Improved Solar Energy Extraction Using a Combined Photo-Electrochemical / Thermal System for Domestic Applications

Hydrogen generation is a significant area of energy research, with the aim to deliver low-cost, renewable energy sources which are environmentally friendly. One possible method is solar water splitting via photo-electrochemical reaction. Photo-electrochemical (PEC) hydrogen generation is a promising technology and alternative to photovoltaic (PV)-electrolyser combined systems. Although the PEC technology is promising, the efficiency of this technology is limited by thermodynamics and technical issues. Recent research has focused on aspects of materials development to improve efficiency. With multiple band-gap electrodes, the thermodynamic efficiency, and so the overall generated hydrogen quantity, can be increased. In the case of applications where there is a heating requirement beyond the need to generate hydrogen, there are further options for extracting energy from the solar resource by utilizing the longer wavelength radiation.

Just as it is possible to have a PV/T hybrid system, the PEC unit may also be used in a PEC/T hybrid mode, thus delivering both heat and power as a CHP system. Despite the promise of PEC technology, there is little research on it in terms of modelling and system simulation. According to the knowledge of the authors there is no published research on such hybrid systems.

In this work, a model of a hybrid PEC/T system has been implemented.  Simulations with this model were carried out to compare PEC technology and its developments in terms of energy gain in a home environment where both heat and electricity demands are used. When there is heat demand, a buffer tank is implemented for heat storage.

Case studies were considered, consisting of a typical three-person household in the UK to investigate the present and the near-future capability of energy supplying and reduction of CO₂ emission according to the UK building energy regulation.

Results show that single band-gap photo-electrode materials are not able to cover completely the energy demands for the household if demand includes space and hot water heating. However, with multiple band-gap electrodes and with extra solar heat (or combined PEC-thermal) utilization the system efficiency can be significantly increased.