Do Solar Street Lights Need Batteries?

The answer is affirmative and beyond doubt! The battery is the energy storage part of the solar street light system and is indispensable. Its performance directly determines whether the solar street light system can operate stably! During sunny days, the battery is responsible for storing the electricity generated by the photovoltaic modules, and at night it releases the electricity to power the leds! In cases of insufficient light such as rainy days, the battery is a crucial redundant guarantee for continuous lighting. Without batteries, solar street lights cannot achieve the core value of "off-grid autonomous power supply" and can only become "decorations" relying on real-time light.
 

The following text will dissect in detail the core functions of solar street light batteries, common types of selection, capacity calculation methods, life maintenance and other key contents, helping you fully master the core knowledge related to batteries - you can first understand the specific role of batteries in the system, or directly view the analysis of common misunderstandings to avoid pitfalls in selection and use.

The Role of Batteries in Solar Street Light Systems

In an off-grid solar street light system, the battery is not an optional accessory component but a core link to ensure the stable operation of the system. Its role runs through the entire process of power generation, energy storage and power supply.
 

When there is sufficient sunlight during the day, the electrical energy generated by photovoltaic modules will be prioritized to be transmitted to the battery for charging, storing the electrical energy in the form of chemical energy and completing the conversion of "light energy - electrical energy - chemical energy". This process not only avoids the waste of electrical energy but also reserves an energy foundation for subsequent power supply at night.
 

When there is no light at night or on rainy days, the battery converts the stored chemical energy into electrical energy through discharge, providing stable power for the LED lights. More importantly, the battery can provide a guarantee of "autonomous operation days (autonomy)". Even if there is no effective light for 2 to 3 consecutive days, it can still maintain lighting by relying on the stored electricity, avoiding lighting interruptions caused by weather conditions.
 

In addition, the charging and discharging process of the battery needs to be precisely managed by a controller or battery management system (BMS). The BMS will monitor the battery voltage and current in real time, achieving overcharge protection (to prevent battery damage due to overcharging), overdischarge protection (to prevent irreversible damage caused by depleted power), and temperature protection (to adapt to extreme outdoor temperature environments), further extending the battery life and ensuring the stability of power supply.

Comparison of Common Solar Street Light Battery Types

LiFePO4  Battery

Lithium iron phosphate batteries are currently the mainstream preferred batteries in the field of solar street lights. Its core advantage lies in its long cycle life. Under normal use, the number of cycles can reach over 2,000 times, far exceeding that of traditional lead-acid batteries. It has excellent thermal stability and can operate stably within a wide temperature range of -20℃ to 60℃, making it suitable for complex outdoor environments such as high and low temperatures. It has high safety and is less likely to cause risks such as thermal runaway.

The drawback is that the initial cost is relatively high, about 30% to 50% higher than the unit price of lead-acid batteries, which may put certain pressure on projects with limited budgets.

Sealed Lead-acid/VRLA/GEL Batteries

The greatest advantage of this type of battery is its low cost, with a unit price of only 50% to 60% of that of lithium iron phosphate batteries, which can significantly reduce the initial investment of the project. However, the drawbacks are equally prominent: high maintenance requirements, regular checks on the electrolyte status (for some types) are needed, and problems such as leakage and bulging are prone to occur; The cycle life is short, usually only 500 to 1,000 times, with a service life of about 2 to 5 years, and frequent replacement is required. It has poor low-temperature performance and its capacity will significantly decline in an environment below -10℃.

This type of battery is more suitable for low-budget projects, temporary lighting scenarios or as a backup solution.

Comparison Table of Core Parameters of Different Battery Types

How to Select the Battery Capacity for Solar Street Lights

The correct selection of battery capacity is the key to ensuring the stable operation of solar street lights. It is necessary to comprehensively calculate based on core parameters such as the power of the light, working time, and redundancy requirements to avoid problems such as insufficient capacity causing lighting interruption or excessive capacity resulting in cost waste.

Description of Core Computing Parameters

• lightpower (W) : The rated power of LED lights. The common power of solar street lights is 10W-60W.
• Daily working hours: The actual lighting duration of street lights. For instance, street lights in residential areas typically operate for 6 to 8 hours per night, while rural roads may work for 8 to 10 hours per night.
• Design redundancy days: The guarantee days for continuous rainy days, usually 2-3 days, and in areas with heavy rain and insufficient sunlight, it can be increased to 3-5 days.
• Depth of Discharge (DoD) : The maximum proportion of charge that a battery can safely release. For LiFePO4 batteries, the recommended DoD is 80% (i.e., up to 80% of the charge can be released), and for lead-acid batteries, it is 50%-60%.
• System efficiency: It includes controller conversion efficiency, line loss, etc., usually taken as 85%-90%.
• System operating voltage: Commonly 12V or 24V. The voltage selection should match the lights and controllers.

