Effective Irradiance Response (EIR) Calculation
The effective irradiance response (EIR) of a module is its relative efficiency at various non-standard conditions. This is sometimes referred to as a module’s “low-light response”. The following algorithm describes how to calculate the relative efficiency at a single condition (non-STC temperature/irradiance). This process can be repeated at various conditions to generate an EIR curve.
- Calculate the maximum power point at Standard Test Conditions (STC).
The maximum power point is calculated using single diode parameters at STC.
- Temperature and irradiance adjust all pertinent single diode parameters to T_actual and G_actual.
See the algorithm documentation section entitled “One-Diode Model Temperature Correction”.
- Calculate the maximum power point from the temperature/irradiance-adjusted single diode parameters.
Using the temperature-adjusted single diode parameters, calculate the maximum power point as in step 1.
- Calculate the relative efficiency.
where EIRi is the relative efficiency at a given irradiance in decimal form, Pmp,i is the maximum power point at a given irradiance, and Pmax,norm is the normalized maximum (ideal) power point at a given irradiance, as described by the following equation:
where Pmp,1000 is the maximum power point at 1000 W/m2 and i is the given irradiance.