Bare minimum PSU

I'm looking to build a new computer. This time, instead of making it powerful, I want to make a "green" PC. Onboard sound and video, 1 HDD, 1 Optical drive. I want to know, what is the bare minimum PSU can I get. Or in other words, how can I calculate how much power I will need to run my system?

 

You may be able to use this but they dont have the latest hardware included

http://www.journeysystems.com/?powercalc

Bare minimum if you choose a basic CPU would be about 300watts but it must be a good quality unit,look at the efficiency of the PSU you choose you want it to be in the 80% range this means that for the the 100% AC power you put in only 20% is wasted creating heat which is just blown out of the computer,this obviously will make your computer more stable and is better for the enviroment

 

all of these are energy efficient, above 80% efficiency
http://www.newegg.com/Product/Produ...&Subcategory=58&description=&Ntk=&srchInDesc=

 

You may find this video of interest which I have just found,one problem I have with the video is she doesnt mention the wattage of the power supply used it looks like a standard 200-300w

http://www.youtube.com/watch?v=gJgzd68Tmcc

Heres more info on the project

http://www.viaarena.com/default.aspx?PageID=432#sub60

I also cant find the mainboard in the demo for sale yet EDIT but there are lots of totally integrated solutions out there

 

Something to remember, it doesn't matter what the max rating is in terms of power consumed. It is the efficiency. A 600W unit would use just as much (or little) juice as a 450W unit, because it is the components that use the electricity, and they don't care (unless their not getting enough juice).

Power supplies convert the electricity, and use a little to run their internal circuitry. It is the conversion rating that is important.

I would still get a high wattage unit with a good efficiency rating, the higher the wattage the less strain you'll be putting on it, which will lengthen the lifespan of the power supply in the long run.