I'm not aware of any building that you absolutely need 3 MTi or more.

In my playthrough, which started with the release of V1.0, I am now at over 30 GTi and have had no problems with the power supply.

Did the error occur automatically when you reached 3 MTi, or did you do something?

I have the same problem, except I got to about 4.00 MTI. Everything stopped working and my power screen shows 0.00 consumption and production.

I had the same problem twice, but I think in my case it had to do with my mods. I suspect that the inventory stacking mod was the main culprit, especially since I changed the stack sizes mid play to move my base around.

Right now I'm on my third playthrough, well over 1 TTI and no issues at all. I'm using a whole bunch of mods, inventory stacking included, all in the versions that were current on akarnokd's github until a few days ago. Haven't installed his newest version because they seem to be for game version 1.003, which isn't on gog yet.

TL/DR: Are you playing with mods?

There is a newer version: 1.003 on Steam in which Miju fixed a problem with energy when loading different games. I play this version on Steam but I also have version 1,002 on GOG, in which I experienced loss of power at a certain moment in the game also.
Hopefully the game on GOG will update soon............

Happened to me, too, also at 3MTi. So I saved, exited, went to bed, restarted the game, everything was fine. Almost like it wants you to take a break every once in a while.

I was wondering why it happened this time, and was afraid it was my new, more optimized playstyle. I've got rocket boots, T4 oxygen and backpack, 4 ore miners going, ready to launch a rocket, just waiting so the meteorite chunks will vanish when it's dark

I've never been able to progress this fast before. Glad it appears to be nothing.