Reference yield

The reference yield represents the number of hours during which the solar radiation would need to be at reference irradiance levels (1000 W/m²) in order to contribute the same incident solar energy as was monitored during the reporting period. It is calculated from the front-side plane-of-array irradiation only and serves as a baseline for comparing actual system performance. For bifacial systems, see Bifacial reference yield.

Output name

Reference yield

Symbol

Y_r

Units

kWh⋅kWp^-1

Formula

$$\frac{H_{POA,f}}{G_{i,\text{ref}}}$$

Where:

• $H_{POA,f}$ is the front-side plane-of-array irradiation in kWh/m²
• $G_{i,\text{ref}}$ is the reference irradiance (1000 W/m²)

The division by 1000 W/m² converts the irradiation (energy per unit area) into equivalent hours at STC conditions, giving units of hours or kWh/kWp.

The reference yield can be understood as the “ideal hours” of operation at rated power. For example, if $Y_r=1500$ kWh/kWp, this means the front-side irradiation was equivalent to 1500 hours of operation at 1000 W/m² irradiance.

The reference yield is therefore the equivalent number of hours that the modules operate under STC irradiance (1000 W/m²).

Usage

Reference yield is used in several key performance metrics:

• Performance ratio: $PR=\frac{E_{out}\mathrm{/}{P}_0}{Y_r}$
• Array capture loss: $L_c=Y_r-Y_A$