POWER FROM THE MOON

Evening Star, Issue 22451, 23 September 1936, Page 12

POWER FROM THE MOON

QUEST FOR TIDAL ENERGY GENERATIONS OF ENGINEERS PUZZLED / Shakespeare, King Canute, King John, and the managing director of General Motors-Holdens Ltd. (Mr L. J. Hartnett) stand on common ground—they have all been impressed by the most tantalising problem of engineering in ancient or modern times (writes P. Crosbie Morrison, in the Melbourne ‘Argus’). Shakespeare pointed a poetic moral from it. “ There is a tide in the affairs of men,” he wrote, “ which, taken at the .flood, leads on to fortune.” King Canute, if the tale be true, used it for religious ends, demonstrating to his Court that the forces of God coul,d not be moved by the command of kings—and getting his feet wet in the process. And King John lost all his baggage in the Wash because _ he chose to disregard the inevitability of the tides. Now Mr Hartnett, still feeling his sea-legs after a voyage across the world, is moved to wonder why the power of the tides has not been hdrnessed. Many generations of engineers have puzzled over this same problem. About the time when scientists were demonstrating that perpetual motion as a source of power was theoretically impracticable, the equally fascinating problem of harnessing the tides began to assume serious proportions. Indeed, one of the minor centenary celebrations of this year might be that of the preparation of the first patent specifications for a tidal engine. The patent was taken out in France early in 1837 by an engineer named Chauvet, who proposed to build a large float in a tidal estuary, to attach to it a system of levers and pulleys, and to use the power generated as the float rose and fell with the tide. Recent calculations have shown that the power available from a 1,000-ton hulk used as a float on a tide which rose and fell 20ft would amount to about 1.62 horse power—just sufficient to supply a modern domestic electric radiator of moderate size. A sledge-hammer, indeed, to crack a nut. So much for Monsieur Chauvet and the dozen other inventors who followed him with patents for tidal engines on similar principles. The next plans were for paddle wheels, anchored on rafts in tidal streams. In a stream with an average speed of three knots—an exceptionally , strong tide—a paddle wheel 20ft in length, with paddles 4ft in width, would produce a continuous supply of three horse power. Another disappointment. GIANT TANKS AND BASINS. Inventors next considered the plan of permitting the rising tide to compress'air inside a huge anchored tank and using the compressed air to operate an engine with cylinders similar to those of a steam engine. Here, again, cold calculation has shown that the most that could be expected from this plan, using a giant tank 50ft in diameter in a tidal rise of 20ft ; would be 0.33 horse power, and the inefficiency of the engine would consume most of that. Even a monstrous tank 100yds square, in a similar tide, would not give more than 15 horse power, leaving the inefficiency of the engine out of the question. Some of our prevailing winds in Victoria, operating on a modern windmill, would make a much better showing than that. But a fourth system was suggested last century, and engineers are still dallying with it because it presents on paper the prospect of generating many thousands of horse power. This is the basin system. In a convenient estuary a retaining wall is built between the river and the sea. Gates are to be opened in this wall to admit the incoming tide, and at high tide the gates are closed. Then, after the tide has receded, the water is, permitted to escape through huge turbines. Some of these operate generators—there is no problem here, for the same thing is done in all countries which possess hydro-electric works such as those at the Eildon Weir in Victoria. Other turbines operate pumps, which pump some of the water into a high level some distance inland. When the tide is coming in and the generator turbines are shut off, water is released from this high-level reservoir through other turbo-generators sets to maintain a continuity of supply. Such a plan on a huge scale was contemplated for the Severn River, in England, with a tidal basin 25 square miles in extent. This system was designed fewer than 10 years ago, and it was estimated that it would supply 500,000 horse power over 10 hours of each working day. Financial stringency, increasing cost of coal, and high costs of laboiir stimulated the efforts of the engineers, but after long consideration the plan was shelved. The capital and maintenance charges would exceed considerably those involved in the present method of generating electrical power. There are several very small tidal mills in operation in various parts of the world. On the river Tamar, in England, there is one which has been in operation since 1790. It is rather a coincidence that the Tasmanian namesake of this river, passing through Launceston, has attracted the attention of those who would generate tidal power in Australia. The Tamar mill is merely a water-wheel operated by the tidal stream. A similar waterwheel, later duplicated, was operated for several centuries on the Thames, under London Bridge, to pump water for the city. It was built by Peter Morrice, a Dutchman, in 1582. Both these mills, however, were operated as much by river flow as by the tidal stream, and therefore they belong to some extent to the more successful group of hydraulic works which attain their zenith in the great Niagara Falls turbo-generating station, and operate on a smaller scale in the Rubicon system in Victoria.

Thus stands to-day ,then, the engineers’ draught of Tantalus. Millions of tons of water rise and fall each day, becoming at one period vast reservoirs of potential energy derived from the moon and the sun by whose attraction they are raised. They dissipate their energy a few hours later in sound and fury, and, often, in the slow destruction of the works of man by erosion and attrition. The tempting prospect is there, the romantic prospect of stealing for earthly use the forces of the moon. Theoretical considerations impose no bar, as they do to the exploitation of perpetual motion. Yet, however high the waters may rise—in the Bay of Fundy, Nova Scotia, they rise and fall 50ft in 12 hours—they never quench the thirst for power of the tantalised engineer. But some day—who knows?—we may yet light our cities by the power of the moon.