Common Types of Solar Batteries:
- Lead Acid: Lead Acid solar batteries are the most common type on the market. Capacities are available from 12 volt to 48 volt and 100 Ah capacities up to 10,000 Ah for larger systems. Lead acid batteries come either flooded of sealed:
- Flooded lead acid: Flooded batteries are the original lead acid battery on the market. They benefit from large capacity availability, and low pricing when compared to other energy storage options. However they require monitoring of electrolyte specific gravity levels and regular watering to maintain desired electrolyte gravity.
- Sealed Lead Acid: Sealed batteries use gel or fiberglass mats to store electrolyte and benefit from being relatively maintenance free.
- NiCd: Nickel Cadmium solar batteries on average are 4x times as expensive as lead acid and offer only twice the capacity. The increased capacity may be desired in larger systems looking for a reliable large capacity bank. They are being phased out in the market due to toxicity concerns with cadmium.
- NiMH: Nickel Metal Hydride solar batteries are the new, eco-friendly, cousin of nickel cadmium. These batteries are very common in small capacities and have not reached a wide market availability in the off grid large capacity market.
- Lithium Ion: Medium and large capacity lithium ion solar batteries have begun to emerge in the market. New Lithium Ion options from LG and TESLA have made this option more affordable. Their much higher energy density allows for a larger battery bank in a smaller area.
Capacities of Solar Batteries:
Solar batteries storage capacities are rated in Amp hours. Most experts reference the batteries 20 hour ratings. This is the amount of amps the batteries can supply per hour over a 20 hour period.
- Under 300 Ah: Small solar batteries are available for small solar pumps and very small off grid living applications. These batteries are available in most technologies.
- 300 – 800 Ah: Medium solar batteries will provide adequate storage for solar pumps and small off grid living situations. This also a good size for grid-tied battery back-up systems utilizing critical load panels.
- 800 – 1200 Ah: Large solar batteries offer adequate storage for medium sized solar pumps, motors, small commercial, and medium (under 1500sqft) off grid living situations.
- 1200-3000 Ah: Extra Large Capacities are available for large motors, medium commercial demand, and medium to large off grid living (under 2000 sqft) applications
- Up to 10,000 Ah capacities: Large solar batteries can be combined in parallel to achieve bank sizes from 3000 Ah to 10,000. These banks will be required for larger commercial demands and off grid living situations.
- Multiple Systems: Multiple off grid systems can be built to accommodate demands exceeding 10,000 Ah.
Sizing solar batteries
System designs are typically custom to the consumer’s needs. Because of this, you should take many considerations in the sizing of the battery bank. Below are the most notable sizing considerations for lead acid batteries:
- Depth of Discharge: Lead Acid electrolyte is compromised when the batteries are depleted to a very low depth of discharge. Batteries have life spans that are measured in “cycles.” Every lead acid battery manufacturer varies but 50% DOD tends to be the sweet spot for most off grid lead acid batteries.
- Environmental Conditions: Temperature Highs and lows will have a large effect on the overall capacity of the solar batteries.
- System Autonomy: This is the amount of time the system is expected to run without solar power or generators support. System autonomy can range from 12 hours to 7 days. Large autonomous systems are extremely large and therefore expensive. Generators are often integrated in off grid systems to lower battery bank sizes. In the event of prolonged solar power outage (days of cloud cover), the off grid system will automatically turn on the solar generator at a certain (50%) depth of discharge. The solar generator will power the loads and charge the batteries before shutting off.