Another builder was looking for an electrical loads analysis, here is what I have so far. The 915iS engine has dual internal generators; the ‘A’ generator provides power to the Engine Management System (EMS) normally, and a second ‘B’ generator supplies power for everything else in the airframe, up to 420W (30A @ 14V). Under steady-state conditions I should be using about ~22 amps in IFR conditions, and <13A in VFR conditions. The worst-case load is a hefty 52A, but that’s a hypothetical situation — it would mean all radios transmitting simultaneously, flap motor running, prop cycling, heated pitot at max draw, etc., so I don’t really size the electrical system for that. For any short-term excess draw above 30A, the battery will augment the generator.
I have not yet heard of, or seen another Sling TSi that has an additional external alternator, and several are already flying, so it appears that the internal generators are adequate for a typical set of electrics.
In my spreadsheet below, I also have some numbers assuming the install of the Edge Performance EP914Ti, an engine option I was considering at one time. The EP914Ti would need an external alternator, as the internal generator in the 912-series only supplies a max of 22A, with some of that used by the Edge Performance ECU and fuel pumps.