71% of the Earth’s surface is water, and almost 97% of that water is in our oceans.[i] Pushed and pulled by winds, the moon’s gravitational pull, and the Earth’s rotation, all 320 million cubic miles[ii] of ocean water is constantly on the move, generating a huge amount of mechanical energy.
For the most part, this energy potential has remained largely untapped, although evidence exists[iii] of humans using the tides to drive water wheels as far back as the 6th century. Currently, however, wave and tidal power generates only .0004%[iv] of global electricity each year.
As a renewable energy, wave and tidal power offer many benefits that even the most common forms—solar and wind—do not. Most importantly, ocean currents generate energy constantly[v], rather than varying with weather patterns and time of day. They are also more predictable; since waves are generated hundreds if not thousands of miles away from the shores on which they break, computer models can easily map them days ahead of time[vi] with more accuracy than wind and cloud forecasts. Wave and tidal plants and turbines are also less of an eyesore[vii] than giant wind or solar farms.
With all of these benefits, why is wave and tidal power still so rare? Unfortunately, the challenges are as outsized as the benefits. It’s harder to install, build, and run machinery in water. Ocean salt corrodes equipment[viii]. Plus, waves move not only back and forth but also up and down; while this three-dimensional oscillation creates more energy, it also makes it more difficult[ix] for machines to stabilize. These challenges make wave and tidal more expensive to implement, and thus more expensive for potential consumers. Industry experts describe wave and tidal technology as three decades behind[x] that of wind and solar.
The best is yet to come with wave and tidal power, as surely technology will catch up over time to the challenges and thus lower prices. Initial investment over the next 30 years, however—the timeframe that the Drawdown organization[xi] uses to estimate the benefits of its top 100 solutions to reverse climate change—will actually produce a net loss[xii] of nearly $600 billion USD. Reducing emissions to ensure humanity and other species survive is priceless, of course, but governments and corporations currently focus more on short-term economic gains. That’s why Drawdown only lists wave and tidal as #29[xiii] on its top 100 list.
Existing Wave and Tidal Systems
Tidal power has existed for longer[xiv]—and is therefore more advanced—than wave, due to its use of natural lagoons, bays, and inlets. La Rance[xv], the world’s first tidal plant, opened in 1966 and remained the largest system in terms of generated capacity (240MW) until the 254MW capacity Shiwa Lake station in South Korea began operation in 2011. La Rance provides 130,000 households[xvi] with electricity each year, while Shiwa has the potential to power 500,000 households[xvii] nearby.
Tidal range stations have four major components[xviii]: (1) embankments that form the boundaries where the tides move in and out (2) rotating turbines that convert the ocean’s mechanical energy into electricity (3) openings that enable the water to move in and out and (4) locks that allow vessels to pass unimpeded by the waves. These stations can capture energy uni- or bi-directionally[xix]: during either the ebb or flow tides, or during both.
While wave power can be harnessed in more places than tidal (which is most efficient where tides ranges are particularly wide), it is also less developed, due to the need for more construction to create embankments where no natural boundaries exist. Some of the latest designs in both wave and tidal are currently being tested at the European Marine Energy Centre[xx] (EMEC) on Scotland’s Orkney Island; since 2003[xxi], the centre has provided test facilities for companies developing wave and tidal energy converters (also known as WECs[xxii], or Wave Energy Converters). Current prototypes[xxiii] include turbines attached to the underside of floating platforms and even floating turbines.
Whereas most tidal power stations are barrages, or dam-like structures, the EMEC features the world’s largest tidal array[xxiv], comprised of a field of underwater turbines. (Picture a wind farm in the ocean[xxv].) While environmentalists have raised concerns about the effects of the rotating blades on marine life, thus far no studies have found a significant impact. Research done by Andrea Copping[xxvi] of the US Department of Energy, for example, found that the blades often move too slowly—7 to 14rpm[xxvii], compared to 10-20rpm for wind[xxviii]—for animals to do more than bruise themselves. Moreover, collisions appear to be rare. It’s still early to say definitively that there are no harmful effects, however, especially when it comes to how the noise[xxix] generated by these turbines may impact wildlife.
The Future of Wave and Tidal
Like wind, wave energy isn’t distributed equally around the world. Because trade winds blow east to west, the latter continental coasts[xxx] have the most powerful waves (think of how much better the surfing is in California than in Florida). Some researchers estimate[xxxi] that the US could get a quarter of its energy needs from wave and tidal, whereas Australia could get 30% and Scotland a whopping 70%.
Crucially, however, wave and tidal are not a silver bullet[xxxii]. For all its benefits, this type of renewable energy is currently too costly and too new to understand both its long-term benefits and drawbacks. Wave and tidal is best understood as a technology that will play a small but increasing role in our quest to divest from fossil fuels and establish 100% renewable energy across the globe.
[iv] Drawdown, 13.
[v] Drawdown, 12.
[vii] Drawdown, 12.
[xii] Drawdown, 13.
[xiv] Drawdown, 13.
[xxx] Drawdown, 12.
[xxxi] Ibid, 13.