WIND POWER

the development of the windmill for electricity generation is mainly—certainly, at any rate, so far as great britain is concerned—a post-war movement. earher attempts were mostly crude and unsatisfactory, and the old sweep-sail mill may be said to have vanished completely, at least in this connection. structures built on gaunt masts or skeleton-like framework towers lack the picturesque attractive- ness of the old types, but possess efficiency and compactness. the windmill was adapted to this new purpose in the hope that the initial outlay (higher perhaps than when supply is by internal combustion engines) would be more than compensated by low running costs and the need of rare personal attention. the only factor preventing widespread use is the fear of discontinuity of supply in calm periods, with its consequent recourse to tempo- rary assistance. adequate storage will meet this objection. experiments.—the windmills used for test experiments con- ducted by the institute of agricultural engineering, university of oxford, were of different heights ranging from 10 ft. to 60 ft. from the ground, and the various wind wheels varied from 8 ft. diameter to 29:5 ft. diameter and were fitted with generators rated at from 0-300 kw. to 10-0 kilowatts. the rating is usually given as the maximum output at wind speeds varying from 18 to 25 m.p.h. according to the design, the smallest size mentioned being sufficient to furnish light to a cottage or small house, while the larger sizes are capable of meeting power demands. wind wheels.—the types of wind wheels in use were of three patterns :— ' (a) multi-bladed, with concave sheet-metal blades. (6) five-bladed, with semi-streamlined metal blades. (¢) four-bladed, with fabric-covered streamlined blades. in the last case the wheels were mounted behind the headpiece and automatically kept their position in the wind stream. the other wheels were mounted in front of their respective structures, and required a tail vane or other auxiliary apparatus to maintain the windwheel in the proper direction. each wind wheel was governed in such a way that on the wind speed reaching a pre- determined value the speed of the wheel was controlled to keep the output of the generator from exceeding the safe limit. in windmill work the “ fuel ” used is free and unlimited and there arises the possibility of a large “inefficient ”’ wheel being preferable to a smaller “ efficient’? one, which is more expensive to manufacture. this is a point of difficulty at the stage of 1037 development of purely stream-lined blades. a windmill plant with an approximate aggregate output of 3,650 units shows charges bringing the unit cost to 4d. only, reckoning on available energy apart from battery losses. calms and storage-——as to the question of calms and the planning of adequate storage to tide over the worst period which may be expected from all the figures and records of wind con- ditions, etc., it may be concluded that, if sufficient storage is provided to cope with the heavy winter load for three days, there is little likelihood of the supply ever being seriously interfered with. if the load is flexible and can be reduced during the critical period, the assurance of continuity of supply is complete. selection of sites -—observation of wind conditions over several years show that when fixing the site for a windmill plant the greatest care should be taken to ensure freedom from interference irom trees, etc., on the sides from which the winds mainly come. the wheel should be as high as possible in order to obtain the utmost use of the winds. at the coast and in exposed hilly dis- tricts there should be no hesitation in adopting wind power to supply electricity. even in ordinary inland parts there are very few districts where a suitable site cannot be found. thus, for isolated districts wind power may be adopted for generating purposes with every assurance of reliability and economy; and even for communal groupings and for medium power work there are larger sets which will provide the same service. bibliography.—p. la cour’s reports forsegsmellen, vol. 1 (1900), vol. 2 (1903), translated into german by j. kauffmann: die windkraft und thre anwendung (leipzig 1905); o. stertz, afoderne windturbinen (leipzig 1912); l. wammel, die ausnutzung der wind- krafte (1925). see also the 36th report of the danish government testing station (copenhagen 1925); report on windmills, institute of agricultural engineering (oxford 1926). (cog ©. br)