have their advantages. While the bottom mounted 2MW turbines used in the Mygen project have done well, Orbital’s CEO has claimed that ‘a boat is a far better solution to be able to manufacture, install cost effectively and - crucially - access for maintenance through life, than an underwater wind turbine’. Then again, Minesto say that, since it can perform figure-of-8 sweeps through the water, their kite system makes it possible to operate well in low tidal flow areas, in effect expanding the tidal resource. 

Tidal projects of whatever type do have the advantage of offering a degree of predictability- although they are cyclic, tidal patterns are fixed and totally predictable. However, they may not be unique in this. Alisdair McLean, executive director of the Offshore Energy Research Association, has pointed out that ‘the benefit of predictable energy from tidal power becomes less powerful if solar-plus-battery or wind-plus-battery can provide the same predictability at a lower price.’

Nevertheless, with some large machines now in place, tidal power is moving ahead quite well, and new designs are also emerging for deployment, like the hydrowing multi turbine tidal stream platform, and some others new projects are making progress, like the  240 MW Morlais Tidal stream project planned off Anglesey. Developer interest has been shown but RSPB hate it!  The Perpetuus tidal stream project proposed off Isle of Wight has been stalled,  but EMEC, the marine renewable test agency in Scotland, have now agreed to link up with it, so that may give it a boost.

Prospects for the future  

Overall, talking it up, an Ocean Energy Systems' report said cumulative output from wave & tidal streams ‘surged from less than 5GWh in 2009 to 45GWh in 2019’, a 10-fold rise in 10 years. Well yes, but that’s from a low starting point. Though it is at least getting started and we might expect several GW of capacity soon, while the long term global potential is quite large-  in the TW range for both wave and tidal power, if all suitable sites were developed. 

The local environmental impacts of wave and tidal stream systems are generally seen as low, with marine life either avoiding the structures or in some cases (e.g. molluscs) colonising it, as a new habitat, as with offshore wind foundations.  However, costs are still high, given that it is mostly at best only prototypes involved, or just concepts. In the UK wave and tidal stream projects are eligible for support under the Contract for Difference system (at a proposed strike price of £305/MWh), but so far none have won contracts, although some MCT tidal turbines did get support for commercial operation under the previous Renewables Obligation system and prices should fall as new technology develops and the market for it grows. There was an attempt to get support for a tidal lagoon off Swansea in Wales, but the up front cost and cost/ kWh was deemed to be too high. Large tidal barrages have been seen as likely to be even more expensive. They are also likely to have much more environmental impact than free standing tidal stream or wave devices, or lagoons, although smaller barrages may yet find niches. 

Barrages and lagoons do offer pumped storage options, which could help with grid balancing, but the sites for these tidal range systems are very geographically determined, whereas it may be easier to deploy tidal current turbines in a range of locations. Indeed, it may be possible to have them distributed widely around the coast, so that, since tidal maxima occur at different times in each place, the system as a whole can supply more nearly continuous power. Otherwise, as with tidal range systems, taking output just from each unit, the power will follow the twice daily tidal cycle. Local energy storage at each site might be an alternative option to multi-site grid integration and the use of hydrogen storage and flow batteries has already been tested with tidal projects at EMEC on Orkney.

As can be seen, it is still early days in the wave and tidal field, with new ideas still emerging. Most of the activity has been in Europe and much of it in the UK, but there have also been projects in the US, Australia and Asia, as defined by location: there are many promising sites around the world.   In the decades ahead we might expect the sea to provide a substantial amount of our power. 

The European Commission’s target, as laid out in a new draft offshore renewables strategy, is to reach installed capacities of 1-3 GW for ‘ocean energy’ by 2030, paving the way for an increase to 60 GW by 2050, and that may be over-cautious. The UK, now outside the EU, already has a pipeline of wave and tidal projects, including a target of 398 MW for the Mygen tidal turbine scheme in Pentland Firth, and, as noted, above many other ideas are being looked at. Though of course, although promising, wave and tidal are outgunned by another marine renewable, offshore wind, with Europe expected to have 60 GW in place by 2030 and 300 GW by 2050 and probably as much or more elsewhere in the world. See my next post.