Harnessing Solar Energy for the Production of Clean Fuel

The European Union and its member states are being urged by leading scientists to make a major multi million Euro commitment to solar driven production of environmentally clean electricity, hydrogen and other fuels, as the only sustainable long-term solution for global energy needs. The most promising routes to eventual full-scale commercial solar energy conversion directly into fuels were identified at a recent international meeting in Regensburg, sponsored by the European Science Foundation (ESF). An interdisciplinary task force was established at this meeting to make the case for substantial investments in these technologies to EU and national government decision makers. This report summarizes the outcome of this meeting. The fundamental issue is that total annual global energy consumption is set at least to double from its current level of 14 TW by 2050, while fossil fuels will start to run out and in any case would produce unacceptable levels of carbon dioxide, bringing global warming accompanied by disastrous effects in many areas, such as food production. Apart from solar energy, the shortfall can only be made up by renewable sources such as wind, along with the other nonfossil, non-renewable fuel source of energy, nuclear. But these will be unable to satisfy the expected increased energy needs, let alone replace fossil fuels entirely, even for electricity production. Another problem is that they will not readily yield stored fuels. Without an unexpected breakthrough in electricity storage, there will be a continued need for fuels for around 70% of total global energy requirements, particularly in transportation, manufacturing,and domestic heating. Electricity only accounts for 30% of global energy consumption at present. Solar energy, however, is plentiful since enough reaches the Earth’s surface every hour to meet the world’s annual energy needs. The problem lies in harnessing it, but nature has perfected in photosynthesis a highly efficient and flexible means of doing this across a wide variety of scales from isolated bacterial colonies to large forests. Substantial progress has been made recently, particularly in Europe, to understand and mimic these processes, sufficient for scientists to be confident that it can work to produce fuels on a commercial scale. The focus of research therefore should be on drawing inspiration from biological systems for the creation of both natural and artificial solar energy conversion systems that allow in the long run for a stable and sustainable energy supply. The focus should also be on reducing the ecological footprint of the human economy and thereby increasing the global ecological capacity using technology that is environmentally clean, for instance by conversion of carbon dioxide back into fuels in a cyclic process. The ESF task force is recommending that three parallel avenues of solar energy research for generating clean fuel cycles should be pursued in Europe: 1) Extending and adapting current photovoltaic technology to generate clean fuels directly from solar radiation. 2) Constructing artificial chemical and biomimetic devices mimicking photosynthesis to collect, direct, and apply solar radiation, for example to split water, convert atmospheric carbon dioxide and thus produce various forms of environmentally clean fuels. 3) Tuning natural systems to produce fuels such as hydrogen and methanol directly rather than carbohydrates that are converted into fuels in an indirect and inefficient process. These three research themes will overlap, and all will exploit fundamental research elucidating the precise molecular mechanisms involved in the splitting of water into hydrogen and oxygen in photosynthesis by both plants and bacteria. This process, which evolved 2.5 billion years ago, created the conditions for animal life by converting atmospheric carbon dioxide into carbohydrates, and also produced all the fossil fuels, which humans are turning back into carbon dioxide at an increasing rate, threatening catastrophic environmental effects. The same process now holds our salvation again. Although the principal products of photosynthesis in plants and bacteria are carbohydrates, certain algae and cyanobacteria can produce hydrogen directly from water using sunlight, providing a basis for genetic modification to increase yields, and for the creation of suitable artificial systems. Furthermore, photosynthesis is also capable of generating other chemicals currently made industrially, such as nitrates, and other high value compounds for chemical industry. The European research program will therefore also seek to develop systems for converting solar energy directly into such chemicals with much greater efficiency, offering the prospect not just of producing unlimited energy, but also fixing atmospheric carbon dioxide to bring concentrations back down to pre-industrial levels as part of the overall thrust for clean renewable energy. There are considerable challenges, with the first being to mimic the functioning of natural photosynthetic systems, particularly photosystem II, the enzyme complex in the leaves of plants that splits water into hydrogen and oxygen via a catalyst comprising four manganese atoms along with some calcium. Significant progress has been made recently on this front. Participants at the ESF’s brainstorming conference, describe the solar fuels project as the quest for building the “artificial leaf”. There is growing conviction in Europe and elsewhere that by 2050 a large proportion of our fuels will come from such “artificial leaves” and that there is no time to lose starting the crucial enabling research, in order to gain technology leadership in this important future key technology.White paper prepared by the ESF task force on converting solar energy into fuelEuropean Science FoundationPopulariserende publicatieFaculteit der Wiskunde en Natuurwetenschappe