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.
That is what I was implying as well. If it’s open source, it doesn’t mean it’s free (as in freedom). Make it free (as in freedom), which would imply that it doesn’t have to cost anything, if you have the knowhow.