In MA, where things may be different, my understanding is that it's $100 KWh, or @200 KWh of installed battery storage, per year, that you will be compensated based upon whether the batteries are linked to the grid on a "targeted" basis, or some higher/lower amount of cycling throughout the year.
If anyone is seeing an electric bill, with volumetric calculation for storage, please chime in. That Tesla is suggesting a ~7KWh Powerwall can receive $700 jives with the "capacity" form of compensation, in electric rates. This would work in the opposite direction of instantaneous "Demand Charges".
When states set targets for batteries, they have been in capacity terms, not volume. For example, CA = 1.3 GW. Though residential compensation may sound volumetric, based upon "KWh", I believe what they're getting at is the potential KW output suggested by 1 KWh of batteries.