Actual energy to heat is only useful in a true excess energy availability situation, but usually you'd start building up heat storage to decouple heat availabil

Actual energy to heat is only useful in a true excess energy availability situation, but usually you'd start building up heat storage to decouple heat availability from electricity demand, which would otherwise be a problem with cogen plants. And heat storage is so much cheaper and efficient than electrical storage, so you want to run your cogen in sync with electricity demand. Once the heat storage is there, it becomes an absolute no-brainer to also use it when you have excess electricity to dump (as electric heating is 100% efficient, it's the production of electricity in thermal plants that makes electric the worst form of heating).