678 ECONOMICAL ASPECTS 



of active demand is from 6 o'clock to noon. In the middle of the 

 day manufacturing establishments cease operations for an hour 

 or less and resume again about 1 o'clock, thus restoring the 

 demand to the level of the forenoon. Between 4 o'clock and 7 

 o'clock in the afternoon there is a distinct overlapping of the three 

 demands. It is during these hours, especially in winter, that 

 practically all the lights are turned on, manufacturing concerns 

 have not yet stopped for the day and street cars are carrying, 

 perhaps, their heaviest loads. It is during this period that the 

 highest demand of the twenty-four hours is reached. 



There is also a seasonal fluctuation in a typical power market. 

 The demand in winter is usually greater than in summer and the 

 daily fluctuation is likewise greater. The increased demand grows 

 out of the increased requirements for lighting and in some cases 

 for traction. The greater fluctuation is mainly due to the fact 

 that between the hours of 4 o'clock and 8 o'clock in the after- 

 noon more power is required for light in winter than in summer. 



LOAD AND DIVERSITY FACTOR 



The load factor of a plant or system is the ratio of the average 

 to the maximum power during a certain period of time. The 

 average load may thus be taken over a period of one year, one 

 month or one day, while the maximum load must necessarily be 

 limited to very short periods, depending on the overload capacity 

 of the water wheel or the generator. In other words, it is the 

 ratio of the actual station output to the maximum possible output 

 with continuous service. 



It is also a measure of the extent to which the necessary total 

 investment is being utilized, as a plant with yearly load factor of 

 50 per cent is turning out just double the energy of another plant 

 of the same maximum load and with a load factor of 25 pe'r cent. 

 This means that, while the fixed charges of both plants are the 

 same, the gross income of the plant with 50 per cent load factor 

 should be nearly twice as great as that of the other. The impor- 

 tance of- a good load factor is thus apparent, and everything that 

 will improve this factor should be sought. 



The nature of the load as measured by the load factor forms 

 necessarily also a very important element in determining the 

 value of water power as compared to steam power. For load 

 factors below 50 per cent the former often turns out to be the 



