Batteries

Available technologies

In the present time, PVsyst treats 2 classes of technologies of batteries: Lead-Acid and Lithium-Ion.

Other technologies possibly used in solar systems are not yet implemented, namely flow-batteries and super capacities. Nickel-cadmium are analogous to Lead-acid, but with specific behaviors; this technology is of marginal use in PV systems, and will probably not be implemented.

Battery descriptions in the help

The battery description and use is extensively described in this Help, at different locations: you have namely:

• A full description of the elements of the model in the pages below (voltage, capacity, aging, etc.
• A description of how it is used in the simulation,
• A description of the dialog, and the procedure for defining a battery,
• A descritpion of the technologies and their properties.

Model choice justification

We have developed a non conventional battery model, trying to avoid the pitfalls which arise in a number of existing PV software: either an extreme simplification, which can only lead to rough evaluations of the system behavior, or adjusted models based on numerous (often interrelated) parameters whose physical meaning is often not clear to the user. The required parameters are rarely mentioned on datasheets, or practically necessitate a complete measurement of each battery used. We have therefore tried to fulfill the following criteria :

• The model should be presented to the user in a rather simple manner, involving à priori only "explicit" parameters specific to each battery: type of technology, voltage, number of elements, nominal capacity, possible internal resistance and Faradic efficiency, ageing properties.
• Most of these parameters should be available from the detailed datasheets. Others are predefined, specific to each technology.
• But it should be sufficiently detailed to satisfy the needs of the simulation of the PV system, where the charging current is practically imposed by the solar generator. In particular, its behavior in voltage is crucial and difficult, as the voltage depends on the current, the state of charge and the temperature. It is important in the intermediate zone for the evaluation of the SOC, and should be realistic enough at the end of charge and discharge to make the controller operating correctly.
• Further, it will be important to be able to estimate the ageing and the possible maintenance imposed by the conditions of use.