How Do Places With Wind And Solar Energy Sustain Their Power?

Some places rely on solar and wind energy right? To power their homes and such. How do they use energy in the night or when there is no wind? Do they have something that stores the energy like a big battery or something?
I have to “make” a green city and it will use renewable energy source including solar and wind energy. How would I make the wind and solar energy sustainable and not have shortages of power?