I used
this company for my solar installtion, I found them to be very professional and they stuck to their quote. They are a little bit more expensive than others, but you get what you pay for as with most things in life.
I am not affliated with them BTW.
Dont worry about leakage. they cut away tiles, anchored the rails to the roof truss, then overlay the lot with flashing etc. I have mine for 2 years now and no probs in the Melbourne rain.
As I said, the things to keep in mind is the inital outlay, the cost of buy in, the hours for off peak, so you can calculate the payback time.
You also need to change a few routines (e.g. washing clothes and run appliances during off peak times).
Good luck.
Bo