Autonomous micro/nano mechanical, chemical and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro-power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage and delivery to the sensor. In this work, we realized solar light driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen is then consumed by the μFC to generate electricity. Importantly, the byproduct water returns back to the photocatalytic μFG via recirculation loop without losses. Functionality of both devices relies on novel phenomena in extended-nano fluidic channels that ensure ultra-fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ~17.2 mWh cm-2 at room temperature.