The electricity from the solar panels is free to you however the cost of the solar panels are not free and that really outweighs any savings that you would be getting with solar panels over just using the mains electricity.
Solar panels are nice especially for remote areas or if you have your power shut off due to non payment or other things but you really do not save money at all when using solar panels.
It takes at least 10 years if not more to get your money back on the solar panels through savings and during that time batteries go bad and need replaced etc.
So it's not really a money saving way to generate electricity although solar panels are nice and do help the environment as well.
I have a few solar panels myself but still use the mains electricity to power the majority of my stuff and there's no way I would save any money getting rid of mains electricity and using just solar panels.