i84 



NATURE 



[October 6, 192 1 



rate estimate of the water-power possibilities of 

 any g-iven site to be predetermined. 



Even more useful results would follow the 

 initiation of a systematic scheme of gauging 

 applied to all streams affording potential power 

 sites. 



Tidal Power. — The question of tidal power ha.«- 

 received much attention during the last few years. 

 In this country it has been considered bv ti"" 

 Water-power Resources Committee of the Board 

 of Trade, which has issued a special tidal power 

 report dealing more particularly with a suggested 

 scheme on the Severn. The outline of a specific 

 scheme on the same estuary was published by the 

 Ministry of Transport towards the end of 1920. 



In France a special commission has been 

 appointed by the Ministry of Public Works to con- 

 sider the development of tidal power, and it has 

 been decided to erect a 3000 kw. experimental 

 plant on the coast of Brittany. With the view of 

 encouraging research the Government proposes 

 to grant concessions, where required, for the 

 laying down of additional installations. 



The tidal rise and fall around our coasts repre- 

 sents an enormous amount of energy, as may be 

 exemplified by the fact that the power obtainable 

 from the suggested Severn installation alone, for 

 a period of eight hours daily throughout the year, 

 would be of the order of 450,000 horse-power. 



Many suggestions for utilising the tides by the 

 use of current motors, float-operated air com- 

 pressors, and the like have been made, but the 

 only practicable means of utilising tidal energy 

 on any large scale would appear to involve the 

 provision of one or more dams, impounding the 

 water in tidal basins, and the use of the im- 

 pounded water to drive turbines. 



The energy thus rendered available is, however, 

 intermittent ; the average working head is low and 

 varies daily within very wide limits, while the 

 maximum daily output varies widely as between 

 spring and neap tides. 



If some electro-chemical or electro-physical pro- 

 cess were available, capable of utilising an inter- 

 mittent energy supply subject to variations of this 

 kind, the value of tidal power would be greatlv 

 increased. At the moment, however, no such 

 process is commercially available, and in order 

 to utilise any isolated tidal scheme for normal 

 industrial application it is necessary to provide 

 means for converting the variable output into a 

 continuous supply constant throughout the normal 

 working period. 



Various schemes have been suggested for 

 obtaining a continuous output by the co-ordinated 

 operation of two or more tidal basins separated 

 from each other and from tlie sea by dams with 

 appropriate sluice gates. This method, however, 

 can get over the diflficulty of equalising the ovit- 

 puts of spring and neap tides only if it be arranged 

 that the maximum rate of output is that governed 

 by the working head at the lowest neap tide, in 

 which case only a small fraction of the available 

 energy is utilised. 



When a single tidal basin is used it is necessary 

 NO. 2710, VOL. 108] 



to provide some storage system to absorb a por- 

 tion of the energy during the daily and fortnightly 

 periods of maximum output, and for this purpose 

 the most promising method at the moment appears 

 to involve the use of an auxiliary high-level reser- 

 voir into which water is pumped when excess 

 energy is available, to be used to drive secondary 

 turbines as required. It is, however, possible that 

 better methods may be devised. -Storage by the 

 use of electrically heated boilers has been sug- 

 gested, and the whole field of storage is one which 

 would probably well repay investigation. 



If a sufllciently extensive electrical network 

 were available, linking up a number of large steam 

 and inland water pKDwer stations, a tidal power 

 scheme might readily be connected into such a 

 network without any storage being necessary, and 

 this would appear to be a possibility which should 

 not be overlooked in the case of our own countrv. 



Investigation necessary. — A tidal power project 

 on any large scale involves a number of special 

 problems for the satisfactory solution of which 

 our present data are inadequate. 



Thus the effect of a barrage on the silting of a 

 large estuary, and the exact effect on the level in 

 the estuary and in the tidal basin at any given 

 time can only be determined by experiment, either 

 on a small installation, or preferably on a model 

 of the large scheme. 



Many of the hydraulic, mechanical, and elec- 

 trical problems involved are comparatively new, 

 and there is little practical experience to serve as 

 a basis for their solution. 



Among these may be mentioned : — 



1. The most advantageous cycle of operations 

 as regards working periods, m.ean head, and 

 variations of head. 



2. The methods of. control and of sluice-gate 

 operation. 



3. Effect of changes of level due to wind cr 

 waves. 



4. The best form of turbine and setting and the 

 most economical turbine capacity. 



5. The possibilities of undue corrosion of turbine 

 parts in salt water. 



6. The best method of operation ; constant cr 

 variable speed. 



7. \\"hether the generators shall be geared or 

 direct driven. 



8. Whether generation shall be by direct jr 

 alternating current. 



The questions of interference with navigation 

 and with fisheries, of utilising the dam for rail or 

 road transport across the estuary, and, above all, 

 economic questions connected with the cost of 

 production, and the disposal of the output of such 

 an installation, also require the most careful con- 

 sideration before a scheme of any magnitude can 

 be embarked upon with assurance of success. 



In view of the magnitude of the interests 

 involved, and of the fact that rough preliminary 

 estimates indicate that to-day current even for an 

 ordinary industrial load could be supplied from 

 such an installation at a price lower than from a 

 steam generating station giving the same output 



I 



