A solar regulator (sometimes referred to as a charge controller) is used in conjunction with a stand alone system, or a grid connect solar power system with a battery bank for backup. For a grid connect system without a battery bank, a solar regulator is not required, just a power inverter.
A solar regulator is a small box situated between the solar panel and your batteries. Its role is to control the amount of charge coming from the panel that enters into the battery bank to ensure that it doesn't overcharge the batteries. A regulator can also offer a direct connection to load; i.e. you can run appliances directly from it, bypassing the battery bank; but the batteries will continue to be charged.
To calculate the size regulator you'll need, add up the amp ratings of your solar panels.
I have a 140 watt panel, which is rated to around 7.7 amps. Considering I'll add another panel in the future, that means the regulator I needed have to handle at least 16 amps, and just to be safe, I bought a 20 amp solar regulator. That's an important point - to take into account your future needs which will save you money as you upgrade your system.
A solar regulator is maintenance-free; you just need to check the connections regularly and ensure where you have it situated there's air flow and it's not placed in direct sunlight. While they are quite robust, extreme summer heat can affect a solar regulator's performance and shorten the serviceable life.
Another tip - always place an appropriately rated fuse between the solar panel and the regulator to help reduce fire risk, protect your batteries, regulator and any appliances you're running.
Some controllers regulate the charge to the battery by simply switching the current totally on or totally off – ON/OFF Control. Others reduce the flow of current gradually. This is called pulse width modulation (PWM) and holds the voltage more constant. A more sophisticated method that has been introduced in the last few years is Maximum Power Point Tracking (MPPT). This device“tracks” the maximum power point of the panel.
