We usually measure or convert the watts into amps of solar panels to figure out how much current (amps) is being stored in the battery. Or we measure the amperage of the solar panel output to select the wire sizefrom solar panels to.
Article 706 applies to energy storage systems (ESS) that have a capacity greater than 1 kWh and that can operate in stand-alone (off-grid) or interactive (grid-tied) mode with other electric power production sources to provide electrical energy to the premises wiring system.