Lead-acid Solar Batteries: Definition, How it Works, and Different Types

Lead-acid batteries are a type of rechargeable battery commonly used for energy storage, and they are a fundamental component in some photovoltaic (PV) solar systems. Known as “solar lead acid batteries” when used for this application, these devices are widely used to store and manage the electrical energy generated from solar panels. Serving as a reliable power source during times when sunlight is scarce, a lead-acid solar battery is key to ensuring a consistent energy supply in both residential and small-scale commercial solar setups.

The function of lead-acid solar batteries is to store the electrical energy generated from solar panels during sunlight hours. The batteries utilize a chemical reaction between lead plates and sulfuric acid electrolytes to convert and store this solar energy into electrical energy. When there's a power demand, such as during the night or on cloudy days when solar panels aren't actively generating electricity, the batteries release the stored energy to provide a consistent power supply.

The main types of lead-acid solar batteries are Flooded Valve Regulated Lead Acid Batteries (VRLAB), Gelled Electrolyte Lead Acid Batteries (GEL), and Advanced Glass Mat Valve Regulated Sealed Lead Acid Batteries (AGM or VRSLAB). Each type presents unique features, from maintenance requirements to performance characteristics, influencing their suitability for different solar applications.

Selecting the right solar lead acid solar battery is a critical decision that impacts the efficiency, reliability, and cost-effectiveness of a solar power system. The choice involves informed knowledge and balancing factors such as capacity, size, weight, and compatibility with solar panel systems. Understanding these aspects is crucial in optimizing solar energy utilization, maintaining system health, and ensuring safety in solar energy storage.

What is a Lead-acid Solar Battery?

A lead-acid solar battery is a type of rechargeable battery that is commonly used in photovoltaic (PV) solar systems. These batteries are designed to store electrical energy generated by solar panels during periods of sunlight and make it available for use when the sun is not shining, such as at night or on cloudy days. The technology behind lead-acid batteries has been in use for over a century and is known for its reliability and cost-effectiveness, making it a popular choice for solar energy storage. Solar lead acid batteries are particularly common in residential and small-scale commercial solar systems.

The basic components of a lead-acid solar battery include lead plates submerged in a solution of sulfuric acid and water. This combination of sulfuric acid and water triggers a chemical reaction that facilitates two separate processes in the battery: charging, where electricity is stored, and discharging, where electricity is released. The design of lead-acid batteries for solar applications specifically provides a deep cycle capability, which means they can be discharged and recharged to a significant extent of their capacity without sustaining damage. Contrary to lead-acid batteries used in vehicles, which are tailored for short, high-power bursts to start an engine, solar lead-acid batteries are optimized for extended, gradual discharges (releasing stored energy) and recharges (storing energy anew). This characteristic makes them ideally suited for the cyclical nature of energy use in solar power systems."

How do Lead-acid Solar Batteries work?

Lead-acid solar batteries store energy through chemical reactions between lead, water, and sulfuric acid. These reactions convert stored chemical energy into electrical energy, enabling the batteries to power devices or store excess energy from solar panels.

The basic components of these batteries include lead (Pb) plates and a sulfuric acid (H₂SO₄) solution, which acts as the electrolyte. During discharging, when the battery powers a load such as a home appliance, the sulfuric acid reacts with the lead plates. This reaction causes the lead to oxidize and generates an electrical current by releasing electrons.

When charging, typically occurring when solar panels produce excess electricity, the reverse reaction takes place. The electrical energy from the panels initiates a chemical change, converting lead sulfate back into lead and sulfuric acid, thus restoring the battery's charge.

This reversible electrochemical reaction is key to the lead-acid battery's ability to recharge. However, repeated cycles of discharging and recharging gradually wear down the lead plates, leading to a decrease in the battery's capacity and efficiency. Consequently, lead-acid batteries have a finite lifespan and require replacement over time.

What are the different types of Lead-acid Solar Batteries?

There are a range of lead-acid solar batteries available, each with varying chemistries, designs and applications.