Capacity Calculation Formula and Example Calculation

Step 1: Calculate the energy required each night (Wh)

The required energy (Wh) = light power (W) × number of working hours per night

Step 2: Calculate the designed battery capacity (Wh)

Design capacity (Wh) = Required energy × (1 + standby days)/(System efficiency × Available DoD)

Example: A solar street light project in a certain community, with a light power of 30W, operates for 7 hours each night, has a design redundancy of 3 days, a system efficiency of 90%, uses LiFePO4 batteries (available DoD=80%), and a system voltage of 24V.

Calculation process

The energy required each night = 30W × 7h = 210Wh

The designed capacity = 210Wh × (1 + 3)/(0.9 × 0.8) = 210 × 4/0.72 ≈ 1166.67Wh

Convert to battery capacity (Ah) : Capacity (Ah) = designed capacity (Wh)/system voltage (V) = 1166.67Wh / 24V ≈ 48.6Ah

In actual selection, a 50Ah/24V LiFePO4 battery can be chosen, with a certain margin reserved to deal with issues such as temperature attenuation.

Suggested Battery Capacity Configuration Table for Different Scenarios

Note: Considering the impact of temperature on capacity and lifespan, more capacity should be reserved at night and in winter when there is insufficient light. For example, in northern winters, the redundant days can be increased to 4-5 days.

Solar Street Light Battery Life, Replacement Cycle and Common Failure Causes

Solar Street Light Battery Life and Replacement Cycle

The lifespan and replacement cycle of solar street light batteries vary significantly depending on the type of battery, usage environment, and maintenance level. Among them, the typical service life of lead-acid batteries (sealed lead-acid /VRLA/GEL) is 2 to 5 years, and the replacement cycle is approximately 2 to 3 years. The typical service life of lithium batteries (mainly LiFePO4) is 5 to 10 years, and the replacement cycle can be extended to 5 to 8 years, with lower long-term usage costs.

The Common Causes of Solar Street Light Battery Failure

• Overcharge/overdischarge damage: Failure to be equipped with a qualified BMS or BMS failure leads to overcharging or overdischarging of the battery, damaging the internal chemical structure;
• Extreme temperature impact: Long-term exposure to low temperatures below -20℃ or high temperatures above 60℃ leads to accelerated capacity attenuation and shortened lifespan.
• Improper charging: Mismatch of photovoltaic module power, insufficient light, resulting in inadequate charging, or unstable charging voltage, remaining in a "undercharged" state for a long time;
• Inferior accessories: Using poor-quality battery cells or BMS, with poor initial performance and prone to failure;
• Cycle depletion: Exceeding the battery's rated cycle count, internal electrodes age, and capacity drops significantly.

Battery Replacement Suggestions and Acceptance Points

When replacing, give priority to choosing the battery type and specification that match the original system. When accepting, it is necessary to test the battery capacity recovery rate (which should be ≥80%), measure the internal resistance (in line with the manufacturer's standards), check the appearance for no leakage, bulging or damage, and at the same time verify whether the charge and discharge protection function of the BMS is normal.

Solar Street Light Battery Installation Form

The installation form of solar street light cells directly affects the installation efficiency, maintenance convenience and service life. It is mainly divided into two forms: integrated and underground/box-type. The choice should be made according to the project requirements.

All-in-one Installation

The battery is integrated into the light body or the head of the light pole, forming an integrated whole with the photovoltaic module, the light and the controller. Its core advantage is that it is easy to install, without the need for additional excavation or construction of installation space, and has a short construction period. The appearance is neat and tidy, and it will not spoil the beauty of the surrounding environment. The drawback is that the battery has limited heat dissipation space and is prone to accelerated aging in high-temperature environments. When replacing the battery in the later stage, the light or the head of the light post needs to be disassembled, which is rather difficult to operate and has a high maintenance cost.

Buried Underground/Box Placement

After installing the battery in the waterproof box, bury it underground at the bottom of the light post or fix it on the side of the light post. The advantage is that it has sufficient heat dissipation space and can effectively avoid the influence of high temperatures. When maintaining and replacing the battery in the later stage, there is no need to disassemble the light, and the operation is convenient. The box body has excellent waterproof and anti-theft performance and is suitable for complex outdoor environments. The drawback is that it requires additional excavation of ground pits or installation of boxes, increasing the construction volume and initial costs. It is necessary to ensure proper sealing and drainage of the box to prevent groundwater from seeping in and causing a short circuit in the battery.

