Harnessing Light Solar energy for a low carbon future win. RISC. Org Registered Charity Number 207890 Solar energy for a low carbon future “Solar energy is the only energy source that is essentially pollution free and distributed across the planet. ” Climate change, energy security, and a looming energy gap are all driving research and development into clean, renewable energy supplies. Scientists and engineers are looking at how to harness sunlight to help meet society demands to mitigate all of these potential problems.
An RISC policy seminar, chaired by Professor Robin Permute, began by looking at how the lied first developed and what challenges still need to be met. Professor Anthony Harriman of the University of Newcastle introduced the field of photochemistry and issues of funding and trained scientists. Exploitation of laboratory research was discussed by Professor Sir Richard Friend of Cambridge university, and new developments In solar cell technology were presented by Professor Michael Geezer, from the Cole Polytechnic’s Federal De Lausanne.
Finally, how nature produces energy from sunlight and what man kind needs to do to emulate this, was discussed by Professor Jim Barber of Imperial College. Hydrochemistry: a beginning One hundred years ago, the 20th century’s most famous scientist, Albert Einstein, worked out how light interacts with matter – the photoelectric effect. It was for this work he was awarded the Nobel Prize in Physics in 1921. Although there was some knowledge of photochemistry, it was down to Einstein that the close relationship between photochemistry and the photoelectric effect was determined.
Einstein work establishing the laws of photochemistry can be seen as the real starting point for understanding and exploiting solar energy. This is true regardless of whether this is taking place n manufactured solar cells, or in natural photosynthetic systems. Challenges for the future There is a need to generate power effectively and efficiently from artificial solar cells, and also to use light to produce fuels, such as methane, methanol or hydrogen. Importantly, this needs to be done on a large scale. After 100 years the question is now: can this be done?
To an extent it can be, and scientists know a great deal about how photochemistry works. Crucially though, there is a need for further understanding of photochemistry and development of new technologies. Currently, about 3 gaga Watts of energy is reduced worldwide from solar cells, but there is a need to reduce their cost so that every household can have one on their roof. There is a surplus of solar energy falling on the planet, and mankind would only need to harness a small proportion of it to meet its needs. There is a massive challenge to get the technology right.
Importantly, solar energy is the only energy source that is both essentially pollution free and distributed across the planet. A huge effort is needed to solve those barriers to exploiting solar energy. It needs scientists, politicians, research fund providers, and many more, on board. It is not just a case of improving energy efficiency for current technologies, even though this is important, but there is a need for massive investment to take solar energy conversion forward. The effort required to attain the next generation of technologies has been compared to the Manhattan project.
Although this is not entirely appropriate because solar energy conversion is a peaceful technology, it does indicate the scale of effort required. Photochemistry Professor Anthony Harriman explained that it is important to contextual solar energy conversion in regards to the fundamental field of photochemistry. Research has been going on for over 30 years concerned with trapping light in molecules in order to do something useful. Photochemistry is using light, and not necessarily just the sun, to make a chemical reaction work. Over a number of years this has divided into two fields.
The first, the fundamental research, has focused on molecular species that are formed when a substance absorbs light. They are often very short-lived, and so there has been a need to measure them on Increasingly short timescales. The second, more applied area is often the reason why people are interested in photochemistry. It is concerned with how we an use light to carry out unusual chemical reactions, and even reactions that may not be possible using alternative techniques. Unusual species, or high energy states, can be created using light and they often have unique chemical properties.
It is the understanding of how to produce these strange intermediates, and subsequently how to exploit them, that has been the driver for applied research. These high energy intermediates can be dangerous. In a similar fashion to radiochemistry, there are examples in which photochemistry can lead to both good and bad consequences. One example is sun exposure. It can lead o painful sunburn and can also lead to skin cancers. Conversely, though, the same photochemistry can be applied to removing cancerous tumors.
Science and nature Scientists aspire to replicate many of the essential features of photosynthesis, the process by which plants use sunlight to produce oxygen and organic molecules. The crude picture is that scientists would like to harness sunlight to obtain oxygen and hydrogen from water, a very difficult process to achieve, and to generate a fuel. In the past hydrogen would have been an acceptable fuel, but now attention has become focused, by warnings of climate change, on removal f carbon dioxide from the atmosphere to furnish a fuel.
Research aimed at producing artificial photosynthetic systems began in earnest in the 1 sass, and carried on at a rapid rate for about 10 years. Since then, fundamental photochemistry research has died away. This is for several reasons, but primarily it is the lack of funding and the change in motivation. If the money and opportunities returned, then chemistry could be put back at the heart of developing artificial photosynthesis. Until that happens, the motivation will be driven elsewhere. How to collect light Considering all known photochemical yester, it becomes possible to divide them quite clearly depending on the objective.
Firstly, it is necessary to collect sunlight. There is plenty of energy in sunlight, but it is dispersed and so it becomes essential to collect energy from a large enough area to be able to do useful chemistry. However, if the idea is to use sunlight to produce fuels then it must be done at a highly localized site otherwise more energy is expended concentrating it than is obtained from burning it. In terms of the chemistry, light needs to be collected and then directed to sites “Fundamental photochemistry research has died way…. Primarily because of a lack of funding. ” within the system in which high energy intermediates are formed.
