Charge Controllers

A charge controller is an unassuming small metal box that is actually a very high-tech and powerful machine. Its role in a green power system is to control the charging of the batteries. It seems like this would be a simple enough role- just tell the solar panels or wind turbine when to stop charging. Alas- it's not that simple.

Basic Functions of a Charge Controller

The first role of the charge controller is exactly what I mentioned above. It simply disconnects the power source (i.e. your solar array or wind turbine) from the batteries when the batteries are fully charged.

It has an additional disconnect effect. When the sun goes down or the wind stops, you don't want the power from your batteries to run back to your solar panel or wind turbine. So the charge controller monitors the output of power in the batteries and the output of power in the solar cells or wind turbine and disconnects the batteries from the generator when that generator is no longer producing power.

More Complicated Functions

It could never be so simple, could it?

First of all, when charging batteries, it is valuable to charge them evenly. This maintains the life of the battery and ensures that the batteries don't stop charging prematurely (in the case that the battery connected to the charge controller is overcharged but the others are not fully charged yet).

It gets much more intense, though. Green power batteries are complicated beasts and in order to charge the batteries to their fullest, the charge controller may use a multi-stage charging approach. It will charge the batteries to close to full, lower the voltage, allow the batteries to get to their fullest, and then lower the voltage again to ensure the batteries stay fully charged. That is, of course, a massive oversimplificaiton- but good enough for our purposes. The main point is that a charge controller that can control the voltage ensures that the batteries end up fully charged. If you tested the batteries five minutes after they were supposedly fully charged, you'd find that they weren't full anymore. The energy didn't disappear- it moved around the array. Hence, the complicated system.

The most intricate systems use a technology that converts extra voltage into amperage, which can be used in the batteries. The reasoning is a complicated feat of physics, but what it comes down to is this. Solar panels operate at higher voltages than the batteries they charge. In order to keep the batteries charging at an optimal level, the voltage needs to be altered using a complicated DC to DC conversion process. Using this technology, called, "maximum power point tracking," means that you will always get the most out of your solar cells.

Conclusion

Thus, bear this in mind. You can buy a cheap charge controller. The trouble is two-fold. First, it will only handle a small amount of the voltage put out by your PV array or wind turbine. Second, even a moderately priced charge controller that lacks the "maximum power point tracking" will fail to optimize the power attained from your system. It's always seemed sort of silly to me to put lots of time and energy into putting up a huge solar array on your roof that could practically be your home business- and then buying a cheap charge controller that dumps most of the power you create.

You probably don't need the world's most high-end charge controller, but if you're going to skimp somewhere on the system, I would not recommend it be on the charge controller.