This is a great start=> Real-time Web Based Household Power Usage Monitor
And here's a leading commercial product => TED
The device can serve residences, organizations, and communities trying to understand and reduce their energy use. .
The data will be hosted online so it can be audited by 3rd parties. The data might be hosted by Google's Power Meter and 3rd parties may gain access to market their energy savings solutions; such as, a new refrigerator, heating system, or efficient lights, etc.
Why do it? well the utilities are not going to... (they're old and slow moving) and the smart grid is a hoax.... and it should be kinda fun to show up the expensive, commercial products available.
Would you like to collaborate on a potential disruptive product?
Step 1: What has been done so far.....
Well beyond the cool instructables that I've already mentioned..... here is where this project is at:
Fabricated a prototype PCB using the ADE 7757 power meter IC (see schematic)
ADE7757 $3.20 - digikey
ADE7757 Analog Inputs
The current sensor (CT sensor) goes to pins V2p and V2n and supplies a max differential voltage of +/- 30 mV to the on board ADC.
The voltage leads go to pins V1N and V1P to supply a max differential signal of +/- 165 mV to the on board ADC.
ADE7757 Analog Outputs
The ADE7757 is a high accuracy electrical energy measurement IC. The ADE7757 supplies average real power information on low frequency outputs in the form of active low pulses with a relatively low pulse rate ~0.175 Hz.
A typical US residence requires qty(2) CT sensors to quantify energy usage. I've experimented with some inexpensive current sensors here.