You will earn 1 energy every 30 minutes, up to a total of 5 energy. If you run out of energy, you can refill it using Gems.
If your Energy is not refilling as expected, please try connecting to Wi-Fi and confirm that your device time is set to the correct local time for your area.
When you receive Unlimited Energy from a purchase or reward, the benefit will immediately activate so you can play levels without using any energy. The Unlimited Energy does not pause and will continue to run down even if you close the app.