The Newcomen steam engine worked at 1 per cent efficiency – that is to say it converted 1 per cent of the heat from burning coal into useful work. Watt’s engine was 10 per cent efficient and rotated much faster. Otto’s internal combustion engine was about 20 per cent efficient and faster still. A modern combined-cycle turbine is about 60 per cent efficient at making electricity from natural gas and runs at 1,000 rpm. Modern civilisation therefore gets more and more work out of each tonne of fossil fuel.
