The air independent propulsion (AIP) versus Lithium-ion Battery (LIB) debate or versus (LIB + AIP) all powering fully submerged Propulsion + Hotel Load (including combat system) continues. This debate extends back to US Combat System May Have Pushed Out AIP in the CEP, November 25, 2016 and beyond.
AIP may be most strongly advocated by Germany because German companies (including Siemens and TKMS) have the most demonstrably highly developed (fuel cell) AIP system. This translates into advantageous product definition in Australia's CEP.
Japan is pushing its LIB (future in submarines) and already built broader diesel-electric propulsion system for the large Soryu. Japan can point to the Soryu being closer to the 4,000 ton weight of the submarine proposed for Australia than SSKs built by the German and French competition. I also suspect that the Japanese diesel electric system is already powering an AN/BYG-1 similar Japanese Combat System
France can point to comprehensive whole submarine integration experience for large nuclear submarines that even exceed 4,000 tons.
As an historical aside Japan could point to the 6,000 ton I-400 class submarines commissioned in 1944-45 and France could point to the 4,000 ton Surcouf commissioned in 1934. Meanwhile Germany packed the highest actual military value into the smallest submarine designs practical.
https://upload.wikimedia.org/wikipedia/commons/e/e8/Imac_16-9.png (400 Watt for 4.0 GHz i7-6700K with 64/64-bit).
((Power usage is related to the display. The 21.5-inch display version needs just 300 Watt))
The Siemens Fuel Cells provide about 300 kW for a Type 212 submarine. Enough power for 1.000 iMacs with a "small" display.
The first methanol reformer for submarines was tested in 1999:
Fuel cells for submarines are mature systems. How many commissioned submarines use LIBs today? The three Japanese submarines will be commissioned far too late to make a decent decision in 2016. [Pete Comment - nevertheless LIBs are planned for the German designed future 216s https://de.wikipedia.org/wiki/U-Boot-Klasse_212_A#Klasse_216 ]
Here on page 10 is a nice scaled and dimensioned drawing:
You can see how big the complete fuel cell system is and how the engine compartment (to the left) is quieted on Type 212 submarines - a double hull around the diesel engine compartment. Just the modules encircled with red and yellow belong to the FC (German: Brennstoff-Zellen - BZ) system. The area marked green is a regular switchboard necessary on every type of submarine (just ask for further translations)."
I understand that the AN/BYG is a fault tolerant multi core multi processor parallel computing architecture. So if each of the node has 8 quad core Xeon or Itanium processors and say there are 512 nodes, the power consumption can get big very fast.
It needs to be remembered that Combat System is just part of a submarine's "Hotel Load". Added to Hotel Load is Propulsion Load. So total reliance on AIP does not equal Combat System electrical demands.
While a submarine combat system may have a clock speed 1,000 times faster than say 10 years ago the software demands may have also increased greatly. This is similar to software demands keeping pace with and steadily passing current home computer hardware storage and speed capabilities.
Historically for a submarine's electrical power requirements AIP doesn't appear to have been rated as a high requirement for Australian submarines. The Collins planners could have included AIP as fitted or retrofitted. Lack of AIP has also not featured on media or official inquiry fault lists for the Collins.
However if the South China Sea may be one of the major patrol areas for Australian submarines then the rising quality of Chinese anti-submarine sensors needs to be anticipated. This boils down to an increased requirement for fully submerged operation in the South China Sea.
For a (say) 30 day operational mission in the South China Sea LIBs may not adequately or safely cover the whole period or whole speed range from (say) 4 knots to 10 knots. AIP may be needed for 4 knot operation and LIBs for 10 knots.
Meanwhile for transit from Fleet Base West (Rockingham) to the South China Sea at 10 knots (as fully submerged as possible ie. short snorting periods) LABs may well be inadequate. So LIBs may be the answer. This perhaps is making LIBs a high priority requirement in Australia's CEP.