Fig. 1,179.—Load curve showing use of storage battery as an aid to the generating machinery. In the diagram, it is seen that the battery discharges at minimum and maximum loads and is charged at other times, the battery furnishing current for the entire minimum load and part of the maximum load.
Ques. How may greater efficiency be secured with steam engines under variable loads?
Ans. Judicious selection of the number and sizes of the engines enable them to be worked in most cases at a considerable fraction of their full capacity nearly all the time.
Ques. What further improvement is secured in most cases with the storage battery?
Ans. The plant is made more flexible, and the economy of the engines is increased by making their loads nearer uniform, and nearer to full capacity while they are running.
Ques. What is the effect of a battery connected in parallel with a dynamo, as in [fig. 1,180]?
Ans. It is not necessary for the dynamo to have a capacity exceeding that which is sufficient for the average daily load, at which it may be worked practically all the time.