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"Energy conversion"
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Solar power and energy storage systems
Extensive study of solar energy is increasing as fast as the serious threat of global warming. Sunlight is a very important alternative source of energy because it can be converted into electricity. Solar energy is considered the best source of renewable energy because it is clean and unlimited. Solar radiation can be harnessed and converted into different forms of energy that does not pollute the environment. In order to transform solar radiation, we need collectors of sunlight, such as solar cells. The main challenges are energy security, the increasing prices of carbon-based energy sources, and minimizing global warming. We cannot use sunlight during the night, so an energy storage system (ESS) is necessary. The best ESS is one with high power and high energy density. This book introduces the basic concepts of an ESS.
Book
Photocatalytic water splitting with a quantum efficiency of almost unity
Overall water splitting, evolving hydrogen and oxygen in a 2:1 stoichiometric ratio, using particulate photocatalysts is a potential means of achieving scalable and economically viable solar hydrogen production. To obtain high solar energy conversion efficiency, the quantum efficiency of the photocatalytic reaction must be increased over a wide range of wavelengths and semiconductors with narrow bandgaps need to be designed. However, the quantum efficiency associated with overall water splitting using existing photocatalysts is typically lower than ten per cent
1
,
2
. Thus, whether a particulate photocatalyst can enable a quantum efficiency of 100 per cent for the greatly endergonic water-splitting reaction remains an open question. Here we demonstrate overall water splitting at an external quantum efficiency of up to 96 per cent at wavelengths between 350 and 360 nanometres, which is equivalent to an internal quantum efficiency of almost unity, using a modified aluminium-doped strontium titanate (SrTiO
3
:Al) photocatalyst
3
,
4
. By selectively photodepositing the cocatalysts Rh/Cr
2
O
3
(ref.
5
) and CoOOH (refs.
3
,
6
) for the hydrogen and oxygen evolution reactions, respectively, on different crystal facets of the semiconductor particles using anisotropic charge transport, the hydrogen and oxygen evolution reactions could be promoted separately. This enabled multiple consecutive forward charge transfers without backward charge transfer, reaching the upper limit of quantum efficiency for overall water splitting. Our work demonstrates the feasibility of overall water splitting free from charge recombination losses and introduces an ideal cocatalyst/photocatalyst structure for efficient water splitting.
Water splitting with an internal quantum efficiency of almost unity is achieved using a modified semiconductor photocatalyst that selectively promotes the hydrogen and oxygen evolution reactions on separate crystal facets.
Journal Article
Energy conversion and green energy storage
\"Energy Conversion and Green Energy Storage presents recent developments in renewable energy conversion and green energy storage. Covering technical expansions in renewable energy and applications, energy storage, and solar photovoltaics, the book features chapters written by global experts in the field. The book serves as a useful reference for researchers, graduate students, and engineers in the field of energy. Providing insights related to various forms of renewable energy, the book discusses developments in solar photovoltaic applications. The book also includes simulation codes and programs, such as Wien2k code, VASP code, and MATLAB®\"-- Provided by publisher.
Book
Grid converters for photovoltaic and wind power systems
Advancements in grid converter technology have been pivotal in the successful integration of renewable energy. The high penetration of renewable energy systems is calling for new more stringent grid requirements. As a consequence, the grid converters should be able to exhibit advanced functions like: dynamic control of active and reactive current injection during faults, and grid services support. <p>This book explains the topologies, modulation and control of grid converters for both photovoltaic and wind power applications. In addition to power electronics, coverage focuses on the specific applications in photovoltaic and wind power systems where grid condition is an essential factor.</p> <p>With a review of the most recent grid requirements for photovoltaic and wind power systems, the relevant issues are discussed:</p> <ul> <li> <div>Modern grid inverter topologies for photovoltaic and wind turbines</div> </li> <li> <div>Islanding detection methods for photovoltaic systems</div> </li> <li> <div>Synchronization techniques based on second order generalized integrators (SOGI)</div> </li> <li> <div>Advanced synchronization techniques with robust operation under grid unbalance condition</div> </li> <li> <div>Resonant controller techniques for current control and harmonic compensation</div> </li> <li> <div>Grid filter design and active damping techniques</div> </li> <li> <div>Power control under grid fault conditions, considering both positive and negative sequences</div> </li> </ul> <p>Throughout, the authors include practical examples, exercises, and simulation models and an accompanying website sets out further modeling techniques using MATLAB® and Simulink environments and physical security information management (PSIM) software.</p> <p><i>Grid Converters for Photovoltaic and Wind Power Systems</i> is intended as a course book for graduate students with a background in electrical engineering and for professionals in the evolving renewable energy industry. For professors interested in adopting the course, a set of slides is available for download from the website.</p> <p><b>Companion Website</b></p> <p><a href=\"http://www.wiley.com/go/grid_converters\">www.wiley.com/go/grid_converters</a></p>
eBook
Wind power
Readers learn about the history of wind power, how it is used today and how it may be used as an energy source in the future.
