The A7 is so efficient, the amount it adds to our NStar bill is pretty insignificant.
When compared to our 42" Plasma TV, or this PC. 
If I have to provide a booster on the A7 during the cold months,
I'll determine if the extra power use is a real $ concern.
If it's not that much money, I would prefer to leave my backup cart, and the PV boiler heater alone.