Plico Team 03/10/2023 11 min read

Can a Solar Panel Overcharge a Battery?

A solar panel can overcharge a battery when the electrical current isn’t regulated properly. Overcharging refers to a battery getting too much electricity for its size. This can happen with a malfunctioning solar inverter or because of problems with the battery itself. When the inverter or battery doesn't stop the electrical current, too much charge flows into the battery’s cells. The consequences of overcharging range from decreased battery life to, on the rare occasion, batteries exploding.


How do solar panels charge batteries?

Solar panels charge batteries using photovoltaic conversion - the process of changing light into electricity. Solar panels can be constructed from different materials, but what they have in common is their ability to absorb sunlight. When panels absorb sunlight, electrons are dislodged from these materials and flow together in a specific direction. This flow of electrons is referred to as an electrical current.

The electric current generated by solar panels flows into a building’s electrical system, powering devices and appliances. Excess electricity is diverted to the solar batteries, which can store the electricity in their cells. The amount of electricity they store depends on the size and amount of cells they have, and the inverter controls where energy is distributed.


What is overcharging a battery?

Overcharging refers to a battery receiving more energy than its recommended capacity. When all the cells within a battery are filled with stored electricity, it is considered fully charged. However, if electricity continues to flow into the battery beyond this point, it becomes overcharged.

The key to understanding overcharging is distinguishing between current and voltage. In an electrical system, current represents the quantity of electricity flowing, while voltage refers to the electrical "pressure" level. 

Battery cells are designed to store a designated amount of electrical current at a specific voltage. When they are at full capacity but continue receiving an electrical current, there is nowhere to safely store it. As a result, the current is squeezed into fully-charged cells and the cells’ voltage increases.


What happens if you overcharge a battery?

Overcharging inflicts varying degrees of damage on a battery, ranging from moderate to severe. When a battery is overcharged, its voltage increases, resulting in a rise in temperature. Prolonged exposure to these conditions exacerbates the damage inflicted on the battery. Minor damage from overcharging can lead to a reduction in the battery's capacity or lifespan. However, if the battery experiences sustained overheating, it runs the risk of entering a state known as thermal runaway. This phenomenon occurs when excessive heat reacts with the chemicals within the battery. The consequences of thermal runaway depend on the type of battery being used.


What happens when you overcharge a lithium-ion battery?

The effects of overcharging a lithium-ion battery depend on how long the overcharging occurs. Slight overcharging results in a lithium-ion battery’s cells having a reduced discharge capacity. This, in turn, causes the battery to over-discharge and generate heat, reducing battery life. Prolonged overcharging causes substantial overheating, which may cause the battery to explode or catch fire. These dangers have been highlighted in mainstream media, with some e-scooter and even household batteries causing a fire risk. The Lithium Iron Phosphate (LifePo4) batteries used in all Plico systems have never been recalled or involved in any fire safety incidents.


What happens when you overcharge a lead-acid battery?

Overcharging a lead-acid battery leads to excessive gassing. Lead-acid batteries naturally produce gases when charging, but overcharging exacerbates this process. The increased heat from overcharging boils the electrolyte solution in the battery, causing more hydrogen and oxygen to form. These gases raise the pressure within the battery, creating a need for release. When the pressure is too much for the batteries to ventilate, the water loss from the electrolyte solution destroys the battery. In extreme cases, too much pressure may result in a lead-acid battery exploding.


Why is my solar battery overcharging?

The most likely reason for a solar battery overcharging is the relevant safeguards malfunctioning. The two factors that typically prevent overcharging are a solar inverter and the battery’s built-in protections. An inverter is a device that manages the flow of electricity in a solar system. Certain systems have separate inverters for solar panels and solar batteries. Other systems use hybrid inverters, which do the jobs of both. A faulty inverter may allow too much electricity to flow into a battery, overcharging it. 

Batteries often incorporate built-in protections specifically designed to prevent overcharging. These safeguards work by disconnecting the battery from the electric current once its cells reach full capacity. However, batteries become more susceptible to overcharging when these protective measures are defective or not functioning correctly.


Can you fix an overcharged battery?

Once a battery has incurred damage from overcharging, it cannot be repaired. If the cells of a battery have been negatively impacted by an excessive voltage increase, the damage is irreversible. Even if the damage is minor, using a compromised battery poses a significant safety risk. The probability of overheating increases, which can lead to various unfavourable, and potentially dangerous, outcomes. If you suspect that your battery has been overcharged, it is advisable to seek assistance from a professional who can assess the condition of your battery accurately.

For Plico members, the 10 years of maintenance and support included in their membership covers this.


How to keep a solar panel from overcharging a battery

The best way to keep a solar panel from overcharging a battery is by ensuring your solar system has compatible components in good condition. Mismatched solar system components increase the risk of overcharging your battery. An undersized battery is more vulnerable to overcharging and sustains damage faster as a result. Similarly, an inverter that is too small for your system can’t manage the electricity produced by your solar panels. 

Talking with your solar system installer is the best way to ensure your system works effectively. In addition to providing expert advice, they can provide regular monitoring and servicing. This helps catch system faults before they create problems for you.

Want to make sure your solar system components are compatible? Chat with one of the switched-on Plico team members on 1300 175 426 to see how they can help.