All You Need To Know About Solar Street Lights Battery

Why Choose Lithium Battery for Solar Street Lights?

Based on the material, solar road lamp batteries can be roughly divided into Gel lead acid batteries and lithium batteries. Over the past decade, Gel lead acid batteries have been the mainstream solar battery. However, most solar street lights carry lithium batteries nowadays. But why?

Although lithium batteries are significantly more expensive than Gel lead acid batteries, they are vent-free and maintenance-free. Also, this new technology is built to be more durable and withstand deeper cycles. Compared to lead-acid batteries, lithium batteries have a much longer lifespan. It will surely save you more money in the long run, considering that you’ll only spend less capacity per kilowatt-hour.

Lithium Iron Phosphate batteries, also known as LiFePO4 or LFP batteries, are the best lithium battery for solar street light applications.

Gel Lead Acid Battery Vs. Lithium Battery

Lithium battery costs roughly double that of the gel battery, and the cycle life is 1000-3000 times. It has a smaller size, is lightweight, and supports deep discharge.

Lead Acid Battery: The cost is roughly half that of lithium batteries, but the cycle life is only about 600 times. It has a large volume, is heavy, and does not support deep discharge.

In addition, the technology of lithium batteries is still being updated and improved. It was also reported that the price of lithium batteries would effectively reduce the cost of solar street lights.

Types of Lithium Batteries

LiFePO4 Vs. LiMn2O4

Generally, you can classify solar lamp lithium batteries into two types. These types are LiFePO4 lithium batteries and LiMn2O4 lithium batteries, which vary according to materials.

Below is a simple comparison of the characteristics of the two types of lithium batteries.

LiMn2O4 energy density is 1/3 higher but not important in Solar lights. The price of LiFePO4 is 10% higher than that of LiMn2O4.

Based on the comparison above, the LiFePO4 lithium battery is more suitable for solar street lights in most cases. No wonder why most solar street lights today use LiFePO4 lithium solar batteries.

3V & 12V/24v Lithium Battery

According to the battery voltage, lithium batteries can be divided into 3V lithium batteries, 12V lithium batteries, and 24V lithium batteries. Among the three types, 3V batteries are the cheapest. More so is the used 3V batteries cost. Almost all home solar street lights on the market have 3V lithium batteries.

On the other hand, 12V/24v batteries require high consistency of battery cells, and additional costs are required to select the battery cells and packing. That said, the higher the voltage of the lithium batteries, the higher the price. Most of the time, all high-power project-type solar street lights opt for 12V/24V batteries.

Square Battery & Cylindrical Battery

Based on their appearance, you can categorize lithium batteries into two types. They are square and cylindrical batteries.

Relatively speaking, the quality of the Cylindrical battery is more stable than the square one. Typically, you can see various models for cylindrical lithium battery cells. But the most popular models available on the market are 18650, 26650, and 36700. To give you an idea of how to know its exact size by just looking at the actual model number, let us take 18650 as an example. In the 18650 model, 18 represents the diameter of the battery cell 18mm, and 650 represents the length of the battery cell 650mm.

Lithium Battery Pack Composition & Parameters

In most cases, you cannot use lithium battery cells directly in solar street lights. Making a battery pack after it can be used in the solar street light system is necessary.

In simple terms, a battery pack consists of cells and a BMS board.

What to Consider When Choosing the Battery For a Solar Street Light?

Capacity

Under certain conditions, the amount of charge released by the battery, in mAh or Ah. Note, however, that the unit for measuring how much energy a battery can store: is Wh (V x AH). The battery’s stored energy is the parameter that determines the lighting time of the solar street light.

Open Circuit Voltage

Open-circuit voltage is the disparity of electrical potential between two devices not connected by any circuit. The open circuit voltage is proportional to the remaining battery energy. Usually, it is the utmost basis for the display principle of the electric vehicle’s remaining power.

Operating Voltage

The potential difference between the positive and negative electrodes is called the load voltage when the battery is functioning. The working voltage is less than the open circuit voltage because the internal resistance must be overcome when the battery is discharged.

Discharge Cut-off Voltage

The voltage is reached when the battery is fully charged and discharged. If it continues to discharge, it will have excessive discharge that will eventually damage the life and performance of the battery.

Depth of Discharge (DoD)

DOD refers to the percentage of the capacity released by the battery to the rated power. The lithium battery supports deep discharge and can reach 80% DOD without affecting the life of the lithium battery.

Round-Trip Efficiency

Round-Trip Efficiency means the amount of DC power you can extract from the battery, regarding the DC power the solar panel injected into it. In other words, it is the battery charge/discharge cycle efficiency. Most batteries deliver an 80% round-trip efficiency, but this varies between technologies and manufacturers.

Cycle Life

After a charge and discharge are called a cycle, the battery capacity will gradually decrease after repeated charges and discharge. Under certain discharge conditions, when the battery capacity drops to 70%, the cycle number experienced by the battery is its cycle life.

Lithium Battery Packing

Earlier, we mentioned assembling the battery into a battery pack before using it for solar street lights. Now, we will briefly share the assembling process of the battery pack.

Detection & Screening of Battery Cells

Note that battery cells’ capacity, resistance, voltage, and other parameters are slightly different. If you mistakenly assemble battery cells with different parameters into a battery pack, it will inflict damage. Why? Because each battery cell will have inconsistent energy storage during the charging and discharging process. In this case, if one cell is overcharged or over-discharged, it will eventually damage the battery.

Therefore, all battery cells must be screened for packaging consistency to avoid these circumstances.

Arrangement & Welding of Battery Cells

Based on the voltage, capacity, and size requirements, the battery cells with high consistency should be welded together in series and parallel.

External Package

Mostly, the soldered battery pack will be connected to the BMS board. Then a waterproof film or a casing is wrapped outside to protect the internal cells.

Battery Pack Detection

Finally, test the assembled battery pack’s capacity, charge, and discharge to ensure its quality.

Top 3 Check Lists for Solar Street Lights Batteries

In purchasing solar street lights, ensure you know these checklists to avoid battery problems. Many suppliers falsely mark battery parameters or use poor-quality lithium battery cells. As a result, the lighting time of solar street lights will fall too short, as well as its lifespan. In some instances, even spontaneous combustion may also happen.

So, we recommend the following three methods to avoid the above circumstances.

1: Measure the size of the battery pack

The basic reminder is that a fixed-type cell also carries a fixed capacity. For example, the capacity of 32700LiFePO4 cells is 5ah to 7ah. In this case, the number of cells in a battery pack with a specific capacity is determined. Correspondingly, the size of the battery pack is also determined.

2: Measure the weight of the battery pack

Similar to the size of the battery pack, you can roughly determine its weight through its capacity.

3: Cell certification

Be guided that the two necessary certifications for lithium battery cells are MSDS and UN38.3. If there are no cells with these two certifications, ADN does not recommend using them. Because a poor-quality cell is like a time bomb, you never know when it will spontaneously ignite.