Water kettle energy consumption logging

Hello,

I want to log energy consumption of a water kettle. On 24x7 and used
through the year. Minimum resolution should be 10 seconds. I don’t really
need absolute values. Only want to know if lowering temperature for a
period is efficient. 

Energy necessary to heat water is easy to find. On Wolfram Alpha as
example. Unknown is the initial temperature. I do have a temperature sensor
accurate in the 30°-99°C  range. 

Another option is a smart plug. But adds friction through proprietary
interfaces. Also found a scientific article casting doubts about accuracy
of consumer devices.

Many articles in scientific literature consider water kettles energy
consumption. As example “Life cycle environmental evaluation of kettles:
Recommendations for the development of eco-design regulations in the
European Union”. Scanning them haven’t found what I need. 

Thanks for sharing.