Off-grid solar energy systems are not as care-free as grid-tied solar power systems. The use of batteries in off-grid or grid-interactive (grid connected with a battery backup) systems does require regular maintenance. The maintenance for off-grid solar systems is not difficult and can be performed by the average homeowner.
The following is a step by step guide on how to maintain your battery bank by measuring the specific gravity (SG) of your batteries. SG is the primary metric used to determine a battery’s “health.” Specific gravity is the ratio of the mass to volume of a substance.
SG = Mass (g) / Volume (mL)
A hydrometer is a device used to measure the SG of the battery electrolyte. There are various hydrometer types but we recommend using a glass hydrometer with a float and a rubber head to draw the battery electrolyte in. Digital hydrometers may be used, but will likely be more expensive than their glass counterparts. Additionally, digital hydrometers may need to be calibrated. Stay away from using hydrometers with floating colored balls, as they will result in very subjective results. The hydrometer should be accurate to +/- 0.005.
Battery maintenance for off grid solar energy systems should occur at least every 6 months, although every 3 months is best practice. The following is the procedure for using glass hydrometers with a float:
1. Put on safety glasses, rubber gloves, long sleeves and covered shoes
2. Disconnect the charge controller and main battery breaker
3. Clean the battery of any dust, dirt or debris
4. Remove the cap on the top of the battery and insert the hydrometer tail into the liquid (be sure to not push down on the interior plates)
5. Draw liquid into the hydrometer up to the measuring line (be sure to not overfill past the line)
6. If bubbles are present in the hydrometer, gently tap the glass to release them
7. With the hydrometer held level, obtain a reading and record it. Discharge the fluid back into the battery. Be careful to not splash the electrolyte.
8. Repeat the steps 2-3 times per battery to minimize any errors in reading
9. Apply temperature corrections if necessary
Above 21 degrees Celsius add value to the SG reading. Below 21 degrees Celsius subtract value from the reading.
Correction factor = (0.595 x Cell Temperature [in degrees Celsius] – 12.5) / 1000
The following values are for Rolls batteries at 25 degrees Celsius. See the manufacturer’s specifications for other batteries types.
If battery electrolyte levels are low, fill up to the original line using only 100% distilled or deionized water.
And of course, contact us if you have any questions regarding your off-grid solar energy system.
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