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GENERAL INFORMATION: BATTERIES
Since many values are dependent on charge and discharge conditions, they have
not been standardized for PV applications and for test purposes until now. Therefore,
the comparison between batteries and selection of the most suitable one for each
application are not easy. Due to particular operating conditions with PV applications
in practical operation, the cycle life given by manufacturer (and in Table 3.1) for
cycling load can be reduced more than half.
According to Table 3.1, it follows that in most cases, the Lead-Acid batteries would be
the best choices for PV applications. The selection of suitable choices should be based
on specific application.
Temperature Compensated Battery Charging
Temperature affects the rate of chemical reactions in the batteries as well as the
rate of diffusion and the resistivity of the electrolyte. Therefore, the charging
characteristics of the battery will vary with temperature. This is nearly linear and
the Voltage Coefficient of the temperature change can vary from -3 mV / ºC / Cell
at 50 ºC to -5 mV / ºC / Cell at -10 ºC. Please note that the Voltage Coefficient of
the temperature change is negative which means that as the temperature rises, the
charging voltage is required to be reduced and as the temperature is decreased, the
charging voltage has to be increased
The Absorption Voltage set point is normally specified at 25 ºC. Battery temperatures
often vary up to 15 ºC from the 25 ºC reference in PV Systems. The Absorption Voltage
for a 12 V sealed battery must then be adjusted as follows:
Battery Temperature Absorption Voltage
40 ºC 13.8V
25 ºC (Reference) 14.1V (Reference)
10 ºC 14.5V
In case temperature compensation is not provided, the warmer battery at 40 ºC will
begin to heat and outgas at 13.8 V and will continue to overcharge until the non-
compensated Absorption Voltage set point is reached (14.1 V). In cooler temperatures,
the 10 ºC battery will experience severe undercharging resulting in sulfation.