Is wave energy the most reliable renewable?

King Canute may be remembered for his vainglorious attempts to stem the tide, but the Danish monarch at least knew how to get tongues wagging.

A thousand years on, the world of Canute’s North Sea Empire is barely recognisable. Yet two constants remain: the tide keeps rising and mankind keeps trying to tame it.

And we do so with good reason. In an era of rapid anthropogenic climate change, the race is on to find alternatives to oil, gas and other energy-dense hydrocarbons.

With per-kilowatt prices dropping by the day, solar and wind power look like an increasingly viable bet for the future. However, they are not perfect as the sun doesn’t always shine and the wind doesn’t always blow.

So how could the renewable energy mix be diversified and strengthened? Is there a reliable, predictable source of clean energy that remains untapped?

Atmosphere of optimism for tidal and wave energy 

Roll forward tidal and wave energy. Its plus points are numerous. Most importantly, it never stops. As long as the moon stays in the sky, the tides will keep rising and receding.

Water is also super-dense, a fact that conventional hydropower has put to good use for decades. Water only needs to be running at one metre a second to turn a turbine, in contrast with three to four metres a second for wind.

The key question, of course, is whether these natural assets can be effectively and efficiently harnessed.

As in Canute’s day, it is not hard to find optimists. A recent report by the analyst firm Zion Market Research forecasts revenues from tidal and wave energy are set to rise more than tenfold over the next five years.

Enthusiasts also abound and the sector is flush with startups, all with promising technologies. Few genuinely merit this confidence more than Minesto. Founded in 2007, the Stockholm-listed firm has developed an award-winning turbine specially adapted for areas with low-flow tidal streams and ocean currents.

The firm’s subsea kite-style technology, which attracted a €13-million investment from the European Regional Development Fund in 2015, is currently being piloted off the Welsh coast and the Faroe Islands.

“2018 was a terrific year for us as we verified our subsea kite technology for the first time with a commercial-scale unit,” says Martin Edlund, Minesto’s chief executive.

Predicting full commercialisation in the next few years, Dr Edlund believes the time is nearing when energy from marine currents will provide a “substantial part of tomorrow’s renewable energy mix”.

Growth of wave energy sector being held back 

European investor InnoEnergy is sufficiently persuaded to have dropped €1 million into the project in December, adding to the €4.5 million it has already invested in the firm.

Others strike a more cautious note. Take the influential International Renewable Energy Agency (Irena). With a potential capacity of 80,000 terawatt hours a year, Irena predicts ocean energy could feasibly satisfy the world’s entire power needs.

Yet the sector’s growth is hindered by a number of uncertainties, says Dolf Gielen, director of Irena’s Innovation and Technology Centre. Top of his list are the disputatious politics of sharing the ocean, lack of resource information, absence of a grid connection and insufficient investment.

“To harness ocean energy at a commercial scale in the face of these barriers, tailored combinations of different policies need to be implemented that encourage research and development, and increase stakeholder engagement,” Mr Gielen says.

Recent news gives weight to such cautious appraisals. The most high-profile setback came last summer when the UK government pulled out of an ambitious tidal lagoon project in Swansea Bay. The £1.3-billion scheme was supposed to act as a pathfinder for five more tidal lagoons.

Falling prices of offshore wind challenge wave energy

Similar large-scale projects have excited hopes in recent years, only to come to naught. All face the same tricky combination of high capital costs, limited site availability, technological uncertainty and possible environmental impacts, in the form of altered currents and the emission of electro-magnetic fields, among other potential downsides.

As a consequence, for nearly half a century, the world counted only a single large-scale tidal barrage. In 2011, the club extended to two, when the long-standing 240-megawatt (MW) Rance Tidal Power Station in Britanny, France was joined by a similar 254MW project on Sihwa Lake, South Korea.

Now the nascent sector is encountering perhaps its biggest challenge yet. The falling costs of offshore wind makes it very difficult for tidal and wave energy of all types to be price competitive.

“Tidal [energy] has to compete with fixed-bottom offshore wind, which is impossible due to a different level of technological maturity,” says Viriginie Lemière, spokesperson for Naval Energies.

As a result, many small tidal and wave energy firms have gone to the wall or been bought up, while others have been forced to take dramatic shifts in strategic direction.

Naval Energies, one of the big names in tidal energy, fits into the second category. Despite recently installing a grid-connected 2MW tidal turbine in Canada and predicting that as many as 50 a year would follow, the Cherbourg-based firm now says it is pulling out of tidal turbines altogether.

Huge potential for tidal and wave energy in the future

Choppy as the waters look right now, don’t go writing off the tidal and wave energy sector just yet. So warns Professor AbuBakr Bahaj of the Sustainable Energy Research Group at Southampton University. As a veteran of the industry, he has seen the sector’s fortunes ebb and flow over the years, but retains a fierce belief in the technology’s innate potential.

Tidal and wave energy never stops. As long as the moon stays in the sky, the tides will keep rising and receding

“Generating power from the tides and waves presents a really interesting technical problem to solve. And there’s a lot of really pioneering work going into this that deserves to be recognised, coupled with perhaps appropriate support from governments to further propel the technologies forward,” he says.

Given its huge potential, the tidal and wave energy industry has good reason to remain committed. Yet, recalling King Canute, its proponents ignore the market’s hard realities at their peril.