Nope. Not the only way. And not a great one either.
Hydro is one. And ultra small scale nuclear will be one in the future too.
Reliability is key.
Discussion
Not everyone has hydro resources to use. It's much easier to have access to sun or wind.
Nuclear needs (nuclear) fuel, and its extraction is largely centralised.
Decentralisation is key.
With wind and solar you also need batteries and those have a very low energy per weight, about 1% of oil, and are also expensive. With hydroelectric, batteries are not necessary.
How many people in the world can own hydro energy generation vs. how many can own solar energy generation?
We are talking energy decentralisation here.
Of course solar or wind are not perfect, but they are the ones that allow more decentralisation.
For electronics that already have batteries and do not use that much, solar is an okay option.
With the cost and low efficiency and batteries, it's not that great of an off-grid option. Perhaps that will improve with better ways to store that energy.