Hydrosphere managing director John Caskey examines why such a promising technology as tidal power is still not popular.

Half of the UK’s renewable energy now comes from wind power, and by 2030 it will get a third of its electricity from offshore wind. But what do we do when there’s no wind?

John Caskey, managing director at Hydrosphere

John Caskey, managing director at Hydrosphere

Despite being the windiest country in Europe, some of Scotland’s wind turbines in the North Sea recently came to a standstill during so-called ‘wind droughts’. This is not something that happens with the tide.

Researchers from the University of Plymouth found that installing tidal stream systems, in addition to solar and offshore wind farms, is around 25% more effective at balancing energy supply with demand than relying on solar and wind technologies alone.

Tidal energy has an estimated potential capacity of around one terawatt, which is roughly equivalent to the total installed capacity of all renewable energy sources put together. It is also an infinite, guaranteed, predictable source.

It also has a high-power output because water is so dense – around 800 times denser than air, which means a tidal turbine will produce much more energy than a wind turbine of the same size.

Yet it’s been largely absent from the discussion of alternative renewable energies. Why?

Hurdles to tidal power

The most common tidal turbines are placed in a barrage (a dam-like structure) across the mouth of a bay or estuary, creating a reservoir that fills during high tide. As water flows in and out, it travels through channels fitted with turbines that generate electricity.

The other way is with stream generators, which operate in deeper water and create power using natural currents.

The main obstacle to tidal power is cost. This infrastructure can cost several times more than solar or wind installations and has typically been underfunded by government schemes.

UK tidal energy prices currently sit at around £260 (€301) per megawatt hour. But as technology advances and bigger economies get involved, these costs should decrease.

With the sector seeing increased backing, the Cost Reduction Pathway of Tidal Stream Energy in the UK and France report says the tidal market could see a cost reduction trajectory, taking prices down to £78 (€90)/MWh by 2035.

Although the tides are predictable and reliable, the intensity of sea waves is not constant, so the energy they generate can fluctuate. However, although this could mean back-up power is still required, the density of water is enough to power a turbine even when water is moving at low speeds.

The strongest currents are close to land, which means systems must be close to coastlines and can be limited to certain sites.

However, as the UK features the second-strongest tides in the world (after Canada), tidal power plants can be built further out to sea.

It has been debated that tidal barrages could affect local ecosystems and wildlife — and installing tidal stream generators may disrupt the seabed and threaten marine life. However, extensive environmental assessments must happen before any tidal energy project is given the green light, ensuring marine life is put at the forefront and protected.

The future of tidal and wind energy

A tidal energy installation

An example of a tidal energy installation

Taking into account the advantages and considerations of tidal energy, could a dual-edged approach be the answer to overcoming periods of high demand and low wind resources?

Because they naturally peak at different times, coupling tidal and wind power could go a long way towards creating a reliable renewable energy source.

Integrating offshore wind farms and tidal turbines with the same foundations can also help to reduce installation costs. Plus, if the two power sources can use the same ocean real estate, fewer navigation or data buoys will be needed around the site — meaning less maintenance and further cost reductions.

The industry group British Hydropower Association currently has projects under development that would deliver 10 gigawatts of new capacity by 2030 if they were to receive permission and adequate funding.

These projects are across Great Britain, including Swansea Bay, Merseyside, the North Somerset Coast and the North Wales Coast.

With research and experimenting by scientists, engineers and investors ramping up, the tidal energy industry will eventually reach a stage of development where pairing tidal and wind power is a practical reality.

Until then, the marine industry must encourage governments to join the conversation and explore how to bring early-stage tidal energy concepts to fruition — instead of remaining just a straw in the wind.