I don't want to get in the middle of an argument but if you change:
"There is 24.6 GWH of storage in the Grid."
to:
"There is 24.6 GWH of power available in the Grid."
Then it makes sense. Power is generated at the source (nuclear, solar, coal, natural gas, wind,etc.). The grid wires then distribute that power via wires. IF there are other things along the way adding power into the grid like a solar array for example then that increases available power within the grid system.
Wires do not ADD power into the grid, the opposite is true. Wires because of resistance drop voltage.
With a meter measure voltage at an outlet.
Plug in a 50 ft. extension cord with light bulb, heater, etc. at the end. Measure THAT voltage and it will be less than source (outlet). The more load the less voltage.