2400 watts x 12 hours = 28.8kwh per day = 864kwh per month
Electricity costs about 8-12 cents per KWH in the US, so it would cost between $69.12 and $103.68 per month. That is a pretty big spike, but could be explained by some high current appliance.

Quote Originally Posted by latewood
It's like running 5 computers all at once.
2400 watts is alot more than 5 computers.