>>12094652Because they produce electrical energy directly. Storing them in batteries is generally the most lossless way of storing the energy.
You can try to store it chemically (for instance by creating hydrogen and oxigen from water using electrolysis) but you lose a lot of energy that way and combustion engines only run at a low efficiency so you lose energy when you store it and when you recover it.
Mechanical / gravitational / kinetic energy stores suffer from the same problems but are generally speaking even more unpractical.
