When we were using incandescent bulbs of 60 or more watts for lighting there was a real power saving in using daylight to illuminate dark rooms.
Now we have installed LED bulbs that only use 3 – 4watts.
That small amount of power doesn’t cost us anything during daylight hours as we have 3 kwatts of solar panels on our roof.
It seems to me that any advantage from the skylight is probably lost due to the lower level insulation as a result of the tube.