We investigate the direct conversion of solar energy and water into a storable fuel via integrated photo-electrochemical (IPEC) devices. Here we focus particularly on a device design which uses concentrated solar irradiation to reduce the use of rare and expensive components, such as light absorbers and catalysts. We present a 2-dimensional coupled multi-physics model using finite element and finite volume methods to predict the performance of the IPEC device. Our model accounts for charge generation and transport in the photoabsorber, charge transport in the membrane-separated catalysts, electrochemical reaction at the catalytic sites, fluid flow and species transport in the porous charge collectors and channels, and radiation absorption and heat transfer for all components. We then develop performance optimization strategies utilizing device design, component and material choice, and adaptation of operational conditions. Our model predicts that operation under high irradiation is possible and that dedicated thermal management can ensure high performant operation. The model shows to be a valuable tool for the design of IPEC devices under concentrated irradiation at elevated temperatures. To our knowledge, it is the most detailed yet computationally low-cost model of an IPEC device reported.