I've been busy on this same problem for some time now, and I can't get it to finish.
My idea in short is; use a sensor from a optical mouse and a raspberry pi, to count the rotation frequency of your kwh meter to determine how much power you are using in your house.
I've been busy on idea like this for a while, and found out that a common mouse sensor (adns 2610) can be used as a 'tiny' scanner. (Sprites mods - Optical mouse-cam - Optical mouse cam)
So it should be possible to use the mouse sensor to find out if the little black dot of your Kwh meter is flying pass.
I'm stuck on two problems;
-I'm not very handy on programming in Linux
-because the wheel is behind glass, you need a different lens for a clear image. But maybe thats not so much of a problem because, you have to only detect the black spot.
I allready have a Pi near to my Kwh meter for my home automation.
