Therefore the PGS will be composed of n fuel power generating stations. It is well known that electricity cannot be stored unless an extremely high cost is assumed. Only batteries and reservoirs can store electric energy. Therefore a PGS is designed to supply instantaneously the power demanded by consumers. 7 Failures in the system occur when demand exceeds supply.
Demand can exceed supply for two main reasons.
First, if there is a very high demand peak that exceeds the installed capacity of the system, the system cannot supply the load peak. Second, if some power stations are out of service because of failures or periodic maintenance, a high demand that does not exceed the installed capacity of the system can exceed the available capacity at that moment. A system failure of either type is referred to as a loss of load. Let S be a random variable representing the available power supply, and let L be the daily load peak. To estimate the LOLP, the first step is the estimation of S , and this is the problem that we have used for teaching purposes.