Variable dt: Rate and amount units for storage models

This issue is to discuss how to make the storage and dispatch models in H2I compatible with variable dt time steps.
Some things that came up on a first pass of this are

• The rate and amount units in H2I are specified as openmdao units. Would it make sense to be able to define rates in units of amount/dt instead of an existing unit. An example of this is should batteries be defined in units of kW/hr for charge/discharge rate, and then converted to kW/dt? Would the electricity time amount be kWh, or kW*dt?
• Similarly, if you are storing/dispatching hydrogen, the charge/discharge rate is in kg/hr. Should this be in kg/dt instead (i.e. kg/half hour for a 30 minute time step)?
• What does the dt_hr variable do, and should this be changed or should the input units be changed?

During initial discussions with/ @elenya-grant, it seems like there might be a benefit to handling mass-based commodities (h2) differently than electricity-based commodities based on the intuitiveness of the units definitions.

Review the storage and dispatch models and trace how the dt_hr variable is currently used. Compare the proposed rate and amount unit conventions for electricity and hydrogen, then define the agreed behavior and document the resulting compatibility requirements.