Chris,
I checked mine and it's a 20 amp 230 volt two prong twist lock plug. You really shouldn't need an extra ground, however you could make something with the extra ground lead with an alligator clip on it if you really want it grounded. I never worry about the extra ground when I'm using low voltage DC. You could look into the Home Power article and see how they hook theirs up. Also there are a couple other solar guys that do the same thing, that are part of the ET scene. You might check their sites to see what you can come up with.
Glad to hear that you got your extra panel up!
Gary