Solar batteries are the most expensive component of an off-grid solar system. And it is really important to practice a regular maintenance schedule so that the batteries run effectively for years. If proper maintenance and setup routine is not followed, the lifespan of the batteries will be shortened. Here we are trying to guide you as to how to program and maintain your battery, whatever its type, so that they run efficiently and smoothly over a long period.
1. First Step – Initial Programming
You have to program your battery chargers to the proper charging settings for the battery bank the very first time you bring your system online. The settings will control other parameters like current and charging voltage. Now you need to set voltage set points which are the charging voltages applied to the battery at each stage of the charging cycle. The three charging phases of the batteries are absorbed, bulk and float. Let us learn a bit more about these –
Bulk – High current to refill charge and increase the voltage as quickly as possible (below 80%)
Absorb – Here the charge rate will slow down as the batteries approach the full state of charge (80 – 100%)
Float – Batteries will receive a trickle charge at 100% to stay completely charged
Each of these stages will require the charger to be set at a particular voltage depending on the needs of your battery. You need to program the voltage set points accurately to ensure the longevity of your batteries. If wrong charge parameters are set, the batteries will charge improperly thus decreasing their lifespan.
Along with this, you need to set certain other values in the initial programming phase, which are –
AC input amps – The input current from the generator or grid has to be maximized so that the combined current from the loads and battery charger does not become more than the generator rating. It also depends on the grid input breaker or generator size.
Temperature Compensation – The battery charger has to be adjusted to operate in different temperature ranges. Most of the chargers come with a battery temperature sensor.
Absorbs Time – It is the amount of time the charger spends in the absorb phase.
Max Charge Current or Charge Rate Limit – The maximum charging current is expressed either as a percentage of the charger output or total maximum charging amps. The charger output is limited by using this setting so that the batteries are not overcharged with the excess current.
The settings will vary with every battery and charger and you should check the installation manuals and spec sheets of the chargers and batteries to find the exact value for each of the above-mentioned settings. You need to program the equipment based on the recommendations in the manual for the long life of the battery bank.
2. Maintenance of Flooded Lead-Acid Battery
Flooded lead-acid batteries need daily maintenance for proper functioning. A check after every 2-4 weeks is necessary for proper tuning of the battery bank.
These batteries lose water during the charge cycle and need regular refilling with distilled water so that they stay healthy and work properly. But you should use distilled water only; otherwise, contaminants and small particles will get introduced into the system weakening the chemistry of the battery.
The water level is to be checked after every 15-30 days and refilled if required. The watering schedule is entirely dependent on the charge settings, local climate, and specific application. It would be wise to maintain a log entry regarding the frequency of refilling batteries.
- Check the water level when the batteries are completely charged
- Check the water level by opening the vent well
- Add water but it has to remain just below the maximum water level line. Overfilling past this line is a strict no-no. You will get to know the location of this maximum water level line from the battery installation manual.
Certain safety procedures need to be followed while working with batteries like wearing gloves and eye protection, securing long hair or loose clothing and removing any jewelry.
3. Checking the Battery State of Charge (SoC)
You need to keep an eye on how charged your batteries are and for that, you need a refractometer. The refractometer keeps a measure of the specific gravity of the batteries. If the batteries are not holding charge even after a complete charge cycle and equalization, they are probably damaged, defective or need retirement and are starting to lose some capacity.
Battery monitors are used by some inverters for measuring the state of charge. The monitors depend on a shunt to measure the total current coming out and in of the battery bank. The monitors are good tools for regular monitoring but need proper setup. If they are programmed or installed incorrectly, they may come up with false readings. Whether you have a battery monitor or not, checking with a refractometer regularly is recommended. It gives you the charge condition and accuracy of your batteries.
Batteries need to be equalized frequently so that each cell is equally charged. A controlled overcharge is to be applied every 30-90 days or whenever there is an imbalance in the individual batteries.
Process of Equalization
- The water level has to be checked before starting the process
- The loads are to be turned off
- The charger has to be set at the Equalize voltage as specified in the battery manual
- The Equalization charge has to be started during which bubbling and gassing are normal.
- Finally, stop charging and take readings of specific gravity every hour and when the specific gravity stops rising, the process is complete
What are the other Maintenance Routines of Flooded Lead-Acid Battery?
- The cables and terminal connections need cleaning to stop corrosion. A paste is to be prepared by mixing distilled water and baking soda and then applied with a wire brush. Then the cleaning residue is to be rinsed and dried with a paper or cloth towel.
- The battery cable connections need to be tightened
- The top of the batteries should be free from debris and dust to prevent the creation of electrical leakage or a current pathway across the top of the battery.
4. Maintenance of Sealed Lead-Acid Battery
Sealed lead-acid batteries require minimal maintenance as these do not need to be filled with water or equalized. Only the state of charge of the battery requires occasional check-up.
Checking the Battery State of Charge (SoC)
You need a multimeter to see how charged the sealed lead-acid batteries are based on the voltage. A multimeter comes with negative and positive probes that allow the meter to get a DC voltage reading from the battery. Guidance in this regard can be got from the battery manual.
For the most accurate readings, the batteries must be tested in a resting state. The batteries should be rested for a minimum of 2 hours before the voltage reading is taken. You will get inaccurate readings if you use the multimeter when the batteries are being charged or discharged.
If the batteries do not approach 100% SoC even after a complete charge cycle, they are damaged, defective or have reached the end of their lifespan. The sealed batteries do not need equalization charges.
5. Maintenance of Lithium-Ion Battery
Lithium batteries need little to no maintenance. They hardly need any check-up after set up except the occasional state-of-charge reading to ensure that the batteries are holding charge.
The state of charge (SoC) of a lithium battery can be measured by a tool that communicates the built-in Battery Management System (BMS) to give an accurate SoC reading. The monitoring tool has to be hooked up to the battery and the SoC value can be read on the display screen.
What are the other Maintenance Routines of Sealed Lead-Acid Battery and Lithium-Ion Battery?
- The top of the batteries should be kept clean to stop them from becoming grimy and dusty.
- The battery cable connections should be tightened
6. Prevent Sulfation
Lead-acid batteries face the risk of sulfation if they remain unchanged for a long time. Sulfation happens when lead sulfate crystallizes and the battery is no longer capable of accepting a charge. Once this happens, the battery is as good as dead. They are no longer able to conduct a current. To avoid sulfation, the battery has to be recharged fully after a discharge cycle. Also, periodic charge cycles are necessary to keep the battery healthy. The ultimate solution for sulfation is prevention.
7. Cooling Off Period to the Battery
The battery needs a ‘rest’ period after usage and recharging when it remains inactive until it cools off. If used immediately after recharging, it runs the risk of getting burnt out making it incapable of working to the best of its abilities. This is because like a lot of heat is generated during a recharge cycle, running it right after it may cause grid corrosion resulting in total battery failure.
8. Avoid Stratification
Stratification of the electrolyte in the battery occurs due to partial charging and discharging occurring again and again. This significantly decreases the performance and capacity of the battery. The balance of chemicals is thrown haywire. The acid seeps to the bottom of the battery and its absence at the top limits plate activation. This can be rectified by the slow process of diffusion, the mechanical stirring of the electrolyte and the regular running of the battery.