Friday, May 15, 2009

Home power usage report system

You know what I'd love to see? Some kind of utility that would show me the kWh power usage of my appliances in real-time. You've all seen the output of "top" -- something like this (numbers picked randomly, so don't pay any attention to them):
load average (kWh): 270, 220, 230
Appliances: 149 total

Appliance kWh %tot
Fridge 130 60
Stove 90 30
Desk lamp 60 10
This can be done -- today, easily and cheaply. Here's how:
  1. Have a simple device that sits on a circuit and measures the power consumption. Kind of like the Kill-a-watt, except without the readout screen and the buttons. These devices can probably be easily built-in into outlets and power bars.
  2. The sensor has a unique identifier (similar to a mac address). This identifier is clearly labelled on the outlet.
  3. Every N seconds/minutes the sensor broadcasts the consumption data along the power line (just like "smart meters" do). Something like "00:0b:db:79:4e:45#120W" to indicate that the sensor with a unique id "00:0b:db:79:4e:45" is currently reporting 120 watts.
  4. A listener device plugs in to the power grid in your home and collects the reports, which it then either presents on a readout screen, or makes available to the network via, say, an SNMP service.
  5. You have some fairly simple software on your computer that connects to the listener device and shows you real-time power usage using nice graphs. You can give human-friendly labels to the sensors to identify them for your own use (e.g. you locate the outlet labelled "00:0b:db:79:4e:45" and know that it's where your fridge is plugged in, so you label that sensor as "Fridge" in your software).
  6. The software can even present the graphs in real money instead of kWh -- this way you'll know that the lights you left on in the bedroom are currently costing you 2 cents per hour, and the 1000W heater you leave on in your garage just in case you have to go down there runs up a nice $2.00 a day.
I'm not an electrical engineer, but I'm pretty sure this is very easy to implement. The sensor shouldn't cost very much, as it's really just a simple watt sensor and a non-programmable broadcaster. The listener device would be a bit more, but should cost about as much as an off-the-shelf wireless router, or less (and can probably be made to fit into breaker panels, providing just a network jack out).

Judging from how much us geeks are obsessed about things like network graphs and memory graphs, I'd say that a system like this would prove pretty popular. Does someone care to take it and run with it? :)

(I have no idea if this has occurred to anyone else before, or if similar systems are already available out there. I didn't find anything from superficial googling, so I assume that no).


Anonymous said...

Something like that perhaps...

Mace said...

Most major appliances don't change their electrical behavior much over their lifetimes. As a result, the Kill-a-Watt is the most cost-effective way to profile your home. Once the data has been collected for a 24-hour period for each appliance, you can easily see the impact each has as a percentage of your total bill. Spending a few thousand dollars to retrofit your outlets won't really get you much more usable data.

Anonymous said...

This one uses XBee modules and a micro to monitor the Kill-A-Watt's opamp -

I'd prefer a digital interface into the guts of the device, but if it works...

Anonymous said...

I don't know much about any of that stuff, however - it sounds really cool to me - especially the idea of having a cost break down - I think it would be good motivation to turn the lights off etc. Nice work.

Anonymous said...