Here we see the journey energy goes through on the US Energy Flowchart, from a fossil fuel to electricity.
A fossil fuel (such as octane) comes out of the ground, loaded with energy in its chemical bonds
Combustion releases this chemical energy as heat
The heat boils steam in a power plant’s boiler
The steam turns a turbine or works a piston, making electricity
The steam is condensed to water, which has to involve rejecting some heat
For this reason, you can’t recover all of the fossil fuel’s chemical energy as electricity. Some must be rejected. Engineers and scientists try to minimize this rejection.
A more thorough explanation of entropy and why heat must be rejected can be found here. 

Here we see the journey energy goes through on the US Energy Flowchart, from a fossil fuel to electricity.

  1. A fossil fuel (such as octane) comes out of the ground, loaded with energy in its chemical bonds
  2. Combustion releases this chemical energy as heat
  3. The heat boils steam in a power plant’s boiler
  4. The steam turns a turbine or works a piston, making electricity
  5. The steam is condensed to water, which has to involve rejecting some heat

For this reason, you can’t recover all of the fossil fuel’s chemical energy as electricity. Some must be rejected. Engineers and scientists try to minimize this rejection.

A more thorough explanation of entropy and why heat must be rejected can be found here