Ocean Power — How Waves, Tides, and Currents Could Power the Planet

The ocean is almost constantly moving.

Waves roll towards shore. Tides rise and fall. Powerful currents move enormous volumes of water around the planet.

All that movement contains energy.

For decades, engineers have been trying to find practical ways to capture some of it and turn it into electricity.

The attraction is easy to understand. Oceans cover most of the Earth’s surface, coastal populations are enormous, and some forms of marine energy — particularly tides — are remarkably predictable.

But the ocean is also one of the harshest environments in which to operate machinery.

Salt water corrodes equipment. Storms create enormous forces. Underwater repairs are difficult and expensive.

Ocean power therefore has considerable potential, but also some very real challenges.

What Is Ocean Energy?

Ocean energy is a broad term covering several technologies that extract energy from the movement or physical properties of the sea.

The main forms include wave energy, tidal-stream energy, tidal-range systems and ocean-current energy.

There are also technologies that attempt to use differences in ocean temperature or salt concentration, although these are much less widely deployed.

Each approach works differently.

Some use the up-and-down movement of waves.

Others place turbines in fast-moving tidal water.

Large tidal systems can use differences in water level between high and low tide.

What they share is an attempt to turn the natural movement of the ocean into useful energy.

How Does Wave Power Work?

Waves are created primarily when wind transfers energy to the surface of the ocean.

Once formed, waves can travel enormous distances while carrying that energy with them.

Wave-energy devices attempt to capture some of this movement.

There isn’t one standard design.

Some devices float on the surface and move with the waves.

Others are anchored offshore or installed near the coast.

Some use the movement of waves to force air through a turbine.

Others use hydraulic systems or generators that convert the physical movement directly into electricity.

This variety tells us something important about wave power.

The industry hasn’t yet settled on one dominant technology in the way solar power has largely standardised around photovoltaic panels.

Why Wave Energy Is So Attractive

Waves can carry substantial amounts of energy.

In some coastal regions, strong and relatively consistent wave conditions create an appealing renewable resource.

Wave energy also follows different patterns from solar and wind.

Waves can continue arriving after the wind that created them has weakened, and they can generate energy after sunset.

That means wave generation could potentially complement other renewable sources.

A coastal electricity system combining solar, wind and wave power might receive energy from each source at different times.

But having a large theoretical resource doesn’t automatically make it economical to use.

Capturing that energy reliably is the difficult part.

The Ocean Is Hard on Machinery

Put almost any piece of machinery in the ocean and life becomes complicated.

Salt water encourages corrosion.

Marine organisms grow on submerged surfaces.

Constant movement places mechanical stress on equipment.

Then there are storms.

A wave-energy device must be sensitive enough to capture energy from normal waves while also being strong enough to survive extreme conditions.

That creates a difficult engineering problem.

Making equipment extremely strong adds weight and cost.

Making it lighter can increase the risk of damage.

And when something breaks offshore, repairs can require boats, specialist crews and suitable weather conditions.

This is one reason wave energy has taken much longer to commercialise than many early supporters expected.

Tides Offer Something Special: Predictability

Tidal energy has one major advantage over many other renewable resources.

Tides are extremely predictable.

They are driven mainly by the gravitational relationship between the Earth, Moon and Sun.

Weather can influence local conditions, but the timing of tides can be calculated far into the future.

That means electricity-system operators can know when tidal generation should rise and fall.

Solar generation can also be broadly predicted, of course, but clouds introduce uncertainty.

Wind forecasts have improved enormously but aren’t perfect.

Tidal movements follow a much more dependable schedule.

How Do Tidal-Stream Turbines Work?

One way to capture tidal energy is with underwater turbines.

Tidal streams can create strong flows as water moves through channels, around headlands or between islands.

A tidal-stream turbine operates somewhat like an underwater wind turbine.

Moving water turns the blades, which drive a generator.

Water is far denser than air, so a relatively compact turbine can experience substantial forces.

Suitable locations, however, are limited.

The water needs to move fast enough to generate useful electricity, while the site also needs to be practical for installation, grid connection and maintenance.

What Are Tidal Barrages?

Another approach uses the difference in water level between high and low tide.

A tidal barrage is essentially a dam-like structure built across an estuary or bay.

As the tide rises and falls, water moves through turbines in the structure and generates electricity.

The technology can produce substantial amounts of predictable power in suitable locations.

But building a large barrier across an estuary can significantly alter the local environment.

Water movement changes.

Sediment patterns may change.

Fish and other marine life can be affected.

Shipping and coastal ecosystems also need consideration.

Tidal barrages can therefore provide renewable electricity, but their environmental footprint can be considerable.

Tidal Lagoons Offer Another Approach

A tidal lagoon uses a wall or barrier to enclose an area of coastal water.

As the tide changes, differences in water level between the lagoon and surrounding sea can drive turbines.

In principle, this can capture tidal-range energy without blocking an entire estuary.

But lagoons still require major coastal construction.

They can be expensive and may affect marine habitats, sediment movement and the appearance of coastal areas.

Like most ocean-energy technologies, the engineering is only part of the decision.

Economics and environmental effects matter just as much.

Could Ocean Currents Generate Electricity?

The world’s oceans contain enormous currents.

Unlike tides, which regularly reverse direction in many locations, major ocean currents can flow predominantly in one direction.

This raises the possibility of placing turbines in persistent currents and generating electricity from the moving water.

The idea is similar to tidal-stream generation but potentially operates on a much larger ocean system.

