Marine energy’s long road to commercial viability — and why it may finally arrive
The world’s oceans contain an almost unimaginable quantity of kinetic and potential energy. Tidal currents driven by the gravitational pull of the moon, wave energy driven by wind across vast ocean fetches, and ocean thermal gradients represent renewable resources that, unlike solar or wind, are entirely predictable and unaffected by local weather. Ocean energy has long been seen as having enormous potential but has proved commercially elusive. A generation of new technologies and the hard lessons of early failures are changing that equation.
Tidal Energy: Predictable and Powerful
Tidal stream generators — underwater turbines that extract kinetic energy from tidal currents — are the most commercially mature form of ocean energy. The basic principle is analogous to a wind turbine, but water is 800 times denser than air, meaning much smaller rotors can generate equivalent power. Tidal current patterns are known centuries in advance with near-perfect accuracy, making tidal energy one of the most predictable renewable sources. Capacity factors for well-sited tidal installations can exceed 40–50% — comparable to nuclear power and far higher than typical solar or wind.
MeyGen: Proof of Commercial Concept
The MeyGen tidal stream project in the Pentland Firth, Scotland — the most energetic tidal strait in Europe — is the world’s largest tidal energy project, with four 1.5 MW turbines installed at depths of 30–40 meters. The project has generated electricity for the UK grid since 2016, demonstrating the technology’s commercial viability at small scale. Atlantis Resources (now DP Energy) plans to expand MeyGen to a full 398 MW project, which would make it the largest marine energy installation in the world. Scotland’s tidal resource is estimated at approximately 25% of the entire European tidal energy potential.
Wave Energy: The Harder Problem
Wave energy converters (WECs) face a more difficult engineering challenge than tidal turbines. Waves exert forces in multiple directions, carry enormous energy in storm conditions (enough to destroy devices), and require systems that can capture energy across a wide range of wave heights and periods. Multiple concepts have been demonstrated at small scale: oscillating water columns that use wave motion to compress air and drive turbines; point absorbers that float on the surface and convert vertical motion; attenuators that flex with waves along their length; and overtopping devices that capture wave crests in elevated reservoirs. Wave energy currently has capacity factors in the 25–40% range at good sites.
CETO and the Australian Contribution
Carnegie Clean Energy’s CETO technology represents a distinctive approach to wave energy. Fully submerged buoys, anchored to the seabed, are moved by wave pressure and drive hydraulic pumps that pressurize seawater for electricity generation or desalination. Operating underwater avoids corrosion from saltwater spray and eliminates the risk of storm damage to surface equipment — a key differentiator from designs that must survive storm seas. CETO has been deployed off the coast of Western Australia.
Ocean Thermal Energy Conversion
OTEC (Ocean Thermal Energy Conversion) exploits the temperature difference between warm surface water and cold deep water in tropical oceans. A heat engine operating between these two temperature reservoirs can generate continuous electricity. While the thermal efficiency is low (only 3–5% of the theoretical Carnot efficiency, due to small temperature differences), the resource is enormous and fully continuous. Japan, South Korea, and Hawaii have operated experimental OTEC plants. OTEC has the additional advantage of producing large volumes of cold, nutrient-rich deep water as a byproduct, which can support aquaculture and air conditioning.
Wave and tidal energy remain nascent industries — global installed capacity is less than 2 GW combined. But their predictability, their high-capacity factors, and their suitability for island nations, coastal communities, and offshore industrial operations give them a niche that onshore renewables cannot easily fill. As manufacturing scales and installation costs fall, ocean energy may become an essential component of diverse clean energy portfolios in the 2030s.