Nuclear Petrochemicals IT Engineering Risk Management Business Subscriber Login Login to EMIS or to pick up your paid subscription. Many people calculate the thermal efficiency of a cogeneration plant in a way that is specifically excluded by the Second law of Thermodynamics. A commercial gas-turbine cogeneration plant, based on a Solar Turbines Centaur unit, provides a useful model for understanding the energy effectiveness of cogeneration systems. Recovering the waste heat from a powerplant to serve the thermal load of a building, process plant, or district-heating loop certainly conserves energy, reduces environmental impact, and saves money. Consider the First Law as describing the quantity of the two energy streams, while the Second Law describes their quality or value .
Electrical energy is of very high value.
Even at its theoretical maximum conversion rate, you run up against Carnot limitations. As energy is used in a system, its exergy irreversibly decreases. What we have is an exergy crisis. The FERC efficiency standard says that the relative value of thermal energy is one-half that of electric energy. You can argue that this standard was arbitrarily set, but at least it was a step forward in recognizing the value of different forms of energy.