Tidal power develops thanks to technological advancements

Over the last couple of years, the global energy market has suffered considerable turmoil, not least because of a plunging oil price and indecision from governments over how to tackle climate change. With fossil fuel sources proving both limited and polluting, there has been a frantic chase to find a sustainable and renewable source of energy that won’t harm the planet, while at the same time being cost efficient. While solar energy has surged ahead of others in recent years, many people have sought to harness another of the world’s natural forces: the ocean.

The seas covers around 71 percent of the world’s surface, greatly outweighing the landmass (which is where the majority of the world’s energy consumption occurs). However, deriving energy from the powerful ocean tides has proven far more difficult than many scientists predicted.

Tidal power converts the powerful ocean tides into electricity. With tides being more predictable than wind or solar, many people believe they could provide a much more reliable source of power than existing renewable technologies. However, tidal power has yet to take off as a reliable source of renewable energy because of the prohibitively high costs of constructing and maintaining underwater generators. Another concern has been that there are relatively few regions where tidal ranges can produce currents strong enough to generate power.

In 1924, the US Federal Power Commission conducted a study into a potential tidal power plant in the northern border region of Maine, as well as the southern area of Canada’s New Brunswick state. This would have involved a number of dams, locks and powerhouses around the Bay of Fundy and Passamaquoddy Bay, but the project was eventually scrapped due to a lack of sufficiently advanced technology and the Great Depression hampering investment.

Another scheme was proposed in the same area in 1956 – specifically in the Nova Scotia part of the Bay of Fundy. While the report said millions of horsepower would be generated by the scheme, it proved far too costly to make commercial sense.

Potential projects and problems
While it is a seemingly renewable and non-polluting source of energy, tidal power generators can have a devastating impact on marine life, with turbines killing sea life and barrages damaging the flow of water into estuaries and the ecologies around them. There is also the issue of the metal equipment corroding due to its constant contact with salt water.

Despite these problems, there remain a number of proposed tidal power schemes. These include a 50-megawatt tidal farm in the Indian state of Gujarat, which began construction in 2012, and a 1.05MW farm of 30 tidal turbines in the East River of New York City.

There are a number of different methods by which tides can be turned into sources of energy. Tidal stream generators utilise the kinetic energy that comes from water passing through power turbines, in much the same way wind turbines operate. In some cases, tidal stream generators have been built into existing structures, such as bridges. The cheapest form of tidal power, they also have the smallest ecological footprint.

Working much like a dam, tidal barrages are some of the oldest forms of tidal power generator, with large-scale projects constructed during the 1960s, including the 1.7MW Kislaya Guba Tidal Power Station in Russia. However, they have been criticised for both their impact on the water that passes through them, and the surrounding environment.

Dynamic tidal power is a method yet to be utilised, but with a number of proponents. A mixture of both potential and kinetic energy flows, the method would use extremely long dams of almost 50km in length, built far out to sea. Because they would not enclose any area, their ecological impact would be less than a traditional tidal barrage.

Another proposed option is a tidal lagoon, which would involve circular walls being constructed in the water to capture potential energy from tides. The Tidal Lagoon Swansea Bay has been proposed in Wales and would have a capacity of 320MW. It was granted planning permission by the UK Government in 2015. However, the scheme has received considerable opposition from local campaigners who fear for the ecological impact of the lagoon, as well as the relatively high cost – set to be £168MW/h, which is almost double the cost of nuclear power generation.

New tech
One group of scientists claims to have devised an alternative method of tidal power generation that would be both cheap and sustainable. Kepler Energy says its technology, which it is working on in collaboration with Oxford University’s Department of Engineering Science, could radically transform the way in which power is generated from the sea. By using a horizontal axis turbine (dubbed ‘a tidal fence’), Kepler hopes it will be able to avoid the use of expensive and large dams and barrages.

The fence could be deployed in shallower water than traditional turbines. The company hopes to deploy it in the UK initially, with a proposed one-kilometre fence in the Bristol Channel potentially operational by 2021, at a cost of £143m.

Speaking to Reuters at the unveiling of the tidal fence research, Kepler Energy Chairman Peter Dixon said the potential output of the technology is considerable. “The design we have at the moment and the proposition we have at the moment is to put a tidal fence, which is a chain of these turbines, in the Bristol Channel, and if we can build up to, say, 10km worth, which is a very extended fence, you’re looking at power outputs of 500 or 600MW. And just to visualise that, it’s like one small nuclear reactor’s worth of electricity being generated from the tides in the Bristol Channel.”

With scarce natural resources and collapsing oil prices shaking up the world’s energy markets, new forms of renewable energy are going to be explored by many companies. While solar has certainly jumped ahead of the pack, the potential for tidal power to play an important and sustained role is something many countries that don’t enjoy endless sunshine – such as the UK – will be hoping can be realised.