Wave and Tidal Energy

Wave and tidal energy are two unrelated technologies that share a funding line, a set of test centres and a reputation. Tidal energy extracts the kinetic energy of currents driven by the gravitational cycle, or the potential energy of the tidal range behind a barrier. Wave energy extracts the energy of wind-generated surface waves. They have different resources, different physics, different failure modes and very different prospects, and treating them as one field has done both of them harm.

Established The record is the content of this brief. Marine renewable energy has been funded, announced and rescued for more than fifty years, and the cumulative result is a global installed base of roughly half a gigawatt, of which about 95 per cent is two tidal-range barrages built in 1966 and 2011. Tidal stream and wave together account for a few tens of megawatts worldwide. Over the same period, wind and solar each went from nothing to terawatt scale. A brief that treated this as a field on the verge of breakthrough would be misreporting its own evidence.

Two unit conventions, because this subject is where energy reporting goes wrong most often. First, installed capacity is not output: a device rated at one megawatt in a resource that delivers a 10 per cent capacity factor is a 100 kilowatt generator. Cumulative exported gigawatt-hours is the honest metric for this field and is quoted far less often than rated capacity. Second, a levelised cost quoted “at 2 gigawatts of cumulative deployment” is a conditional projection about a world that does not exist, not a measurement; the deployed base is two orders of magnitude below that condition.

Established Where this brief stops. Ocean thermal gradients are a separate technology with its own record and belong to ocean thermal energy conversion. Offshore wind on moored platforms is treated in floating offshore wind. Seabed law, marine consenting capacity and the environmental evidence base belong to ocean engineering. This brief owns survivability, the power take-off, moorings and connectors, maintenance access, array effects and the bankable capacity factor.

Established The claim this brief lands. Tidal stream is a real but small technology with a genuine system-value argument and a plausible path to a niche; it is expensive, predictable, and resource-limited to a few percent of demand in the few countries that have the sites. Wave energy, after half a century and several billion dollars, has not converged on a device archetype, has no bankable capacity factor, and remains defeated by the same problem it started with: the sea that pays is not the sea that must be survived. The honest position is not that wave energy is impossible. It is that nothing in the record supports treating it as near-term energy infrastructure.

Established A note on sourcing. This brief was commissioned in September 2026 from the Institute’s research base. Reading-list entries without links are cited from the bibliographic record rather than re-fetched, and claims are dated no later than early 2026 unless carried by a linked source.

Established Almost all the world’s ocean energy is two barrages built decades ago. La Rance in Brittany, 240 megawatts, has run since 1966 and generates in the region of 500 gigawatt-hours a year at a capacity factor in the mid-twenties per cent. Sihwa Lake in South Korea, 254 megawatts, opened in 2011 inside an existing seawall built for another purpose. Together they are the overwhelming majority of installed ocean energy capacity worldwide. Both are tidal-range schemes, both are civil-engineering projects rather than device programmes, and neither has been replicated at scale anywhere in the fifteen years since.

Established Tidal range keeps being studied and keeps being rejected on cost. The United Kingdom’s Swansea Bay tidal lagoon proposal was the subject of a favourable independent review in 2016 and was refused government support in June 2018 on value-for-money grounds, the sponsor having sought a long-dated contract at a price well above alternatives. Severn estuary barrage proposals of several gigawatts have been studied repeatedly since the 1970s and rejected each time on capital cost and environmental impact. Annapolis Royal in Nova Scotia, 20 megawatts, ran from 1984 and was shut in 2019. The pattern is consistent: the schemes are technically buildable, very capital-intensive, and have never survived a value-for-money test in a market with alternatives.

Established Tidal stream has one array with a substantial operating record and it is in Scotland. MeyGen in the Pentland Firth deployed four turbines of about 1.5 megawatts in 2016–17 and is the largest cumulative producer in the sector, passing 50 gigawatt-hours of exported electricity by 2022 and continuing since. Nova Innovation’s Bluemull Sound array in Shetland has run small turbines continuously since 2016. Orbital Marine Power’s O2, a 2 megawatt floating tidal unit, has operated at the European Marine Energy Centre in Orkney since 2021 with the specific advantage that its rotors can be raised to the surface for maintenance. These are genuine, verifiable operating records, and they are measured in tens of gigawatt-hours rather than terawatt-hours.