Book
Pyroelectric energy conversion with large energy and power density in relaxor ferroelectric thin films
The need for efficient energy utilization is driving research into ways to harvest ubiquitous waste heat. Here, we explore pyroelectric energy conversion from low-grade thermal sources that exploits strong field- and temperature-induced polarization susceptibilities in the relaxor ferroelectric 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3. Electric-field-driven enhancement of the pyroelectric response (as large as −550 μC m−2 K−1) and suppression of the dielectric response (by 72%) yield substantial figures of merit for pyroelectric energy conversion. Field- and temperature-dependent pyroelectric measurements highlight the role of polarization rotation and field-induced polarization in mediating these effects. Solid-state, thin-film devices that convert low-grade heat into electrical energy are demonstrated using pyroelectric Ericsson cycles, and optimized to yield maximum energy density, power density and efficiency of 1.06 J cm−3, 526 W cm−3 and 19% of Carnot, respectively; the highest values reported to date and equivalent to the performance of a thermoelectric with an effective ZT ≈ 1.16 for a temperature change of 10 K. Our findings suggest that pyroelectric devices may be competitive with thermoelectric devices for low-grade thermal harvesting.
Journal Article
Flexo-photovoltaic effect
Noncentrosymmetric crystal structure can lead to a peculiar kind of charge separation under illumination called the bulk photovoltaic (BPV) effect. Solar cells made of such materials, however, typically have low efficiency. Yang
et al.
expanded the class of materials capable of exhibiting the BPV effect by making ordinarily centrosymmetric materials, such as SrTiO
3
and TiO
2
, lose their inversion symmetry. The authors accomplished this by applying a point force on the surface of the material. This induced a strain gradient and the loss of inversion symmetry, resulting in large photovoltaic currents under illumination. The mechanism, dubbed the flexo-photovoltaic effect, is expected to apply to most semiconductors.
Science
, this issue p.
904
A bulk photoelectric effect is induced in centrosymmetric semiconductors by applying a point force on the materials’ surfaces.
It is highly desirable to discover photovoltaic mechanisms that enable enhanced efficiency of solar cells. Here we report that the bulk photovoltaic effect, which is free from the thermodynamic Shockley-Queisser limit but usually manifested only in noncentrosymmetric (piezoelectric or ferroelectric) materials, can be realized in any semiconductor, including silicon, by mediation of flexoelectric effect. We used either an atomic force microscope or a micrometer-scale indentation system to introduce strain gradients, thus creating very large photovoltaic currents from centrosymmetric single crystals of strontium titanate, titanium dioxide, and silicon. This strain gradient–induced bulk photovoltaic effect, which we call the flexo-photovoltaic effect, functions in the absence of a p-n junction. This finding may extend present solar cell technologies by boosting the solar energy conversion efficiency from a wide pool of established semiconductors.
Journal Article
Wind towers : architecture, climate and sustainability
This book offers a holistic treatment of wind towers, from their underlying scientific principles to design and operation. It includes suggestions for optimization based on the authors' own research findings from recent analytical studies.
Book
Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion
An ideal solar-thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion. Despite various solar absorbers having been demonstrated, these conditions are challenging to achieve simultaneously using conventional materials and structures. Here, we propose and demonstrate three-dimensional structured graphene metamaterial (SGM) that takes advantages of wavelength selectivity from metallic trench-like structures and broadband dispersionless nature and excellent thermal conductivity from the ultrathin graphene metamaterial film. The SGM absorbers exhibit superior solar selective and omnidirectional absorption, flexible tunability of wavelength selective absorption, excellent photothermal performance, and high thermal stability. Impressive solar-to-thermal conversion efficiency of 90.1% and solar-to-vapor efficiency of 96.2% have been achieved. These superior properties of the SGM absorber suggest it has a great potential for practical applications of solar thermal energy harvesting and manipulation.
Here, the authors demonstrate a selective solar thermal absorber with wavelength selectivity, arising from metallic trench-like structures, using broadband dispersionless ultrathin graphene metamaterial film, with excellent thermal conductivity.
Journal Article