Energy Storage devices have gained lots of importance. Batteries along with solar arrays and inverters have become crucial components in renewable energy segment. Even smart grids need them to stabilize the sudden load variations. Battery sizing for meeting requirement of a renewable energy driven system has always been a challenge.
Battery sizing calculations are simplified below. However, these are good for estimating purposes but one must seek opinion of a professional before buying and fitting it.
|Total Load in Watts||A||Watts|
|Nominal DC Voltage (12, 24, 48, 96,120VDC etc.) Normally taken as 12V||B||Volts|
|Expected Total Load Operating Time per Day (hours)||C||Hours|
|Required System Amp-hour Capacity (AH)||D=AxC/B||AH|
|Battery Depth of Discharge (DOD)||DOD||DOD/100|
Amp-hour Capacity (AH)
To meet AH requirement as calculated above, one can opt for many combinations of batteries. However for the most efficient operation and long life, always use the option with the highest battery capacity and fewest parallel strings.
Depth of Discharge(DOD) is very important for batteries. For solar systems the DOD is taken as 50%. Over discharge may shorten battery life.
Another factor which is somewhat important is Ambient Temperature in sizing of the batteries. The Temperature correction multiplier ranges from 1.0 to 1.59. Lower the ambient winter temperature, higher is the multiplication factor. For ambient winter temperature of around 26 Deg C the value is 1.0 and for -7 Deg C it will be about 1.6. Battery sizing has to have that much additional margin in the size of the batteries which is being used in the system.