The Swing 🎢 unlocks at level 15 and can be built on Home Island. You need to complete the quests "Get the Ancestor's Halo" and "Upgrade the Loom" to unlock it.
Build the Swing 🎢. and it will generate energy. But keep in mind that it will break down from time-to-time, and you will need to use resources to fix it.
To learn more about Generators like the Swing, check out the articles in the Gameplay section!