Moon Power
Hydro-electric power is obviously available only in certain geographical locations. The energy of moving water is not limited to that flowing from high ground, though, anyone who has watched waves crashing against rock or simply the sea's relentless ebb and flow on the beach must have felt it's power. But could This be harnassed?
The alternate rising and falling of the sea's surface which we call the tides are caused by the gravitational pull of the Sun and Moon, but especially the latter as it circles th Earth every 24 hours 50 minutes. The range in height is from 30cm in the Mediterranean to 16m in eastern Canada. A water-wheel making use of this twice daily variation was to trap the incoming tide behind gates, then use out-flowing water ot drive a mill when the gates were opened, after the tide had edded. The constantly-altering time of high tide was an obvious inconvenience. On a larger scale, the tidal flow can fill an empty large reservoir, creating a difference in levels as in the hydro-electric system on the previous page, with or without pumped storage.
The first, and, apart from one Russian project pilot project, only full-scale tidal installation is in the estuary of the Rance river in France, where the average tidal change is 8.4m (peak 13.5m). The sorage basin has an area of 22 squared kilometers and the station has an maximum output of 240 MW. A number of schemes have been put forward over the years to build a barrage in the Severn Estuary, and although the CEGB has "reluctantly abandoned" the project on grounds of cost (an estimate of 9 billion pounds sterling and taking 20 years to build.) it has said that the scheme could contribute about 3% to the present total primary energy needs of the UK.Again, the environmental effects of such a barrage need to be examined carefully.
An unusual tidal/air storage scheme using gas turbines to generate electricity. Tidal turbines produce large quanttities of compressed air which is stored in artificial underground caves and released to drive gas turbines at peak demand times. Some additional heat energy would be added at the time of generation.
The sea has (at least) one further trick up it's sleeve. Thanks very largely to the efforts of one man, Dr. Stephen Salter fo Edinburgh University, Brittain now has a 1 million pound sterling wave energy R & D programme, based on four systems. This brings us into the province of "wind energy" (hence solar, since winds are caused by the unequal heating of the atomosphere), but waves transfer energy with very high efficiency - waves arriving at one point may have origanated in a storm a long way off.
From experiments in a tank with balsa wood, transistors and ballocks, Salter improved the amount of energy taken out of artifitial waves from 15% with an up-and-down movement to 60% with the to- and-fro. The eventual shape and movement of "Salter's ducks", as they are now known, are shown inthe diagram below. Other wavepower devices - "contouring rafts" - have been designed by Sir Christopher Cockerell's compony, Wavepower Limited, and have been tested by Brittish Hovercraft Corporation. Their aim is to produce simple, cheap, massproduced units which can be installed and maintained a section at a time.
1. Salter's ducks. A number of segmentsrock on a central turbular backbone, forming a 500mj string, sideways-on to the waves. Pumps/turbines are housed in the inner section. Lanchester Polytechnic, Coventry, has tested a scale model on the Loch Ness. 2.Cockerell's contouring rafts. Hydrolic motors and pumps between each raft convert the energy of wave motion into pressure in a fluid. 3.Air pressure ring buoy. 4.The Russel rectifier. Sea water is seen entering the upper reservoir through vrtical non-return flaps, and (small drawing) leaving the lower, generating power on the way.
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