I kind of doubt they will ask, but if they did, there are all sorts of things that use that kind of power. A couple of computers might do it. My computer has a 420 watt (no kidding) power supply, and I don't know what the monitor draws, but its an old 21" CRT so I'm sure its significant.
If you haven't already done so, definetly switch out incandescent light bulbs for CFL's, maybe turn your hot water down a couple of degrees, things like that. Save as much energy as possible to offset the HPS.