It reads yesterday's generation mix from ENTSO-E and the EIA, works out the carbon intensity hour by hour, and compares a normal tariff against two carbon-aware ones.
It started for Switzerland, which turned out to be a good place to start for an odd reason. Swiss electricity is already very clean — about 34 gCO₂/kWh — and yet it's one of the best grids in the set at 2.4%, because it imports from dirtier neighbours and its carbon intensity swings through the day. Louisville, at 741 g/kWh, gets 0.01%: it burns coal at the same rate around the clock, so there's no cleaner hour to move into.
Across 38 grids, the correlation between the saving and how dirty a grid is comes out slightly negative. With how much it varies, it's 0.91. Being dirty doesn't help at all — being uneven is the whole thing.
Fair warning: the demand response is a model rather than measured behaviour, and it uses average carbon intensity, not marginal. Happy to hear your thoughts.