Can A Solar Panel Overcharge A Battery?

In solar PV systems, batteries are responsible for storing solar energy so that it can be used later.

However, what if the amount of energy being sent to the battery by solar panels is more than what the battery can handle?

Will solar panels overcharge a battery?

The answer is YES.

It is possible to overcharge a battery if batteries are not connected to a charge controller or the charge controller is not properly configured to regulate the amount of power entering the battery.

When there is no charge controller installed, solar panels continue to charge batteries at full power, regardless of how much energy they are absorbing. The result is overcharging and damage to the battery cells.

Therefore, the only way to protect batteries from overcharging is by using a charge controller or disconnecting them once they are fully charged.

Charge controllers used in solar PV systems are generally named “Solar Charge Controller (SCC)”.

Why do you need an SCC (Solar Charge Controller)for a solar PV system? 

A solar panel is a device that converts sunlight into electricity by the photovoltaic effect. A battery then takes this stored energy and releases it as a current through an electric circuit to do work, such as powering your home appliances.

However, there is no way for a solar panel to check how full the battery is, and thus stop charging it. If you don't have a charge controller, the solar panel will keep sending electricity to your battery to point that it damages it or even explodes.

The charge controller regulates the voltage and current from a solar panel in order to prevent batteries from being damaged by deep discharging or overcharging. A number of different kinds of charge controllers are available, each with its own pros and cons depending on your needs for power output, battery type, budget, etc.

But the main thing is that they prevent your solar panel from overcharging and damaging your battery. By doing so prevents overcharging and thus extends battery life while using rechargeable batteries like Lead Acid, Lithium Iron Phosphate, or Nickel-based Batteries that are commonly used in solar energy systems.

Overcharge happens when there's a mismatch between the charge controller's voltage regulation and battery bank.

In a 12-volt system, if your solar panel produces 17 volts or more, set it to 13.0-13.30V to avoid overcharging your batteries (the two important things to remember here are that the voltage cutoff is set by SCC and not panel and that batteries can take a lot more current than panels produce).

This may seem counterintuitive as you might think of it as “overvoltage” but the batteries can actually take a lot more than 13.0-13.30V, and the panels only produce 17+ volts for short periods of time (it depends on how much light they are getting).

If left alone, overcharge would cause the batteries to heat up, release gasses, and decrease their useful lifespan.

Blocking diodes are used between the panels and the battery bank for a very similar reason. To prevent backflow from batteries into the solar panels when they are out of light which means that they can no longer produce electricity.

Another thing to mention is the solar charge controller will also prevent overcharging and has an auto shut-off feature, usually between 13.0-13.45 volts depending on the model of the controller itself (it should be mentioned in its manual).

So if you are using a controller, you do not have to worry about any of the above-mentioned risks.

What do all these mean then?

Solar panels will not overcharge batteries if there is no light or they produce less voltage than what your battery bank requires (which happens when it's dark). But even in this case, blocking diodes and charge controllers will save your batteries and prevent under and overcharging.

A solar panel will not overcharge your battery if you have the appropriate equipment (a solar charge controller) or when there is no light. But even without them, it won't cause any damage to your system as long as the voltage is within the required range for charging!

So far we have mentioned the importance of having the SCC (solar charge controller) in your energy solar PV system. But not all SCC is created equal. There are two most commonly used SCC: PWM and MPPT.

PWM stands for Pulse Width Modulation, while MPPT is a Maximum Power Point Tracking. Both of them are equally good, but the main difference between these two types is that a Solar Charge Controller with maximum power point tracking can extract more energy from solar panels than others.

Let's take a closer look at the difference between PWM and MPPT.

MPPT Charge Controller

A Maximum Power Point Tracking (MPPT) charge controller is a device that is used to extract maximum power from a solar panel at any given time. It does this by tracking the output of your solar panels and adjusting the voltage to match them to the batteries.

It is the best SCC option for your solar panel and battery bank because it can be set to provide a lower voltage than what's needed to prevent overcharging.

The MPPT controller can extract a little bit more energy from your solar panels due to the fact that it is constantly matching the voltage of your solar panels to your battery.

This means you can get more charge in a shorter period of time, which results in less wear on both components.

