Our new energy report, Energy Independence 2025, identifies the options for increasing renewable energy generation within the Exeter region. We’ve already looked at how Solar, Wind and Hydro power is generated, in this last Energy Explainers blog we will be introducing Marine Energy.

When it comes to water there are multiple ways it can be used to generate electrical power, we’ve already explained the one most people are familiar with – Hydroelectric. Another way of generating watts from the wet stuff is by capturing Marine energy created by tides and waves.

Both Hydroelectric and Tidal Energy can be captured using similar technology, the main difference between them is what is causing the water to move. With Hydroelectric power water is artificially stored in a high place, so it can be released and flow to a low place and through a generator.

With Tidal energy the movement of water is also used to power a generator, but the flow of water is caused by the changing tides. Another form of Marine Energy is Wave, but the technologies for capturing it are still being developed.

If you’re ready let’s hang 10TWh and surf on a wave of marine Energy.

Tidal Stream

Tides are created by the combined effect of the Earth, Moon and Sun’s gravity. As the moon moves around the earth it pulls the oceans along with it, and so does the sun, while the Earth tries to pull the water back. The effect of the Sun’s gravity on the Earth is only half that of the moon – so it’s like a cosmic tug-of-war where the Moon is winning.

All this movement combined with the rotation of the earth, and the movement of the earth and moon around the sun, results in two high tides and two low tides a day. These rising and falling tides create tidal streams, a horizontal flow of water which can be used to generate electricity.

Energy can be captured from tidal streams by using turbines, which work in a similar way to wind turbines. The easiest way to think of Tidal Stream is as underwater wind power!



The problem with Tidal Stream is that it only works for half the day when the water flows fastest. Power is not generated when the tide is moving slowly around the high and low water marks.


Barrage and Lagoon

Barrage and Lagoon installations work on the same principal as tidal stream except that water is stored behind an artificial wall built mid-stream, or wall that creates a pool around the shore. Because of the difference in height created by storing the water behind a wall, Barrage and Lagoon generators are able to compensate for the times when the water is flowing slower.

The mouth of the Exe, looking towards Exmouth.


Within the region the mouth of the Exe has the potential for a tidal barrier to capture tidal stream energy, but this is unlikely to happen. Aside from the significant environmental concerns it would raise the low range of the Exe’s tides means it would only generate enough electricity to meet the minimum requirements for building one.


Another way to generate marine power is by capturing and converting the kinetic energy of waves into electricity. As this energy is created by the up and down motion of the waves, and not by flowing water, it is harder to capture and several solutions are still being tested like Wavehub in Cornwall. Although there is a huge potential to generate energy in this way it is unlikely full-scale prototypes will be ready before 2020.



You can find out more about the Exeter Region’s tidal potential in Energy Independence 2025 which is available through our Insights page. It will provide a detailed analysis of how marine power can be generated in the region, in addition to other forms of renewable energy, and offer key recommendations for becoming energy independent.