PV Student

Q:

Good Morning Dr,

To which extent we can consider the stand alone systems. I mean is there any maximum capacity for stand alone systems that we can't go further capacity.

The charge controller is very important device that will help to save the batteries longer. Is there any other function other than preventing the batteries over/under charging? And what are the protection schemes related to this device if any.

Thanks

A:

If a stand alone system is big enough, it can be more of a micro-grid and if a micro-grid is big enough it can approach being a utility.

There are no size limitations, but as the system becomes larger, there are different criteria to take into consideration.

With battery selection, it is best to avoid multiple parallel connections, so if you wanted to have one large battery bank, you would often have to use parallel connections. With small systems, this is not a problem, but with larger systems there are different ways of splitting up the battery banks into smaller units in a micro-grid system. There are also large container sized battery banks.

If you would be working on one of these larger systems, you would most likely be working with the manufacturer to make sure all of the products properly communicate with each other.

Mostly the charge controller will function to prevent overcharging and undercharging, however the charge controller can also do maintenance on a battery. Many flooded lead-acid batteries can be equalized, which is a controlled overcharge that will help prolong the batteries life.

Equalizing is overcharging a battery, which will split H20 molecules into hydrogen and oxygen gas bubbles. These bubbles will stir up the heavy stationary batteries to prevent stratification. Stratification is the heavier acidic electrolyte settling to the bottom and the less acidic lighter electrolyte settling on the top.

Also equalization will help remove led sulfate buildup on the lead plates. We call this scraping the places. Lead sulfate buildup can occur when the battery does not receive a full charge often.

Charge controllers may have overcurrent devices built in and they may require separate overcurrent devices. I recommend reading the detailed manufacturers installation manual.

Thanks for the good questions!

Sean White