More specifically the light is used to drive what is called charge separation; one part of the system will become positively charged and another will become negatively charged. These charged species can then facilitate reactions to produce fuel. On this scale is currently beyond them. Considering molecules on this scale Of complexity illustrates the need for repair mechanisms. It would take a huge effort to reproduce the photosynthetic centers artificially, and so if components get damaged here needs to be a way to remove and replace them instead of beginning again from scratch.
In plants it is chlorophyll that absorbs light, and this is renewed naturally on a frequent basis, and the human body is capable of repairing itself when sunburns. Scientists can duplicate many of the essential features of photosynthesis, from collecting light to carrying out reactions, but so far coupling them all together into one system has proved elusive. Through the study Of photosynthetic systems it has become apparent, however, that organic molecules exposed to sunlight for an extended amount of time will degrade.
This raises problems if artificial systems are constructed from expensive molecules. If they are fragile and degrade then it raises the question of how to repair them. Learning how to interrogate a complex system, find damaged components and then renew them is at least as challenging as it is to harness sunlight in the first instance. If you consider the solar flux across the UK there is enough sunlight available in the North of Scotland to run solar cells efficiently. In Cornwall, it may become necessary to attenuate the light so as to avoid damage to the molecules in the solar cells.
Photovoltaic cells An alternative method to harness energy from sunlight is to exploit minerals and inorganic materials. Currently, this is the way that the field is developing, and arguably this is the less intellectually challenging in the first instance. It is looking at the problem in a more applied manner. Rods, porous tubes and other structures can be produced from inorganic materials and minerals. Catalysts can then be embedded in these structures and light used to produce the intermediates that will generate the desired reactions.
This is the direction that the field of photochemistry is taking at the moment. The same principles are being exploited, but with different materials. The many uses of photochemistry The beginnings of artificial photosynthesis “Photochemistry has brought, and can bring, many more beneficial applications than just energy generation. ” Initially it was thought that photosynthesis in plants was occurring through a random distribution of chlorophyll in leaves, and that this should be relatively easy to replicate in the laboratory.
However, an increased understanding of photosynthesis shows us that this is not the case. Nature has learnt to position molecules precisely, with angles, orientations and distances carefully determined. Scientists may be able to reproduce parts of this system, and to understand the different reactions occurring, but to build and manipulate artificial systems Photochemistry has brought more, and can bring many more, beneficial applications than just energy generation. Importantly, they all rely upon the same basic principles: the interaction of light with matter to create unusual chemical species.
Applications are highly diverse, and range from advanced molecular computers to medical diagnostics. Photochemistry can provide answers to many of the challenges facing society, especially in pollution control and environmental clean-up. Systems based upon the use of titanium dioxide can already be found commercially, and can be used for large scale clean-up of buildings. Large scale ultraviolet systems can also be used to purify water supplies. This could be done in remote and developing countries with current technology and to massive benefit.
The cleaning of stagnant Water with dye molecules could also be achieved, leading to temporary eradication of mosquitoes, and hence malaria. Photosynthetic therapy (PDP) works along the same principles. A molecular compound is injected into a tumor, and then a laser is used to excite it and generate chemical pieces that will burn out the tumor. This can be done selectively, so that damage to neighboring tissues IS minimized. A recent system based on gadolinium was used to both image the tumor and then to remove it. Another application is in the development of fluorescent sensors.
Species can be developed that will detect chemicals or antibodies, which is particularly relevant for the detection of diseases. Literally any substance or species can be detected in an automated way and photochemical processes used to count and separate them. Fluorescence facilities can be found in all forensic laboratories and dyes are also used as security markers in bank notes. The development of new pigments and dyes is essential to achieving artificial photosynthesis, but will have many spin-offs in diverse areas.
The majority of scientists working in photochemistry now work in the fields of molecular electronics and molecular photonic, and these fields could be competing with that of artificial photosynthesis by TA king away the intellectual challenge. For example, it could be argued that the same circuitry used in artificial photosynthesis can be used to duplicate everything needed to make a computer work. In summary, a great deal of the basic search that could have gone into solving the energy crisis has gone into other areas.
Whilst there have been some spectacular discoveries, is the development of a new computer more important than solving the energy crisis? Many scientists with the right expertise are now coming to the ends of their research active careers. There is a risk that their knowledge and skills could be lost. The problems of energy generation from sunlight can be solved, but for many reasons time is now running out. Industrial exploitation Professor Sir Richard Friend discussed the need to match good laboratory science with engineering at a large enough scale to make it work.
The ability to transfer science to industry is crucial to achieving solar energy generation on a useful scale. The current problem is that people will pay more money to have a nice laptop screen than they will to have the same area of photovoltaic cell. This is because electricity is cheap, and high value products are needed to justify large investments in laboratories. However, some good news is that much of the technology developed in displays is directly transferable to solar cells. One of the icons of the 20th century was the silicon chip.
Fantastic functionality can e achieved in a small area, which is useful for producing computers. However, they require expensive clean rooms and the price of silicon is rising. Silicon solar cells can produce energy from sunlight at reasonable efficiencies, but, even after considering the rising costs of fossil fuels, they do not seem commercially attractive. New technologies are required. A much older technology is movable type face, used to print books and newspapers for 500 years or so. Importantly, it allows cheap, variable printing day after day, whereas a $2 billion silicon chip plant can only produce one type of product.