@xiaowang1984 I think marginal emissions are just the wrong way to think about the long term impacts of adding load to grids.

@xiaowang1984 First order effect is that marginal emissions go up, but that ignores the fact that it’s a complex system of supply and demand investment signals. The signal from the additional demand will travel through the supply stack and encourage new generation investment.

@xiaowang1984 The whole thing will find a new equilibrium with an emissions intensity similar to what is was before, but shifted by the effects of any changes to the shape of demand.

@xiaowang1984 Think about a battery as an example case. Let’s say as an extreme example there are periods when the grid is on 90% wind and solar and the last 10% is a brown coal plant (low cost, high marginal emissions).

@xiaowang1984 VRE decreases and CCGTs come online at a higher price (but lower marginal emissions) to flex and fill the gap. Under a marginal emissions framework, the battery shouldn’t charge when clean energy is plentiful and discharge when it’s scarce, because marginal emissions went up.

@xiaowang1984 Without the battery though there’s no price signal to build more wind and solar and you’ll never get rid of the coal plant.