Enter the thermal energy input and the electrical energy output to determine thermal efficiency. Use the Heat Rate / Power tab to calculate heat rate (for example, kJ/kWh or Btu/kWh) from heat input rate and power output.
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Heat Rate and Efficiency Formula
The following equations relate heat rate and (thermal) efficiency.
HR = TEI / EEO \eta(\%) = (EEO / TEI)\times 100
- Where HR is the heat rate (for example, kJ/kWh or Btu/kWh)
- Where η is the thermal efficiency (%)
- TEI is the thermal energy input
- EEO is the electrical energy output
To calculate heat rate, divide the thermal energy input by the electrical energy output (for example, use kJ and kWh to get kJ/kWh, or Btu and kWh to get Btu/kWh). To calculate efficiency, divide electrical output energy by thermal input energy and multiply by 100.
What is Heat Rate (Efficiency)?
Definition:
Heat rate is a measure of how much thermal (fuel) energy a power plant must supply to produce one unit of electrical energy, commonly expressed as Btu/kWh (or kJ/kWh). A lower heat rate means the plant converts fuel to electricity more efficiently (higher thermal efficiency).
Heat rate is useful for comparing generating units, estimating fuel use, and estimating fuel cost and emissions (when combined with fuel heating value and emission factors). However, overall cost-effectiveness depends on many factors besides heat rate, including fuel price, capital cost, operating and maintenance costs, and capacity factor.
Heat rate and efficiency are inversely related. For example:
- Efficiency (%) ≈ (3412.142 / Heat Rate in Btu/kWh) × 100
- Efficiency (%) ≈ (3600 / Heat Rate in kJ/kWh) × 100
Typical net plant heat rates vary by technology and operating conditions. As a rough reference, modern combined-cycle natural gas plants can be around 6,000–7,500 Btu/kWh, while steam-cycle coal and nuclear plants are often roughly 9,000–11,500 Btu/kWh.
