Power Generation and Distribution. 473 



The actual cost in a given case will, of course, vary according 

 to the size of the station and the local conditions, which latter 

 include the costs of coal_ and water, the cost of skilled and rough 

 labour, also transport and import charges. 



The Table shows costs applicable to a large power distribution 

 scheme on the Rand. Whatever adjustments might be necessary 

 for any given scheme, as between work's costs, distributing costs, 

 and capital charges, it is not considered probable that a public 

 supply will be given throughout this district at lower charges than 

 are here shown. 



A public supply system must include capital charges on a higher 

 scale than would be required in the case of a private plant, in order 

 to recover in later years the losses incurred during the time taken 

 in building up the load from small beginnings to the scale that is 

 necessary in order to reach the low working costs per unit sold, 

 corresponding to the low tariff, which must be low from the outset, in 

 order to justify consumers in adopting the public supply in preference 

 to their own plant. 



It has also to be borne in mind that public electric power supply 

 undertakings are never completed. They are bound to keep ahead 

 of the demand, which results in new capital always being spent, 

 and, for the time being, unproductive. 



In estimating the cost of supplying electric energy to a group 

 of mines, it must not be overlooked that the " diversity factor " in 

 such cases is somewhere near unity, as the maximum loads on the 

 several mines practically occur simultaneously. The supplier cannot 

 therefore in such a case secure the advantage, previously referred to, 

 of being able to meet the consumer's requirements, with a lower 

 capital outlay per Killowatt than the consumers would themselves 

 incur in adopting their own independent power plant. 



Where the load is practically constant — as, for example, a 

 battery of stamp mills — there is no economical advantage in trans- 

 mitting the power electrically. This would only be done when 

 electric energy could be bought at a price which would show an 

 advantage compared with the cost of applying the power direct from 

 one large engine. 



The following table (B) has been prepared in order to establish 

 comparison between the assumed prices at which electrical energy 

 may be purchased (Table A) and the cost of supplying power from 

 the consumer's own plant, with or without electrical transformation. 



The working costs are given for four sizes of engine — ranging 

 from 125 Brake H.P. to 1000 B.H.P. — and for two load factors, 

 namely 25 per cent, and 50 per cent. 



The estimates are each based on the use of a single gas engine 

 with gas producer plant, suitable for the use of bitumenous coal. 



The cost of coal is assumed to be 12/6 per ton (200 lbs.) for 

 the largest engine, rising to 14/- for the smallest engine, to allow 

 for the smaller consumer buying less cheaply than the larger one. 



