To assess the solar resource or energy yield potential of a site we model the solar resource/energy yield using best available information and methods. The resulting estimate is the P50 estimate or in other words the “best estimate”.
It is expected that 50% of the time, the solar resource/energy yield predicted (P50 estimate) will not be achieved. This might be too much risk for some investors. Therefore other probabilities of exceedance values such as P90 (exceeded 90% of the time) or P75 (exceeded 75% of the time) are considered.
Lender and investor typically use P90 estimate as in such case they can be confident that enough energy will be generated in order to repay their project debt