Established The developer mortality rate is the field’s most reliable statistic. Pelamis Wave Power, which built the world’s first multi-device wave farm off Portugal in 2008, went into administration in 2014. Aquamarine Power, developer of the Oyster oscillating wave surge converter, followed in 2015. Wavebob, Oceanlinx, Wello and Seabased all failed or retrenched. OpenHydro, whose open-centre tidal turbine had been deployed in the Bay of Fundy, was put into liquidation by its parent in 2018, leaving hardware on the seabed. The MeyGen developer itself was restructured and its turbine business changed hands. Each of these companies had a working prototype in the water at the time of failure. The failures were of financing and of the gap between prototype and product, not of the demonstration.

Established Canada has its own complete case and it is instructive. Sustainable Marine Energy delivered the first floating in-stream tidal power to the Nova Scotia grid in 2021 from its platform in the Bay of Fundy, and entered creditor protection in 2023 after failing to obtain the federal fisheries authorisations its expansion required. The Bay of Fundy has the largest tidal range in the world and a long-standing test infrastructure. The binding constraint there was not the resource, the engineering or even the capital: it was a consenting process that outlasted the company’s runway.

Established Wave energy has never converged on a device architecture, and that is the single most diagnostic fact about it. Wind converged on the three-bladed upwind horizontal-axis turbine by about 1990, after which every improvement compounded on a shared design. Wave energy still has point absorbers, attenuators, oscillating water columns, overtopping devices, oscillating wave surge converters, submerged pressure differentials and rotating mass devices under active development, with no dominant form after fifty years. Hundreds of concepts have been built. The absence of convergence means there is no shared learning curve, and a learning curve is the mechanism by which every other renewable technology became cheap.

Established The survivability problem is structural, not a matter of better engineering. Wave power flux in a severe storm can exceed the annual mean by two orders of magnitude. A converter must therefore be designed to survive loads roughly a hundred times larger than the loads that generate its revenue, in a corrosive, biofouling, fatigue-driving environment, while remaining cheap enough to sell electricity. A wind turbine feathers its blades and sheds most of the extreme load; a wave device sits in the water and takes it. This ratio is the reason wave energy is hard, and no device family has yet shown a convincing answer that survives the economics as well as the storm.

Frontier The most credible current wave programme is a single Swedish device off Portugal. CorPower Ocean’s C4 point absorber, deployed off Aguadoura in 2023, is built around a detuning principle that deliberately reduces response in extreme seas, which is a direct attack on the load-ratio problem rather than an attempt to build around it. It has reported surviving severe storm conditions (developer’s own figures). It is one device, the programme is young, and a brief written in 2019 would have said something similar about two companies that no longer exist.

Established There is exactly one real market price in the sector and it is very high. The United Kingdom introduced a ring-fenced tidal-stream allocation in its contract-for-difference auctions from 2022, and the awarded strike prices have sat in the region of £170 to £200 per megawatt-hour in 2012 prices, which is materially higher in money of the day and several times the fixed-bottom offshore wind clearing price in the same rounds. Total capacity awarded across those rounds was in the low hundreds of megawatts at most. Wave energy has no equivalent price because no wave project has been contracted at scale anywhere.

Frontier The published cost figures are projections conditioned on a deployment that has not happened. The standard intergovernmental cost reference gives wave at about US$120 per megawatt-hour and tidal stream at about US$140, both stated at 2 gigawatts of cumulative deployment, against solar photovoltaics at US$44, onshore wind at US$33 and offshore wind at US$78 as observed 2025 costs. Cumulative marine energy deployment excluding the two barrages is around one or two per cent of the 2 gigawatt condition. Quoting those figures as current costs, which happens routinely, inverts their meaning: they are what the technologies might cost if they were first deployed at a scale they have never approached.

