About 200+ Watts of idle power can easily be reached with a dual core machine running two graphics cards.

My desktop system I am using now is an Athlon 64 machine with an ATI X800 graphics card. It draws approximately 120 W in idle which equals 1051 kWh per year. Although energy costs can differ quite a lot, the 15 cents per kWh I pay should be a good average to reckon up from a global perspective. This equals $158 per year for having the system running 24/7 only. As soon as I turn my displays on or put the system under load, the number inflates quite a lot. An average of $230 is what I am actually paying per year.

This system is all but sophisticated today. Any fast Pentium 4 will help driving the power consumption up to 150 W or more, together with a decent graphics card of course. Using a dual core system will get you close to 200 and a CrossFire or SLI based dual graphics machine has no problems exceeding that. Please keep in mind that we are talking about idle power consumption only! Running CPU and/or graphics intensive applications will drive a single core, single graphics machine to somewhere between 200 and 250 W and a fully-featured dual core, dual graphics monster to energy consumptions of far more than 300 W.

Let's repeat the calculation with an idle power of 225 W for a dual core SLI machine. In this case, the annual idle power drawn would be 1971 kWh or almost $300! Of course the power consumption may vary with the efficiency of the power supply, but energy prices are certainly not going down again.

The following table lists the power consumption for low-end, average and high-end systems at low, medium and high energy costs. According to an article from USA Today, the U.S. has an average price of 8 Cent per kWh today. The high energy costs column can be considered quite normal for Europe.