You don't need to sand the primer down smooth, you really just need to sand it a little bit to actually roughen it up so the topcoat adheres better.

What's your price per kWh, how much energy does you kettle use and for long does it run before it boils a batch of water? How much did the vacuum bottle cost?

I'm really having a hard time seeing how this can have a reasonable payback period considering how little energy we're talking about saving here.