Solar panels come in many shapes and sizes... 100W, 300W, 600W, Monocrystalline, Polycrystalline, Monofacial, Bifacial, A-grade and moon panels (not yet available). Hence, various properties exist and each panel behaves differently. We can discuss solar panels a little bit later in much more detail.

The purpose of the solar charge controller is to obtain the solar power from the solar panel and to convert it to charge the battery. Yet again, various technologies exist on the solar charge controller.

PWM: Pulse Width Modulation solar charge controller. It connects the solar panel directly to the battery and controls the current and voltage accordingly by means of connecting-disconnecting very quickly. It is very affordable, but not very efficient on large panels (where panel volts are larger than the battery volts).

MPPT: Maximum Power Point Tracking solar charge controller. It uses a microcontroller, a few MOSFETS and fancy mathematics to extract the maximum power out of the solar panels. These controllers allow you to use panels that have higher voltages than the battery voltage.

Low Voltage Solar Charge Controller: This refers to the solar panel voltage input range, usually, of a MPPT solar charge controller being "low". When having a look at a 48V inverter, a MPPT solar charge controller allows you to use a panel or panels with voltages larger than 48V. But there is an upper limit. That limit is usually about 115V. Hence you can configure your solar panels in such a way to supply the inverter with voltage between 60V and 115V.

High Voltage Solar Charge Controller: Similar to the Low Voltage solar charge controller, it has a voltage input range of, usually, 120V to 450V. Hence, you will need to place a lot of panels in series to make up the solar power supply voltage.

VERY IMPORTANT - With all these confusing technical terms, just take note that "low voltage" and "low frequency" are not the same thing. The low voltage refers to the solar charge controller input voltage range and the low frequency refers to a big, bulky, heavy inverter that can run your lawn mower.

Homework Assignment:

Try to figure out the following...

Mary bought a 48V High Frequency Hybrid MPPT Low Voltage Solar Inverter that she will install in her log cabin in an Off-grid configuration.

The answer: Mary's inverter runs from a 48V battery bank. It is high frequency, so it is small and light, with no heavy transformer (keep it away from dust and damp, and don't expect it to start her welder). It is a hybrid, so it has a built-in charger for grid or generator power and a built-in MPPT solar charge controller. Its solar input is low voltage, so her panels must be wired to give roughly 60V to 115V. And because it runs off-grid, the cabin runs only on batteries and panels, so a qualified installer should do the earthing properly.

Missed the start? Read Chapter 1: Understanding inverters. To compare products, see our MPPT and PWM charge controllers and our charge controller guide.

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