Abstract: The need for sustainable renewable energy has never been more urgent. Harnessing solar power to drive the electrolysis of water to produce green hydrogen is a promising future source for energy capture, conversion and importantly, storage. The EU’s Horizon Europe project, “FreeHydroCells” is dedicated to developing new materials systems made from earth abundant elements to capture solar power to drive photoelectrochemical (PEC) water splitting for the production of truly green hydrogen. Measuring the on-set of Hydrogen production at photoelectrodes, in an open system during research phase, is highly challenging. Here we show how Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) can readily track gas evolution in real time. We also show how it can be used to determine efficiencies of new materials by tracking the kinetics of gas evolution during PEC. Previous approaches required gas collection in a closed system with no real time information with regards to gas evolution on-set or its kinetics. In addition, BARDS allows characterisation of custom architectures of photoelectrodes for the most efficient bubble growth and release. Our independent BARDS and PEC methods, combined with a high-precision solar simulator, will possibly permit the direct assessment of Faradaic and Solar-To-Hydrogen critical efficiencies for the novel materials systems through the assessment of gas evolution on-set and production at photoelectrode surfaces in comparison to photocurrents. We anticipate our results will improve the accuracy of the efficiency measurement and enable the optimization of the most efficient solar photoelectrode configurations coupled to the appropriate architecture for efficient PEC for green hydrogen. Acknowledgements: This project work has received funding from the European Union under grant agreement No 101084261 (FreeHydroCells). This publication has been financially supported(in part)by the Science Foundation Ireland (SFI) Centres Grant, Grant Number 12/RC/2278-P2 (AMBER). © 2023, the Authors.