Solar charge controllers: What are the differences between them and DOES IT REALLY MATTER?
However, if you love comparing spec sheets, or you just want to make the best decision for your solar energy system, continue reading.
What is a charge controller? In the old days, referred to as “battery chargers”, charge controllers could damage lead acid batteries pretty easily. If left on for too long, they could get overcharged and eventually fail. That’s not all though. An overcharged lead acid battery will boil the sulfuric acid and distilled water mix, the case becomes hot to the touch and, eventually, there is a chance that the battery could explode sending plastic and lead shrapnel flying along with acid spraying everywhere. It sounds ugly and it is.
A charge controller is designed to prevent this overcharging, overheating and as we mentioned before, possible explosions. As it is designed to work with a battery, a “battery chargers”, charge controller is a necessary component of off-grid systems. On-grid systems typically do not need charge controllers since they do not usually have batteries.
We’ll break up modern solar charge controllers into 3 main types. (It’s important for us to let you know, there are other types of solar charge controllers available, but these are the 3 we feel are most common.)
- On-off, or, Series charge controllers: On-off charge controllers are the simplest type. Wired in series, they monitor your battery voltage and when it rises to a set voltage, they open the solar panel(s) circuit. This completely removes the solar panels from charging the battery. As the battery voltage lowers over time, the on-off charge controller will engage and connect the circuit at another specified voltage. In our xxxxon-off solar charge controller the solar panel(s) are disconnected at 14.2 volts. Then when the battery voltage lowers to 12.9 volts, the solar panel(s) are connected again. On-off charge controllers are typically about 55-60% efficient.
Why would you want an on-off charge controller: On-off charge controllers are typically the lowest cost option. They are old technology, but reliable. They are very useful when handling large currents, like 150+ amps. They are also very easy to set up and troubleshoot. The downside is that they are not as efficient as other options.
- PWM charge controllers: PWM stands for Pulse Width Modulation. PWM in general has been around for a long time and has been used in pressure regulating controls, industrial controls and many other applications. Instead of turning completely on or off, PWM charge controllers send pulses of varying amounts. PWM charge controllers generally have an efficiency of about 75-80%. PWM charge controllers also usually include extra features like load control, USB outputs, etc.
Why would you want a PWM charge controller: A good combination of efficiency and added features, PWM charge controllers are the modern standard for solar energy.
- MPPT charge controllers: MPPT charge controllers are quickly becoming the most popular option on the market. MPPT stands for Maximum Power Point Tracking. These controllers are certainly going to become mainstream in the future. By varying the solar panel input, an MPPT charge controller can find the point at which the solar panel produces the maximum power. Take for example a 12 volt battery at 12 volts, (which is about 50% full). Most charge controllers would charge your battery at the solar panel voltage of 17.6 volts and 7.4 amps. But the MPPT charge controller is able to convert the solar panel voltage from 17.6 volts at 7.4 amps to 12 volts at 10.8 amps. Being able to convert to the most efficient charging voltage enables the MPPT charge controller to be about 94-99% efficient.
Why would you want an MPPT charge controller: MPPT charge controllers are quickly becoming the standard because they are so much more efficient than PWM or on-off controllers. They are almost twice the cost of a PWM charge controller, but the efficiency savings of 20-25% over 7+ years can add up to a huge amount.
Typical 12 volt lead acid battery state of charge table for your reference: