C&D Technologies RS-2061 Standby Batteries for Renewable Energy Applications - Manual (Page 9)

Battery Operation and Charging
General Principles of Operation
Shallow and Deep Cycling Applications
Although there are many different types of battery applications in photovoltaic and other renewable energy
systems there are two main types of battery applications. The most common application is in cycling
applications where the battery carries the load when the solar resource or other renewable energy source is
not available. This can be during the night or during cloudy days. Depending on how the system is designed
the batteries are regularly discharged and regularly re-charged. In these applications, the charging system
should be sized so that, on the average, the battery is returned to between 85 to 90% state of charge daily.
On a weekly basis the battery should be charged to 100% or fully charged state.
Float Charging Applications
The second main type of battery application is for backup power on grid-tied systems. These systems charge
he backup batteries by putting them on Float Charge. Under normal operation of the backup battery system,
the batteries are maintained a full state of chare by a continuous constant voltage charging. When the grid
connection fails then the batteries carry the load and when the grid is reconnected, the battery is recharged
using the float voltage setting.
Battery Charging in Cycling Applications
Cycling applications in photovoltaic applications are the most demanding applications that lead acid batteries
are subjected. In many cases the batteries are in a constant state of either being charges or discharged.
Knowing how the system is operates is critical to understanding how the batteries should be charged.
In optimal conditions the battery is fully charged after every discharge cycle. Under these circumstances,
the battery will be brought back to full charge using a charging rate designed to bring the batteries back to full
charge before the next discharge.
If the system cannot achieve a full charge between discharging cycles then additional charging needs to be
employed to bring it back to full charge at least once a week. The charging system should be capable of
automatically adjusting the charging voltage based on the temperature of the battery. The measurement of the
battery temperature must be taken at the battery not ambient temperature. (Please see the Charging Voltage
Temperature Compensation Chart).
If the system is a solar-only system then the charging strategy is solely based on the photovoltaic panels
returning all of the energy to the battery every day. The ratio to the photovoltaic array to the load during the
worst conditions should be able to bring the batteries to full charge at least once a week.
If the system is a hybrid system where there is dispatch able battery charging capability, the batteries should
be charged to between 85 and 90% of full charge on a daily basis (daily charge). Weekly they should be given
a weekly charge to insure that they were fully charged.
The following Cycling Battery Charging Chart provides the voltage for daily charging, and weekly charging for
different types of C&D Technologies solar batteries.
RS02061/0514/CD 9 www.cdtechno.com