Zero Point Energy
or
tapping into a possible alternate dimension

so in theory, there are ways

Pin a rose on your nose! It's a book not a reality.

Solar is the best bet. Now batteries as we know them are not. But if you use the excess solar power to run some pumps to fill an elevated storage tank, then during periods of low light let gravity do it’s thing and use the falling water to run a turbine......you now have a “renewable” battery.