Dear Prof. Erkan Aydin,

   The following attached papers and the mentioned link will be useful for your analysis..

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b08397?journalCode=jpccck

Thanks for your answer Maharaja. So, what is your comment depending on the papers you send?

Erkan

Dear Erkan,

Your question is very interesting and i worked on it where i was in King Saud University. There was a project called Hydrogen Solar, Hysolar. The main objectives of the project was to study and develop photoelectrochemical electrodes for hydrogen analysis. The existing hysolar electrolysers are composed of a separate photovoltaic power generator driving a conventional electrolysers at maximum power transfer condition. This system gives the highest efficiency since one can optimize the working conditions of the photo-voltaic array and the electrolyzer separately and there will be sufficeint degrees of freedom to do that.

In case of combining the two functions to be performed by photoelectrochemical electrodes, the degrees of freedom of the structure will be less except one uses complicated structures. From the conceptual point of view according to my preliminary analysis the highest achieved conversion efficiency will be at the best equal to the separate components system. 

The development of efficient photoelectrochemical electrodes for hydrogen analysis is very important issue and can save in the costruction cost of the system

The saving will be in the materials when one combine the two functions. Since this effort i did not follow the topic in spite of its importance. I moved from King SAud University to Ain Shams University.

My best wishes

Thanks for you commands Prof. Zekry. I am pretty sure that hydrogen generation using sunlight (in both forms) has a tremendous potential. Is there any report in literature explaining the theoretical solar-to-hydrogen efficiency limit of photoelectrochemical cells?  My question is also a bit different. If we have a snapshot of the current technological developments and consider the practical maximum efficiency and economic constraints of two state of the art technology, which one has more potential in near future?

I would of course agree with Prof Zekry. I have looked at this issue over a period of many years and despite coming across many innovative and attractive methods for using sunlight to electrolyse water in a single cell, or single structure, when you calculate the photonic efficiencies they are not as good as just generating electricity in a good silicon PV array and electrolysing water with suitable electrodes to reduce the overvoltage and increase the efficiency. Sadly. Then you have the problem of managing the hydrogen in a 'hydrogen economy'. But that's another story.

Dear Erkan, 

I think that up till now there is no commercial direct photoelectrochemical system for water splitting since simply it is under development. For more information please follow the paper in the link:http://www.nature.com/articles/ncomms11943

Other very important paper in the link:https://arxiv.org/pdf/1604.01094.pdf compares the indirect and the direct photo analysis of water for hydrogen production.

wish you success.

Thank you all for your answers. Basically, we have numerous technical and economic analysis in literature for the generation of hydrogen using solar energy. However, most of them reflect the possible scenarios and projections for the future. You can find attached some of them.

A recent comprehensive techno-economic analysis of Pinaud et al. (2013) suggests that for a PEC device produced at a hypothetical cost of $80 m−2 with a solar-to-hydrogen efficiency of 10% and a lifetime of 10 years, would produce hydrogen only as low as $7 kg−1, which does not put it at a large advantage over PV-electrolysis. However, you know that there has been a surge of interest in developing PEC electrodes In recent years. Moreover, it should be noted that new families of catalysts have emerged in the last years due to the intense interest in the field. 

You know that economic considerations are the ultimate driving force for this kind of technologies. Hence, it seems that we should wait to until the first attempt for the grid scale fabrication of hydrogen using PEC cells to see the competitiveness of this technology. 

Article Technical and economic feasibility of centralized facilities...

Article Modeling, simulation, and design criteria for photoelectroch...

Article Semiconducting materials for photoelectrochemical energy conversion

Be aware that a pure electrolyser can generate hydrogen under quite high pressure whereas a PEC generator may be limited to atmospheric pressure or near it, otherwise it would burst. So you have to factor in the cost and effectiveness of compressing the 1 bar hydrogen with a PEC generator.

I don't want to rain on your parade but it is much better for the environment if you use the electricity you produce to back out coal fired or any other fossil fuel base power generation and use steam methane reforming to produce all of the  Hydrogen you need.

I will concede that some commercial solar installations could sometimes produce more electricity than the grid can handle and producing H2 with this otherwise wasted electricity could be a viable option.