What is the difference between thermal power plant and captive thermal power plant?

The basis of differentiation is end user. A thermal power plant produces electricity to sell the same to different end users through grid. But, in case of a captive thermal power plant generation of electricity generally is to meet the demand of power by the parent industry. For e.g. an Alumunium smelter plant requires huge quntity of elctric energy to operate. To secure undisrupted source of energy it may set up its own power plant which in turn can be termed as the captive power plant. But, in certain cases excess electricity can be sold to the market.