Solar Panels, Charge Controllers, and Why you should....
Are Charge Controllers Mandatory for Solar Panels?
You would think they would just make solar made easy, right? Well, they have. A fair analogy might be:
don't get a truck to run a drag race, get a dragster.!
But the minute you say that, you get hate mail, as a few trucks are designed to drag race and win. Thus a truck's use depends on how it's used and implemented, basic design only goes so far!
Solar panels are very similar to the truck. Solar panels are designed in several different classes. Some are like the drag truck, some are like the dump truck. Just like these vehicles all have different horsepower, yet all do 55 down a highway, each solar panel, from each manufacturer, comes with varied voltage and amperage ratings, and they are never 12 volts. Once you get within a manufacturer's line, the voltage and amperage are still inconsistent, as the output of the solar panel (wattage rating) chosen dictates the final amps and volts. Charge controllers are the only sane way to normalize these varying currents, so we can use them.
Bottom line, a solar panel makes power from the light of the sun and sends it down a wire but the voltage and amperage are most often not set up to go directly into a 12 volt battery. Charge controllers not only make that possible, they make it so you can walk away.
What about 12 volt panels?
Most "12 volt" panels put out about 16 to 20 volts under normal operation. We have even seen 12 volt panels output 24 or 29 volts under peak sun conditions. If these solar panels were hooked directly up to a battery bank without regulation, the batteries would be damaged first by too much voltage, and then by sustained overcharging. The problem is that most 12 volt batteries need between 13 and 15 volts to charge. To fully charge a battery requires a more refined 14.2 - 14.8 volts, and sensitive electronics to "TELL" the battery when it is full. Otherwise the power will not shut off, and the battery over flows.
Do I always need a charge controller?
Not always, but usually yes, a charge controller is a good idea on panels above 10 watts except when used with any type of GEL or AGM battery.
WHY?
Generally, a charge controller is overkill and a waste of money for very small panels, especially those under 10 watts. With small maintenance solar panels and or trickle charge solar panels, a very small amount of power is generated. This amount of power is less than the power a battery loses by just sitting there (batteries don't hold power forever). We call this the self discharge rate, and trickle panels are designed to just be under this self discharge, so they don't hurt the battery.
So how do you do the math?
An AGM or GEL battery loses 2% of it's power in 24 hours, a flooded battery 10% in 24 hours. So a trickle charger putting out 10 watts for 8 hours of daylight makes 80 watts, or 6.7 AH. ( = 80w/12v). A battery bank that will lose 6.7ah (Amp Hours)in one day can be computed as follows:
6.7ah / 2% =333 ah AGM or GEL battery Bank
6.7ah / 10% self discharge rate = 67ah Flooded Battery Bank
A rough rule for AGM batteries: if the panel puts out about 2 watts or less for each 70 ah of AGM battery bank, a charge controller is not needed.
A rough rule for Flooded batteries: if the panel puts out about 5 watts or less for each 50 ah of AGM battery bank, a charge controller is not needed.
The type of battery you use dictates when you need a charge controller.
Are Charge Controllers Mandatory for Solar Panels?