There are plenty of ways to earn energy:
  1. Rest in the hammock (unlock by completing missions on the home island) once every 3 hours
  2. Complete missions
  3. Have a meal at the bungalow on your home island once every 2-6 hours, depending on the meal
  4. Make an offering at the altar once every 4 hours
  5. Set up the smoothie bar on your farm and make invigorating cocktails
  6. Feed Chip the Chipmunk while you travel, and he will sometimes give you energy
  7. Open energy chests hidden throughout the game world
  8. Receive in chests obtained by filling orders on the Board (they are awarded as the meter at the bottom of the Board fills up, and when you complete orders particularly difficult to fill)
  9. Increase your level
  10. Collect seashells, sea stars and energetic crabs
  11. Feed the lemur on the Island of Toru Kai Tangata (available after building the lemur's house)
  12. Purchase with diamonds by tapping the "+" button next to your energy bar at the top of the screen
  13. Purchase bundles containing energy in the Shop
  14. Open gifts attached to in-game news