BS PD IEC TR 63292:2020

PVPS component and system reliability engineering works to define the PVPS probability of making the indicated value such as energy or revenue, also at a given statistical confidence level for an estimate. This needs to be assessed properly as an accurate levelized cost of energy (LCOE) results from identifying and acting on a set of quantifiable metrics based upon real measured data of actual plants under the widest variety of real site conditions. In many instances, the use of P numbers (which stands for "percentile") may not be clearly understood and as a result, inappropriate conclusions drawn which have a financial result. P values are used to establish the confidence that one can require to provide the assurance that the item will meet specification. A P50 value, for example, provides that there is a 50 % confidence in the value used in reliability predictions. This value of confidence translates to the median of the population or in other words, it is equivalent to a coin toss on whether the value is valid. It is better to have a higher confidence that the system will work to specification. For reliability metrics, this is typically defined as being a P90 or P95 values. This level of confidence significantly characterizes financial and technical risk plant availability.