Reductions in the cost of PV and batteries encourage households to invest in PV battery prosumage. We explore the implications for the rest of the power sector by applying two open-source techno-economic models to scenarios in Western Australia for the year 2030. Household PV capacity generally substitutes utility PV, but slightly less so as additional household batteries are installed. Wind power is less affected, especially in scenarios with higher shares of renewables. With household batteries operating to maximise self-consumption, utility battery capacities are hardly substituted. Wholesale prices to supply households, including those not engaging in prosumage, slightly decrease, while prices for other consumers slightly increase. Given the power sector repercussions modeled here, we conclude that the growing adoption of prosumage needs to be carefully considered by power system planners and investors of long-lived utility-scale renewable generation and storage assets to prevent overinvestment. Likewise, regulators should encourage greater system-oriented use of battery flexibility from prosumagers in the energy transition.