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A silly tidal idea?

By Dave Elliott

In a press article, one-time Secretary of State for Wales Peter Hain puts the case for the new privately funded tidal barrage across the Severn proposed by Hafren. He says it would “make a greater contribution to tackling climate change than any other green energy project”, supplying “fully 5% of the UK’s electricity (16.5 TWh per year) of clean, low carbon, predictable and therefore base load energy”.

In fact, it would not generate 5% of UK electricity. 16.5 TWh is 4.5% of 2011 demand, and when the barrage might be working (it will take ~10 years to build), demand may have risen above the 2011 level of 365 TWh, even given efforts to cut it. Moreover, it is not base load. Not all the annual output could be used. Due to the daily lunar cycle, peak output would often occur when there was no demand for it, and, at other times, there may be high demand when there is no output, the peaks also shifting by 50 minutes or so each day and varying in size with the spring/neap cycle.

Operating two ways, on both the ebb and flood cycles, as proposed by Hafren, does extend the period during which power can be produced, it says up to 16 hours per day, but the two-way turbines needed will be expensive, wear out faster and suffer more breakdowns. That all adds to the cost, which overall is put at £25 billion, to be raised it seems from sovereign wealth funds.

Major capital intensive projects like this can have long pay-back times, but also run for long periods, so the economic viability depends on the financing arrangements. Most studies have suggested that it would be hard to finance a big barrage given the rates of return expected in the private sector. Hain, however, says it can be done and even claims the barrage “will reduce overall consumer electricity bills by 3.5% a year on average over its life. So it would be the cheapest electricity source in the UK, 50-75% cheaper than coal, gas, wind or nuclear for over 100 years”. But, tellingly, he adds, “an electricity contract will have to be negotiated containing the usual price support mechanism for all renewable energy projects over 30 years”. So there would be a long interim subsidy, much like the nuclear industry is seeking.

Is it worth it? The Sustainable Development Commission’s study of the previous barrage concept found that it would only save around 0.9% of UK emissions, and the new version would be no better. You would get far better results from almost any other green energy investment. Frontier Economics’ study for the WWF showed that big barrages would cost much more than any other supply option, even nuclear. And it would also impose massive environmental costs.

Hafren has tried to address the environmental impacts by proposing using a larger number of slower-speed turbines and by operating two ways, on a lower head. But it still blocks the entire estuary and its eco impacts will still be huge, despite the modifications, which add to the capital and operating costs.

The 150-page proposal Hafren submitted to the government did not fare well. The government had indicated that, although it would not provide financial support for large barrages, it was open to companies developing proposals for private projects. A meeting with David Cameron had reputedly gone well and it was said Lord Heseltine had backed the idea, as one his proposed major infrastructure projects. However, Greg Barker, energy and climate change minister, has now indicated that Hafren had not provided enough information to be convincing. Too many questions remained over the project’s affordability, environmental impact and its effect on the port of Bristol, upstream of the proposed barrage. He was quoted by the BBC as saying ‘The information that the department has seen so far doesn’t allow us to assess if the proposal is credible.”

Labour MP John Robertson was less charitable. He said the amount of information provided by Hafren was “embarrassing”. In a session of the Energy and Climate Change Committee, which has been looking at the issue, he told the minister: “I’m surprised you haven’t just thrown it out completely.” There is a 41 page version of Hafren’s case at

Barker made clear that it was unlikely that the hybrid bill required for the project would be considered before the election in 2015, but that, although Hafren’s evidence was not sufficiently compelling, the government had left the door open.

For the moment it looks a very unlikely contender. Unless very large energy storage facilities are built, or major new under-sea inter-connectors constructed to export the excess power to the continent, a big multi-GW barrage would just not fit in the UK energy system. It’s even worse in that respect than large nuclear plants – they are only 1.6 GW.

Most environmental groups have opposed large barrages strongly on the basis of their eco impact. But the strategic case against them has also been recognized. For example, the Green Party has come out against the proposed new variant, preferring less invasive lagoons and tidal reefs/fences instead:

A recent report by Regen SW and consultancy firm Marine Energy Matters says that tidal lagoons and tidal fences, tidal stream technology, wave and wind power, could be far less harmful to the environment, and provide up to 14 GW of low-carbon energy capacity, at least twice that of the proposed Hafren barrage. The UK’s potential tidal current resource alone is put at about 8 GW. There is also an interesting new proposal for a 250 MW tidal lagoon off Swansea:

A multi-technology, multi-site approach would be modular (lots of faster to install, smaller projects, so easier to finance) and more flexible (better matched to daily demand patterns). By contrast, with a single large barrage you get large pulses of often unusable energy, and in terms of construction, it’s all or nothing. You can’t build half of one, and if it turns out to have problems (e.g. silting up), you may be stuck with expensive remedial measures, or even complete failure.

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