Batteries store electricity generated by the Solar PV Panels and thus, are a critical part of Off-Grid and Hybrid Solar PV Systems. Batteries should be regularly and carefully maintained to ensure their long useful life and the safety of the system.
Battery maintenance comprises of three major activities:
- Inspecting and cleaning regularly
- Checking the electrolyte level (not for Gel Batteries)
- Keeping the batteries in a high state of charge
Here, we shall discuss topping up the battery electrolyte level.
Battery Electrolyte Check and Top up:
The Electrolyte level in batteries should be checked at least once a month. The cells should be watered back to the original acid levels, which is usually about a quarter to a half inch below the bottom of the vent well (tube inside battery cell with slots on each side).
Only distilled water should be used to top up the batteries.
The state of charge of each individual cell can be accurately measured by testing the specific gravity of electrolyte in the battery.
The electrolyte specific gravity for a ‘Deep Cycle Flooded’ lead acid battery can be checked with following steps:
- Remove caps from each cell, one at a time. Insert hydrometer into the cell.
- Draw liquid into the hydrometer while avoiding bumping the hydrometer. The float should not be flooded or stick to the sides of the glass tube.
- Obtain a reading by observing the float which should correspond to a level on the tube. The acid level in the batteries should be within two centimetres of the top of the battery. Record the cell number and the reading.
- A visual inspection of the plates should also be done to check the condition of the plates.
- Do not replace the liquid from one cell to another.
Specific gravity varies with the battery type and brand and also with the battery temperature. You should refer to your battery specific tables.
A representative table is shown below:
The specific gravity readings of each cell should be recorded and logged periodically as part of routine maintenance.
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