The three main types of lead-acid solar batteries are listed below. :

• Flooded Valve Regulated Lead Acid Batteries (VRLAB): Commonly called “flooded lead acid batteries', VRLAB batteries are the most common type of lead-acid solar batteries. VRLAB batteries y contain lead plates submerged in a liquid called electrolyte (a mixture of water and sulfuric acid). Electrolytes are essential for the battery's operation as they facilitate the flow of electricity. VRLABs feature a valve system that releases excess gas to prevent overpressure and enhance safety. Maintenance is required for these batteries, including monitoring and refilling the electrolyte level and ensuring they are not overcharged. They must be installed in areas with good ventilation due to gas release during charging.
• Gelled Electrolyte Lead Acid Battery (GEL): GEL batteries use a gel-like electrolyte made by mixing sulfuric acid with silica. This gel form prevents leakage, making the battery spill-proof and versatile in installation. GEL batteries are maintenance-free and are less prone to "sulfation" (a process where lead sulfate crystals accumulate, reducing battery efficiency). GEL batteries are suitable for deep cycle use (long periods of discharge and recharge) but require careful charging to avoid damage.
• Advanced Glass Mat Valve Regulated Sealed Lead Acid Battery Construction (AGM or VRSLAB): AGM batteries represent a more advanced form of VRLAB. They have a fiberglass mat that absorbs the electrolyte, making them spill-proof and eliminating the need for maintenance. AGM batteries provide better performance, including quicker charging and greater resistance to physical shocks. They are suitable for a wide range of temperatures and are ideal for long-duration energy use. However, AGM batteries for solar are generally more expensive than traditional flooded lead-acid batteries.

What type of AGM Lead-acid Solar Battery should I use for a Solar Panel?

For most situations requiring a lead-acid battery, a sealed AGM (Absorbed Glass Mat) battery is indeed the safest and best option. AGM batteries require little maintenance, are lighter, less expensive, and easier to recharge. When it comes to choosing the specific type of AGM lead-acid solar battery for your solar panel system, several key criteria stand out, including the battery’s capacity, the depth of discharge, and its size and weight.

Firstly, the battery's capacity should match your energy needs. This involves determining your daily power usage and ensuring the chosen AGM battery provides adequate storage and energy supply. The capacity, measured in ampere-hours (Ah), must meet your daily energy consumption without being excessively taxed.

Secondly, the Depth of Discharge (DoD) is a pivotal factor. DoD refers to the extent to which a battery's total capacity is utilized. AGM batteries typically allow a higher DoD compared to other lead-acid types, meaning you're able to use a larger portion of their total energy capacity without negatively affecting the battery's lifespan. For example, a battery with a high DoD enables more of its stored energy to be utilized before it requires recharging. Selecting an AGM battery with a substantial DoD is efficient and proves economical over time, optimizing energy usage while maintaining the battery's health.

Lastly, the size and weight of the battery are vital considerations. When selecting a battery, it's essential to ensure that it will physically fit in the designated space and that the structure supporting the battery is able to handle its weight. For example, in a residential solar power setup, you often have a dedicated utility area where the battery bank will be installed. In this case, you need to measure that space to make sure the batteries you're considering will fit. If you have a limited area, you might opt for batteries with a smaller footprint but higher energy density.

By focusing on these three criteria of capacity, Depth of Discharge, and physical dimensions, you will be well-equipped to select an AGM lead-acid solar battery that optimally aligns with the requirements of your solar panel system.

What is the difference between a Deep Cycle Lead-acid Battery and a Regular Lead-acid Battery?

The primary difference between deep-cycle lead-acid batteries and regular lead-acid batteries lies in their design and application. Deep-cycle lead-acid batteries are designed for prolonged discharge and recharge cycles, making them ideal for solar systems. They have thicker plates and denser active material. Regular lead-acid batteries are for short, high-power bursts like starting vehicles and cannot handle frequent deep discharges, so they are unsuitable for solar.

