Module Performance Model

In SolarFarmer, I-V curves of modules are simulated using theoretical models, as described in Models of Cell Behaviour.

There are two stages in the module modelling process:

• The model parameters for a given module type are derived through numerical fitting to datasheet or measurement data, but SolarFarmer does not currently provide the functionality;

• The model is then used with the parameters derived above to extrapolate module behaviour to conditions other than those considered in the datasheet or measurement. The module electrical power, current and voltage are calculated under given temperature and irradiance conditions, either at specific points on the modelled I-V curve (frequently the Maximum Power Point), or the entire I-V curve can be returned.

SolarFarmer works at the level of the submodule (sometimes called substring), the string of typically 10 or 12 cells that share a bypass diode. Typically there are three submodule on each module. A single value of irradiance and temperature is used to calculate a maximum power point for the submodule (denoted \(P_{\text{submod,mpp}}\)) or an I-V curve for a submodule (denoted \(IV_{\text{submod}}\)).

During the calculation the maximum power point, \(P_{\text{submod,mpp}}\), is calculated several times for each submodule using the different irradiance values output by the irradiance calculation, or different temperature assumptions. This allows the impact each of those irradiance effects has on the power produced. The I-V curve is calculated just once as that is a computationally expensive calculation.