Solar Charge Controller

Strictly speaking, there is no such thing as a solar charge controller. A charge controller, however, is an important component of stand-alone, off-grid solar power systems, so we can perhaps speak of a “solar charge controller” as a charge controller that is part of a solar power system, and in that capacity it’s also known as a solar regulator.

What It Does

A charge controller is also known as a charge regulator or a battery regulator. It regulates or limits the rate at which electric current goes into or out of a battery. There are many applications for such a device. They can be used to prevent a battery from “deep discharging” (or fully emptying), which helps to lengthen battery life. Completely emptying a battery can damage its ability to hold a charge. In that function, charge controllers are often incorporated into battery systems as integrated components in devices such as mobile phones, laptop computers, MP3 players, and similar portable electronic devices that rely on rechargeable batteries.

In Home Power Systems

For purposes of home solar and wind power systems, however, the normal type of charge controller is a stand-alone device. Such a device isn’t universally used with an on-grid, net-metering type of solar system; normally in such a system the power is fed into the electric grid which contains its own safety regulation systems, “sold” to the power utility for credit, and power drawn from the grid to meet household uses and “paid for” with the credit from the home-generated electricity. For a truly independent, off-grid, stand-alone solar or wind system, however, a battery system is necessary to provide power because times of peak use are usually not the same as times of peak power generations. That’s especially true of a home solar system, in that more power is likely to be used in the evening after the sun goes down for home lighting, entertainment, and heating, but the times when the most solar power is being generated is during the daylight.

In order for the battery system to function properly, the power going into or being drawn from the batteries needs to be regulated to safeguard the batteries and maximize battery life.


The first thing the charge controller does is to prevent overcharging. Current is flowing into the batteries at all times during solar power generation and it’s possible for too much power to be shoved into the batteries, possibly damaging them and even creating a safety hazard. There are two types of charge controller that meet this need. A series regulator or series charge controller simply measures the voltage from the battery continuously and stops current flow into the batteries when the voltage meter indicates that the batteries are full. A more sophisticated type of charge controller called a shunt charge controller (or shunt regulator) diverts power to an intermittently-used electrical appliance when the batteries require no more charging – an electric water heater is a good candidate for this use. A shunt charge controller makes for more energy efficiency than a series charge controller in that the simpler device allows excess energy production to be wasted when the batteries are full. Charging is re-enabled by the device when the batteries’ voltage drops below a safety margin.

More sophisticated solar charge controllers make use of pulse width modulation technology or of maximum power point tracking technology to adjust the rate of charging in response to the battery’s charge level, letting the batteries be charged closer to the maximum charge level without risking damage to the battery system.

Sensors And Feedback

All solar charge controllers monitor the voltage output of the batteries in order to determine when to permit or prevent charging. Some more sophisticated versions monitor the batteries’ temperature as well, as a secondary feedback signal to prevent overheating. Overheating of the batteries not only poses a risk of damage to the home electrical system, but could also risk damage to the home itself. Optional components include display data, either on-site or remote, and data tracking to allow manual maintenance and oversight of the system.

Charge Controllers And Output

Besides regulating the charging of the battery system, the other important function of a solar charge controller is to regulate the power output of the batteries themselves to the devices and appliances in use in the home. The charge controller allows a consistent, regular output of current from the batteries, which may be necessary for many appliances.

Also, the output charge controller is normally connected to an inverter. Power from either storage batteries or direct from solar panels is DC (direct current), but most normal household appliances use AC (alternating current); that’s especially true of electric motors, but since the electricity from electric utilities is always alternating current, devices commonly in use are made to run on this type of electricity.