I think at the start of residential solar, there were really only two %'s that gave good insights into how your panels were going to translate into savings… But with the advent of all new billing structures meant to match supply to demand, time-of-use, demand charges, etc., those %'s are becoming meaningless. The real question now is what your bill would have been if you hadn’t had solar vs. what it is with solar.
I actually wrote a calculator that roughly calculated my bill using virtually all the rate plans for publicly owned utilities in the US and charted my monthly (billing period) savings by having solar. The benefits / savings are much more pronounced in the summer months, as one would expect.