Hi,
I have been trying to figure out a mysterious drop in power usage at home everyday.

I have a Effergy Engage power meter with the sensor on the main phase cable going into the meter outside, the usage it is reporting reflects what the meter is saying on the occasions I have checked.

There are a number of gadgets and stuff running 24x7, no electrical heating though (gas heating and hot water).  Idle load sits around 400w, which is a little high for my liking but seems to ring true to my IT and comms stack (about 100W), two aquariums with 100W heaters (not on all the time though) plus fridge and other idle stuff.

The screenshot below is fairly typical of power use, shows the idle then a jump when I get home from work and turn stuff on, there is often a peak in the morning too if I have time for a coffee :)

 

The strange thing is the 11am drop.  If I am not home it lasts from 11am to 9pm and is about 100W.  The only thing that I can find that changes in that time is the one of the aquariums, its lights turn on at 11am and switch off at 9pm, but that should result in an increase in power.  The lighting is 36W of fluros and 7.2W of LEDs.  I haven't measured real usage at the point yet on that though.

Now for the kicker.  I unplugged the timer and lights this morning to see what happens.  11am has been and gone and the power hasn't dropped today!

Now how on earth do those lights reduce power usage?  Surely they are not heating the aquarium more efficiently than the heater?  Probably worth pointing out that the heater is in the external filter so not exposed to the lights in anyway so doubt its the lights messing with the thermostat.

This is all very weird.