Bifacial Tests

This section discusses how pvcaptest can be used to conduct a capacity test for a project with bifacial modules.

NREL Modified Bifacial Capacity Test

Pvcaptest can be used to conduct a bifacial capacity test following the NREL Suggested Modifications for Bifacial Capacity Testing.

The suggested approach uses the standard ASTM regression equation:

\[P = E_{POA}\left(a_{1} + a_{2} * E_{POA} + a_{3} * T_{a} + a_{4} * v\right)\]

but, replaces the \(E_{POA}\) term with \(E_{Total}\):

\[E_{Total} = E_{POA} + E_{Rear} * \varphi\]

where,

\(E_{Rear}\) is the rear POA irradiance and

\(\varphi\) is the bifaciality factor.

To conduct a bifacial capacity test you should make the following adjustments.

The regression equation default does not need to be changed.

You will need an \(E_{Total}\) term in the CapData.data and CapData.data_filtered dataframes.

CapData.data['E_Total'] = CapData.data['E_POA'] + CapData.data['E_Rear'] * bifaciality
# either of the below lines will copy the modified data `data_filtered`
CapData.data_filtered = CapData.data.copy()
CapData.reset_filter()

You will then also need to adjust the CapData.regression_columns to map the poa term of the regression equation to the new E_Total column in the dataframe.

CapData.set_regression_cols(
    power='real_power_column',
    poa='E_Total',
    t_amb='temp_col_or_group',
    w_vel='wind_speed_col_or_group'
)

Other Bifacial Capacity Test Approaches

The regression equation can be easily modified by simply assigning an new regression formula. For example, to conduct a regression of temperature corrected power against front side POA irradiance and rear side POA irradiance, you could use the following:

CapData.regression_formula = 'power_temp_adj ~ poa_front + poa_rear'

The regression columns would also need to be updated to map the regression terms to the correct columns or groups of columns. In this case a dictionary should be assigned to the regression_cols attribute directly rather than using the set_regression_cols method.

CapData.regression_cols = {
    'power_temp_adj': 'poa_front',
    'poa_front': 'E_POA',
    'poa_rear': 'E_Rear'
}