Figuring out how we are going to keep generating energy is a political nightmare, and technologically challenging.  There are all sorts of issues with fossil fuels, and renewable energy solutions are (at the moment) generally a little more costly to get up and running.  There are also some issues over energy-delivery reliability.  These aren’t insurmountable problems, and slowly but surely people around the globe and thinking of new – and sometimes old solutions to producing more sustainable and less polluting energy.  Solutions like harnessing the power of the ocean.

Tides occur from the rotation of the Earth around the sun, and moon around the Earth. Each orbiting body exerts a gravitational force that pulls the ocean around.  

There are two important things about the tides that make them intriguing from an energy point of view.  

First, tides exert energy.

Second, tides are predictable – we already know what the tides are going to do for the next few years.  

So if we can capture that energy efficiently, we could power our fancy electronic gizmos with tidal power.  This isn’t a new concept as such.  Many of you will have seen images or even visited old mills next to streams and rivers with a big wooden wheel sitting in the water.  Those wheels are pushed by the water movement, and in turn, that wheel turns some cogs which grind up some wheat which throws out the flour.

The development of tidal power as a viable energy source is ongoing.  There are a number of projects in progress across the globe.  Some are very small scale, some much larger.  Here are just a few examples of the latest thinking on tidal power.  All links are open access.

What are the options

Generally speaking, there are three ways in which we could harness the power of the tides – turbine farms, barrages, or fences.  Here’s an example of each:

><> Turbine Farms are a little like wind farms – but underwater. Scottish Power is in the process of developing a ‘tidal array’ consisting of 10 turbines in the Sound of Islay, Scotland.

><> Tidal barrages are like damns built across the entrance of a bay or estuary that control water flow through sluices. In these sluices are turbines which are powered by water flowing past them.  La Rance Barrage in France opened back in 1966 as the world’s first tidal power station.  It’s still going today and provides around 90% of Brittany’s energy needs.

><> Tidal fences are rows of turbines laid over the mouth of an estuary.  Unlike barrages, they are not surrounded by any sort of dam, and so don’t have the same environmental impacts.  The downside is that they are less efficient.  For this reason, proposals for a barrage across the Severn estuary in the UK were thrown out, and consideration into a tidal fence is in.  Back in 2010, the Severn Tidal Fence Consortium explored the pros and cons of a fence system.  Their final report makes for an interesting read

How much can we get

Tidal flow is pretty powerful, but just how much energy can we expect to gain from trying to harness tidal flow?  The figure is likely to differ depending on where you are in the world (different tidal flows) and on what sort of tidal power technology is used.  In this study by Roy Walters of the Institute of Ocean Sciences and other Canadian-based researchers focused on a hypothetical turbine farm in the Bay of Fundy – an area well known for having the highest tide in the world.  Using a ‘numerical flow model’, the researchers demonstrate that the amount of power that could be realised from the turbine farm is far less than its theoretical maximum.  It seems that there are physical barriers to the technology itself.

Understanding the impacts

Everything we do has an impact on the environment and other species.  The trick is to minimise our footprint.  There has been a fair bit of research to determine the potential impacts of tidal power systems on marine ecosystems.  Here are just a few examples:

><>  Shallin Busch and colleagues at the Northwest Fisheries Science Centre undertook some simulation work to determine how tidal power development in the Puget Sound, USA and climate change may affect species listed under the US Endangered Species Act.  They took a whole host of things into consideration, including ocean acidification and changes to primary production.  Climate change came out as likely to have the biggest impact, but concerns about blade strikes from the turbines couldn’t really be fully assessed simply because we do not know if and how individuals may avoid the blade.

><> Back in 2010, Andrew Gill and Mark Bartlett of Cranfield University produced a report for Scottish Natural Heritage focusing on the impact of marine renewable energy – particularly wave and tidal power – on three species of fish.  The Atlantic salmon (Salmo salar), sea trout (Salmo trutta), and European eel (Anguilla Anguilla)are all considered species of ‘conservation importance’, and we have done a number of studies on these species.  Never the less Andrew and Mark hit a similar problem to Shallin’s team.  We just don’t know how the species will react to the energy plants – including electromagnetic fields, and noise.

><> Because La Rance is the oldest tidal power plant, it is a good place to look for environmental impacts.  Which is exactly what Engineer Richard Kirby and Christian Retière of the Muséum National d’Histoire did back in 2008.  As you can expect a whole host of changes to the estuary were found, including changes to species composition and sediment flow.