TABLE OF CONTENTS To express the results of the reliability and production analysis an adequate set of indices is required. With careful interpretation these can be used to quantitatively compare different systems and to measure the benefit of alternative designs, strategies and impact of embedded generation.
One measure that has become associated with embedded generation is the term capacity credit . This is said to be the effective capacity for which the generation source can be credited and is evaluated by dividing the energy generated in a period by the number of hours in that period. It therefore gives the average capacity that the system sees measured over the period considered. Although this may seem to provide a useful measure, it is only useful to a generator as an indicator of overall contribution but is flawed as a useful reliability index for either customers or energy suppliers, particularly in connection with intermittent sources such as wind. To illustrate one weakness, consider a capacity credit of say 25%, which may be considered typical for a wind farm. This implies that, on average, it supplies 25% of the installed capacity continuously, whereas in real life it could supply either full capacity (four times its capacity credit) for 25% of the time and nothing for 75% of the time. This may be much less of a problem for sources not dependent on the environment and which can be scheduled and controlled, in which case the value of capacity credit...
