Storage is measured in units of energy, i.e. something akin to Joules. Watts (and thus kW) are a measure of power, i.e. energy rate: 1 W is 1 Joule per second.

Storage is measured in units of energy, i.e. something akin to Joules. Watts (and thus kW) are a measure of power, i.e. energy rate: 1 W is 1 Joule per second. kWh is a measure of energy (a kW for an hour) and is directly convertible to Joules. You could of course price based on energy discharge rate in kW, but not that alone...