Summer Power Issues

You want a Furman with AR (voltage regulation)

solar with 90+ degrees works great. i know how to get them cheap.

Ditto on the Furman.  I use an M8X AR, which will handle 15 amps.  Last summer my line voltage dropped as low as 113VAC, and my tube amps and tube preamp really suffered.  The Furman keeps it at 118-120, and I have not felt it affected the sound.  On the contrary, everyone sounds happier to be operating where they should be.  Prices for this unit have gone up--I paid $385 for mine, they're now $500-700.  But well worth it, IMO.

Even if you just go with a conditioner, the Furmans are affordably priced and are regularly used by recording studios.

Besides summer demand droops, my grid has a bad habit of blinking off and on all year round on perfectly sunny days. I have used a Square D 1 kva isolation transformer at my distribution panel with a dedicated 20 amp circuit to feed a Furman SPR-20i conditioner/regulator since I moved here and have been very pleased with it's performance. One kva sounds low but delivers 8.33 amps which is more than enough for my system. The SPR-20i is very quick and has no trouble tracking voltage changes, and the surge suppression circuit is non-sacrificial. I have no idea if it affects the sound, but my system sounds the way I want it to sound using it, and I'm 100 % sure it sounds better than a fried system 😉.

I work for a utility and 4 to 5 pm is near the peak and probably still increasing.  Now some solar will come off if you have solar.  Solar and wind are the worst power--not synchronized to the grid and have to be managed by the system.  I have an oscilloscope on my power and total harmonic distortion does not change much with the clock.  the thought that your system sounds better at night because the power is cleaner is an old wives tale.  It sounds better because less ambient noise, relaxed listener, and pehaps a glass of wine.

I would not expect bad power to make your system sound harsh since that implies a change in bass/treble balance.  It would more affect transparency, detail, accuracy and soundstage.  

As for fixing summer bad power, the only way to do it is regenerative.  "conditioners" that just try to filter noise are either useless or worse.

JErry