Maybe they have changed, but the XU Solar Generator couldn't generate and transmit power at the same time last I played with them. I find this to be less than a perfect solution, even if it is "set and forget" passive power.
I feel that a BR Turbine is easy enough to automate for considerably more power (24k RF/t without any outside input, if you build the self-sustaining system). Considering the costs, the BR Turbine might be just as easy (if not easier) to build mid game, especially since you can start off with a small Turbine and upgrade it as materials become available. You could do the same with solar (building base level gens, then compacting them as materials become available), I suppose, but the outputs would still be lacking.
Maybe I've just never been a big solar guy in MC. Real life, I love the idea. In MC, there are more fun systems to play with.