  The rapid urbanization of developing countries coupled with explosion in
construction of high rising buildings and the high power usage in them calls
for conservation and efficient energy program. Such a program require
monitoring of end-use appliances energy consumption in real-time. The worldwide
recent adoption of smart-meter in smart-grid, has led to the rise of
Non-Intrusive Load Monitoring (NILM); which enables estimation of
appliance-specific power consumption from building's aggregate power
consumption reading. NILM provides households with cost-effective real-time
monitoring of end-use appliances to help them understand their consumption
pattern and become part and parcel of energy conservation strategy. This paper
presents an up to date overview of NILM system and its associated methods and
techniques for energy disaggregation problem. This is followed by the review of
the state-of-the art NILM algorithms. Furthermore, we review several
performance metrics used by NILM researcher to evaluate NILM algorithms and
discuss existing benchmarking framework for direct comparison of the state of
the art NILM algorithms. Finally, the paper discuss potential NILM use-cases,
presents an overview of the public available dataset and highlight challenges
and future research directions.
