For folks living “off grid” batteries are the center of attention. The deep cycle lead acid battery is the most popular type of battery in this market. Of all the equipment in the solar (PV) system, batteries require the most care. The manuals from the manufacturers on battery maintenance should be read and understood. If the manuals were condensed into three basic principles, they would be to keep them:
- Clean
- Properly watered
- Charged up
Dust and dirt tend to accumulate on the tops of batteries. Eventually, moisture and vapors from the battery will mix with this grime. This could create a path for energy to cross from one pole to the other and slowly drain the battery. Battery cables must be kept corrosion free. The acidic environment of the battery promotes corrosion at the battery post and cable connection. The corrosion causes resistants and this can lead to imbalance in the state of charge between battery cells and if left unchecked, the post and cable will disintegrate. A solution of baking soda and water can be used in conjunction with a paint brush to clean battery tops to neutralize the acid and keep batteries clean. Be sure not to let any of the solution get into the battery cells. Some recommend not using this high pH solution on battery tops for fear it may get into the battery cell and neutralize some of the acid. There are other cleaning solution’s sold on the market. Either way, it’s good to have baking soda and water for washing your hands and tools after working on the batteries.
When the top is taken off the battery one can see a funnel with a slit cut into the side of it. It was once recommended that water be replaced in the battery to the point that the electrolyte comes in contact the funnel. This may be OK for a battery that is at a 100% state of charge, but we now add water so that it comes to within ¼ inch of touching the funnel. Electrolyte will literally boil when the battery is being charged. If the battery is over filled acid will be spit out during the absorption cycle. The acid lands on the top of the battery and will cause corrosion and other problems. Never take acid out of a battery. If a cell is over filled, make a note to clean the batteries more frequently. Charging batteries causes the water in the acid to evaporate. Check the electrolyte level at least once a month. Do not allow the electrolyte to expose the plates to the air. This will permanently damage the plates and the battery will not last as long as it could have. Never add acid to a battery. Always use distilled water to replace lost electrolytes.
Every battery has a given number of cycles. Discharge and charge is a cycle. There are many factors that determine how many cycles in a battery. One of which is depth of discharge (DOD). The same battery that is taken to a DOD of 50% on every cycle will not last as long as one taken to only 75% DOD. This is where sizing the battery, charging source and the load so that they are balanced is so important. If the battery is to big compared to the charging source it may be very difficult to charge the battery to 100% state of charge (SOC). If the load is too big for the battery it will suffer from low DOD. Size the system so there is balance between load, charging source and battery size. This way you can keep the battery charged up to 100% SOS and get the most cycles out of them.
Cleanliness, watering and charging are the basic foundation to battery maintenance. These principals can help you get started in understanding how to get the most out of your batteries. However, this does not replace the manufactures recommendations or other battery safety practices. There is a great deal to be learned about the dangers of working around these storage systems that was not covered here. Working with electricity can be dangerous and batteries emit explosive gas. It is always best to have a trained and qualified person to work on any part of a solar system, including the batteries.