However, practical development remains challenging.

Major currents can occur in deep water and far offshore.

Equipment must be anchored, maintained and connected to electricity networks.

The ecological effects of extracting energy from major currents also need careful study.

For now, ocean-current power remains much less developed than mainstream renewable technologies.

Ocean Thermal Energy Takes a Completely Different Approach

Not all ocean energy relies on moving water.

In tropical regions, surface seawater can be much warmer than water deep below.

Ocean thermal energy conversion, usually called OTEC, attempts to use this temperature difference to generate electricity.

Warm surface water is used within a system that drives a turbine, while cold deep-ocean water helps complete the cycle.

The concept has been known for a long time.

The difficulty is that the temperature difference is relatively small compared with conventional thermal power systems.

Large amounts of seawater therefore need to be moved through the system.

This makes OTEC technically possible but difficult to make economically competitive.

Islands Could Be Important Testing Grounds

Island communities are particularly interesting for ocean energy.

Many islands rely heavily on imported diesel or other fuels to generate electricity.

Fuel can be expensive because it must be transported by ship.

At the same time, islands are surrounded by the very resource ocean-energy technologies are designed to use.

Wave, tidal or ocean-thermal energy could potentially complement solar, wind and battery storage in suitable island locations.

The challenge is cost.

Small island electricity systems may have limited budgets and cannot afford experimental technology that isn’t reliable.

For ocean energy to become genuinely useful, it needs to work outside research projects and survive real-world conditions for many years.

Could Ocean Power Work With Offshore Wind?

One interesting possibility is combining different offshore technologies.

An offshore wind farm already requires subsea cables, grid connections, maintenance vessels and other infrastructure.

In some locations, wave-energy devices could potentially share parts of that infrastructure.

Wind and waves don’t always peak at exactly the same time, so combining technologies could create a more varied energy supply.

Floating offshore wind may create further possibilities as renewable-energy development moves into deeper water.

Whether these combinations prove economically worthwhile will depend on how successfully wave-energy technology develops.

But using shared infrastructure could potentially reduce some of the cost of operating far offshore.

What About Marine Life?

Renewable doesn’t automatically mean harmless.

Ocean-energy projects can affect marine environments.

Underwater turbines may interact with fish and marine mammals.

Construction can create underwater noise.

Cables and anchors disturb parts of the seabed.

Tidal barriers can alter water movement and sediment.

Wave-energy arrays could potentially change local wave conditions.

The scale of these effects depends heavily on the technology and location.

Careful site selection and long-term monitoring are therefore essential.

A clean-energy project shouldn’t solve one environmental problem by unnecessarily creating another.

Could Ocean Energy Affect Surf and Beaches?

This is particularly relevant for wave-energy projects near shore.

Wave devices extract energy from waves.

If a large enough array were installed, it could potentially alter wave conditions behind it.

That could affect coastal processes, recreational surfing or sediment movement.

The effects would depend on the size and design of the project and how much wave energy was removed.

These issues don’t automatically prevent wave power development.

They simply need to be considered before projects are built.

Local communities often have strong connections to coastlines, so public consultation can be particularly important.

Why Isn’t Ocean Power Everywhere Already?

The answer largely comes down to cost, reliability and engineering.

Solar panels can be manufactured in enormous factories and installed almost anywhere with sufficient sunlight.

Wind turbines have benefited from decades of commercial development and increasing scale.

Ocean-energy devices are still relatively specialised.

They have to operate in difficult conditions and may require expensive offshore installation and maintenance.

The industry also lacks the enormous manufacturing scale that helped drive down solar and wind costs.

Ocean energy therefore faces a difficult cycle.

Costs need to fall for deployment to grow, but greater deployment can be needed to bring costs down.

Ocean Energy Doesn’t Need to Power the Entire Planet

The title may ask whether waves, tides and currents could help power the planet, but that doesn’t mean ocean energy needs to become the world’s dominant electricity source.

Energy systems rarely depend on one technology.

Solar may be best in one location.

Wind may dominate somewhere else.

Hydropower may suit another region.

Geothermal can be valuable where underground conditions allow it.

Ocean power may ultimately make the most sense in particular coastal locations with excellent resources.

That would still make it useful.

A technology doesn’t have to power every home on Earth to earn a place in the clean-energy mix.

What Would Make Ocean Power Successful?

Several things need to happen.

Equipment must become more reliable.

Installation and maintenance costs need to fall.

Developers need confidence that devices can survive years of harsh ocean conditions.

Environmental effects need to be properly understood.

Projects also need practical access to electricity networks.

Perhaps most importantly, ocean-energy technology has to compete with solar, wind and batteries that continue improving themselves.

That is a demanding benchmark.

But the size of the ocean resource means engineers are unlikely to stop trying.

An Enormous Resource Waiting Offshore

Stand on almost any exposed coastline and the potential is easy to see.

Wave after wave arrives.

Tides continue their predictable cycle.

Powerful currents move beneath the surface.

The ocean contains an extraordinary amount of energy.

The challenge has never been proving that energy exists.

The challenge is capturing it reliably, economically and with acceptable environmental impacts.

Wave and tidal power are not yet ready to replace solar or wind as mainstream renewable technologies.

They may never reach the same scale.

But in the right locations, ocean energy could become another useful part of a diverse clean-energy system.

After all, renewable energy is about learning to use the natural energy flows already surrounding us.

And few things on Earth move with more persistence and power than the sea.