Solar Panels Overcharging A Battery (Batteries Full)

If you wonder how to keep a solar panel from overcharging a battery, rest easy, as the process is pretty simple. Some additional pieces of information are essential:

  • Keep you safe
  • Extend battery life
  • Increase energy independence, 
  • Decrease reliance on grid-based energy. 

Because solar batteries are costly, it is essential to understand how to protect them from early burnout and premature replacement. 

Can you keep a solar panel from overcharging a solar battery? Yes, you can. 

In this blog, we discuss the following: 

  • How do you keep a solar panel from overcharging a battery
  • The issues around why a solar panel can overcharge a battery
  • Solar battery health and safety 
  • The different types of solar controllers
  • And some other essential bits of information. 
Batteries Overcharged

Can you overcharge a battery with solar?

You can. The solar panel or solar array and the battery do not communicate. If left unchecked, the solar panel will continue to feed energy to the battery until the battery stops functioning, explodes, or potentially catches fire. 

How Do You Keep A Solar Panel from Overcharging A Solar Battery?

You might think connecting a solar panel directly to a solar battery is okay. After all, solar panels and batteries both use DC voltage.

However, when you connect the solar panel to the solar battery is overcharging because the solar panel cannot tell when the battery is approaching full saturation or fully charged.

Therefore, the panel continues to send energy to the battery. Here is what happens when solar battery overcharging occurs:

  1. The internal parts of the batter heat up when charging is underway. If you have ever taken a batter out of a household charger, you might remember it being warm. That heat is caused by energy entering the battery. 
  2. As overcharging occurs, the battery continues to heat up. Inside the battery are chemicals or enzymes that work to store energy. The hotter they become, the more they change until they stop working. 
  3. After the enzymes stop working, the batter still receives energy from the panel. What happens here is the temperature of the battery builds as more energy continues pumping into the battery. At this point, the fluid in the battery or enzymes evaporates as the heat builds. Solar batteries either have lead-acid, lithium-ion, or saltwater as fluid.
  4. If overcharging occurs long enough, the battery can explode or catch fire — self-combust. 

Overcharging a solar batter decreases its lifecycle quickly. One overcharging episode can ruin a solar battery. 

See also: How to Charge a Battery with a Solar Panel: A Comprehensive Guide for Beginners

What Is The Problem with Solar Panels and Solar Batteries?

The problem, and there can be a few, is that the solar panel does not know when the solar battery is full. Solar panels are not smart devices, so they continue to pump energy into the battery.

The solar battery is also not a smart device. It cannot communicate with the solar panel and tell it when the charging cycle is complete. 

That is a big problem because solar batteries for a solar array can easily cost one-half the total cost of the array.

Another problem is that solar batteries have a shorter lifecycle than the array. That means that you will have to replace the batteries at least once before replacing the solar panels.

Therefore, it would be best to protect solar batteries, so that premature die-out does not occur for those reasons. 

What Is the Solution for Solar Panel and Solar Battery Communication?

The solution to prevent solar panels from overcharging solar batteries is a solar controller. These in-line devices are sometimes called solar regulators.

They monitor the energy level of the battery and decrease or shut off power from the solar panel. The result is the battery charges without overcharging. 

We did warn you at the beginning that the answer was pretty simple, and it is. You can think of solar regulators as gas pedals on vehicles.

The more your press the throttle down, the more the engine revs. The less pressure you put on the gas pedal, the slower the engine goes.

That is really what the solar controller does. It speeds up the flow of energy, or it decreases the flow of energy. 

While the solution is simple, there is more information you may find essential. 

Are There More Than One Type of Solar Controller? 

Suppose you are excited that there is an easy solution to keeping solar panels from overcharging batteries. In that case, you might be surprised to find out that there are different types of solar regulators. Unfortunately, not all of those are suitable for entire solar arrays. 

The different types of solar regulators include four applications. Those are:

  1. Shunt Regulators
  2. Series Regulators
  3. PWM Regulators
  4. MPPT Charge Controllers 

They each work slightly differently, but all regulate the power between a solar panel and a solar battery. These are also different from solar inverters.

