Suggestion: lunar panels, they would output more eu in the night then the day.
They would be crafted with lunarium and have the same teir system as the solar panels.
Then you would craft them together surrounded with some form of combination between sunnarium and lunarium to create the ultimate solar/lunar panel.
That's really cool idea! In minecraft night and day time are 1:1, so they should output the same EU amount as solar panels. It is really easy to implement it. Just put "if (isNight)" instead of "if (!isNight)", for instance.