Established Permitting and environmental monitoring are a measurable share of the cost, not an overhead. Work for the United States Department of Energy attributing costs to environmental siting and permitting requirements for wave energy devices established the method and the result that these requirements are a material component of levelised cost for small marine projects — because the monitoring burden is close to fixed while the project is tiny. A single-device deployment can carry monitoring obligations comparable to a large wind farm’s, spread over a thousandth of the output.

Frontier The environmental evidence, where it exists, is mildly reassuring and thin. Tidal-stream monitoring at the operating arrays has not recorded confirmed marine mammal or fish collisions with rotors, and the international environmental knowledge base for marine energy has moved several effects from “unknown” toward “low risk at small scale”. That is a real finding and it is bounded: the deployed base is so small that a low observed incidence establishes little about arrays an order of magnitude larger, and detecting a rare collision in turbid, fast-moving water is genuinely hard.

Frontier Whether tidal stream has a maintainable design. The operating question for a seabed turbine in a five-knot current is not whether it generates but what it costs to recover, service and redeploy, and how often. Surface-accessible designs such as floating platforms with retrievable rotors attack this directly; seabed-mounted designs depend on vessels that can hold station in strong flow. The field’s cost case turns on this and the comparative data are not public.

Frontier Whether subsea connectors and cables survive tidal duty. High-current sites impose scour, vibration, abrasion and heavy biofouling on cables, wet-mate connectors and foundations. Connector and cable faults have caused a large share of the downtime reported anecdotally at demonstration sites. There is no published failure-rate dataset for marine energy subsea hardware, which is the same gap this corpus identifies in floating wind.

Frontier Whether array interaction helps or hurts. Turbines in a channel extract momentum from a flow whose total extractable power is bounded by the channel’s dynamics rather than by the kinetic flux through the rotor plane, so naive resource estimates that multiply flux by area overstate what an array can take without changing the flow. The theory is well developed; the field validation, which requires an array large enough to perturb its channel, has not been done anywhere.

Speculative Whether a wave archetype converges. If one device family accumulates enough operating hours to establish a shared design basis, the field acquires a learning curve for the first time. Detuning point absorbers are the current best candidate. Nothing in the last two decades of the record suggests convergence is imminent, and the brief flags this speculative rather than frontier because the evidence for imminent convergence is an argument rather than a dataset.

Established The extreme-to-operational load ratio. For wave devices this is the master constraint, and it is set by the ocean rather than by the designer. Every mitigation — submerging, detuning, declutching, latching, over-design — costs capital or capture, and no demonstrated combination leaves a competitive cost of energy standing.

Established Corrosion, biofouling and marine growth. Fouling changes the hydrodynamics of a wave device and the drag on a tidal rotor, adds mass to moorings, and drives an inspection and cleaning schedule that is itself a vessel campaign. This is unglamorous, universal, and appears in every operator account of why marine energy costs more than modelled.

Frontier Maintenance access and weather windows. Marine intervention is weather-limited rather than equipment-limited, with planning done against forecast horizons of weeks; tidal sites add a slack-water constraint that reduces workable windows to short daily intervals. The practical consequence is that a fault which would take hours to fix onshore can cost weeks of lost production offshore, and every published capacity factor assumption embeds an access rate that has not been measured across a fleet.

Established The absence of a supply chain. Devices are built in ones and twos by companies that are also the developer, operator and financier. There is no independent component market and no second source for a power take-off or a wet-mate connector at these volumes. This is what distinguishes an industry from a programme, and marine energy remains a programme.

Established Consenting duration against company runway. Marine consenting is slow because the evidence base is thin, and the evidence base is thin because there are few deployments. Developers are small and venture-funded with runways of two to four years. Where a consent decision takes longer than that, the technology loses regardless of merit — which is what happened in Nova Scotia.

Established Marine consenting capacity and the environmental evidence base. Both are treated in ocean engineering, whose central finding — that the institutions governing deep-water industry have published far less environmental evidence than their remit implies — is the direct cause of the consenting delays that have killed marine energy developers.

