I don't know why, but after restarting the server a few times it fixed itself... I have no idea how the problem was caused or how it was fixed, but problem resolved.

Before you answer, yes, everything is properly wired together. My friend and I are playing together, and share a power source. Our bases our relatively far apart (about 300 blocks apart.) Whenever I go to his base, MY solar panels stop functioning and we get blackouts. We have come to a conclusion ...