  With Australia's significant capacity of household PV, decreasing battery
costs may lead to widespread use of household PV-battery systems. As the
adoption of these systems are heavily influenced by retail tariffs, this paper
analyses the effects of flat retail tariffs with households free to invest in
PV battery systems. Using Perth, Australia for context, an open-source model is
used to simulate household PV battery investments over a 20-year period. We
find that flat usage and feed-in tariffs lead to distinct residual demand
patterns as households' transition from PV-only to PV-battery systems.
Analysing these patterns qualitatively from the bottom-up, we identify tipping
point transitions that may challenge future electricity system management,
market participation and energy policy. The continued use of flat tariffs
incentivises PV-battery households to maximise self-consumption, which reduces
annual grid-imports, increases annual grid-exports, and shifts residual demand
towards winter. Diurnal and seasonal demand patterns continue to change as
PV-battery households eventually become net-generators. Unmanaged, these
bottom-up changes may complicate energy decarbonisation efforts within
centralised electricity markets and suggests that policymakers should prepare
for PV-battery households to play a more active role in the energy system.
