Off Grid Solar Power Battery Maintenance

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 tomaintain your battery bank by measuring the specific gravity (SG) of yourbatteries.  SG is the primary metric usedto determine a battery’s “health.” Specific gravity is the ratio of the mass to volume ofa substance.

SG = Mass(g) / Volume (mL)

Hydrometers

A hydrometer is a device used to measure the SG of thebattery electrolyte.  There are varioushydrometer types but we recommend using a glass hydrometer with a float and arubber head to draw the battery electrolyte in. Digital hydrometers may be used, but will likely be more expensive thantheir glass counterparts. Additionally, digital hydrometers may need to becalibrated.  Stay away from usinghydrometers with floating colored balls, as they will result in very subjectiveresults.  The hydrometer should beaccurate to +/- 0.005.

Using ahydrometer

Battery maintenance for off grid solar energy systems should occur at least every 6months, although every 3 months is best practice.  The following is the procedure for usingglass hydrometers with a float:

1.   Put on safety glasses, rubbergloves, long sleeves and covered shoes

2.   Disconnect the charge controllerand main battery breaker

3.   Clean the battery of any dust, dirtor debris

4.   Remove the cap on the top of thebattery and insert the hydrometer tail into the liquid (be sure to not pushdown on the interior plates)

5.   Draw liquid into the hydrometer upto the measuring line (be sure to not overfill past the line)

6.   If bubbles are present in thehydrometer, 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 perbattery to minimize any errors in reading

9.   Apply temperature corrections ifnecessary

TemperatureCorrection

Above 21 degrees Celsius add value to the SGreading.  Below 21 degrees Celsius subtractvalue from the reading.

Correction factor = (0.595 x Cell Temperature [in degrees Celsius]– 12.5) / 1000

SpecificGravity

The following values are for Rolls batteries at 25 degrees Celsius.  See the manufacturer’s specifications forother batteries types.

If battery electrolyte levels are low, fill up to theoriginal 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.