Blog post

Swimming against the tide – When will tidal energy take off?

Energy Blog, 20 February 2020

Matthew Taylor outlines the hurdles to the tidal sector that have preventd it from becoming a mainstream energy source.

When I was young I’d holiday every summer on a small camping site near Porlock, Somerset or on the west coast of the Lake District. Since meeting my wife in 2004 we’ve spent a lot of our holiday time on the north-west coast of Cornwall, near Tintagel. Aside from the obvious environmental credits, the upside of doing so many staycations is I am very well versed on the relative merits of three British delicacies: the Somerset cream tea (cream first of course), Cornish pasties and the ubiquitous sticky toffee pudding.

An unseen consequence though is that I have inadvertently spent a lot of time in areas with huge tidal resource. Sadly I wasn’t alert enough as a teenager to appreciate the true beauty of such a natural resource (I was too focussed on ensuring I got my jam and cream in the right order) but now I am a bit wiser and educated on the matter, I have become a bit obsessed with the tide.

Tidal energy has long been championed as a great untapped natural resource surrounding these green and pleasant lands, something all the more relevant in this rapidly evolving energy market and for today’s environmentally conscious electorate. Being roughly 800 times more dense than air, surely the energy that can be captured from this enormous volume of flowing water is huge? Surely it’s the chance to grow a new UK manufacturing and skills sector for use not only at home but also for export to all the other nations with great tidal resource like Canada and India? Surely as a clean and predictable source of energy (tides can be accurately forecast indefinitely) it provides a more reliable source of power than intermittent wind and solar and a more environmentally acceptable one than conventional power sources? You’d think the answer to all of these things would be yes but you would be wrong. Despite all the arguments in favour of tidal power, the sector has failed to gain any material traction in the UK or international markets. Why is this?

Firstly, we have to consider the two technology options; tidal power can be harnessed through lagoons (like La Rance in France or the proposed Swansea Bay lagoon) or through the tidal stream itself, in the same way we capture wind power. At a high level the technology in tidal lagoons is nothing new (it’s similar in many ways to hydro, which is implemented successfully the world over) but determining the right way of harnessing tidal stream has proved more challenging. Only recently has there been convergence on the most appropriate technology solutions and perhaps unsurprisingly these look very similar to the now ubiquitous horizontal axis wind turbines we see on our green mountains and blue seas.

This means the tidal stream sector has to date focussed largely on developing technology. The tidal range sector has been more focussed on developing sites, but this brings us to the next hurdle; tidal range, when connected to the intertidal zone raises major environmental and planning challenges and is not easily scalable. Given the limited number of environmentally acceptable sites a site needs to be used to its maximum potential from the beginning. This is less a concern with offshore lagoons or tidal stream as more sites are potentially available.

The third and most challenging hurdle to the tidal sector is one of cost. Despite the relatively high density of water, capacity factors (i.e. the actual production expressed as a proportion of the theoretical maximum energy available over a period of time) are lower than those of wind and solar farms. The tide only comes in and goes out twice a day. This means lower levels of energy production (over a year) than offshore wind for example and all other things being equal that means a higher electricity price is needed. Combining this lower yield production with relatively high capex (at least relative to offshore wind) means tidal cannot compete cost wise with its more mature cousins in wind and solar. A feather in tidal’s cap and potential (partial) mitigation of the cost challenge is its predictability, but the current allocation mechanism for subsidy support in the UK doesn’t enable this additional value to be captured financially and in any case while this is valuable, what we really need is baseload power (so one that is both predictable and constant) which is perhaps why nuclear still gets promoted in the UK despite the eye watering costs and environmental consequences.

Developers do argue that tidal baseload could be achieved by installing sites around the UK to capture the different tidal flows (presumably this would require tidal stream and offshore lagoons given the limited deployment areas for intertidal lagoons and in any case would need validating), and hopefully tidal costs will converge rapidly given the chance, but, and it’s quite a big but, this requires investment in early projects to build experience and scale. A similar approach was of course taken with other mainstream renewable sources and this has led to the huge success of solar and wind (in particular offshore wind). However this success also acts against the tidal sector because understandably the Government’s main focus is on deploying large amounts or renewables quickly at minimum cost to the consumer. This means it is hard to justify special support for a particular technology such as the tidal sector. We believe this is somewhat short sighted and that tidal should be given the opportunity to be an active part of the UK energy mix.

So despite the relentless nature of the tides and the huge amount of energy just off the shore of the UK, unfortunately it does not look like this technology is going to become mainstream anytime soon. Whether you holiday in Cornwall, Somerset, Cumbria or elsewhere in this green and pleasant land don’t expect to have your holiday treats cooked with power from tidal farms this decade.