Calculating GDP is a matter of adding things up. You can certainly use it in a time function, but attempting to do so in order to argue that electricity consumption over time must go up is not coherent. Variables affecting GDP are not fixed and of course the premise that you cannot expand an economy without expanding energy consumption is also not true.
This entire conversation has been increasingly silly because there are plenty of criticisms you can make of the US economy without trying to argue that US economic data just "makes no sense".
