1) Why buy something when I can frustrate myself? In all seriousness, I've been looking for a project that will hook together a number of different interests as well as to being sufficiently large that I have to break the problem down into a number of discrete parts.
2) A lot of the solutions look at monitoring by measuring in series with an appliance (or extension cord) from a plug as oppossed to the whole house. I think the ideal solution is a combination of both but the majority of documented projects concentrate on the plug side of things.
3) The UK is somewhat behind the curve in offering smart metering and measurement so I want to provide a local example for a change!
In the UK, as houses are slowly upgraded to new digital meters, the handy hacker has access to a means of monitoring without worrying about induced electric fields (e.g. measurement through Hall effect sensors) or through cracking open the meter itself (which would no doubt get you in trouble if not shocked!).
"What is the capability?" I hear you cry, well it's an LED that flashes for each 1/1000KWh consumed from the mains and as its a BSI certified product its reliable.
So this instructable documents the process of creating a device that monitors the number of flashes being produced by a UK Electric meter and sending the count to a computer for data logging and visualisation.
The system consists of two parts, a unit that sits in the meter cupboard (based around a photdiode, an Arduino, a DS1307 Real Time Clock and an XBee wireless board) and a computer based reader (an XBee via a USB explorer board and a Mac OS X logging application).
It can be used in conjunction with other solutions such as adafruit's Tweet A Watt to provide a very detailed picture of consumption within your home and gets you one step closer to having a home smart grid.
From my perspective this project has green credentials because if you can't measure your consumption, how can you begin to understand your impact? As an added bonus, if you can see when you use your electricity, you can start looking at how to cut back, not only saving the earth, but saving money too.