The distinction between deep-cycle lead-acid batteries and regular lead-acid batteries is crucial in understanding their suitability for solar energy storage. Deep cycle batteries, specifically designed for prolonged discharge and recharge cycles, are ideal for solar panel systems. They withstand approximately 2,000 full discharge and recharge cycles. The robustness of deep-cycle lead-acid batteries comes from their thicker lead plates and denser active material, which enable a consistent and prolonged release of power. This makes them highly suitable for solar systems, where the battery needs to store energy during the day and provide a steady power supply when sunlight is not available, such as at night or during cloudy weather.

On the other hand, regular lead-acid batteries, often used for starting vehicles, are not suited for solar applications. Their design focuses on delivering a quick burst of high power necessary for starting engines. They typically endure only about 200 cycles of deep discharging. The composition and structure of these batteries, with thinner lead plates, are not meant to handle the consistent, deep discharging that solar panel systems require. Using a regular lead-acid battery in a solar setup would lead to a significantly reduced lifespan and inefficiency due to its inability to handle frequent and deep discharges.

In short, when selecting batteries for solar panel systems, deep-cycle lead-acid batteries are the preferred choice due to their design and endurance, which align with the operational demands of solar energy storage. Unlike regular lead-acid batteries, which are more suited for short bursts of high power in starting applications, deep-cycle lead-acid batteries are the preferred choice.

What are the most common Lead-acid Solar Batteries?

The most common types of lead-acid batteries used in solar applications are flooded-lead acid batteries (FLA), Absorbed Glass Mat (AGM), and Gel Cell batteries.

More information about the three most common lead-acid batteries is listed below.

• Flooded Lead-Acid Batteries (FLA): Flooded lead-acid batteries are the traditional type of lead-acid batteries, where the electrolyte is in a liquid form (a mixture of sulfuric acid and water). They are often used in off-grid solar systems due to their affordability and reliability. However, they require regular maintenance, including water top-ups and ensuring the cells are not overcharged.
• Absorbed Glass Mat (AGM): In AGM batteries, the electrolyte is absorbed in a fiberglass mat. This mat holds the electrolyte close to the battery's lead plates, which allows efficient transmission of electrical current while preventing spillage. They are more expensive than FLA batteries but require less maintenance and are spill-proof. AGM batteries for solar are known for their good performance in a wide range of temperatures and their ability to withstand frequent charging and discharging cycles. AGM batteries are sealed, meaning they do not require regular maintenance, like adding water or checking electrolyte levels, making them more convenient and safer to use.
• Gel Cell: Gel batteries contain a gelified electrolyte, which is essentially the sulfuric acid mixed with a gelling agent (like silica) to make it set into a jelly-like substance. This gel form immobilizes the electrolyte, making these batteries highly resistant to spillage and leakage compared to AGM batteries. Gel batteries excel in deep-cycle applications and are maintenance-free. However, they are more sensitive to overcharging and typically more expensive than both FLA and AGM batteries.

Understanding the key differences between different types of lead-acid batteries is crucial when implementing energy storage for your solar panel system. There are a number of factors to consider beyond type, when choosing the best solar panel battery for your needs. These factors include capacity, depth of discharge, round-trip efficiency, warranty, price, compatibility, brand reputation, safety features, and installation requirements. Starting with the type of lead-acid solar battery is a smart move for ensuring your storage needs are met.

Why is it important to select the correct Lead-acid Solar Battery for Solar Panels?

Selecting the correct lead-acid solar battery for your solar panel system is important for several reasons. It ensures maximum energy storage, enhances system efficiency and reliability, promotes cost-effectiveness, optimizes solar energy utilization, and ensures compliance with safety and maintenance requirements.

The capacity of lead-acid batteries is critical to ensure that your solar power system is able to store sufficient energy to meet your needs. Accurately calculating your daily energy requirements allows you to choose a battery bank with enough capacity to store that energy. If the capacity is too low, you won't have enough power during times when your solar panels aren't generating electricity, like at night or during cloudy days.

