What kind of battery is ideal for solar street lights? (Recommendation for you)

Because they don’t rely on the power grid for illumination at night, solar street lights are particularly practical. The solar module and battery used in these lighting systems enable the gadget to produce electricity during the day, store it in the battery, and use it at night.

Each solar street light must have the proper battery, as this will affect the light’s autonomy, appearance, level of maintenance, and other factors. This post is for you if you wish to install batteries on solar street lighting.

Which battery types are applicated in the solar industry?

For solar street lighting, there are numerous solar cell technologies available, each with a variety of benefits and drawbacks. We describe each of these methods below in this section:

Cadmium Nickel

Batteries made of nickel-cadmium (Ni-Cd) are robust, able to tolerate high temperatures, and maintenance-free. Ni-Cd cells, which use cadmium as the cathode and an oxide-hydroxide electrode as the anode, are widely used in solar applications in addition to civil and military aerospace.

Due to their high reliability and minimal maintenance requirements, Ni-Cd batteries are perfect for use in street lights in outlying locations. These batteries are less expensive than Li-ion batteries and are perfect for solar applications because they can be depleted to 60% depth of discharge (DOD) while producing 2,500 cycles.

Lead-acid

Lead-acid batteries are the industry standard and have been for a long time because of their affordability and longevity. They are composed of a lead oxide cathode and a metallic lead anode that are both submerged in an electrolyte of sulfuric acid.

We do not advise using lead-acid batteries for subterranean installations of solar street lights because they may need frequent maintenance despite being inexpensive. Both 500 and 1,200 cycles at 50% DOD are available from these batteries. There are two types of lead-acid batteries that the most frequently used for solar street lights, they are AGM and gel batteries.

Lithium-ion

As everyone known that lithium-ion (Li-Ion) batteries are one of the most frequently utilized for solar street lights while being the most expensive. A lithium salt electrolyte served as the electrolyte for the lithium carbon anode and lithium metal oxide cathode that were employed.

Due to its better energy density, which leads to bigger capacity and more compact designs, lithium-ion batteries have grown in popularity. For street lights, these batteries have a 2,000–3,000 cycle life and may be depleted to 80% DOD.

Lithium iron phosphate

Another great lithium battery technology that is less expensive is lithium iron phosphate (LiFePO4) batteries. These batteries have a 4,500 cycle life, a high energy density, and are 80% DOD depleted.

A lithium salt electrolyte surrounds a lithium iron phosphate cathode, which is the component of LiFePO4 batteries. Because it is less expensive than lithium-ion batteries while still providing a high energy density maintenance-free solution, this lithium technology is the preferred choice for solar street lighting.

Flooded battery

One half-cell contains the anode and the first electrolyte, and the other half-cell contains the cathode and the second electrolyte in flow redox batteries, a specific instance of two electrolytes. Vanadium/vanadium (in different states), iron/chromium, or zinc/bromine are the most common electrolyte couples.

They are less prevalent in the solar and street lighting industries because they are a more recent technology. Flow batteries can function at low temperatures, offer more cycles than the majority of batteries, and are easily scalable to the majority of applications.

What considerations must be made when choosing solar street light batteries?

Understanding the factors that must be taken into account when selecting a solar street light will help you choose the best battery after learning about the various battery technologies.

Capacity and Size

How long a solar street light can operate depends on the solar battery’s capacity, which is influenced by how much energy the street light fixtures need. When choosing a battery, think about how many watt-hours (Wh) or ampere-hours (Ah) it can produce because this will affect how long your solar street light will operate.

It is useful to use the following expression to calculate the necessary battery capacity:

The equation used to calculate how much power a solar street light can store in its battery

A 1,500 lumen light fixture, for instance, uses almost 15W, while a 12,000 lumen solar street light uses 120W. In order to run a 12V solar street light continuously for 12 hours, you would need a 75Ah @ 12V battery for a 1,500 lumen bulb and nearly a 600Ah At 12V battery pack for a 12,000 lumen street light due to the loss of 80% round-trip efficiency, 50% DOD, and two days of autonomy (19:00 to 07:00).

The space inside the battery pack case is another aspect that might put a cap on the size of batteries you can use. If you utilize a battery technology with a high energy density, like lithium, you can install batteries that are smaller than lead-acid batteries. As a result, it is crucial to take into account the size of the battery models to determine whether they fit in the battery box.

Power and voltage ratings

The potential difference between a battery’s terminals, expressed in volts, is the voltage of the battery (V). Always make sure that the battery voltage is the same as what the light fixture needs.

Similar to that, a battery’s power rating indicates how much power it can provide and is expressed in kilowatts (kW). We calculate solar street lights in watts because they don’t need a lot of power (W). The power requirements of solar street light installations should always be met or exceeded by batteries.

