Search

The Severn Estuary provides the UK with a unique opportunity to harness a large amount of renewable energy from the tides. A barrage 10 miles (16 km) long has been proposed as a means of harnessing this energy. The scheme would be similar, but on a larger scale, to that in the Rance Estuary, northern France, which has consistently and predictably produced electricity over the last 40 years. The studies presented here illustrate the output patterns of the Severn Barrage once the barrage is closed but before project completion, taking into consideration important factors such as: National Grid integration; environmental sensitivities and turbine and pumping characteristics. Assuming the main determine and of operating procedure is production of maximum energy, total barrage output could be 33 TWh by project completion. This is equivalent to almost two years of output from the completed scheme. Furthermore, if barrage closure were to occur earlier than previously envisaged, significantly more electricity would be produced during the construction phase, thus further enhancing the projects economic prospects.

The predictable, regular reversal of the tides makes this an important renewable energy resource, one which is large, technically well proven and reliable if exploited by applying the conventional principles of hydroelectric power. The basic operating principles of tidal power stations were explored in depth in many studies carried out throughout the twentieth century. With few exceptions, a basic premise was to maximise energy output. Less attention was given to identifying the design and operating procedures needed to maximise aggregated energy value, it presumably being assumed that the latter followed the former. The studies reported in this paper are based on the now strongly established commercial trend for electricity to be marketed competitively, having regard for such factors as time of day and guarantee of use. Consumer technologies have taken advantage of the differential tariff structures which have emerged and will continue to evolve, and this in turn is being reflected in the composition of the supply industry. The much-valued versatility of hydro generation applies equally to tidal power plant. The opportunities for a tidal barrage to be operated flexibly, having regard for fundamental resource constraints, are set out, though without regard for tariff structures because these will depend on the particular network conditions in which any project will operate. The studies have been carried out in the context of a Severn Estuary barrage.

Low head, doubly-regulated (Kaplan) axial flow turbines are well suited to working in reverse as pumps. For good efficiency in both operations, the generating and pumping heads must be complementary. The Rance tidal power scheme in Brittany has been carrying out matched generating and pumping operations to good effect since it was commissioned in 1966. Some simplifications to the range of operations performed at Rance have been identified. There is also potential for these operations to be extended, in particular to make greater use of pumping now that energy storage promises to become a more important function of electricity network operation. The results of the studies reported here explore this opportunity, together with its associated benefit of allowing the timing of generation from the enhanced resource to be varied to best suit that of energy demands.