Appendix B: Electricity Generation Cost Sensitivities
Variations in plant cost, finance, operating and maintenance costs, and operating regime affect the electricity generating costs to differing degrees. Sensitivity to the unit cost to changes in these inputs is shown in the tornado diagrams for the options given previously.
The variations chosen are:
Capital Cost -10% and +25%
O&M ± 20%
WACC 5% and 10% (base level is 7.5%)
Load factor 60% (base level is 90%)
Fuel Costs
- Gas 4.50 $/GJ and 6.00 $/GJ (base is 5.00 $/GJ)
- Bituminous coal on the West Coast (SI) 2.00 $/GJ and 3.00 $/GJ (base is 2.50 $/GJ)
- Bituminous coal elsewhere in NZ, 3.00 $/GJ and 4.00 $/GJ (base is 3.50 $/GJ)
- Sub-bituminous coal 3.00 $/GJ and 4.00 $/GJ (base is 3.50 $/GJ)
- Lignite coal 1.00 $/GJ and 2.00 $/GJ (base is 1.50 $/GJ)
The unit cost range in the tornado diagrams is the same for all cases to allow direct comparisons to be made (except for the gas costs which cover a 1.50 $/GJ range instead of coal's 1.00 $/GJ range.)
The tornado diagrams are arranged in increasing order of lowest to the highest base unit cost for all plant except the coal fired plant without FGD. These have been placed at the end. Tornado diagrams place the most sensitive parameter at the top of the diagram and the least sensitive at the bottom.
It can be seen that in the gas turbine based technologies fuel cost followed by load factor are the most sensitive parameters. Whereas, for coal based technologies load factor followed by WACC are the most sensitive parameters.
Figure B1: Advanced Combined Cycle Gas Turbine (400 MW)
Figure B2: Combined Cycle Gas Turbine (250 MW)
Figure B3: Southland Lignite Coal with FGD (500 MW)
Figure B4: Advanced Open Cycle Gas Turbine (230 MW)
Figure B5: Southland Lignite Coal with FGD (150 MW)
Figure B6: Open Cycle Gas Turbine (160 MW)
Figure B7: North Island Sub-Bituminous Coal with FGD (500 MW)
Figure B8: Bituminous Coal with FGD (500 MW)
Figure B9: West Coast (SI) Bituminous Coal with FGD (150 MW)
Figure B10: West Coast (SI) Bituminous Coal, Subcritical with FGD (150 MW)
Figure B11: Southland Lignite Coal without FGD (500 MW)
Figure B12: Southland Lignite Coal without FGD (150 MW)
Figure B13: Bituminous Coal without FGD (500 MW)
Figure B14: North Island Sub-Bituminous Coal without FGD (500 MW)
Figure B15: West Coast (SI) Bituminous Coal without FGD (150 MW)
Figure B16: West Coast (SI) Bituminous Coal, Subcritical plant without FGD (150 MW)
B.1 Comment
Coal fired plant exhibits a wider range of unit costs for the range of sensitivities than does gas fired plant.
Load factor and capex are the most sensitive inputs for coal fired plant, whereas fuel costs, followed by load factor, are the most sensitive for gas fired plant.
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