In many installations, MPPT Charge Controller even replaces blocking diodes that protect against discharging a battery bank through the solar panel at night. This way, an MPPT charge controller prevents both under-voltage and overcharge.

Pulse Width Modulation (PWM) Charge Controller

A Pulse Width Modulation (PWM) charge controller is a device that adjusts voltage in accordance with battery level and reduces it when needed, thus preventing overcharging of your solar power system's batteries.

PWM controllers are less expensive than MPPT controllers, but they aren’t as efficient therefore they are typically recommended for use in smaller systems.

Why should you avoid overcharging batteries?

Overcharging is a common cause of battery failure. It can also reduce the overall performance and lifespan of a battery bank.

A typical battery is rated for a particular number of charge-discharge cycles, or its useful lifespan in years.

However, if you overcharge the batteries they will gradually lose their capacity to hold a full charge until they can no longer accept a full charge, thus reducing their overall lifespan.

A battery bank is only as good as its weakest cell in most cases and you don’t want to do anything that will reduce the capacity of your batteries over time.

Also, overcharging batteries will increase the internal temperature and pressure within a battery bank by forcing current into a battery that cannot accept it. This increase in temperature and pressure can cause them to explode and/or catch fire.

If you are using lead-acid batteries for your solar-powered system, the batteries need to be equalized from time to time.

Equalization is a process that restores the batteries’ capacity by forcing current into all of the cells, even ones that can't accept it normally. It prevents the accumulation of negative chemical effects such as stratification, which occurs when the acid concentration is higher at the bottom of the battery than at the top.

Equalizing also aids in the removal of sulfate crystals that may have formed on the plates. If left uncontrolled, this condition, known as sulfation, will lower the battery's overall capacity.

If you have lithium-ion batteries, you don't have to worry about sulfation, as it is not a problem with these battery types.

Oversized Solar Panels Can Cause Overcharging

If you have a solar array that is significantly larger than the battery bank, it will attempt to overcharge the batteries at all times. This is because the solar array will continue to deliver power even after your batteries are fully charged.

If you have a charge controller in place, this overcharging does not harm your battery. However, it can significantly reduce their lifetime if left unchecked for a long period of time.

Therefore, if you have a solar array that is larger than your battery bank, you should consider investing in more and/or higher capacity batteries.

Why is proper battery management important?

A lot of solar PV system owners assume that batteries are “maintenance-free” and that they should not be checked or replaced for the life of their system. However, this assumption is incorrect.

Batteries are electrochemical devices that are sensitive to the temperature, charge level, and charging environment. Therefore, they need regular maintenance in order to last as long as possible.

If you fail to provide adequate battery care or replace your batteries when needed, the overall performance of your solar PV system will suffer. Ultimately this can lead to the complete failure of some or all components in your system.

How to maintain solar PV system batteries?

Batteries require proper care and maintenance. But, with so many different battery types, how do you know what maintenance is required?

Here is what kind of maintenance is needed for the most popular solar PV system batteries.

Lead-acid batteries

Lead-acid batteries are the most popular choice when it comes to solar PV system batteries. Maintenance for these types of batteries is simple and straightforward but critical to maximizing battery life.

Here is what you need to do if you want to maintain your lead-acid batteries:

• Check the specific gravity in each cell once a month with a hydrometer. Make sure it is in the acceptable range for the type of battery.
• Clean the battery terminals with a wire brush and baking soda once every six months, or more often if the connection at the terminal is loose or corroded.
• Ensure that all vent caps are tight so they do not evaporate electrolytes in storage. This will get rid of the sulfation that occurs when batteries are not fully recharged after use.
• Every month, remove the filler caps and check the electrolyte level. Fill the battery to just above the battery plates with deionized or distilled water. Don't overfill, and remove any water spills immediately.
• Equalize them once a month or every 10 discharge cycles: An equalizing charge for a 12-volt battery needs that it be charged at a voltage of at least 14.4 volts An equalizing charge avoids battery stratification and lowers sulfation, the major cause of power failures.
• The battery must be securely fastened in its cradle. Battery vibrations can cause damage to the battery plates. Battery terminals that are loose or corroded might cause problems.
• Keep them cool and dry with specific ventilation requirements for each manufacturer's product line to prevent thermal runaway.

