Day 1: You fight with 100 hash power, your total electricity bill is $1 in PWR.
Day 2: You fight with 100 hash power, your total electricity bill is $2 in PWR.
Day 3: You don't fight but the price of the PWR double, your total electricity bill is now $4 in PWR. Day 4: You fight and then the price of the PWR is divided by two, your electricity bill is $3 in PWR.
...