August 6, 2008 By

We recently received the following question from one of our users:  Is it ok to connect a 100 watt and a 45 watt solar panel together ??? and what is the best way to do this to charge a battery bank the quickest?

In order to answer the question properly we reached out to a few of our engineering friends around the country and came up with the following: The answer is maybe…

If you just connect a solar panel to a battery, when there is light, the battery charges. But at night the solar panel looks like a resistor and will slightly discharge the battery. Completely discharging it over time.

So they usually put a diode between the panel and the battery. This diode does lose about 5 percent of the power (.5 volt drop, so more with a 6 volt system, less in a 24 volt) .5/6 about 15 percent 5/24 about 2 percent.

If the panels are the same voltage, and they both contain a diode to prevent reverse current, then yes you can.

A diode allows current to flow in only one direction. Much like a hydraulic check valve, or those gates at 6 flags that let the people move in only one direction :)

In short, must be the same voltage. Matched voltage even better. Both panels within a few hundreds of a volt. Both must have a diode, or both not have a diode and some kind of external power control to protect the battery.

Properly done, yes you can parallel the panels for more current.

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