ELECTRICAL POWER IN AGRICULTURE. Great strides have been made in the application of electricity to agri culture. Already, many farmers are using electric light and power. With the growth of regional electricity schemes we may expect to see agricultural operations everywhere modified by the use of electric energy. Good light is as beneficial in a farmhouse as in an urban dwelling, in a cowstall as in a factory. The electric motor is simple, robust and easy to start and stop; it gives a steady pull, and, with the usual charge ranging in Great Britain from Ind. to 3d. an electric unit for power, it is cheap to work.
Barn Machinery.—Most English farmers rely on an oil engine which is used (roughly in proportion to the acreage of the farm) to drive barn machinery, i.e., chaff-cutters, root-pulpers, cake and oat crushers, etc. These machines absorb from i to 5 H.P. according to size. On a grass farm, the engine, perhaps i # to 3 H.P., may work only two or three hours a week in winter and be hardly used in summer when all the stock is out on the pastures. The annual consumption may be something like 1 H.P. hour per acre of land or, say, 600 H.P. hours per square mile of country, equivalent to 450 electric units or kilowatt hours. On an arable farm, where there is much preparation of food, including perhaps the grinding of barley-meal, an engine of 5 to 8 H.P. may work several hours a day, and the annual consumption amount to about 12 H.P. hours per ac., that is, about 7,000 H.P. hours or 5,000 electric units per square mile.
Cultivation.—The greatest consumption of power in agricul ture 'is in field cultivations such as ploughing. On most farms, this work is still done by horses. The only places where they have been replaced successfully by mechanical power are in flat areas with large arable fields. There ploughing can be done more economically by tractors on light land and by steam tackle on the heavier clay. On a farm where three quarters of the area is arable land, the annual consumption of energy in ploughing may amount to 15,000 to 20,000 H.P. hours per sq.m., and half as much again may be used for other cultivations, a total of 22,000 to 30,00o H.P. hours per square mile. Thus, on arable farms the energy needed for field work is considerably greater than that required to drive barn machinery.
Electric Ploughing.—Electric ploughing has been tried in France, Germany, Italy and elsewhere, and is generally carried out by contractors. The most usual method is to haul the plough backwards and forwards by means of a wire rope pulled by a motor mounted on a wagon at each side of the field, just as in steam ploughing. In a modification of this method, a single motor only is used, the wire rope passing round four anchored pulleys, two of which are moved as the plough proceeds. Experiments have also been made in which the motor is placed on a carriage attached to the plough, and current supplied to it through an in sulated, flexible cable, which is unwound as the carriage and plough move one way across the field and wound up again as they move back in the other direction.
Costs.—It is difficult to get comparable figures of costs. A committee of the Institution of Electrical Engineers (Aug. 1925) quoted the prices of French contractors for ploughing to depths of 6 to 14 inches at sums equivalent to 16s. to 32S. per acre. The quotations of East Anglian contractors for steam ploughing range from 17s. to 25s. per ac. according to depth (say 8 to 14 in.) and soil. The cost to a farmer of ploughing with horses is generally reckoned at about 15s. for light and 28s. for heavy land per ac. but, if this too were done by contractors, something must be added for profit.
Both steam and oil engines have the great advantage of being self-mobile ; they can move about the roads and on to the field under their own power. With electric ploughing, the need of taking wires to each field, the great weight of the motors and carriage, and the cost of hauling them about with horses or tractors, militate against its success. It seems likely that, unless some new method or improvement is applied, electric ploughing will make no head way, and that the use of electric power in agriculture will be restricted to the driving of stationary machinery.
Special Machinery.—Besides the ordinary barn machines, less common implements must be brought under review. For threshing corn, smaller farms mostly rely on travelling threshing machines worked by steam traction engines. Some larger arable farms, however, have their own threshing plants. Where current is available, the machine can well be driven electrically with a motor of from 12 to 15 H.P. according to size. It is stated that, owing to the steadier pull of the electric motor, better threshing is done than with a steam-engine. On certain farms, power is used in other special ways. For instance, where a tower silo is installed, power is wanted to cut up the fodder and to lift it into the silo. Ensilage is sweet or sour chiefly according as it is made above or below a temperature of C., and German experiments show that it may possibly be worth while to heat the fodder arti ficially by passing an electric current through the silo.
Perhaps the greatest advantage of electric current is that power need only be used to the amount actually required. Motors of quite small size are made which will drive light dairy machinery, horse-clippers, fans for incubators, and other implements which absorb too little power to make it worth while to start an oil engine to run them. The number of such implements is sure to increase as electric supply becomes more common. As regards dairies, milking-machines and also separators, clarifiers and butter churns are very suitable for electric drive. Dairymen, and per haps fruit-growers, may find it profitable as time goes on to install refrigerating machinery. This may give another demand for power on certain specialized farms.