Frontier A market that pays for predictability. Tidal generation is deterministic decades ahead, which has real system value, but almost no electricity market prices forecastability separately from energy and capacity. Whether that value can be captured depends on market design questions owned by energy corridors and the storage economics in energy storage revolutions, not by device engineering.

Frontier The decisive result is a published operating and cost record from the tidal-stream arrays now being built, and it has a date. The United Kingdom’s ring-fenced contracts commit a small fleet of tidal-stream capacity to deliver across the second half of this decade at a known strike price. The result that would most change this brief’s assessment is that fleet publishing, on a common basis, its achieved capacity factor, its availability, its operating cost per megawatt-hour, and every component recovery and replacement event with duration and cause. That converts the sector’s central claim — that tidal stream is on a cost-reduction path — from a projection into a measured trajectory or a refutation.

Frontier The wave experiment that matters is a survivability campaign with published loads. Instrument a full-scale converter, hold it on station through a winter including at least one severe storm, and publish the measured structural and mooring loads against the design basis alongside the energy captured in the same period. The field’s central unresolved question is the ratio between those two quantities, and no public dataset states it for any device at full scale.

Frontier The array-interaction field test nobody has funded. Deploy enough tidal turbines in one channel to measurably perturb the flow, and compare the measured array output and channel response against the momentum-limited theory. Until that is done, every national tidal resource estimate rests on theory validated at single-device scale.

Speculative The cheapest useful exercise is archival rather than experimental. A systematic post-mortem of the two dozen failed wave and tidal developers — what was spent, what was built, what the device achieved before the company failed, and which failure was technical, financial or regulatory — would be the most valuable document in the field and would cost one researcher a year. Its absence is why the same claims recur each funding cycle.

Established The power take-off is where wave devices are decided. Converting slow, high-force, irregular, reversing motion into grid-quality electricity is the central mechanical problem. Hydraulic circuits are compact and lossy and leak; direct-drive linear generators are efficient and heavy and expensive; air turbines in oscillating water columns are simple and inefficient. Every architecture trades efficiency against reliability against cost, and no choice has proven dominant.

Established Tidal turbines are a known machine in a hostile place. A tidal rotor is hydrodynamically a slow, heavily loaded wind turbine in a fluid eight hundred times denser, which makes the blades thick, the torque high and the gearbox or direct-drive generator large for the rating. The engineering is well understood. The hard parts are sealing, cathodic protection, bearing life in a bidirectional flow, blade erosion and cavitation near the surface, and the fact that everything must be designed for recovery.

Established Moorings and foundations differ sharply between the two. Wave devices are compliantly moored and must survive extreme excursions while transmitting reaction forces, which makes the mooring part of the power conversion rather than a support. Tidal machines are gravity-based, piled or floating, and their loads are steady and directional rather than extreme and oscillatory. The mooring failure modes of floating systems — out-of-plane bending fatigue, chain wear, abrasion, marine growth — apply to both.

Frontier Design for recovery is the discriminator. Devices that can be disconnected and floated to the surface for service — retractable rotor arms, buoyant hulls, quick-disconnect umbilicals — have a fundamentally different operating cost from devices requiring a jack-up or heavy-lift intervention in a strong current. The programmes with the best operating records are consistently the ones that made recovery a design requirement rather than a contingency.

Frontier Scaling is not the answer it is in wind. Wave power arrives per metre of wave crest, so capture scales with width rather than with swept area, and a larger device does not automatically capture disproportionately more. Tidal rotors face a diameter limit set by water depth and by the need to clear navigation and the seabed. Neither technology has wind’s cube-law scaling reward, which removes the main mechanism by which wind became cheap.

Established The nearest cautionary sibling is in this corpus. Ocean thermal energy conversion documents a technology whose all-time net power record is about 103 kilowatts, set in the 1990s at a plant since decommissioned. Wave energy is at an earlier point on the same curve with more money spent, and the shared lesson is that an ocean energy technology can sustain fifty years of programmes without producing a bankable plant.

Frontier Floating wind is the competitor for every shared input. Floating offshore wind needs the same moorings, dynamic cables, anchor-handling vessels, quays and consenting staff, is two orders of magnitude larger, and will win those inputs whenever they are contested. The most likely route by which marine energy hardware becomes cheap is as a by-product of floating wind volume, not through its own scale.

