Payable savings represent the total energy reduction associated with an energy efficiency project. Payable savings are calculated by first using consumption and weather data from the baseline period to establish what consumption during the reporting period would have been in the absence of an intervention. The actual energy usage during the reporting period is then subtracted from this counterfactual (what consumption would have been) to yield payable savings. Payable savings can be used as the performance metric in pay-for-performance settings and can also provide readily available feedback with respect to the savings yields of energy efficiency projects.
Another way to quantify energy efficiency savings is "normal year savings." This is the expected annual savings over a “normal” weather year. The “normal” weather year is an idealized, hypothetical year which is constructed by drawing from observed weather data. This effectively “normalizes” the data by removing some weather uncertainty, and allows for comparison over a number of years.