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Low Cost Energy Monitoring

March 21, 2009
Wheres the usb jack?

Where's the USB jack on this thing?

WattsGoingDown Building Systems Insight requires a low cost solution for putting energy measurements on the Internet. Our short-term plan is to use off-the-shelf hardware to create and deploy systems that send energy use data to our servers every minute or two.  A key driver of the software-as-a-service (SaaS) energy monitoring business model will be the balance of the savings realized by customers offset by the cost of the initial installation and WGD’s BSI’s monthly monitoring fees.

When the costs are justified purely by energy savings, monitoring system costing a few hundreds of dollars per monitored circuit only makes sense for higher-voltage, high current systems, or for circuits that are representative of many in the building or facility.

This is because, for a single circuit, the power used scales as voltage and current,  P= V x I . This is why business models centered on home energy monitoring are difficult to justify based on energy savings alone–customers have to be data geeks to make them work.  A typical home circuit runs at 120 volts and up to 20 amps.  This gives a maximum capacity of 2400 Watts per circuit (about two hair dryers).

Over a year, a home owner might run this circuit at capacity a quarter of the time (365 days x 6 hrs/day = 2200 hours).  At $0.10 per kWH, the total cost of running this example circuit is 2200 hours x 2400 Watts x 0.10 cents/kWH = $528.  If energy monitoring enables savings of 25% (aggressive!), you can pay no more than $132 per circuit for the hardware and monitoring to reach 1-year break even.

Without utility or government subsidy, the Tendril system costs quite a bit more. The Kill-A-Watt can be purchased for about $35 but provides no logging, network or analytics.  There is a clever hack, the tweet-a-watt, that adds a wireless Xbee module to the Kill-A-Watt, but you’ll need to be comfortable with soldering and analyzing the raw data yourself. The typical commercial network/analytic-enabled solutions run $750+ (e.g. WattNode + PLC).

So one challenge will be to create low-cost, dependable web-enabled measuring devices, devices so cheap that there will be no hesitation to install them and no motivation to remove them.


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