Gamespot cites the results of a test that investigated the power consumption of various consumer electronic devices. Here's a snip on the consumption of consoles:
The PS3, while on and running a game, consumes some 33.34kWh weekly--equivalent to around A$5 ($4.79). When on but idle, it uses almost as much, sapping 31.74kWh, or A$4.76 ($4.56). When the machine was off (with the back switch on), power usage plummeted to 0.30kWh, or A$0.04 ($0.04) a week.
In comparison, the Xbox 360 used up 26kWh per week in power when on and running a game--about A$3.90 ($3.73) in real money. When on but idle, the figure was slightly reduced to 23.47kWh or around A$3.53 ($3.37), and when off used up only 0.40kWh or A$0.06 ($0.06) a week.
Unsurprisingly, the Nintendo Wii used the least power--under 10 percent of that needed for the PS3. Playing a game, it uses 3.14kWh costing A$0.47 ($0.45) a week, and on but idle it drained 2.97kWh or A$0.45 ($0.43). When the console was switched off, but WiiConnect24 remained on, this dropped to 1.78kWh, costing A$0.27 ($0.26) a week. When WiiConnect24 was also turned off, this figure became 0.32kWh or A$0.05 ($0.05) a week.