"A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. That's more than 10,000 times the world's total energy use." [1]
We have a long way to go before humanity's heat output is anywhere rivalling the heat the Sun dumps on us. Most of our power generation (except nuclear) is just repurposing the Sun's energy anyways, delaying its conversion into heat so that we can extract work from the process. The same heat is generated with or without our power plants. (Fossil fuels delay for so long that the energy release occurs at a much faster rate than it was gathered, but still insignificant compared to the regular solar energy incident on the Earth).