Project design > Simulation > Simulation process: stand alone system

Simulation simultaneously manages Array production, Battery, eventually Back-up production, and the user consumption. At the meeting point (battery terminals), all voltages are the same and simulation has to perform a current balance.

For each component, the current is a complex function of the voltage:

- PV-array: search the operating point on the I/V array characteristics, (irradiation and temperature already known), paying attention that ohmic, module quality and mismatch losses have an action on the actual current, for a given voltage

- Battery: voltage characteristics of the battery model depends on state of charge (SOC), temperature and current,

- Load: Given energy, states current as function of the voltage,

- Back-up generator: Given energy, states current as function of the voltage,

so that balance has to be achieved by successive iterations.

Once the currents are determined, SOC and battery voltage are calculated for the end of the time interval.

Moreover, the system behaviour depends on the regulation state. They could be:

- PV-array disconnected when full battery,

- Load disconnected in case of deep battery discharge,

- Back-up generator eventually running (if defined in the system) according to battery voltage.

Due to battery voltage evolution, these operating conditions may change during the time step. In this case the program determines the exact time when a regulator threshold condition is met, evaluates the energies for this hour fraction, and starts again a balance loop according to the new operating conditions.

Several variables are computed during and after this process: array running characteristics, battery storage and ageing, load an used energies, etc.