Record your power usage over time using simple and cheap hardware (Arduino) to capture the flashing LED on the electricity meter.
I attached the LDR to analog pin 2 instead of analog pin 3 as showed in this
To prevent the Arduino to reset when opening the COM port, the resistor coming from the DTR line of the FTDI chip going to the reset pin (R3) has to be removed.
I use a variant of the Arduino, the Freeduino, on which I had to make the capacitor indicated as CRS removable to prevent the Freeduino to reset.Example
of a chart generated using this hard+software.