Power-Plant Net Heat Rate (BTU/kWh & kJ/kWh) & Stirling Cycle Efficiency

Keep the heat-input basis and net output definition consistent

Heat rate is thermal energy input divided by net electrical energy output. Efficiency is the inverse ratio in consistent units. Thus heat rate in kJ/kWh is 3600/eta; in Btu/kWh this example uses approximately 3412.14/eta. The Btu conversion constant is rounded, not exact.

Use decimal efficiency: 38% is 0.38, not 38. Net output excludes the plant’s own electrical consumption. Efficiency and heat rate must use the same fuel heating-value basis, such as HHV or LHV, and the same output boundary.

The 38% and 60% examples are hypothetical input scenarios, not measured benchmarks for specific plant technologies. This worksheet converts a known efficiency; it does not calculate a Rankine cycle from steam enthalpies or predict actual plant performance.

The separate Stirling calculation assumes a reversible cycle with perfect regeneration and absolute reservoir temperatures. It gives 1-Tc/Th, the Carnot limit for those temperatures. It is not a prediction of real engine efficiency, and its temperatures do not constrain the independent heat-rate scenario unless that relationship is explicitly modeled.

Heat rate in Btu/kWh, D2

Uses the rounded conversion constant 3412.14. Lower heat rate means higher efficiency only when comparing consistent bases.

=IF(COUNT(B4)<>1,"Enter numeric efficiency",IF(OR(B4<=0,B4>1),"Efficiency must be >0 and <=1",3412.14/B4))

Heat rate in kJ/kWh, D3

One kWh is 3600 kJ. Retain full precision in the intermediate result.

=IF(COUNT(B4)<>1,"Enter numeric efficiency",IF(OR(B4<=0,B4>1),"Efficiency must be >0 and <=1",3600/B4))

Ideal Stirling efficiency, D4

Supply positive Kelvin temperatures with hot >= cold. Equal temperatures give zero ideal efficiency. Celsius values cannot be used directly.

=IF(COUNT(B2:B3)<>2,"Enter numeric Kelvin temperatures",IF(OR(B2<=0,B3<=0,B3>B2),"Require Th>=Tc>0 Kelvin",1-B3/B2))

Further reading

• Microsoft Support — ROUND function
• EIA — Power plant efficiency and net heat rate
• OpenStax University Physics — Ideal Stirling engine and perfect regeneration