02 Sep, 2026
I. Battery Classification
1. Lead-acid batteries: Lead-acid technology is mature and relatively inexpensive, making it suitable for projects with limited budgets. However, lead-acid batteries have relatively low energy density and a shorter cycle life (typically 500–1,000 cycles), and they require regular maintenance. They are suitable for small off-grid systems or backup power supplies.
2. Lithium-ion batteries: Lithium-ion batteries have high energy density, long cycle life (up to 2,000–5,000 cycles), and are maintenance-free. Although their initial cost is higher, they offer better long-term cost performance. Lithium iron phosphate (LiFePO4) batteries, due to their high safety and long service life, have become a preferred choice for photovoltaic energy storage. They are suitable for residential energy storage and commercial/industrial energy storage.
3. Flow batteries: Flow batteries (such as vanadium redox flow batteries) have an ultra-long cycle life (more than 10,000 cycles) and good scalability, making them suitable for large-scale energy-storage projects. However, they are bulky and expensive and are currently used mainly for grid-scale energy storage.
4. Sodium-sulfur batteries: Sodium-sulfur batteries have high energy density but operate at high temperatures (around 300°C), making them suitable for certain large-scale energy-storage applications.
5. Nickel-cadmium batteries: Nickel-cadmium batteries perform well at high temperatures, but their use is gradually decreasing because of memory effect and environmental-pollution concerns.
II. Battery Pack Selection
1. Capacity Matching Must Be Accurate—Bigger Is Not Always Better
The degree of matching between battery-pack capacity and photovoltaic-panel power directly determines the charging and discharging efficiency of the system.
Risk of improper sizing: if the capacity is too large, the PV array may not fully charge the batteries during the available sunlight period, leaving the batteries chronically undercharged and accelerating aging. If the capacity is too small, over-discharge may occur easily, shortening battery life.
Practical recommendation: based on PV array power (for example, 20 kWp) and daily electricity demand, calculate the average daily energy generation and then work backward to determine battery-pack capacity. In customized solutions, Baoding Zhenglian Optoelectronics generally recommends a PV-to-battery capacity ratio of 1:1.2 to 1:1.5 to maintain system balance.
2. Voltage Level Must Be Compatible with the System
The nominal voltage of a lithium iron phosphate battery pack (for example, 314 V) must match the input-voltage range of the inverter and MPPT controller.
Risk of incompatibility: a voltage mismatch may prevent the inverter from starting normally or may cause the controller to enter protection frequently, resulting in system shutdown.
Practical recommendation: before selection, confirm the voltage ranges of the inverter and battery in the equipment list. Customized battery packs from Baoding Zhenglian Optoelectronics can be configured with voltage platforms according to customer requirements for plug-and-play compatibility.
3. Prefer Long-Cycle-Life Cells, but Do Not Ignore the Lithium-Battery BMS
Long cycle life is a key advantage of lithium iron phosphate batteries. However, without a high-quality BMS (Battery Management System), cell aging may accelerate.
Risk of inadequate BMS: absence of a BMS or poor BMS performance may cause overcharging, over-discharging, loss of temperature control, and even thermal-runaway risks.
Practical recommendation: select a BMS with active balancing to keep the voltage of each cell consistent. Lithium iron phosphate battery packs from Baoding Zhenglian Optoelectronics are equipped with multi-layer BMS protection as standard, helping to extend system service life.
4. Ambient Temperature Control Is a Hidden Critical Factor
Lithium iron phosphate batteries are sensitive to temperature, with an optimum operating range of 15°C to 35°C.
Risk of poor temperature control: high temperatures accelerate chemical reactions and may cause swelling and capacity degradation; low temperatures increase internal resistance and reduce discharge capability.
Practical recommendation: install battery packs in well-ventilated locations away from direct sunlight. For use in northern regions during winter, an insulated enclosure or low-temperature heating module is recommended. In off-grid PV projects, Baoding Zhenglian Optoelectronics often configures temperature-control solutions for customers.
5. Perform Periodic Balanced Charge/Discharge Cycles Instead of Waiting Until the Battery Is Empty
Lithium iron phosphate batteries have no memory effect, but long-term unbalanced operation can increase voltage differences between cells.