Speculative Wave energy has a plausible secondary life as a structural function. The engineering literature on very large floating structures includes work treating incident wave energy as a resource to be extracted rather than a load to be resisted, which reframes a converter as a breakwater or a motion-damping element that also generates. Where a structure must be built anyway, the marginal case for wave capture is much stronger than the standalone case.

Established The ring-fenced auction is the instrument that keeps the sector alive. Tidal stream exists commercially because a government carved out a protected allocation at a price it would never clear in open competition. That is a deliberate, defensible technology-push policy. It also means the sector’s revenue is a political decision reviewed at each auction round, and the developers know it.

Established The public-programme response to the wave failures was to nationalise the research, and it was the right call. After the collapse of the two leading United Kingdom wave developers, the Scottish public sector created a programme that funds sub-systems and components competitively rather than funding whole-device companies, on the explicit reasoning that the previous model had repeatedly spent venture capital on full-scale demonstrations before the components were ready. It is the most clear-sighted institutional response the field has produced, and it implies a much longer timeline than the one the field advertises.

Frontier Consenting is where national policy and national practice diverge. Several governments have marine energy targets and simultaneously operate consenting processes whose duration exceeds the lifespan of the companies the targets are meant to support. The Canadian case is the cleanest example, and the remedy is not a new technology but a consenting route with a stated maximum duration and an adaptive-management monitoring condition instead of a pre-deployment evidence requirement that only deployment can satisfy.

Frontier Test centres are real public infrastructure and their existence is a genuine achievement. Grid-connected open-water test berths in Orkney, Nova Scotia, Oregon and elsewhere let a developer demonstrate without building a project, and the American open-water testing programme funds exactly this. They lower the cost of failure, which is valuable and is also why the field can keep producing demonstrations without producing an industry.

Established The public money is real and the accounting is poor. Marine energy has absorbed billions of euros and pounds of public research funding, national programme spending and consumer-funded contract subsidies over five decades. No public retrospective has stated the total or what it bought. That is not an argument against the funding; it is an argument that a field with this record should be the best-audited in the energy portfolio and is among the least.

Frontier Coastal communities bear the siting costs and are offered the benefits last. Tidal and wave sites are in fishing grounds, navigation channels and viewsheds belonging to small coastal populations, frequently including Indigenous communities with treaty rights to the water. The energy is national. Where the sector has succeeded socially — in Orkney and Shetland — it has been through local ownership and local supply chains, which is a finding about legitimacy rather than about generation.

Established Persistent overpromise has a cost that is paid by the next technology. Fifty years of imminent commercialisation claims, each followed by an insolvency, have made marine energy uninvestable on private terms and have trained public funders toward scepticism that lands on whichever programme is current. A field whose advocates had been more honest earlier would now be better funded, not worse.

Established The resource ceiling is the fact that settles the scale question. Practical tidal-stream resource is concentrated in a small number of channels with strong flows and is estimated at a few per cent of national electricity demand even in the best-endowed countries. Wave resource is much larger in theory and its practical fraction is unknown because no device has established a capture cost. Tidal stream is therefore, at best, a valuable few-per-cent contributor in a handful of maritime states, and no honest projection makes it more.

Frontier The real argument for tidal is predictability, and it is undersold. Tidal output is deterministic for decades ahead, unlike any other renewable. In a system dominated by variable wind and solar, generation whose timing is known exactly has system value out of proportion to its energy — it reduces reserve requirements and is dispatchable in planning if not in operation. That value is real and is almost never priced, which means the technology is currently judged on the metric where it is weakest.

These horizons track deployment and cost evidence, and they are deliberately more conservative than the sector’s own roadmaps, which have been wrong in the same direction for fifty years.

