If you want some evidence of what it can do, here's our stats.
SolarEdge
(this is since Early January when we moved in)
Since National Grid didn't finalize the rule change to give us a better rate for power put back into the grid until late in the year, we're not going to break even for the year (We have through december in rebates, January will be partial, maybe February), but next year, we will not pay a single cent in electricity costs overall.