Solar Panel

The Solar Panel is a Minion Fuel that can be used to speed up a Minion, and is unlocked at. It increases the speed of your minion by 25% during the day when placed inside the Minion Fuel slot in the Minion GUI (orange glass). Unlike most other fuels, it has an unlimited duration. It is not consumed and will be returned when clicked or a minion is picked up.

Day Saver
Using it in addition to a Day Saver will cause it to run permanently.

However, the Day Saver does not work when you are offline thus the Solar Panel only provides an effective ~12.5% increase in minion speed when you are not around. It might be better than the Enchanted Lava Bucket if you have a Day Saver and an alternate account that is constantly AFK on your island as it will then give a 25% boost to minion efficiency and is 3x cheaper than an Enchanted Lava Bucket.