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What is a solar charge controller?

How to choose the right one for your off-grid system

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    solar charge controller

    A solar charge controller is a device found in a photovoltaic (PV) energy system that controls the amount of power that can be transmitted to an electric storage battery. By controlling the charge sent to your battery, charge controllers regulate and condition the solar power generated by your panels for efficient storage and to prevent your system from “overcharging.”

    If you’re planning a grid-tied solar panel installation for your home, it’s unlikely you need a solar charge controller as part of your system. While it’s important to talk to a professional about any new solar energy system, charge controllers are typically only required in battery-backed “off-grid” or “hybrid” installations.

    Key insights

    • Charge controllers are essential when installing solar batteries.
    • MPPT charge controllers are more expensive and efficient than PWM devices.
    • Choosing the right charge controller size can maximize your system’s performance.

    What does a solar charge controller do?

    Solar charge controllers prepare the electricity generated by your panels to be stored (or not stored) in your battery reserve. While stand-alone “grid-tied” solar panels send their electricity directly through an inverter before it heads to the grid, battery-backed systems have a different process to ensure safe and efficient energy production and storage.

    In an off-grid solar energy system, power generated by the panels travels through the charge controller and into the battery in the form of DC electricity. Once discharged from the battery, the power is sent through the inverter to be used in your home as AC electricity.

    Finding the right charge controller is essential when designing an off-grid solar system. Without one, your battery would lose its efficiency very quickly.”
    — Hayden Kleinhans, manager of land development, Invenergy

    Hayden Kleinhans, manager of land development at Invenergy, a multinational sustainable energy company, emphasized that “finding the right charge controller is essential when designing an off-grid solar system. Without one, your battery would lose its efficiency very quickly.”

    Let’s say you’ve installed a large solar array and want to wire the panels directly to your battery. Without a charge controller, the energy would continue to flow into your battery when the sun is shining, even if its reserve capacity is full. Overcharging a battery can lead to reduced storage capacity, multiple safety hazards and possible malfunctions, so solar charge controllers add a necessary layer of overcharge protection for your PV system.

    Types of solar charge controllers

    In the wide world of solar energy technology, there are two main types of charge controllers: pulse width modulation (PWM) and maximum power point tracking (MPPT).

    PWM charge controllers

    As a longer-standing technology, PWM charge controllers utilize a more basic (and inexpensive) form of solar energy regulation than MPPT devices. PWM charge controllers work by slowly limiting the amount of electric power that can be sent to a solar battery until it reaches capacity.

    To understand how a PWM charge controller works, imagine you are filling a glass of water at the sink. In this scenario, the glass is your battery, and the water is new solar energy. If you were to place a PWM charge controller on your faucet lever, you could start filling your glass with a bunch of water at once, then slowly reduce the flow until the glass is full.

    MPPT charge controllers

    Although more expensive than PWM devices, MPPT charge controllers offer more efficient battery charging than their cheaper counterparts. MPPT charge controllers work by actively regulating the amount of solar electricity sent to a battery at optimal efficiency.

    In the example above, an MPPT charge controller would also slowly decrease the water pressure from your faucet until your glass is almost full. However, if water were to leave your glass (i.e., if electricity were to leave your battery), an MPPT charge controller could then speed the flow of water, while a PWM would remain a trickle until the glass is full.

    With the ability to regulate electrical flow with more flexibility, MPPT charge controllers are more helpful in capturing the maximum amount of solar power generated at different intensities throughout the day.

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      How to select a solar charge controller

      When designing your off-grid solar energy system, selecting the right solar charge controller is crucial to maximizing the efficiency of your power generation and storage. Although the technology can be a little intimidating for first-timers, there are a handful of things to pay attention to while making your purchase.

      PWM vs. MPPT: MPPT charge controllers are recommended to get the most "juice" from solar panels in most off-grid solar energy systems. While PWM devices can do the trick for simple, single-purpose systems (such as solar energy lights or a solar-powered gate opener), MPPT charge controllers can adapt more quickly to real-world changes in energy potential and battery use.

      PWM controllers are cheaper and can work for small systems, but if you have a standard solar system and can afford an MPPT device, that’s the way to go.

      Input rating: A charge controller’s input rating, measured in both amperes (amps) and volts, corresponds to the amount of solar power the device can process. Your charge controller’s input rating should match the voltage of your battery and solar array, with most DIY systems rated at  12, 24 and 48 volts. Your charge controller’s amperage input rating is recommended to be slightly higher than the amperage of your expected solar production.

      Cost: While it can be tempting to go for a cheaper option, solar charge controllers are a vital part of an off-grid solar energy system. With everyday use, opting for a higher-price charge controller can help guarantee better overall performance and return on investment.

      Warranty: It’s always a good idea to verify your charge controller’s warranty period. In the event of a part malfunction, a charge controller replaced under warranty can help limit additional costs for your off-grid solar energy system.

      Stand-alone charge controllers vs. integrated systems

      When you're evaluating your options for an off-grid solar energy system, you'll likely stumble upon a few portable solar generators. Solar generators are typically paired with a set of portable solar panels, which makes it simple to purchase a charge controller that’s already packaged with a battery and other system components for maximum compatibility, efficiency and performance.

      Whether you’re planning an installation in your city or way off the grid somewhere, consider talking to a professional solar energy company first. By working with an expert, you can maximize your budget with a safe and efficient solar energy system design.

      ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
      1. University of Evansville, “Solar Charge Controller.” Accessed Feb. 9, 2023.
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