Solar Charge Controllers: What They Are, Why You Need One and Cost (2023)

Oct 22, 2023

A solar charge controller regulates voltage and current when you use photovoltaic panels to charge a battery. Without this device, your batteries would be damaged by overcharge.

Charge controllers are only required in off-grid solar systems. They are not necessary in grid-tied systems, since the inverter sends excess energy to the grid automatically. While the price of a solar charge controller can range from about $20 to $500, it's important to keep in mind that an off-grid system has a higher cost overall than one tied to the grid. The best solar companies will advise you on whether you need one and will ensure everything is set up correctly.

If you connect a battery directly to your home's solar panels, there is no device controlling the charging process. In this case, your battery will most likely be damaged by excessive voltage and current. A solar charge controller or solar regulator accomplishes three important functions:

A charge controller can be described as a smart battery charger, and this device is very important when charging a battery with solar panels. Their voltage and current output varies depending on sunlight, and batteries need a stable and controlled input.

The main function of solar charge controllers is regulating battery charge, but they can also provide electrical protection by:

Solar charge controllers are only necessary in off-grid systems. Most home solar systems are connected to the grid, and no charge controller is needed in this case.

The configuration of a solar power system with a battery bank changes depending on the type of inverter. You can use a hybrid inverter, which connects to solar panels and batteries simultaneously, or you can have a separate solar inverter and battery inverter. In both cases, the inverter has a built-in charge controller function, and you don't need a separate device.

Solar charge controllers can be classified into two main types: pulse-width modulation (PWM) controllers and maximum power point tracking (MPPT) controllers.

PWM solar charge controllers are simpler and more affordable, but also less efficient. PWM controllers reduce their current output gradually as the battery charges. Once the battery reaches 100% charge, the controller can keep it full by providing small amounts of power without overcharging.

PWM charge controllers are designed to be used with solar panels that match the battery voltage. For example, if you want to charge a 12V battery, you also need photovoltaic modules with a rated output of 12 volts.

According to EnergySage, you can expect to pay between $15 and $125 for a PWM solar charge controller, where the price depends on the rated wattage and amperage. PWM controllers have a typical efficiency of less than 80%.

Pros and Cons

MPPT solar charge controllers are also known as smart DC-to-DC converters, and they are more advanced than PWM controllers. An MPPT charge controller can match a battery system with solar panels of higher voltage.

According to EnergySage, you can expect to pay between $28 and $324 for an MPPT solar charge controller. The best MPPT controllers can reach an efficiency of over 95%.

As a quick example, assume a small solar array is operating at 36 volts and 10 amps, providing 360 watts of power. Using a PWM charge controller, you cannot use this power output to charge a 12V battery. However, an MPPT charge controller can lower the voltage to 12V while increasing the current to 40 amps, which makes charging possible.

Pros and Cons

+ You can charge batteries with solar panels of higher voltage

+ Up to 20% more efficient than PWM charge controllers

– Can handle higher wattages efficiently

– MPPT technology is more expensive

– Installation is more complex

– Less efficient in systems smaller than 170W

Before purchasing a charge controller, you should check its technical specifications carefully. If there is a mismatch between your charge controller and your solar panels and batteries, your system will not work, and you may even damage components.

Your charge controller should be compatible with the output voltage supplied by the solar panels and the input voltage required by the battery. These voltages are equal when you use a PWM controller, but the solar panel voltage can be higher when you use an MPPT controller.

Like in any electrical system, you also need current compatibility between components. Your charge controller should not exceed the rated input current of your battery, and it should be able to handle the highest possible current from the solar array. For example, if your battery system has a maximum current of 30 amps, you should not use a 40-amp charge controller.

The charge controllers used for renewable energy systems such as solar panels and wind turbines are often equipped with a diversion load, which is used to dump excess energy once the battery is fully charged.

Many charge controllers include an LCD display where you can check operating parameters or a Bluetooth module that allows monitoring via smartphone. Ideally, you should look for a charge controller capable of displaying its operating conditions.

High temperature can greatly reduce the service life of your battery, but the best charge controllers have a temperature compensation feature. They monitor the battery with a temperature sensor, and they reduce the charging voltage as necessary to prevent overheating.

The efficiency of your charge controller is an important metric, since it determines the amount of solar energy that gets converted into battery charge. MPPT charge controllers can achieve a charging efficiency of over 95%, but they are more expensive. PWM charge controllers are generally less than 80% efficient, but they are also more affordable.

Solar charge controllers are not very expensive on their own. Even a high-quality MPPT controller may only cost a few hundred dollars, making it one of the cheapest components of an off-grid solar system. However, the total cost of an off-grid system is typically much higher than one that's connected to the grid, potentially by tens of thousands of dollars.

The difficulty of installing a charge controller can vary depending on the specific product you purchase and the size of your system. Some charge controllers have a simple plug-and-play design, which means you only need to connect solar panels and batteries of matching voltage and current ratings.

However, if you need a large off-grid solar system for a home, a professional solar installation is strongly recommended. The power and current ratings involved are higher, and DIY projects can be dangerous.

Since charge controllers have no moving parts, their maintenance needs are very simple. However, you should check the wiring regularly, since loose connections create electrical resistance and heating. Having a charge controller with an LCD display is also helpful for maintenance purposes, since the screen will notify you of any issues that need attention.

There are many charge controller providers in the market, and reading product reviews is strongly recommended before making your purchase. Victron Energy and Renogy are widely regarded as two of the best brands:

Victron SmartSolar Series = 12/24/36/48V, 10–100 Amp MPPT controllers

Renogy Rover Series = 12/24/36/48V, 20–100 Amp MPPT controllers

Solar charge controllers are necessary to charge batteries safely in off-grid solar systems. They can be used with both lead-acid and lithium batteries, but you must ensure that their voltage and current ratings match.

If you plan to install solar panels in a home that will remain connected to the grid, there is no need for a charge controller. A hybrid inverter or a battery inverter can control the charging process by itself, and excess electricity is simply sent to the grid.

Keep in mind that off-grid home solar systems are more expensive than grid-tied systems. The typical cost of a home solar system is $15,000 to $20,000, and it can drop below $10,000 after incentives like the federal tax credit. However, an off-grid solar system can exceed $50,000 since it needs large batteries and additional control systems.

The size of the solar charge controller depends on the total wattage of your solar panel system and the size of your battery. You need a charge controller capable of handling the voltage and current output of your panels, while providing a suitable voltage and current input for the battery.

MPPT charge controllers are recommended if you want maximum charging efficiency, and for larger off-grid installations with multiple panels.

PWM charge controllers are less efficient, but cost-effective for small portable solar systems.

Both PWM and MPPT controllers have pros and cons. PWM controllers are more affordable, but MPPT controllers are up to 20% more efficient. PWM controllers are cost-effective in low wattage systems, while MPPT controllers are recommended for solar systems over 170W.

The two types of solar charge controllers are pulse width modulation (PWM) and maximum power point tracking (MPPT).

Leonardo David is an electromechanical engineer, MBA, energy consultant and technical writer. His energy-efficiency and solar consulting experience covers sectors including banking, textile manufacturing, plastics processing, pharmaceutics, education, food processing, real estate and retail. He has also been writing articles about energy and engineering topics since 2015.

Sabrina Lopez is an editor with over six years of experience writing and editing digital content with a particular focus on home services, home products and personal finance. When she is not working on articles to help consumers make informed decisions, Sabrina enjoys creative writing and spending time with her family and their two parrots.