Selection Suggestion

For projects with limited budgets, a pursuit of rapid installation, and weak maintenance capabilities (such as small residential areas and temporary lighting), integrated installation can be chosen. For large-scale projects, long-term use, high maintenance frequency or harsh environments (high temperature, heavy rain), it is recommended to choose underground or box installation.

How to Extend Solar Street Light Battery Life?

Scientific maintenance can significantly extend the lifespan of solar street light batteries and reduce operation and maintenance costs. The core maintenance points and practical suggestions are as follows:

Regular Inspection

At least one inspection should be conducted every month, with a focus on checking whether the battery voltage and charging current are normal, whether the terminal blocks are loose or oxidized, and whether the battery box or light body is well sealed (to prevent water and dust from entering). It is recommended to conduct a comprehensive inspection once every quarter, recording parameters such as battery capacity and internal resistance, and tracking performance changes.

Environmental Protection

Give priority to choosing a well-ventilated and dry installation location to avoid keeping the battery in low-lying and waterlogged areas for a long time. In high-temperature seasons, an insulating layer can be installed on the outside of the battery box. In low-temperature seasons, insulation measures (such as wrapping with insulation cotton) can be taken. Strictly avoid over-discharging the battery to ensure the normal operation of the BMS.

Strategy Optimization

Adjust the lighting duration according to the season. When there is insufficient light in winter or the rainy season, the lighting duration can be appropriately shortened (for example, from 10 hours to 8 hours), and at the same time increase the number of redundant days to avoid battery depletion. Use qualified BMS and controllers to ensure that the charging and discharging parameters match the battery.

Backup and Monitoring

It adopts a modular battery design, which is convenient for individual replacement and reduces the overall replacement cost. It is recommended to install an IoT remote monitoring system to monitor parameters such as battery voltage, capacity and temperature in real time. When any abnormality occurs, it will promptly issue an alarm to reduce the frequency of manual inspection.

FAQ

Q1: What would happen to solar street lights without batteries?

Answer: It cannot achieve the energy storage function. It can only supply power in real time when there is sunlight during the day. At night or on rainy days, it is completely unable to provide lighting. It loses the core value of "off-grid autonomous operation" and cannot meet the basic needs of street lighting at night.

Q2: How often do solar street light batteries generally need to be replaced?

Answer: It depends on the battery type and the usage environment. Lead-acid batteries (sealed lead-acid /VRLA/GEL) usually need to be replaced every 2 to 5 years. Lithium batteries (mainly LiFePO4) usually need to be replaced every 5 to 10 years. Under proper maintenance and suitable environmental conditions, the replacement cycle can be appropriately extended.

Q3: Why choose LiFePO4 batteries?

The core advantages lie in three points: First, it has a long cycle life (2,000 to 3,000 times), which is 2 to 3 times that of lead-acid batteries. Second, it has high thermal stability and safety, is suitable for complex outdoor environments ranging from -20℃ to 60℃, and is less likely to experience thermal runaway. Third, it has low maintenance requirements and is almost maintenance-free, which can reduce long-term operation and maintenance costs.

Q4: Where is it more appropriate to place the battery on the light post?

Answer: It should be determined based on maintenance convenience, heat dissipation effect and safety. For small-scale projects and scenarios with weak maintenance capabilities, it can be placed on the light body or the head of the light pole (integrated installation). For large-scale projects, scenarios with frequent maintenance or harsh environments, it is recommended to place them in underground boxes or side boxes at the bottom of the light post, which is convenient for maintenance and heat dissipation.

Q5: How to determine if the battery is really broken?

Answer: The main focus is on four indicators: First, the capacity drops significantly, with the actual capacity being less than 50% of the rated capacity; The second is that the internal resistance has risen significantly, exceeding the manufacturer's standard value. The third is abnormal charging, such as charging for too long or failing to fully charge. The fourth is that the BMS frequently alarms, or the battery has appearance problems such as leakage, bulging, and damage. If any of the above situations occur, it indicates that the battery may have failed and needs to be replaced in time.
 

The battery is the core energy storage component of the solar street light system and is indispensable. Choosing the right battery type (such as LiFePO4 batteries suitable for long-term projects), accurately calculating capacity, and properly installing and maintaining can significantly enhance system reliability and reduce the long-term total cost of ownership. Conversely, if low-quality and low-priced batteries are blindly chosen, it will lead to frequent replacements and a sharp increase in maintenance costs, which will affect the project's returns.

If you need further precise selection, you can also directly contact our technical support team to obtain a one-on-one project customization plan.