The reserve capacity maintains the reliability of electricity system as it ensures that there is more supply available than the demand. If the system has the capacity which is exactly equal to the demand, there can be electricity shortage when just one power plant cannot operate as usual or there is a sudden increasing demand. That is why we need to monitor the supply situation using reserve margin.

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          According to U.S. Energy Information Administration, reserve margin is capacity minus demand, where "capacity" is the expected maximum available supply, and "demand" is expected peak demand. For instance, a reserve margin of 15% means that an electric system has excess capacity in the amount of 15% of expected peak demand.

          Some might think that the capacity reserve margin would be based on “nameplate” capacity. Actually, the capacity reserve margin is based on “dependable” and should be 14% to 19% of the annual peak load. Thailand’s PDP 2015 (in which the reserve margin is set at 15%) also refers to reserve margin as the differences between the dependable capacity of a utility's system and the anticipated peak load for a specified period.


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EGAT Magazine 2018 - Oct-Dec