The ideal battery of solar power generator is resistant to over-charge and over-discharge, high C rate, high power capacity, long cycle life and can be operated wide temperature range.
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Lead acid Batteries
Lead-acid batteries have been used for off-grid solar systems for decades.
- Inexpensive and simple to manufacture; low cost per watt-hour
- Low self-discharge; lowest among rechargeable batteries
- High specific power, capable of high discharge currents
- Good low and high temperature performance
- Low power capacity
- Low C rate
- Limited cycle life
- Not environmentally friendly
- Refill water regularly
Lithium-ion batteries have been used for e-vehicle power bank recent years and have grown to become the most popular method of storage.
- High energy density - potential for yet higher capacities.
- Does not need prolonged priming when new. One regular charge is all that's needed.
- Relatively low self-discharge - self-discharge is less than half that of nickel-based batteries.
- Low Maintenance - no periodic discharge is needed; there is no memory.
- Specialty cells can provide very high current to applications such as power tools.
- Requires protection circuit to maintain voltage and current within safe limits.
- Subject to aging, even if not in use - storage in a cool place at 40% charge reduces the aging effect.
- Transportation restrictions - shipment of larger quantities may be subject to regulatory control. This restriction does not apply to personal carry-on batteries.
- Expensive to manufacture - about 40 percent higher in cost than nickel-cadmium.
- Not fully mature - metals and chemicals are changing on a continuing basis.
A NiMH battery can have two to three times the capacity of an equivalent size NiCd, and its energy density can approach that of a Li-ion battery.
- 30–40 percent higher capacity than a standard NiCd
- Less prone to memory than NiCd, can be rejuvenated
- Simple storage and transportation; not subject to regulatory control
- Environmentally friendly; contains only mild toxins
- Nickel content makes recycling profitable
- Wide temperature range
- Relatively low specific energy compared with newer systems
- Memory effect; needs periodic full discharges and can be rejuvenated
- Cadmium is a toxic metal. Cannot be disposed of in landfills
- High self-discharge; needs recharging after storage
- Low cell voltage of 1.20V requires many cells to achieve high voltage
Overall, when battery charging under sun light, the generated power is “unstable”. First problem is charging efficiency then we choose high efficiency solar panel. Then second problem coming with how we keep the generated power into batteries, therefore, we better choose high C rate as a buffer combined with high capacity as a power storage. Between different batteries, we suggest Lead acid+ L-ion battery or NiMH or NiCd. The reason is BMS cost is lower and not complicated.