Nonintrusive load monitoring

Nonintrusive load monitoring (NILM), nonintrusive appliance load monitoring (NIALM),[1] or energy disaggregation[2] is a process for analyzing changes in the voltage and current going into a house and deducing what appliances are used in the house as well as their individual energy consumption.

Nonintrusive load monitoring was invented by George W. Hart, Ed Kern and Fred Schweppe of MIT in the early 1980s with funding from the Electric Power Research Institute.

As shown in figure 1 from the patent, a digital AC monitor is attached to the single-phase power going into a residence.

A stand-alone in-home system, under the control of the user, can provide feedback about energy use, without revealing information to others.

The accuracy and capability of this technology is still developing and is not 100% reliable in near-real-time, such that complete information is accumulated and analyzed over periods ranging from minutes to hours.

Figure 1 from US patent 4858141 showing basic process for NILM
Figure 8 from US patent 4858141 showing how differences in reactive power can help distinguish one appliance from another