The barely perceptible jump around 21:00 is, I think, me turning on the switch,
Compare this to the much sharper and more well defined jump around 01:00 where I was playing a game on my desktop causing increased CPU/GPU load.
Assuming worst case 75W 24/7 that's 1.8 kWh a day, or about $11 a month at my current power prices. But that's a worst-case number and I expect the actual number will be quite a bit less.
Put a different way, this time of year on a sunny day *one* of my solar panels puts out enough power during daylight hours to run this switch for the entire day, including overnight.