It is very important not to smoke or have naked flame nearby when working on a battery since batteries create hydrogen gas. Lead-acid batteries should be stored in moderate temperatures because they cannot tolerate extreme temperatures.

Lithium iron phosphate (LFP) batteries

Although Lithium iron phosphate (LFP) batteries do not require maintenance, the location in which they are installed may have an impact on performance.

To optimum performance, all lithium batteries contain a battery management system (BMS) that automatically checks each battery cell for temperature, state of charge, cycle life, and other factors. Maintenance is minimal as long as the storage system is installed in suitable temperature and altitude ranges.

However, it is critical to keep the battery temperature away from extremes to guarantee proper functioning. It is not necessary to prepare the batteries for seasonal temperature variations.

LFP batteries can be overcharged, overheated, and even physically damaged by a car running into them in a garage while they are still safe. Choosing the safest chemistry as the basic element for the system is vital when employing batteries in or near residential spaces.

Lithium nickel manganese cobalt oxide (NMC) batteries

The NMC chemistry, like all lithium battery chemistries, does not require much maintenance. The BMS will monitor cell voltages, currents, and temperatures to guarantee safety and extended life.

Excessive operation reduces battery life, and BMS records excursions to inform warranty claims. In the event of potentially hazardous operating situations, the BMS shuts off the system.

As long as safe temperature ranges are observed, there are no particular guidelines for winter use for NMC batteries. If they need to be stored for a season, they should be done so indoors.

Flow batteries like Zinc bromine (ZNBR)

ZNBR flow batteries are ideal for large-scale, long-duration energy storage. Flow batteries function similarly to fuel cells, therefore they are just boxes with electronics and an electrolyte tank.

Most types require a yearly maintenance visit from a professional O&M specialist for basic inspection, new air filters, and electrolyte topping off. Flow batteries do not need to be winterized and can be deployed in extremely cold temperatures.

Nickel-cadmium (NiCd) batteries

Nickel-based batteries are good for remote, off-grid installations since their composition is suitable for demanding applications requiring stable backup power and where maintenance cannot be undertaken on a regular basis.

They perform excellently in severe temperatures and deep discharge circumstances.

Electrolyte levels in NiCd batteries should be monitored and replenished on a regular basis, just as lead-acid batteries.

Because nickel batteries can operate in a wide temperature range, they do not need to be prepared for extreme cold in the winter, but the space in which the battery is housed should not drop below -22°F. NiCd batteries can be stored (unconnected to a load) for up to 12 months if kept dry and within the proper temperature range.

Owners of NiCd batteries may easily do voltage readings and electrolyte level checks. Water additions can be performed by the owner, but they must be familiar with the safety considerations mentioned in the installation and operating instructions.

Capacity tests and other electronic testing should be performed by qualified specialists.

Battery Management Practices Applicable All Type of Batteries

There are certain practices that are universal to all batteries, including the following:

1. Avoid overcharging and undercharging batteries.
2. Maintain the correct charge voltage.
3. Avoid keeping a battery fully charged for an extended period of time connected to a load.
4. Avoid draining a battery fully, especially if it is flooded with lead-acid or lithium-ion batteries.
5. Make sure that the source of power to your battery bank does not share any common wiring with other electrical.
6. Do not expose batteries to excessive heat or cold temperatures. The ideal temperature range is between 20°F (-28°C) and 100°F (37°C).
7. Ensure that there is no physical damage to batteries, cables, or electrical connections.

Conclusion

It is possible to overcharge a battery if you don't have a charge controller installed in your system.

Because a charge controller regulates the amount of power flowing from a solar panel to your battery bank. If you are unsure if your panel is overcharging the battery, check with manufacturer specs on how to properly set up a charge controller.

Batteries deteriorate with time and usage, reducing their capacity and extending their life span. Knowing how to properly take care of your batteries will ensure that you get the most out of them. This will not only save you money but make your solar system safer.

It's better to be safe than sorry, given all of these factors. Be sure to follow all of the manufacturer’s guidelines for your batteries at all times. your solar cells.