Is tidal power the future of energy supply?

‘Baseload’ is the minimum level of electrical demand which is required to keep basic services working. This is a constant load: it is required every hour, every day of every year. Up until now, baseload has always been supplied by burning oil, coal or gas in power stations – renewable energy has not been able to supply baseload, because the supply from systems like wind turbines or solar panels is not continuous.

By combining an array of three tidal turbines installed in Bluemull Sound, between the northern Shetland Isles of Yell and Unst, with a Tesla battery system, Nova Power’s Shetland Tidal Array became the first tidal power system to generate constant power. This electricity is transferred to the UK grid, and a tiny part of it is used by everyone consuming electricity, including here at the University of Derby. Electricity generated in this way has carbon emissions around 20 times lower than from traditional power stations.

So, what is tidal power?

If you’re not familiar with tidal power, the underlying principle is identical to that of a wind turbine, though the source of the energy is different. While wind comes from pressure variation in the atmosphere, tides are driven by gravity. The gravitational effect of the Moon, and to a lesser extent, the Sun, pulls the water around our planet into a rugby ball shape, while the land remains spherical. As the relative orbits of the Sun, Moon and Earth move this rugby ball of water around the planet, the effect for an observer on Earth is the ebb and flow of the tide.

The major advantage of tide over other sources of renewable energy is predictability. We know exactly what the tide will be like at any point in the future, so we know how much power will be generated from a working tidal turbine. This has major implications for the decarbonisation (reducing the amount of carbon dioxide produced per unit of electricity) of the UK’s electricity grid, as predictable tidal power could replace fossil fuel (coal and gas) power stations in a way that other forms of renewable energy cannot.

The supply of this underlying constant load, known as baseload, is seen as the holy grail of renewable energy. This is what everyone is so excited about. But what about the turbines themselves?

Scale models are key in testing design concepts

My PhD was on the design of tidal turbines, with a particular focus on the “hydrodynamic interactions” of multiple turbines. Hydrodynamics is the study of how water moves over objects, in the same way that aerodynamics tells us about the movement of air. I’m now a researcher at the Institute for Innovation in Sustainable Engineering at the University’s College of Science and Engineering and work on a wide range of carbon reduction research with small to medium-sized local businesses, but I am still involved in tidal power research and recently won funding to carry out some scale model testing at the University of Florence in Italy.

Scale models are a key way to test design concepts without the huge cost of building a full-scale turbine, and are used in combination with computer modelling to develop the next generation of tidal turbines. The turbines installed in the Shetland Array may only survive 10 years or so, and will require extensive maintenance. To generate clean energy at a cost comparable to fossil fuels, tidal turbines must be engineered for longer lifetimes with minimal maintenance, and this is the focus of current research.

A real tidal turbine is around 15m tall, but our scale models are closer to 20cm in height. After installing the first model in the centre of the large experimental water channel at the University of Florence, the channel was filled with over 10,000 litres of water and the recirculating pump turned on to simulate the tidal flow.

Over an intensive week of testing, we studied the effect of the harsh marine environment on the turbine and looked at how waves and storms can cause a turbine to speed up, slow down, or stop generating power altogether. Waves also place huge stresses on the structure of the turbine, and the results of these models will help us design future turbines to better cope with the broadening extremes of climate and weather whilst also being lower cost, easier to install, simpler to maintain, and recyclable at the end of their life.

One step closer for tidal power

There is plenty of work to be done, but the UK is a world leader in this field, and seeing the first grid-connected turbine generating power is a great step forward for tidal power!

It is imperative that the UK reduces its carbon emissions in order to avoid the worst effects of climate change, and this technology is part of a number of initiatives that will help us to do this. Tidal power alone will not achieve the necessary reductions, but with other current and future technologies, we can achieve the required reductions. Some of these technologies may be developed by students on our electrical and mechanical engineering courses, who have hands-on access to these renewable energy technologies in our Markeaton Street research laboratories.

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