The Base load & peak load plant are intricate element of power generation system. Load duration curve divided under three parts a) Peak load b) Base load c) Intermediate load.

The base load is the load below which the demand never falls and is supplied 100% of the time. The peaking load occurs for about 15% of the time. The intermediate load represents the remaining load region. Since peaking load plants are used only for a small fraction of time, the fuel cost is not of major importance, Minimum capital cost should be the criterion.

The base load plants are plants which are loaded very heavily. Operating cost of such plants are very important. A high capital cost is permissible if low operating costs can be maintained (e.g. new, large coal and nuclear power stations). Intermediate load plant can be somewhat smaller than older units. By judicious combination of all the tree types of generation – peak, intermediate and base-maximum economy can be achieved.

The variable load problem affects power plant design and operation as well as the cost of generation. A careful study of the load duration curve helps to decide the capacity of the base load plant and also of the peak load plant. The base load plant should be run at high load factor. The peak load plant should be of smaller capacity to reduce the cost of generation. It could be a gas turbine unit, pumped hydro-system, compressed air energy storage system or a diesel engine depending on the size and scope of availability.

If the whole of load is to be supplied by the same power plant then the prime movers and generators should act fairly quickly and take up or shed load without variation of the voltage of frequency of the system. It is the function of governor to control the supply of fuel to the prime mover according to load. The capacity of the generators should be so chosen as to sit and fit into the portions of the predicted load curve. If the load conditions differ too much from this capacity, the cost of energy increases.