Discharge Depth (DoD)

A battery can safely discharge up to a certain percentage, or depth of discharge (DoD). This is connected to the battery’s cycle life, as the battery can only support a specific amount of cycles depending on how frequently it is used.

Some manufacturers advise 20% DOD for lead-acid batteries in order to increase the lifespan of solar street lights, although a value of 30–40% is also acceptable to strike a fair compromise between performance and lifespan. DOD can be raised by 75% for lithium batteries.

Efficiency for circular trips

The term “round-trip efficiency” describes how much DC power can be extracted from the battery in comparison to the DC power that the solar panel feeds into it. Alternatively put, the battery’s cycle efficiency for charging and discharging. The average battery has a round-trip efficiency of 80%, though this varies by technology and manufacturer.

Battery life (Life cycle)

This is an estimation of the battery’s cycle life; battery life is sometimes expressed in years. How many charge/discharge cycles a battery can withstand at a given DoD before its capacity (lifetime) starts to decline. This number varies depending on the technology used and the DoD at which the battery is drained.

When discharged to 50% DoD, for instance, ordinary lead-acid batteries have a lifespan of around 2,000 cycles, but certain sophisticated lead-acid battery models may do so for nearly 11 years, or 4,250 cycles. For solar street lights, using 80% DoD on a single battery reduces its lifespan to roughly 2,700 cycles, or 7 years. As a more sophisticated technology, lithium batteries can operate between 80% and 100% DoD for around 4,000 cycles.

Impact on the environment and safety

Every battery is subject to various manufacturing and electrolyte chemical safety standards. Battery power for solar street lighting must be UL-8750 certified or safer.

Safety precautions must be taken to prevent thermal runaway of the battery, which could cause it to rapidly heat up and explode or emit hazardous gases. Installing high temperature resistant, temperature sensitive batteries or looking into batteries with cutting-edge battery management systems are both recommended to prevent this (BMS).

Lower temperature changes by mounting the battery underground help prevent thermal runaway, but the battery must be resilient to the environment’s lack of ventilation (applicable to AGM, GEL, or lithium batteries only).

Price

The biggest restraint and one that cannot be avoided is the budget. Consider your financial limitations when choosing a battery for a solar street light, and go with the option that offers the most performance and cycles.

If you take into account the 1,500–12,00 batteries mentioned above for solar street light installations, you can obtain these approximate costs in both situations:

Lead-acid AGM batteries cost between $12 and 96 ($0.80/Ah).

Lead Acid Gel Batteries: $15–120 ($1.00/Ah)

Lithium Iron Phosphate: $18-144.0 ($1.20/Ah)

Li-Ion: $23.7-189.6 ($1.58/Ah)

Which kind of battery is best? How do I decide?

While it’s crucial to comprehend the various factors to take into account when selecting a battery, you need also be aware of how each factor relates to the various battery technologies. The optimum battery technology is described here for many scenarios.

When should you pick NiCd batteries?

Batteries made of nickel-cadmium are robust, dependable, and temperature resistant. They deliver lots of cycles, have a respectable power density, and are yet within budget. These batteries are excellent for solar street lights that are frequently exposed to extreme temperatures and where you require batteries with a medium capacity yet a low cost. However, several of the components in NiCd batteries are hazardous to handle.

When is an AGM lead-acid battery appropriate?

The most popular economical option is AGM lead-acid batteries, which have a reduced energy density and a constrained DoD range. It is possible to combine several batteries to achieve a lithium battery’s capacity, but we only advise using these methods for installations below ground. They require minimum maintenance and do not outgas like flooded batteries, making them perfect for underground installations.

When should you pick a lithium-ion battery?

The most expensive alternative is lithium-ion batteries, which are nonetheless quite good. When compared to conventional batteries, lithium-ion batteries offer a higher energy density, are more compact, are scarcely detectable, and can operate lamps for longer periods of time. We do not recommend utilizing them for solar street lighting in severely cold or hot weather because they can only be charged at temperatures between 32°F and 113°F.

When should you choose a lithium-ion polymer battery?

To be honest, lithium iron phosphate batteries are typically the best option. The highest performance for Li-ion batteries is provided by these batteries, which can run in a temperature range of -40oF-158oF and are more expensive than Ni-Cd or lead-acid batteries but less expensive than Li-ion batteries. Due to their great energy density and lack of maintenance, these batteries can be installed for solar street lights in either underground or pole mount configurations.

Final thought

The solar industry employs a variety of technologies. A number of variables, including the technical requirements of the luminaire or panel, the desired aesthetics of the street light, and the budget, must be taken into consideration when selecting the correct battery for a solar street light.

Think about the topics addressed in the article and the advice in the preceding section when searching for batteries for your specific solar street light. You may choose the best battery that will provide excellent performance and obtain the best investment over the long term by combining these technical requirements with the desired aesthetics of your luminaire.