Marginal Mix

Unlike the average mix (aggregating all sources over a period), the marginal mix corresponds to balancing power stations started at peak times to meet a demand spike. In Europe, these are usually combined-cycle gas stations (CCGT) emitting 400 to 550 gCO2/kWh, or remaining coal (700 to 1,000 gCO2/kWh) depending on the country. In France, RTE estimates the marginal factor of a heatwave peak at between 400 and 700 gCO2/kWh, or 15 to 25 times the annual average factor (30 gCO2/kWh). Implication: additional electricity use at peak times (an air conditioner during a heatwave, for example) emits much more than the average factor reported by climate policies suggests. Central concept for rigorously assessing new energy uses (electric mobility, air conditioning, data centres).