• 10 yr: Frontier Tidal stream at a few hundred megawatts globally, concentrated in the United Kingdom, France, Canada and East Asia, with the first multi-year fleet cost and availability data published; wave energy still at demonstration scale with one or two device families accumulating hours and no contracted commercial project.
• 25 yr: Speculative Tidal stream plausibly a few gigawatts worldwide if the cost curve turns and if predictability acquires a market value, still a niche by any national accounting; wave energy either has converged on an archetype and begun a learning curve, or has been quietly reclassified as a component-research field.
• 50 yr: Speculative Tidal range schemes revisited in a few estuaries if long-dated capital becomes cheap and carbon constraints bind harder, on civil-engineering rather than device logic; marine energy hardware cheap mainly as a by-product of floating wind volume.
• 100 / 250+ yr: Handwave Projections of ocean energy supplying a large share of world electricity rest on resource estimates that ignore momentum limits in channels, capture-width limits in waves, and the absence of any cost trajectory; the brief declines to project past the point where the constraints stop being measurable.

• Depends on the marine consenting capacity and environmental evidence base documented in ocean engineering, the vessel and quay capacity treated in floating offshore wind and future ports and shipping, and the market-design question of whether forecastability is paid for, which sits with energy corridors.
• Requires (not on this map) a wave device family that enough programmes share for a learning curve to exist at all; an independent component market for tidal power take-offs, seals and bearings rather than one-off builds by the developer; an electricity market that pays separately for generation whose timing is known decades ahead; a consenting process that reaches a decision inside the two-to-four-year runway of the companies it governs; vessels able to install and recover hardware in five-knot flows without competing against offshore oil; and subsea connectors and cables qualified for scour, vibration and biofouling at tidal sites.
• Enables a small, predictable, non-weather-correlated contribution to maritime national grids; energy independence for remote islands with strong tidal races now burning shipped diesel; and a mooring, connector and subsea intervention skills base shared with other deep-water industries.
• Adjacent to ocean thermal energy conversion as the corpus’s other long-running ocean energy case, floating offshore wind for the shared supply chain, and floating cities for the structural treatment of incident wave energy as a resource rather than a load.

Handwave “The oceans contain enough energy to power the world several times over.” Theoretical resource is not extractable resource. Tidal-stream extraction is limited by channel dynamics, not by the kinetic flux through a rotor, so beyond a modest fraction the turbines slow the flow that feeds them. Wave capture is limited by capture width and by the cost of surviving the storm that also delivers the peak. The brief flags this handwave because the arithmetic that would qualify the claim is available and is never shown by those making it.

Established “Wave energy is about twenty years behind wind.” Wind at twenty years behind its present state had already converged on a single architecture and was compounding improvements on it. Wave energy has not converged after fifty years, which is a categorical difference rather than a lag. The comparison is used to imply an arrival date; the evidence supports no arrival date.

Frontier “Tidal energy is the same thing as wave energy.” They share a funding line and nothing else that matters. Tidal stream has a converged rotor architecture, a deterministic resource, operating arrays with multi-year records and an auction price. Wave energy has none of those. Reporting that averages the two consistently flatters wave and damages tidal, and it is the most common error in coverage of the sector.

Established “Recent cost figures show marine energy approaching competitiveness.” The figures in circulation — around US$120 per megawatt-hour for wave and US$140 for tidal — are explicitly conditioned on 2 gigawatts of cumulative deployment. Actual deployment excluding the two legacy barrages is one or two per cent of that. The only observed prices are auction strike prices several times higher. Quoting the conditional figure as a current cost is the field’s signature misrepresentation.

Frontier “This time the technology is different.” Some of it is: detuning architectures attack the load-ratio problem at its root, surface-retrievable tidal platforms attack maintenance cost at its root, and both are genuine improvements over what failed. The pattern to be suspicious of is not innovation but the inference from a working prototype to a commercial product, which is precisely the step at which every failed developer in this brief was standing when it ran out of money.

Speculative “Tidal barrages are a proven technology we should simply build more of.” They are proven and they have been rejected repeatedly on cost and estuarine impact by governments that studied them seriously. Both operating examples exploited an existing structure or an exceptional site. The honest statement is that tidal range is a civil-engineering investment decision with a very long payback, which is a different argument from a technology-readiness one and should be made on its own terms.