Alternative and Renewable Energy - Advanced Materials ...

Spiral 2: 3/28/20117.3.3.5 Heat RateDepartment of Defense Energy HandbookAlternative and Renewable Energy Options for DoD Facilities and BasesHeat rate is a quantity often used to describe the thermal efficiency of a power generation unit or plant.It is essentially is a ratio of the energy content of the fuel to the net energy produced. The heat rate istypically presented as BTUs per net KWh, which is dimensionless but has more meaning when the unitsare retained. The heat rate can be calculated according to the formula shown in Equation 6. Examples ofsome heat rates are given in Table 28.Equation 6WhereHR – heat rate, BTU/kWhE f – energy content of the fuel, BTUTable 28. Typical heat rates for several energy sources. 125Energy SourceHeat Rate (BTU/kWh) xlixPetroleum 10,730Nuclear 10,400Coal 10,350Natural Gas 8,9007.3.3.6 Thermal EfficiencyThe thermal efficiency of a power generating unit can be described as the net energy produced (i.e.,converted to usable energy) divided by the heat absorbed by the working fluid as shown in Equation 7.Alternatively, this is the inverse of the HR using a conversion factor to convert the energy to the sameunits. Depending on the type of power plant that is used, variations of the HR and thermal efficiencyequations may be used.Equation 7Whereη th – thermal efficiency1 Wh = 3.412 BTUs7.3.3.7 Economic EfficiencyThe economic efficiency quantifies the production costs per energy production. For instance, it can becalculated by the sum of production costs, which includes fuel, labor, materials, services, and divide thistotal by the cumulative energy produced during the period over which the costs were summed, asshown in Equation 8. 126xlixHeat rate is the average value from 2001 – 2008.101