A solar inverter changes the electrical wave shape from DC to AC. They do not regulate power. Here is a short description of each type of solar regulator. 

Shunt Regulators

These work by shutting off the flow of electricity or turning it on. They also can and do pulse energy to the battery as the battery nears the fully charged state.

When the battery’s energy level drops, the shunt regulator opens the “valve,” and energy flows to the battery.

When the battery is not in use, a trickle or pulse of energy now and then keeps the battery full. 

Some regulators will only allow energy to flow to the battery when it discharges a certain percentage of its energy. 

Series Regulators

Control the connection within a circuit — Solar Array to Series Regulator to Solar Battery. When the battery level is nearly complete, the series regulator breaks the circuit so that the solar array cannot send energy to the battery.

In grid-tied systems, the solar regulator may shuttle energy away from the batter to an inverter where the excess energy would enter the grid, and solar credits may begin “flowing.” 

Pulse Width Modulation (PWM) — differs from series regulators just slightly.

With a pulse width modulation regulator, a transistor keeps the voltage at an even flow. The transistor also adjusts the energy flow. 

There is a relay instead of a transistor with a series regulator that either allows energy to pass or blocks it completely. It is an on-off unit where a PWM determines how much energy should pass to the battery and opens or decreases energy flow. 

Maximum Power Point Tracking (MPPT)

You could say that the MPPT controller is an improved PWM. The MPPT converts the DC energy from the solar array into AC voltage and then reconverts to DC voltage but at a voltage or current level that matches the battery.

These are highly efficient and less stressful on batteries.

Which Type of Solar Controller You Need? 

You would choose between a PWM or an MPPT controller for larger arrays. Both are acceptable and do a fine job of protecting the battery. However, the MPPT controller is more sophisticated, and the energy that enters the battery is more streamlined. 

For smaller arrays and single-panel solar stations, any of the four controllers that we discuss are suitable. You often find shunt regulators and series regulators in smaller gadgets. 

Now that you know that you can protect a solar battery from overcharging, the big question is, how do you connect a solar regulator to the battery and the solar panel. 

Can I Leave a Solar Trickle Charger on All the Time?

You can leave a solar trickle charge on all the time as a Trickle Charger send such a small amount of voltage that there is little danger of overheating or overcharging the batteries.

These are excellent devices for small appliances and gadgets, such as cell phones and laptops. They are also excellent for off-grid applications when a home power outlet is unavailable or tied to the grid. 

Where Does Solar Energy Go When Batteries Are Full?

When your solar battery system fully charges, any excess power is shuttled to the inverter, which inverts the energy from DC to AC.

From there, the power is used by the home or equipment to which the inverter connects. If there is still extra energy available, the inverter shuttles it to the utility grid.

If the energy goes to the utility grid, you may receive solar credits if your utility company has a solar credit program.

What happens when off-grid solar batteries are full?

If there is no use for extra solar energy, the energy is lost through heat transfer. If your solar array produces too much power, the extra power is called an opportunity load.

You can disconnect solar panels to lower energy production or increase energy consumption. Heating and AC are two of the most significant users of energy in a home.

You could increase the ambient temperature in winter or blast the AC in summer. 

Can A 5 Watt Solar Panel Overcharge A Battery?

Absolutely a 5-watt solar panel can overcharge a battery. That process is dependent upon the relationship between the panel and the battery.

The battery would need to be 12-volts or smaller. You can prevent overcharging the battery by installing a solar converter or regulator. 

Do You Need to Know How To Connect a Solar Regulator To The Solar Circuit?

A solar circuit links the solar panels to the solar battery or other solar components, such as a controller or inverter. 

The good news is many solar controllers have snap connectors that connect them to the solar panel. If not, then direct wiring is necessary.

You will need to understand wiring basics and how to work with electricity safely. The solar controller connects to the solar batteries through a series of connections.

The raw wire inserts into a port, and a screw mechanism secures it in place. The other end of the wire connects to the battery with a clamp.

Other systems also connect the solar controller to the battery, but the port and clamp method is prevalent. 


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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