ETASECS aims at making a breakthrough in the development of photoelectrochemical (PEC) cells for solar-powered water splitting that can be readily integrated with PV cells to provide storage capacity in the form of hydrogen. It builds upon our recent invention for resonant light trapping in ultrathin films of iron oxide (a-Fe2O3), which enables overcoming the deleterious trade-off between light absorption and charge carrier collection efficiency. Although we recently broke the water photo-oxidation record by any a-Fe2O3 photoanode reported to date, the losses are still high and there is plenty of room for further improvements that will lead to a remakable enhancement in the performance of our photoanodes, reaching quantum efficiency level similar to state-of-the-art PV cells. ETASECS aims at reaching this ambitious goal, which is essential for demonstrating the competitiveness of PEC+PV tandem systems for solar energy conversion and storage. Towards this end WP1 will combine theory, modelling and simulations, state-of-the-art experimental methods and advanced diagnostic techniques in order to identify and quantify the different losses in our devices. This work will guide the optimization work in WP2 that will suppress the losses at the photoanode and insure optimal electrical and optical coupling of the PEC and PV cells. We will also explore advanced photon management schemes that will go beyond our current light trapping scheme by combining synergic optical and nanophotonics effects. WP3 will integrate the PEC and PV cells and test their properties and performance. WP4 will disseminate our progress and achievements in professional and public forums. The innovations that will emerge from this frontier research will be further pursued in proof of concept follow up investigations that will demonstrate the feasibility of this technology. Success along these lines holds exciting promises for ground breaking progress towards large scale deployment of solar energy.