Base Load and Peak Load on Power Plants

The load on the power plant is seldom constant rather it varies from time to time, as shown in Fig. 10.1.

The load on any power plant can be conveniently considered into two parts namely:

(i) Base load, and

(ii) Peak load.

The unvarying load, which occurs almost the whole day on the power plant is called the base load whereas the various peak demands of the load over and above the base load of the power plant is called the peak load.

Co-Ordination of Base Load and Peak Load on Power Plants:

If the load represented by Fig. 10.1 is to be supplied from one power plant only, then the installed capacity of the plant should be equal to the peak load or more. Such a power plant would be uneconomical since the peak load occurs only for a short period in a year and, therefore, the capacity equal to the difference of the peak load and base load would remain idle for the major portion of the year.

Hence such a power load should not be supplied from a single power plant. There would be some power stations supplying the base load and others, possibly of different types, supplying the peak load. Thus the co-ordination of operation of different power stations is essential.

The power plants to be employed as base power plants should have:

(i) Low operating cost,

(ii) Capability of working continuously for the long periods, and

(iii) Requirement of few operating personnel and their repair should be economical and speedy.

The power plants to be employed as peak power plants should have the capability of quick start, synchronisation and taking up of system load and quick response to load variations.

The hydro power plants are well suited for both base load and peak load operations. The hydro power plants should be employed for base load operation as far as possible because of their higher capital cost. However, during the periods of draught, the hydro power plants may be used as peak load plants.

A steam power plant gives minimum cost of generation per unit when employed as base load plant. However, in order to save fuel it may be used as peak load plant.

Nuclear power plants are suitable only for base load operation at high load factors of over 0.8.

Gas turbine power plants are suitable for supplying peak loads.

Diesel engine power plants are playing a very little role in bulk power generation because of their uneconomical operating costs.

A typical load allocation to various power stations is illustrated in Fig. 10.2.