Tidal power and the Severn Barrage

After reviewing the principal projected tidal-power schemes in various parts of the world, the first part of the paper is devoted to consideration of the principles of single- and double-tide working and their application under the conditions prevailing in the Severn Estuary. A single-basin scheme was recommended for the Severn Barrage and, in common with other tidal-power projects, ebb-tide working was adopted. A capacity of 800 MW was proposed, with plant to suit the conditions peculiar to tidal power stations. The engineering features of the project are described, and in view of the economic importance of plant costs, consideration is given to the possibilities of reducing the capital invested in water turbines and alternators. The characteristics of tidal power focus attention on the following factors which affect the development of the Severn Barrage. Technical. (i) Negligible value as a substitute for thermal power plant. (ii) Variable and intermittent output. Consideration of direct and indirect methods of output regulation lead to the conclusion that 75% of the energy should be transmitted at 220 kV to London and Birmingham, where the tidal output would be small relative to the thermal plant connected to the system. Parallel operation of the tidal power station with the Grid is considered, and the proposed transmission system is described. Economic. (i) Cost of the barrage and associated works. (ii) Cost of coal for thermal power stations. The annual charges on the Barrage and transmission system which determine the cost of energy delivered to the load centres are given, and these, together with the coal saved in thermal stations by combined operation, provide the economic basis for judging the value of tidal energy. The paper concludes that the future possibilities for tidal-power development are not unfavourable, and further investigation of economic factors, constructional methods and plant design are justified.