Tidal News for MARINET — How will the Commission report?

Tidal Power — How will the Commission report?

The Sustainable Development Commission (SDC) aims to report on its tidal power studies early in October 2007. www.sd-commission.org.uk/pages/tidal.html

The government has asked them for a clear answer on the various competing claims and technologies. However the unknowns in the marine environment and technologies mean that the rational answer is to pursue a variety of options. Pilot projects, modular expandable systems, short timescales, and deferring irreversible commitments should guide the strategy. Hopefully the SDC will also speak up for some direct funding (or German-style feed-in funding), rather than sticking to the ‘Renewable Obligation’ subsidy mechanism, which has served renewables in the UK so poorly.

Intermittency and demands on the National Grid present large problems for the mega-barrage, in the absence of storage. The Natura 2000Natura 2000 A European network of protected sites developed to maintain or restore natural habitats and species of wild flora and fauna to favourable conservation status within the European Union. status and value of the Severn is a show-stopper. Barrages and lagoons are respectively major and minor development projects, which can also give greater or lesser coastal protection from rising sea level and storms.

The three tidal technologies are largely compatible, using different marine sites. So it makes sense to deploy tidal streamtidal stream The flow of water through channels or around coastlines as a result of tidal water movement turbines (several designs), construct a pilot OTI-lagoon and progress studies of the Severn ‘Shoots’ barrage.

In regard to CO2 and renewable energy targets up to 2020 and transition to a low carbon and renewable power future, tidal lagoons and ‘farms’ of marine turbines appear of high significance. They could be the large technology end of a decentralised power system.

The SDC’s tidal project manager appraised the new review as part of their work and would correct my assertion that the Carbon Trust and the Sustainable Development Commission seem influenced by business interests. They responded:
“The SDC acts independently and takes a sustainable development approach to assessing issues and seeking to integrate environmental as well as economic and social concerns.”
The assertion conflates two points, that the SDC Workshop events were dominated by an in-group of official bodies and project promoters, and that the Carbon Trust had adopted a gross under-estimate of tidal stream resource and turbine economics, when this could supply a significant percentage (20-50%) of the UK electricity needs.

Tidal Power – call for a strategic rethink

Conwy Cllr Dr Stuart Anderson, a local GP at the time of the 1990 Towyn Flood Disaster, advocates a basic rethink about tidal energy storage and release (TESAR) schemes. He believes (with the Environment Agency) that the Severn Barrage Project has become a white elephant through failure to give it energy-strategic purpose, with ebb-generation only.

Anderson reminds us that the tidal barrage at La Rance in Normandy was originally run successfully as a two-way generation scheme with two-way pumping as well. This reduced the output discontinuity. But it was then discovered that too little capacity was built in to allow this mode to yield as much net power as ebb-only generation with pumping. Anderson argues this outcome represented a scoping deficit at La Rance rather than evidence that ebb-only generation was the ideal model for the Severn Barrage (or anywhere else).

The summary of Anderson’s Ecostar (Eco-Storage for Tidally Amplified Release) concept is available here, also his full article written for the British Hydropower Association. (Both of these are large pdf files.)

Anderson shows how a doubling of turbine/pump capacity would counter many environmental objections to a Severn Barrage by allowing behind-barrage rise-and-fall to equal the natural average tidal sine wave. Meanwhile, quadrupling it would allow behind-barrage amplitude to equal that of high spring tides. Broadly speaking, net power outputs would rise linearly with such increases in installed capacity.

As tides in Liverpool Bay are delayed by four hours, a series of coastally-attached tidal impoundment (‘CATI’) schemes built there could work in parallel with a redesigned Severn Barrage or the Shoots Barrage to cross-supply pumping requirements. A network of further schemes in NW Wales and SE Scotland as well (where tides arrive 2 hours after Cardiff’s) could be devised to supply continuous net power output, even allowing for pumping requirements, that could meet the entire 20 GW UK electrical base-load – i.e. three times more than presently provided by nuclear power.

However the immediate need is for a pilot scheme. Here Anderson suggests that a £150m, 3 sq km offshore tidal impoundment (‘OTI’) off Rhyl on the N Wales coast (see Fig. below) could be relatively uncontroversial and quick to build. Npower, the builders of the N Hoyle and planned Gwynt y Môr offshore wind farms, have their renewables base at Dolgarrog and have offered a preliminary view on practical and financial feasibility. Attached to the coast by a new-build pier, the scheme might provide a round-the-clock base for servicing the wind farms, besides a maritime facility and local attraction. Progress depends on a political decision that such a pilot scheme is in the national interest. There’s an analogy with the pilot off-shore wind turbines set up at Blyth.

map showing possible tidal power site in the Severn


Max Wallis – 14th September 2007 for MARINET site

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