•Integrated cost optimisation model of PV BESS systems including system sizing and battery ageing.•Self-consumption of real-world applications can be increased by BESS up to about 58%.•Break-even battery system price is approx. 900–1200€/kWh.•Importance of realistic consumer load and PV generation profiles for cost optimisation is high.•Results are highly sensitive to economic and regulative framework including support schemes. This contribution presents cost optimisation results from a techno-economic perspective of photovoltaic battery systems. The simulation based optimisation takes into consideration temporal high-resolution consumer load and PV production profiles, technical and economical PV and battery system parameters as well as the regulatory framework in Germany. The results include the cost optimal system configuration under the given framework, the share of self-consumption, degree of autarky, grid feed-in and supply as well as various battery system parameters. The ratio of the installed PV peak power to the useable capacity of the battery was found to have a significant impact on self-consumption, autarky and economic efficiency of the overall system and is one of technical key parameters for a cost-optimised system sizing. The break-even battery system price compared to PV systems without BESS is calculated to approx. 900€/kWh (without BESS support scheme) to 1200€/kWh (with German BESS support scheme). However, the individual taxation of revenues can lower the break-even costs significantly. Furthermore, the techno-economic analysis identifies a high sensitivity to regulation frame conditions and support schemes of PV and BESS for cost optimisation. Another key finding is that realistic load and production profiles must be used in order to allow for reliable statements concerning technical parameters and economic feasibility. Otherwise, cost optimisation results might overestimate self-consumption and lead to an incorrect calculation of the total costs.