A solar charge controller uses a solar+storage system. The solar+storage system enables customers to use solar energy off the grid, either full-time or as a backup in the event of power failures. The controller controls the amount of energy sent to the battery backup so the battery does not exceed its voltage capacity – thereby extending battery life and preventing damage to it.
Depending on the type of solar and storage system you have, you may need a solar charge controller. In this article, we’ll go through everything you need to know about this tool.
advantages and types
A solar panel’s performance can vary depending on solar radiation, ambient temperature, the quality of the solar cells in the panel, and other factors. All of these factors affect the efficiency of the modules in converting sunlight into electricity.
A solar charge controller compensates for these fluctuations so that the batteries are constantly and safely supplied with electricity. It also sends a “trickle charge” when the battery is almost full. Because batteries regularly lose a small amount of charge, trickle charging keeps the battery replenished without overcharging it.
If you have a grid-tied solar and storage system, either on the ground or on your roof, you most likely do not need a solar charge controller. Your surplus solar energy automatically flows into the grid when your battery is full. But if your solar system is off-grid, a controller could be a wise investment.
There are two main types of solar charge controllers, Pulse Width Modulated (PWM) and Maximum Power Point Tracking (MPPT). PWM controllers are better suited for small solar and storage systems with low-voltage modules and small batteries. MPPT controllers are more expensive but have more features and benefits; They are recommended for any solar system over 200 watts.
PWM controller
The main function of a PWM controller is to protect your battery by ensuring that solar panels are at the same voltage as the battery. The voltage of the battery must match a solar panel’s ‘nominal voltage’ – ie the voltage that the panel is marketed as, although the actual voltage may vary and is often slightly higher.
As the name suggests, a PWM controller controls the flow by pulsing the power sent to the battery to slow down or speed up the charging process. Some PWM controllers can only handle one voltage level, while others can handle different levels. In any case, the voltage of the battery and panel must still be the same.
PWM controllers are straightforward devices, although some can add additional functionality to their essentially simple systems.
MPPT controller
Unlike PWM systems, which require the voltage of the battery and panel to be the same, MPPT controllers can charge a lower voltage battery from a higher voltage solar array, and in some cases a higher voltage battery from a lower voltage solar array .
In electrical systems, voltage and current are inversely related: the higher the voltage, the lower the current (amperage) and vice versa. Because an MPPT controller controls the rate and current of voltage flowing from solar panels to a battery, off-grid solar and storage systems can have panels with a different voltage than their batteries.
While a solar panel alone rated at 24 volts is not enough to power a 48 volt battery, an MPPT controller makes the job possible by halving the current, thereby doubling the voltage flowing into the battery.
Treehugger tip
For golf or boondocking fans (off-grid RV living), an MPPT controller allows you to charge a 36-volt or 48-volt battery with a single flexible 12-volt solar panel mounted on the roof of your RV or golf cart is.
Cindy Shebley/Getty Images
MPPT controllers can increase the efficiency of your solar panels by 20% to 30% by tracking the optimum voltage to current ratio to maximize a battery’s performance. It’s their increased efficiency that can make their higher cost worthwhile.
costs
The simplest PWM controllers can cost $60 or more. Those with additional features can cost as much as $200.
MPPT controllers can do more, but cost more, ranging from $500 to over $1,000 depending on features. However, if there is a long distance between your panels and the battery, you can save money by using lighter gauge electrical wire between the two since MPPT controllers modulate current and voltage.
And because MPPT controllers can convert the higher output of a solar array to the lower voltage of a battery, a battery can capture more solar energy. This increases efficiency and potentially shortens the payback time of the more expensive system and increases your ability to rely solely on solar power.
Some optional controller features that come with an additional cost include:
- LEDs that allow users to monitor the system voltage and current.
- Internet-enabled controllers for remote monitoring.
- Multiple outputs for charging two separate batteries.
- Longer cables for longer distances between panels and battery.
- Temperature sensors that maximize charging efficiency as batteries charge at different rates at different temperatures.
- Low voltage circuit breaker that automatically disconnects a connected DC powered device (e.g. a golf cart) when the battery is low.
As always with solar products, you should anticipate your solar needs and capabilities and calculate the cost and payback time to see what type of system will work best for you.
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