The goal of sizing a battery bank in a stand alone photovoltaic
system is to provide the user with a number of days of autonomy. Days
of autonomy are the number of days the battery bank can
support the project load without the solar contribution.
After making the choice of the battery type, the Days
of autonomy can be modified by the designer along with the Depth
of discharge (DOD) and the battery Voltage,
the program calculates the size of the batteries bank to
achieve the desired autonomy.
Depending on the user consumption
setting, average daily consumption is considered to start sizing the
battery bank. The Parameters section has the options that the
designer can modify for sizing.
Days of autonomy
Depth of discharge (DOD)
Voltage of battery bank
The Suggested capacity that
the battery bank needs to have is calculated as:
Capacity = (Average daily consumption * Days of autonomy) / ( Depth
of discharge * Voltage of battery bank )
The battery bank should have a higher capacity than the Suggested
capacity. By combining in series and in parallel the model of the
chosen battery, the program realizes the sizing to achieve the
required autonomy.
The size of the PV array must be able to provide the energy consumed
on average in a day. The amount of energy needed to be produced by
the photovoltaic field will be reported in
Project settings in Constrained
arrangement by energy to be produced so that the wizard
continues to design the system with the goal of producing that amount
of energy.
If the system is DC-coupled battery
storage, it will be necessary to size a charge controller compatible
with battery bank and PV field. Compatibility between battery bank
and charge controller is verified by:
Open circuit Voltage < Maximum voltage of charge controller
Maximum current from PV (short circuit current) < Maximum current
capabilities of charge controller
Maximum power from PV < Maximum operative power of charge controller
The nominal operative voltage of charge controller = Nominal voltage
of battery bank
furthermore if charge controller is Mppt:
Minimum Mppt voltage from PV > Minimum voltage MPP allowed by
charge controller
Maximum Mppt voltage from PV < Maximum voltage MPP allowed by
charge controller
The program will propose a list of compatible charge controllers
among those present in the archive
If the system is AC-coupled battery
storage, you need to insert an inverter/charger in the AC section,
the compatibility battery bank and inverter/charger is verified by:
Power of inverter/charger >= Peak power of users consumption
Battery voltage <= Maximum charging voltage of inverter/charger
Battery voltage >= Minimum charging voltage of inverter/charger