Because the input heat normally has a real financial cost , a memorable , generic definition of thermal efficiency is From the first law of thermodynamics , the energy output can not exceed the input , so When expressed as a percentage , the thermal efficiency must be between 0 % and 100 % .
Because the input heat normally has a real financial cost , a memorable , generic definition of thermal efficiency is From the first and second law of thermodynamics , the output can not exceed what is input , so When expressed as a percentage , the thermal efficiency must be between 0 % and 100 % .