P50 and P90 are confidence levels attached to a predicted annual energy yield. P90 is the yield that should be exceeded in 90 percent of cases and P50 is the yield exceeded in 50 percent of cases, which makes P50 the expected value. Other levels such as P75 are used too, and a good yield report for investors gives at least the P50 and P90 values. The gap between P50 and P90 comes from uncertainty in the solar resource data, uncertainty in the modelling process and year-to-year variation in the solar resource. Resource data uncertainty usually has more effect than modelling accuracy, because energy yield depends roughly linearly on plane-of-array irradiance. Lenders often use a one-year P90 to cover the yearly debt payments and a ten-year P90 to cover resource variation across a decade. The exact requirement depends on how the project is financed. Combined uncertainty becomes smaller over the life of the plant. On an uncertainty chart, P90 is the lower bound and P10 is the upper bound. During operation, O&M reports often compare actual irradiance, production and revenue with the expected P50, P75 and P90 values each month, quarter or year.
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part_ofc1 drafted · lead Energy yield assessment
Yield prediction reports state the predicted annual energy at confidence levels such as P50 and P90.
sec=6.3 h=d3be6f14d355sec=h103 h=673da6cc7487related_toc2 drafted · lead Typical meteorological year
The P50 figure in the case study came from an hourly simulation of a typical year, before inter-annual resource variation was considered.
sec=h103 h=673da6cc7487c3 drafted · lead O&M contract
The O&M service schedules list reports that compare actual irradiance, production and revenue with expected values at P50, P75 and P90.
sec=h259 h=c499f46fa49etbl=49.r12 h=73dea483eed2tbl=50.r1 h=dca7b28a281btbl=50.r2 h=d475e522e26atbl=50.r5 h=723bc87e873crelated_to c1related_to c9