The Future of Coal (Glossary and Appendices)

Th e electricity generating effi ciency is the energy in the net electricity generated divided by the energy in the fuel used to generate that electricity on an all-in basis. Higher effi ciency means less coal consumed and reduced emissions per unit of electricity. Th e chemical energy in the fuel can be expressed as either its Lower Heating Value (LHV) or its Higher Heating Value (HHV) [5]. In U. S. engineering practice, HHV is generally used for steam cycle plants; whereas in European practice, effi ciency calculations are uniformly LHV based. Th e diff erence in effi ciency between HHV and LHV for bituminous coal is about 2 percentage points absolute (5% relative), but for high-moisture subbituminous coals and lignites the diff erence is 3 to 4 percentage points. Th e effi ciency of gas turbines is on an LHV basis in the U. S. and Europe. Th e thermal effi ciency of an electricity generating plant may also be expressed as the “heat rate”, the fuel thermal energy consumption per unit of electricity produced, in kJ/kWe-h or Btu/kWe-h [6].