Inspired by this Mastodon account, I programmed an ESP8266 microcontroller to act as a traffic light, indicating the current electricity mix. Check it out on Codeberg! It uses an API from the Fraunhofer Institute and the parts cost around 5€. In my shared flat we use it as an indicator on when to run demanding devices, like the washing machine.
Not a monetary one, no.
* (there might exist some business power tariffs that coincidentally benefit from this but nothing you’d use at home)