Poultry.—To turn on electric light in poultry houses on winter evenings and give the birds an extra feed is found to increase the number of eggs laid. The rise in the total number laid throughout the year is insignificant, but, since eggs are worth more in winter, the redistribution more than pays for the cost of light, food and extra labour. Incubators can more conveniently be heated elec trically than in other ways; by passing heated air through the ap paratus by means of an electrically driven fan, uniform tempera ture and efficient ventilation can be secured.
Plant Growth.—Experiments indicate that plant growth is stimulated by a high voltage current of some milliampere per ac. passing as a discharge to the crop from a network of overhead wires, which are kept at 20,000 to 6o,000 volts above the potential of the earth. Application for six hours a day for one month early in the growth of the crop seems quite as effective as a longer treatment. With certain cereals, an increase in yield of 20% has been obtained, but the results are not always assured, and the matter is still in an early experimental stage. Other experiments, carried out in America and elsewhere, show that electric light, both arc and incandescent, in greenhouses, has an effect in acceler ating the germination of seeds and hastening the growth of certain vegetables, the effect depending somewhat on the colour of the light.
Electric Supply.—In the neighbourhood of towns, and in industrial and mining areas, many English farms are supplied with current from central power stations. Most of these stations now produce three-phase alternating current, and the corresponding squirrel-cage type of motor is very suitable for farm use. Further developments of this kind may be expected, but the purely agri cultural demand is not enough to carry a network of mains over the countryside with the high costs of erection prevalent in Great Britain. Experience shows that the demand for light and power combined varies from i,000 to 6,000 electric units per sq.m., in good agreement with the estimate for power alone from oil-en gines, as given above. In towns, the consumption may be a thou sand times more. Again, for long distances, in order to economize copper, high voltages must be used ; these are dangerous, and must be transformed to lower pressures for domestic or industrial pur poses. Transformers are expensive, and no ordinary sized farm consumes enough power to carry the cost of a high voltage trans f ormer. Hence arises the apparent anomaly that a farm with high voltage mains running through it may be unable to get power. But, where a chain of villages creates a considerable demand along a definite line, or where pumping or irrigation needs a steady supply of power, the distribution of central station current in rural areas may become possible, especially if produced by cheap water power.
In many other countries rural electrification has been developed further than in England, partly owing to the less expensive standard exacted by legislation for the erection of overhead con ductors. As an example of what has been done in a country often cited as a model, the following details of electric supply in an agricultural area in the south-east of Sweden may be given. The total area is 194 square miles, containing 161 square miles of arable land, with a population of 157 to the square mile, of whom 6o% are dependent on agriculture. The district is supplied from a transformer on a high tension main ; from this station current is distributed at 20,000 volts and transformed down by steps to 220 volts. There are 2,600 consumers in the whole area, and the total annual consumption is about 1,o5o,000 electric units (kilowatt hours). This is equivalent to 404 units per consumer, or 33 units per inhabitant; 5,40o units per square mile or 81 units per acre. The total cost of installation of the country lines and transformers was about L6o,000. The average charge for energy is 3*d. per unit, which, with meter rents, gives a revenue of £14,300. This is found to cover the total costs and leave a small profit.
It will be seen that the consumption of power is about the same as that estimated above for stationary farm machinery in corre sponding areas in England. The advantage held by Sweden is not that more power is used, but that the costs of construction and distribution are less.
The establishment in 1927 of an Electricity Commission for Great Britain will lead to greater uniformity in voltage and frequency, to a decrease in the number of generating stations, and, it is hoped, to a cheapening in costs.
Where current from a large power station is not available, a village supply may be feasible ; a considerable number have been successfully installed in England, some worked by small water falls, others by oil-engines. If water be plentiful, turbines and dynamos may run day and night, and a very cheap supply be obtained ; but in other cases the energy must be stored in batteries of accumulator cells, which are costly and short lived. Whenever cells are to be charged, alternating current is, of course, inappli cable, and direct or continuous current must be used.
When no public supply can be obtained, there remains the question of a private installation. If occasional power to drive barn machines alone is wanted, it is obviously better to drive directly from a small oil-engine. But, if good light be wanted, and use can be found for motors of fractional horse power in dairy or house, a private electric plant may be worth considera tion. The dynamo is generally driven by a water turbine or oil engine, but the use of windmills seems now becoming possible. (See also FARM MACHINERY and TRACTORS.) BIBLIOGRAPHY.-A. H. Allen, Electricity in Agriculture (192 2) ; R. Bibliography.-A. H. Allen, Electricity in Agriculture (192 2) ; R. Borlase Matthews, Jour. Inst. Elec. Eng. (July 1922 ; Aug. 1926 and Dec. 1927) ; Electro-farming (1928) ; R. W. Trullinger, Amer. Soc. of Agric. Eng., Lincoln, Nebr. (June 1924) ; C. Dampier-Whetham, Jour. Roy. Agric. Soc. (1924; Report of a Committee of the Inst. of Elec. Eng., Journal of the Institution (Aug. 1925) ; Alfred Ehstrom, Rural Electrification in Sweden (1926) . Report of Conference on Electricity Supply in Rural Areas Electricity Commission (1928) . (C. D.-W.)