A buyer’s guide to solar charge controllers

If you're considering installing an off-grid solar project with a battery attached, you'll want to look into a solar charge controller for your system. Charge controllers act as a gateway to your battery and ensure that you don't overcharge and damage your energy storage system. In this article, we'll cover what a solar charge controller is and compare the two major types—pulse width modulation (PWM) and maximum power point tracking (MPPT).

A solar charge controller is a regulator for your solar battery that prevents it from overcharging. Batteries are rated for reasonable volts and voltage capacity, and exceeding that voltage can lead to permanent battery damage and loss of functionality over time. Solar charge controllers act as a gateway to your battery storage system, making sure damage doesn't occur from overloading it.

Charge controllers are only necessary in a few specific cases. Most commonly, you will want to look into charge controllers if you are trying to install an off-grid solar system – from rooftop systems to smaller setups on RVs or boats. If you're a homeowner looking to install a solar array with a battery that is connected to the electric grid, there's no need for a charge controller – once your battery is full, excess energy will be directed to the grid automatically instead, helping you avoid overloading your battery. This is known as load control.

To help you find the best match, we created a list of the best portable solar products of 2022. Many of these include built-in solar charge controllers for ease of use.

For the majority of solar shoppers, there's no need to worry about charge controllers. Rooftop or ground-mount solar installations with a battery backup are almost always linked to the electric grid, and in the case that your battery is completely charged, your excess solar energy will automatically reroute there.

If you're interested in installing a small off-grid solar energy system with battery backup, you might need to look into a charge controller to ensure that your battery is safely charged. For relatively small batteries paired with low-output 5-10 watt (W) solar panels, a PWM charge controller should do the job. For more complex DIY solar projects with higher output panels, you may want to consider an MPPT charge controller.

If you want to use solar to go completely off-grid, there are two types of charge controllers to consider: PWM controllers and MPPT controllers.

Pulse width modulation solar charge controllers

PWM solar charge controllers are the standard type of charge controller available to solar shoppers. They are simpler than MPPT controllers and generally less expensive. PWM controllers work by slowly reducing the amount of power going into your battery as it approaches capacity. When your battery is full, PWM controllers maintain a state of "trickle," which means they supply a tiny amount of power constantly to keep the battery topped off.

With a PWM controller, your solar panel system and your home battery need to have matching voltages. In larger solar panel systems designed to power your whole home, panel and battery voltage aren't typically the same. As a result, PWM controllers are more suited for small DIY solar systems with a couple of low-voltage panels and a small battery.

Maximum Power Point Tracking solar charge controllers

MPPT solar charge controllers are a more expensive and complex charge controller option, often coming with items like lcd displays and bluetooth. They provide the same switch-like protection that a PWM controller does and will reduce the power flowing to your home battery as it nears capacity.

Unlike PWM controllers, MPPT charge controllers can pair non-matching input voltages from panels and batteries. MPPT controllers adjust their input to bring in the maximum power possible from your solar array and can also vary their output power to match the attached battery. This means that MPPT charge controllers are more efficient than PWM controllers and more effectively utilize the full power of your solar panels to charge a home battery system.

If efficiency were the only concern in purchasing a controller, an MPPT controller would be the best choice every time. But it's not always practical. Selecting the right solar charge controller involves several factors beyond just efficiency.

PWM vs. MPPT solar charge controller comparison

To determine what controller is right for you, answer these questions:

What type of panels do you have?

Most off-grid solar panels are 36-cell panels designed for 12-Volt battery charging current and amperage ratings of typically around 30 amps. These systems work well with PWM controllers and lithium batteries. 60-cell and 72-cell panels are typically used with a grid-tie solar panel system and have a higher voltage (24-volt systems or more), thus requiring an MPPT controller.

How big is your system?

A PWM controller works with any system size as long as the voltage between the solar power system and home battery are matched, even at low voltage —though typically, they don't match in larger systems, making a PWM ideal for smaller setups. MPPT controllers are less efficient unless your array is at least 170 W.

What temperatures can you expect?

MPPT controllers work better than PWM controllers when it gets colder. As the temperature drops, the voltage increases, and an MPPT controller can capture the excess voltage. In warm climates where the temperature doesn't typically get very low, there isn't extra voltage and an MPPT controller isn't necessary. Temperature sensors are another additional feature that could be added.

What is your budget for a controller?

In general, MPPT charge controllers are more expensive than PWM controllers due to their higher charging efficiency. An MPPT controller can reach up to 20 percent higher efficiency – this is due to its four-stage charging method, which is healthier for your battery life. PWM solar charge controllers are more versatile and more easily installed, but their lower efficiency usually means lower prices.

Once you've determined which type of solar charge controller you need, it can be challenging to decide which specific brand to purchase from. We've listed out some of the major brands and their products to help you get started.

Buyer's guide: solar charge controllers

Renogy

Renogy produces DIY-friendly products for off-grid projects of all sizes. Their offerings include solar panels, batteries, inverters, and more. Their line of charge controllers is ideal for small projects that require a PWM charge controller or larger projects that need the more robust MPPT charge controller. Each type of charge controller comes in different sizes, so you can match your system's requirements.

BougeRV

BougeRV is a reliable resource for RV travelers and others seeking off-grid power solutions. Both their PWM and MPPT chargers are well-rated and have size and compatibility options to make them work with your system. BougeRV also develops other outdoor appliances and power solutions, which is great if you are concerned about overall system compatibility.

Victron Energy

Victron Energy offers a wide range of off-grid energy supply and storage solutions. The company has been in the industry for 45 years and continues to develop new products to meet changing consumer needs. The amp MPPT charge controller linked above is just one of many they have at different sizes and price points to suit your system requirements.

Are charge controllers necessary for a solar panel system?

Charge controllers aren’t necessary for all solar panel systems – but they are necessary for any solar-plus-storage system that is off-grid. They provide the essential function of preventing batteries from overcharging and discharging when panels are not in use. If your solar system is connected to the grid, it does not require a charge controller, as any excess power will be diverted from your battery system and directed back to the grid.

How big of a solar charge controller do I need?

Multiply the number of panels and wattage of each panel to get the total watts (more likely kilowatts) of the solar array. Then, divide this number by the voltage of your battery bank to get amperage. Finally, add 25 percent if you live in a colder climate.

Where can I purchase charge controllers?

Solar charge controllers can be purchased online at major retailers including Amazon.

On the EnergySage Marketplace, you can register your property to begin receiving quality quotes for solar installations. If you are interested in storage solutions to pair with your panels, you can simply indicate your interest on your profile for installers to see. Connecting your solar project to the grid (even with battery backup) is a smart move, as it provides a second backup for your system, and in the case that your battery storage capacity isn't enough, you won't simply run out of power to use.

While going completely off-grid with a DIY solar project may work in some cases, if your main concern is saving money, hiring a qualified installer to help you go, solar is still a sound financial decision. What's more, having a professional installer work on your solar project ensures that you are getting the expertise you need to have a functional and effective solar system. Installers also offer warranties and protections for their products that you can't always get with a DIY project. If you want to see how much you can save by going solar, check out our Solar Calculator for an instant estimate based on your unique property.