1912] on Electricity Supply : Past, Present (ind Future. 443 



thoutrh at the start this country was fully as far advanced as any 

 other, it got left behind owing to this direful legislative effort which 

 Parliament passed with the laudable intention of giving the country 

 electricity supply on the most economical terms, but which resulted, 

 as we have seen, for a considerable time at all events, in the country 

 obtaining no supply worth speaking of at all. 



The factors which lead to the best economy in the generation of 

 electricity in power stations are numerous. First of all, we have such 

 local conditions as cheap fuel (which is, of course, a matter of para- 

 mount importance), cheap labour, cheap land, and, if steam is to be 

 used as a source of power, an ample provision of cheap water for con- 

 densing. Then there is the question of the nature of the load, the 

 " load factor," as it is termed among engineers, and this is a matter 

 of the greatest importimce, and one the influence of which was not 

 realized at all in early days. The load factor may be defined as the 

 ratio between the number of Board of Trade units actually supplied 

 from a generating station during the year, to the number of Board of 

 Trade units that would have been supplied supposing the consump- 

 tion had, at the maximum rate demanded at any one moment, 

 extended over the whole of the 8,760 hours of which the year is 

 composed. 



In the case of companies supplying electric energy chiefly for 

 lighting, the consumption in winter falls to a minimum during the 

 early hours of the morning ; rises for a short time to some extent 

 while the population is getting up and having its breakfast ; falls 

 again during the day-time to the small amount required for lighting 

 cellars, basements and other dark places ; begins to rise again in the 

 afternoon and evening at hours that vary according to the period of 

 the year ; reaches a maximum during those portions of the year when 

 it is* dark at six o'clock, at the moment when shop lighting is still 

 continuing, and gradually dies away again as the shops are shut, and 

 later as the population goes to bed. In a case like this of stations 

 supplying chiefly lighting, the load factor varies from 16 to 20 per 

 cent, 'in London, down to as low as 6 to 10 per cent, in the provinces, 

 in places where the shops shut and the people go to bed early. 



On the other hand, the load diagrams of concerns which supply 

 a great deal of energy for traction, power, and other purposes, give 

 load factors as high as 25 per cent. ; while the figures of the great 

 power companies with stations supplying electricity for railway work- 

 ing furnish still higher load factors again. 



Now, the reasons for the importance of the load factor are several. 

 First of all, it is olwious that if you spend money on a generating 

 plant and only use this plant one or two hours out of the twenty-four, 

 or to the extent, say, of only 10 per cent, of its available output, you 

 are only earning a small percentage of the interest that that plant 

 would be producing were it working at full power all the time, that 

 is to say, on a 100 per cent, load factor. Further, these sudden 



