I noticed that if I get enough power AA in S7 (especially if I replicate an Integrated Singularity Reactor), I can beat extended even after losing all my reactors. So maybe I could evolve an additional utility slot instead of a power slot?
I tried it. The plan here was to use energy-related utils, until I could get power AAs. Unfortunately, I decided on this AFTER -7, which is the best floor to pick up a Fusion Compressor, which would be an excellent item for this! Instead I got myself a Zio. Light DM Reactor, which I had to pair up with a Zio. Biocell (I was imprinted) for factory floors. This was a CProg farming run, so I was using hover propulsion and I had EMDS, which uses more energy than regular energy weapons, hence I needed some storage (and Zio. reactors have 0 storage). That's quite an energy devouring build, whether moving or fighting.
At -4 Zhirov gave me +10 energy! Just in time! Energy was getting really tight by that point. At -3 I got my hands on an Imp. Fusion Compressor schematic (from a green terminal in large unaware base in -3/Proximity Caves) and managed to fab it in Research, in case I will need more energy generation soon. It proved to be super useful soon (QC + EMDS, more hover slots, other high tier utils consume a lot of energy as well...)! At -3 I went to L instead of Q. Got CE (weapon slot) and Heat Dissipator. -2 had T and S7. I didn't find any strong energy cannon (I recognized from DC intel that none of the barriers held Potential Cannons; maybe I should've checked them anyway for a Null Cannon or a Cld. Nova Cannon?). S7 had no energy AAs. Not a single one. Even LRC Energy Well would help greatly, but no!
I considered evolving a 2nd power slot for the final floor. But I decided otherwise. Imp. Fusion Compressor really carried this run and matter wasn't an issue (but I wasn't using it until my energy reserves got very low -- that's why it survived for so long). I ended up using a Zio. Heavy DM Reactor + Imp. Fusion Compressor + Exp. Energy Well, with a backup Exp. Energy Well and a Graviton Reactor. I could use QC + Energy Cannon (or Molecular Deconstructor) and AEGIS Shield. Ended up with a w6++.
Some conclusions about single power slot builds from this experiment:
Single reactor builds have a problem with energy storage and often need a slot dedicated to Energy Well anyway.
Ground-based builds would probably be just fine with a single F-Cell Engine (great storage for combat, enough generation to replenish energy stores while moving) in Factory floors. I didn't need 1000 energy stored in my Biocell until lategame and if I didn't hover, I probably wouldn't need 20+ energy generation from Zio. reactors. Visiting Cetus for a Quantum Reactor might be enough for Factory floors as well (without any energy utils, such as Energy Wells).
F-Cell Engine + a Fusion Compressor would probably be the best combination. -7 is the best floor to grab some rating 4 Fusion Compressors. That could be enough to solve your energy issues until you get energy AAs (or survive to the next evolution if you find none).
In the end, I used 3 slots for energy management, which is pretty normal if I don't get energy AAs. But if I got a Subatomic Replicator and an Integrated Singularity Reactor, I could probably take it all down to just one slot with a Quantum Reactor, used for energy storage rather than energy generation
And an LRC Energy Well would be really useful for a single power slot build, since energy storage is quite an issue there. Saving on a power slot only to spend a slot for an Energy Well might not be that great. Then again, Energy Wells are much lighter than reactors and don't generate any heat.
I might be going for this kind of build more often now. Partly, because I'd like to see how it fares if I get a Subatomic Replicator + Integrated Singularity Reactor combo (my usual way of spending SR anyway).