It would hopefully be difficult for differences in mains electricity (say at different times of day, assuming no extreme problems like blackouts or bad brownouts) to cause appreciable changes in signals delivered, but that's not how it was for the "reference" tube amp to be emulated in the Carver challenge, for example. The mains power can readily be measured, and so can be output of electronics and transducers, and these things can make a difference in certain scenarios (the key point being the magnitude of such changes and also the type; magnitude may be undetectably small in many cases for certain measurement apparatus or our ears). I don't know that there's anything controversial there.
My expectation would still be that, very much especially for gear with better power supply filtering and/or lower susceptibility to power line fluctuations, the more key contributing factors would be ambient noise level and listener state of mind.
By the way, it depends on where you live but many people feel more comfortable in spring and early fall because of the typical weather patterns. In many homes it is also less likely in those times for heating or cooling systems to be running—as you point out—and many of those make noise.
As humans, it is a good thing that subjective experiences vary. However, when proving a point or at least providing arguments about cause and effect relationships, it helps to be mindful of confounding variables and address them. A lot more is different between two listening experiences than just the electricity going to the electronics, even given the same gear and music and even same volume (though it was unspecified whether volume was kept constant, and that is a big deal perceptually). And some of these aspects definitely do alter the perception of those experiences.
Usually when offering discussion with respect to new or not by-the-books ideas with respect to science (which is a good thing; that's often a way how knowledge is expanded), it is better to provide solid evidence or at least some well-reasoned concepts and ideas. Hopefully this was posted here in earnest and not to troll, which is an intent that may be inferred by the childish-sounding name calling right out of the gate.
Edited by mikeaj - 1/9/14 at 11:03pm