Risk: frequent shallow charging and discharging may accelerate cell inconsistency and reduce usable system capacity.
Practical recommendation: perform one complete charge/discharge cycle (from 10% to 100%) every 1–2 months so that the BMS can recalibrate cell balancing. Battery packs from Baoding Zhenglian Optoelectronics support remote monitoring for convenient viewing of charging and discharging status.
III. Selection of Specific Battery Types
1. Lead-Acid Batteries
Lead-acid batteries use lead and lead dioxide as active materials and dilute sulfuric acid as the electrolyte, converting electrical energy and chemical energy through electrochemical reactions. These batteries are commonly used in energy-storage systems, emergency power supplies, and soft-start/black-start systems.
The original document states that a single lead-acid cell has a nominal voltage of 0 V, can discharge to 5 V, and can charge to 4 V. In actual applications, six cells are generally connected in series to form a nominal 12 V battery module. Based on this, suitable series-parallel combinations can provide required system voltages such as 48 V or 96 V, ensuring normal battery charging and discharging.
The main components of a lead-acid battery include positive and negative terminals, plates, separators, electrolyte, and container. Because it contains a large amount of chemical solution, a lead-acid battery is relatively heavy. Lead-acid batteries include conventional flooded lead-acid batteries, maintenance-free gel batteries designed for solar applications, and lead-carbon batteries.
In practical applications, the proportion of gel and lead-carbon batteries is gradually increasing. Gel batteries provide excellent recovery after over-discharge and good low-temperature charging/discharging performance. Lead-carbon batteries add carbon (graphene) to the electrolyte, effectively suppressing negative-electrode sulfation, reducing the probability of battery failure, and significantly extending service life.
Lead-acid batteries normally use constant-current, constant-voltage, and float-charging modes, also known as three-stage charging. Charging current is a key parameter and is commonly expressed as C; the maximum charging current is specified in the battery specifications. For example, for a 200 Ah battery, if the maximum charging current is stated as 1C, the corresponding charging current is 20 A; if it is 2C, it is 40 A. For maintenance-free lead-acid batteries, the optimum charging current is about 1C. Charging current that is too high or too low can adversely affect battery life.
2. Lithium Batteries
Lithium batteries use lithium metal or lithium alloys as positive/negative electrode materials and a non-aqueous electrolyte solution. They are mainly divided into lithium-metal batteries and lithium-ion batteries; what is commonly called a lithium battery usually refers to a lithium-ion battery. This is a secondary (rechargeable) battery. In lithium-ion batteries, the positive electrode generally uses a lithium-alloy metal oxide, while the negative electrode commonly uses graphite. The negative-electrode material plays a key role in storing lithium and has a major influence on charging/discharging efficiency, cycle life, and other performance characteristics.
The positive-electrode material is one of the key factors determining lithium-ion battery performance. According to the cathode material, lithium-ion batteries can be divided into lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, and ternary lithium batteries. Considering cost, performance, and safety, lithium iron phosphate batteries occupy a large market share in practical energy-storage systems. They use LiFePO4 as the positive-electrode material and carbon as the negative-electrode material. The original document states a single-cell rated voltage of 2 V and a charge cut-off voltage in the range of 6 V to 65 V. Appropriate series-parallel designs can meet different voltage and capacity requirements.
Core performance indicators of a lithium iron phosphate cell include:
• Nominal capacity: measured in Ah or mAh.
• Nominal voltage: typically about 2 V according to the original document.
• Charge termination voltage: typically stated as 55 V to 6 V in the original document.
• Discharge termination voltage: typically stated as 2 V to 5 V in the original document.
• Internal resistance: generally less than 20 mΩ.
• Battery cycle life: generally more than 3,000 cycles.
• Self-discharge rate: approximately 5%–8%.
In addition, lithium batteries require a Battery Management System (BMS) in practical applications. The system consists of a central control unit, acquisition unit, display unit, data-recording unit, and external expansion units. The main functions of the BMS include individual-cell parameter monitoring, SOC calculation, temperature monitoring and management, battery-energy balancing control, fault diagnosis and alarms, information display, data recording, and communication with the host computer.