The right battery ensures the overall efficiency and reliability of your solar system. Batteries that are too small may end up being overworked, reducing their lifespan and efficiency. Conversely, excessively large batteries are uneconomical. A correctly sized battery bank will optimize the performance of your solar setup, ensuring a steady supply of power and minimizing wear on the batteries.

While solar panels are a significant part of the investment in a solar power system, the cost of batteries is substantial. Selecting the right type and size of battery ensures you're not spending more than necessary for your energy needs. It prevents future costs associated with premature battery replacement due to incorrect sizing or selection.

A well-chosen battery bank maximizes the utilization of the solar energy collected by your panels. It ensures that excess energy produced during sunny days is effectively stored for later use, reducing waste and increasing the system's overall value.

Different types of lead-acid batteries have varying maintenance and safety requirements. Choosing the appropriate battery type for your setup and usage patterns ensures easier maintenance and enhances safety. For instance, flooded lead-acid batteries require regular maintenance, while sealed batteries like AGM or Gel types require less attention.

Can I use an Automotive Lead-acid Battery for Solar Panels?

Yes, it is technically possible to use an automotive lead-acid battery with solar panels, but it is not recommended. Automotive batteries, designed for short, high-power bursts to start a vehicle, differ significantly from solar batteries, which are intended for prolonged, deep discharge cycles. Lead-acid car batteries have a lower depth of discharge and are not designed for the continuous energy drain required by solar systems, leading to a significantly shorter lifespan and potentially premature failure. Despite their similar voltage levels, car batteries cannot sustain the regular, deep discharges needed for effective solar energy storage, resulting in inefficiency and increased wear. Therefore, for sustainable and efficient solar energy storage, dedicated solar batteries, particularly deep-cycle lithium or specialized lead-acid types, are strongly advised to avoid the issues associated with repurposing car batteries for solar use.

Can I use 12v Lead-acid Solar Batteries for Solar Panels?

Yes, it is possible to connect a solar panel directly to a 12-volt lead acid battery, but it is not advisable without a charge controller. This is because the solar panel generate voltages higher than the battery's required 12 volts, especially under strong sunlight conditions. Direct connection leads to overcharging and excessive heat, significantly reducing the battery's lifespan and potentially causing it to explode. A charge controller is essential as it regulates the voltage and current from the solar panels to the 12v battery, ensuring it is charged correctly and safely. This setup prevents overcharging and damage, making a charge controller a critical component for maintaining battery health and safety in solar panel systems.

What are the benefits of using Lead-acid Solar Batteries for Solar Panels?

While not the most efficient batteries in the solar industry, lead-acid solar batteries do have some benefits for solar panel users. The main advantage of lead-acid batteries is their affordability. Lead-acid batteries are much cheaper at around $150 than lithium ion ones, which cost anywhere from $300 to $600. Other advantages are their off-grid capabilities and their reliability.

The three key advantages of lead-acid batteries for solar panel use are explained further below.

• Affordability: From a financial standpoint, lead-acid batteries present a cost-effective solution. For instance, a decent quality 2 kWh lead-acid battery system is usually purchased for approximately $150, significantly lower than the cost of lithium-ion batteries, which typically range from $300 to $600 for a comparable capacity. This price difference makes lead-acid batteries a preferred option for budget-conscious solar system users.
• Off-Grid Capability: These batteries shine in off-grid solar systems where external electricity is non-existent. Unlike other types that require consistent electrical input for recharging, lead-acid batteries are able to store and supply solar energy independently, making them indispensable for remote homes or businesses looking to maintain power autonomy from the utility grid.
• Reliability: While they require regular maintenance, lead-acid batteries are a tried-and-true technology that many users are familiar with. This is advantageous for those who are comfortable with routine upkeep and want a reliable, well-understood battery technology that is found at any nearby hardware or automotive supply shops. Additionally, due to their widespread usage, numerous guides and support resources are available to assist you in selecting the appropriate battery for your setup.

What are the drawbacks of using Lead-acid Solar Batteries for Solar Panels?

