Design and Cost Considerations of Solar-Fuel Devices

Recent environmental concerns have led to an increased interest in the deployment of renewable energy technologies. Electrochemical energy conversion devices that can directly capture and store solar energy in the form of fuels are a promising alternative to increase the share of renewables in our current energy landscape. In order to deploy solar-fuel technologies in large scale, practical devices need to operate continuously and stably over long periods of times, need produce more energy over their lifetime than they require for their fabrication and need to generate fuels in an economically viable way. To this end, significant research efforts have been devoted towards the development of photoelectrochemical components that are able to spontaneously split water in the presence of solar irradiation. These efforts have resulted in major advances in the solar-fuels field over the past decade, while only limited attention has been given to understanding the factors that drive economically viable solar-fuel generators. In this presentation we will describe a system agnostic approach that allows for the understanding of economic factors behind the design of solar-hydrogen generators.(1) Using this framework, we evaluate the effects of the material selection for the light absorption and water splitting components on the cost of the generated fuel ($/Kg of H₂). Furthermore, guidelines for optimal designs for solar water-splitting devices are formulated in order to minimize the cost of hydrogen production. The results presented here provide insights into engineering aspects related to device design and the use of light concentration components that, when optimized, can lead to costs below $2.90 per kilogram of hydrogen after compression and distribution (reaching comparable cost levels to hydrogen produced from fossil fuel). In order to achieve these low hydrogen production costs, optimized devices will need to be fabricated with water splitting components that are significantly smaller in area than light absorption units (by a factor 10-100’s). Moreover, the analysis demonstrates that in optimized devices the cost of hydrogen is primarily driven by the light-absorbing component while the material selection for the electrolysis components has minor effects. This suggests that the development of highly efficient and inexpensive photovoltaic components for solar water-splitting can greatly facilitate the implementation of the technology. The findings discussed here can help direct research and development efforts towards the fabrication of scalable solar-hydrogen generators that are cost competitive with commercial energy sources.       

1.         C. A. Rodriguez, M. A. Modestino, D. Psaltis, C. Moser, Design and cost considerations for practical solar-hydrogen generators. Energy & Environmental Science,  (2014). DOI: 10.1039/c4ee01453g