Oh the lag, every cable junction causes more lag, which is why normal solar plants minimize them.
This is the most popular design:
It uses a tin cable surrounded by solar panels, it can be extended run 39 blocks outwards and is maximum possible efficiency (in this picture I have two rows running parallel to each other):]
An MFSU has been put on the end of one to collect energy (the other is left open so you can see the tin cables inside). Kane Hart had a similar setup with the tin cables merging at the end (they cannot be longer than 39 blocks thou!) running 250+EU/t through tin cables.
Solar flowers were IC1 stuff, IC2 outdated them. This is probably the best design, in terms of maximum coverage, minimum junction and loads of panels.
I have 70+ FPS and i have only clasic 4GB ram, dual core AMD, HD4650 G.Card so.. i dont know if that is some problem ..I had problems .. lag spikes but that was because chicken farm sound problem.. and I figure out that. So dont worry if you want to have nice flat roof I have 7 mass fabricators and lots of other but still energy.. i dont know how to use that much.. and i mine with dynamits long tunnels 3*3 always throw 1 in the middle and nice tunnels.. so I have all materials i need.. what else if not miners 
I do not have idea