While lead-acid batteries have their advantages, they come with significant drawbacks. The three main disadvantages of lead-acid solar batteries include their reduced efficiency and depth of discharge, limited durability, and maintenance requirements, all of which impact the overall convenience of your solar energy system.

More information on the three key disadvantages of lead-acid batteries follows below.

• Reduced Efficiency and Depth of Discharge: Lead-acid batteries reach only about 80-85% of the stored energy being usable compared to 95% or more in lithium-ion batteries. Furthermore, they are able to be safely discharged to about 80% of their total capacity without risking damage, effectively halving their usable energy. For comparison, lithium-ion batteries are typically discharged without problems up to 80% or more.
• Maintenance Demands: Lead-acid batteries require regular upkeep to ensure their longevity and proper functioning. This includes routine checks and topping up the water levels in flooded lead-acid (FLA) batteries, which is cumbersome and time-consuming. Neglecting this maintenance often leads to reduced battery life and effectiveness, making them less reliable than maintenance-free options like lithium-ion batteries.
• Limited Durability: Lead-acid batteries typically have a short lifespan, lasting between 3 to 12 years, depending on usage and maintenance. Their cycle life—the number of charge and discharge cycles they are able to undergo before performance significantly degrades—is lower. This means that while lead-acid batteries are cheaper upfront, they require more frequent replacements.

How long do Lead-acid Solar Batteries last?

Lead-acid solar batteries typically have a lifespan ranging from three to ten years, influenced by several factors, including maintenance practices, usage intensity, and design type (whether flooded or sealed).

Maintenance practices refer to the regular care and upkeep required to keep batteries in optimal condition. For example, it's important to check and replenish water levels in flooded batteries, ensure proper charge levels, and clean terminals to prevent corrosion. These measures help acid-lead batteries last longer.

Usage intensity relates to how frequently and deeply the batteries are discharged and recharged. Frequent deep discharges and high loads are known to accelerate wear and reduce the battery's overall lifespan. In simple terms, the more that a lead-acid battery is used, the more quickly it wears out.

The third factor affecting the durability of lead-acid batteries is whether they have a flooded or sealed design. Flooded lead-acid (FLA) batteries, known as wet cells, contain electrolyte liquid covering the internal plates. Sealed lead-acid (SLA) batteries, encompassing Absorbent Glass Mat (AGM) and Gel types, often offer a longer lifespan due to their sealed design, which minimizes degradation from external factors and reduces maintenance needs.

Which is better: Lead-acid Solar Battery or a Lithium Solar Battery?

Lithium Solar Batteries are better compared to Lead-acid Solar Batteries due to their superior depth of discharge, longer cycle life and lifespan, lower self-discharge rate, lighter weight and compact size, and higher charging efficiency. These key factors significantly impact the performance, durability, and overall value of lead-acid and lithium-ion solar panel batteries.

More details on the five key reasons why lithium solar batteries are better than lead-acid solar panel batteries are given below.

• Depth of Discharge: Lithium batteries offer a significantly higher depth of discharge than lead-acid batteries. This means a larger portion of the stored energy is available for use without harming the battery's lifespan, making lithium batteries more efficient in energy utilization.
• Cycle Life and Lifespan: Lithium batteries have a considerably longer cycle life and overall lifespan (3-4 times longer) compared to lead-acid batteries. Lithium-ion solar panel batteries are able to undergo thousands of charge cycles without significant degradation, ensuring lasting service and reducing the need for frequent replacements.
• Self-Discharge Rate (SDR): Lithium batteries have a much lower self-discharge rate compared to lead-acid batteries, maintaining their charge for longer periods when not in use. This makes them more reliable and reduces the need for constant recharging.
• Size and Weight: Lithium batteries are much lighter and more compact than lead-acid batteries, offering greater energy density. This makes the installation of lithium batteries easier and expands the possibilities for battery placement and mobility.
• Charging Efficiency: Lithium batteries are more efficient during the charging process (95% against 85% for lead acid batteries), which means they are able more of the incoming power into usable energy. This results in faster charging times and less energy wasted.