Equation 5.3 makes it clear that a plant’s expenditure on fuel and carbon will be strongly influenced by its net thermal efficiency (i. e. thermal efficiency after allowing for on-site electricity usage). The thermal efficiency data provided by PCGE are not net values and the figures presented here in Table 5.2 are therefore set at about two percentage points lower than what is normally expected from modern plant.

As shown in the table, there is an expectation that the addition of carbon capture equipment will reduce the thermal efficiency of coal-fired plant from 40% to around 35%. Use of waste heat, as in combined heat and power schemes (CHP), is an obvious way to conserve energy and generate additional income; it does not, of course improve thermal efficiency in the sense of the efficiency of electrical conversion: the contrary, in fact. Such schemes are not included here.

The table provides a simple calculation of the additional cost of generation if CO2 emissions are priced at $50 per tonne. Coal with carbon capture is assumed to remove 90% of the CO2 so that the carbon cost is 10% of that without removal. The fact that CO2 releases are lower from natural gas than from coal is a result of the higher calorific value of gas (when expressed in terms of the mass of fuel) and the greater thermal efficiency of CCGT.