My previous firm (in Australia) attempted to do this for commercial buildings by monitoring the 5 minute wholesale electricity price from the National Electricity Market [0]. We installed current meters on each circuit in the buiding, HVAC, lighting etc. then were able to estimate cost savings for a given 30 or 15 minute period if that circuit was shut off. We even tried to estimate the savings if HVAC was e.g. reduced by 1 degree C in the building for a given time of day, occupancy, and weather conditions by using 1-2 years of 15-30 min resolution historical energy usage data for that building.

[0] - https://aemo.com.au/Energy-systems/Electricity/National-Elec...