Design run to bankable P90 bridge

Apply reviewer changes to a design-tool annual energy, then take a 1-year P90 from your uncertainty list.

A teaching aid, not a yield assessment. Every default is invented. This page is not an assessment, and a lender decides what to rely on. Enter changes as signed percentages of energy, for example -1.8.

Examples (invented):

Design-tool annual energy (MWh, or any unit)

Reviewer changes to energy, percent (negative lowers energy)

Weather: long series instead of one TMY year

Soiling: site-specific instead of tool default

Availability below 100%

MV cable and transformer losses added

Horizon shading from survey

Uncertainty, one standard deviation, percent of P50 (1-year basis)

Irradiance data

Year-to-year weather

Transposition to plane of array

PV model

Soiling estimate

Availability

Result

Bankable P50 (after changes)	-
Change from design-tool run	-
Total uncertainty (root sum of squares)	-
Factor z for P90	-
1-year P90	-
P90 below P50	-
P90 below design-tool run	-

Method: the changes compound (each applies to the energy left), so -1.8 and -1.0 give -2.78, not -2.8. Total uncertainty is the square root of the sum of squares of the six terms. P90 = P50 x (1 - z x total / 100), with z from the normal distribution. Degradation is not included. Decimal commas (0,5) and thousands commas (12,800) are read. A value such as 1.000 is refused because it could mean 1 or 1,000.