Charge Controllers

Though many homeowners choose to get a grid tie inverter and forego having to buy batteries, applications where there is not existing electrical grid connection point will require some type of storage and charge controllers to keep those expensive batteries from being charged or discharged too quickly.

Today, a solar charge controller is required equipment on just about any remote PV system that uses a battery. Charge controllers are also useful for panels that give off more than 5V or so, regardless of the battery size. A good rule of thumb is to use charge control on any photovoltaic (PV) system that is capable of supplying more than 1/60th the current the battery can hold in a single day.

The so-called trickle charge of low power panels generally doesn’t require a battery charge controller, but it might be a good idea to plan for the expansion and use one anyway. For very low power applications that still require conditioning, the Sun Wize solar charge controller is a particularly inexpensive option.

The technology has been used for many years with mobile systems, though RV charge controllers tend operate far less precisely than their modern counterparts. Such one or two stage charge controllers just open the circuit when the battery is too full, but these shunt-types don’t regulate the voltage, condition the input or charge the cells evenly.

The industry standard now is a 3-stage controller and one would be hard-pressed to find any of the more ancient type used today. Though still expensive, the most current technology is the MPPT (maximum power point tracking) systems produced by Blue Sky. These charge controllers may be up to 98% efficient while other systems can loose up to 30% of the PV power produced between the panel and the battery.

Some systems, such as those from Apollo Solar feature charge controllers with integrated computer control and data storage, providing up to a month of information at a time. On the other hand, units such as those relatively low power offerings from ICP, feature small charge controllers that have only a few LED lights to indicate their current status.

While most devices are designed for 12-14V batteries, some systems use higher voltage storage devices. For instance, if you’re using a 36 volt battery (or 3 batteries in parallel), you’ll need to use a 36 volt charge controller. You should also plan on tailoring the controller you use to the environment. Be sure the device will work in the temperatures the device is likely to be operated at. If operating in a marine environment, companies such as ASC make a charge controller that’s covered in waterproof epoxy

Many who want to put a system together as quickly as possible choose to invest in a combination device with a charge controller and inverter in one. Another option that is commonly used is a load output that is often used to power non-critical or low power systems such as accent lighting. Morningstar makes a charge controller that is the industry standard for such applications.