100% is the typical claimed number as it is easy to measure watts of electric in and find that is exactly equal to watts of heat out - or if not the difference is easially explained by measurement error. There is no hypothesis (much less theory!) of where the energy could go it it isn’t heat and conservation of energy is enough to also decide 100% efficient.
The above isn’t the whole story though. If you could somehow measure watts from the power plant output you would discover that 4-12% (depending on a bunch of factors) of the energy is lost before it even gets to your house and so your efficiency goes down. If you measure fuel into the power plant, those range for 10% (old systems from the 1920s only run in emergencies) to 60% (combined cycle power plants) - I’m not sure how you would measure wind and solar. Eventually the universe will die a heat death and 0% long term.
100% is the typical claimed number as it is easy to measure watts of electric in and find that is exactly equal to watts of heat out - or if not the difference is easially explained by measurement error. There is no hypothesis (much less theory!) of where the energy could go it it isn’t heat and conservation of energy is enough to also decide 100% efficient.
The above isn’t the whole story though. If you could somehow measure watts from the power plant output you would discover that 4-12% (depending on a bunch of factors) of the energy is lost before it even gets to your house and so your efficiency goes down. If you measure fuel into the power plant, those range for 10% (old systems from the 1920s only run in emergencies) to 60% (combined cycle power plants) - I’m not sure how you would measure wind and solar. Eventually the universe will die a heat death and 0% long term.