[see
Forum Thread this is taken from for more]
When solar panels are hooked up in
series you connect the minus of one panel to the plus of the next panel.
The voltages are summed, but the current remains the same:
Putting panels in series is desirable as it keeps the amperage low, and amperage is the key factor in cost of the wire.
Now let's look at panels in parallel. Here all the negatives are connected to each other, and all the positives are connected to each other. So the voltage stays constant and you sum the currents.
With a PWM charge controller you'll want to put the panels in parallel as those devices reduce the voltage to the battery's voltage; and would otherwise waste a lot of power.
When using an MPPT charge controller it will have a maximum voltage and current that you can put on any input. You typically put the most panels you can together in series (called a string); but not so many you exceed the voltage. You repeat that for as many panels as you have and then connect the strings together in parallel.
For example, if you had 6 panels with Vmpp= 22.5, Impp=5.75 and an MPPT with 60 volts and 20 amps max; then you might arrange your panels into three
parallel strings of 2 panels in
series.
When a panel in a series is affected by shade, it can reduce the voltage of the entire string, reducing the power output of the string.
One way around this is to use diodes as shown below:
Note that most modern solar charge controllers have blocking diodes built in to prevent draining your batteries at night.
