MC4 is the industry standard for connecting panels together and feeding solar power to your controller.
They are fully waterproof and can handle a fairly high voltage and current. If you're going to buy a few
decent panels and don't want to cut the ends off them to solder on your own contacts, I suggest getting a
bag of MC4's to have on-hand for making connections or fabricating adapters to whatever else it is you want
to use.
I prefer to use Anderson 35A solderable powerpoles for most of my low voltage needs. I use green shells
instead of red to distinguish my solar (and other battery-charging power), and use blue for the high voltage
feed connecting the array to the controller. So all my panels have pigtails with powerpoles on the end.
Due to the effort required to connect and disconnect the MC4's, I suggest only using them where they won't
need to be connected and disconnected with any regularity, or where long-term waterproofing is required.
Important note - the female connector has a plastic plug that inserts into the male connector. This may seem
backward, but the pin insite the "female looking" connector is a male pin. So outward physically the male
appears female and the female appears male. Remember, connector gender is always assigned based on the gender
of the electrical contact. The attached picture below is marked wrong, demonstrating this common confusion.
Staubli (a swiss company) created and patented the MC4 connector, and Amphenol appears to be their main
distributor, so I'm going by their datasheet, which indicates gender is determined by the contact, not the
housing.
Also be careful about polarity, since coupled connectors have opposite gender but same polarity. Connectors
on solar panels have their positive on the female connector, meaning female contact inside male housing. On
the controller side, the positive will have a male connector, inside a female housing.
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