Efficiency solar hydrogen conversion

An efficient solar energy conversion system for hydrogen production from water, referred to as a solar-hydrogen system, is most important for genuinely sustainable development. However, for such a system to be practical and economical, we must address several remaining issues related to solar-to-H2 efficiency, cost, and stability. 

For the longer term, there is the solar energy conversion challenge. Once solar radiation is efficiently captured it will be stored in the form of hydrogen or electricity, with major challenges again for electrocatalysis. 

Both direct and indirect biophotolysis routes suffer from a number of challenges that currently prohibit them from becoming commercially viable processes [180] these include, but are not limited to, solar energy conversion efficiency and the difficulty of bioreactor design. In particular the low solar energy to hydrogen conversion efficiency is a matter of major concern in the field of biophotolysis. The efficiency is calculated as [180,172] ... 

These systems are based on immersion of two photoactive electrodes in an electrolyte solution with connection via an external circuit. An overall solar-spectrum hydrogen conversion efficiency of 0.25% was found at zero bias for the n-Ti02/p-GaP cell. Nozik further designed a new type of cell, so-called photochemical diodes that do not require external wires and functions without electrical bias [26]. This device [26], consisting of a small sandwich-like structure, Fig.7.2, such as Pt/n-GaP, and n-Ti02/p-GaP connected through ohmic contacts, when suspended in an appropriate electrolyte causes decomposition of water upon exposure to light. 

Over 18% solar energy conversion to generation of hydrogen fuel theory and experiment for efficient solar water splitting, Int J Hydrogen Energy 26 653-659... 

Part IV, "Sustainability" (Chapters 13 through 18), deals with the topics of sustainable development, efficiency, and sustainability in the chemical process industry and a very topical topic, carbon dioxide (C02). The sense and nonsense of green chemistry and biofuels is expounded in this part as well, followed by solar energy conversion and musings on hydrogen in the final chapter of this part. 

Suppose that this energy is to be supplied to cars in the form of hydrogen in a fuel cell from re-formed methanol, (c) How many moles of C02 andH2 would be required to form the methanol (d) Calculate the cubic meters of air per day that would have to be collected at a given gas station to allow extraction of the necessary C02 (0.3% in air), (e) Then calculate the number of moles per day of H2 needed to form the corresponding methanol (fuel cell efficiency is 60%). (f) Calculate the area of solar panels (number of square meters for a 10-kW sunny day) required to produce this H2 at 20% efficiency for the conversion of solar... 

Moore compared the technological branch of solar energy conversion, essentially photovoltaics, with the biological branch. He explained how a standard fuel cell that operates on oxygen and hydrogen produces water and electromotive force. A typical human-engineered fuel cell operates at 50-60 percent power conversion efficiency and uses platinum or other noble metals as catalysts. 

These early tests were not conducted with the most efficient solar cells available at that time. The record efficiency then was about 30% for a laboratory cell (see Fig. 4) and those cells were not easily obtainable. Today s record efficiency is 40.7%, and 35% efficient cells are commercially available.18 Therefore, 40% solar to hydrogen efficiency is expected in the near term assuming a heat boost of 40%, a multijunction solar cell efficiency of 35%, and an optical efficiency of 85%. A 40% multijunction solar cell would yield a solar to hydrogen conversion efficiency of almost 50%. Nevertheless, electrochemical theoretical results calculated by Licht, shown in Figure 10, are consistent with these predictions based on Solar Systems early experiments.15... 

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