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Concept: Solar power


Decisions determining the use of land for energy are of exigent concern as land scarcity, the need for ecosystem services, and demands for energy generation have concomitantly increased globally. Utility-scale solar energy (USSE) [i.e., ≥1 megawatt (MW)] development requires large quantities of space and land; however, studies quantifying the effect of USSE on land cover change and protected areas are limited. We assessed siting impacts of >160 USSE installations by technology type [photovoltaic (PV) vs. concentrating solar power (CSP)], area (in square kilometers), and capacity (in MW) within the global solar hot spot of the state of California (United States). Additionally, we used the Carnegie Energy and Environmental Compatibility model, a multiple criteria model, to quantify each installation according to environmental and technical compatibility. Last, we evaluated installations according to their proximity to protected areas, including inventoried roadless areas, endangered and threatened species habitat, and federally protected areas. We found the plurality of USSE (6,995 MW) in California is sited in shrublands and scrublands, comprising 375 km(2) of land cover change. Twenty-eight percent of USSE installations are located in croplands and pastures, comprising 155 km(2) of change. Less than 15% of USSE installations are sited in “Compatible” areas. The majority of “Incompatible” USSE power plants are sited far from existing transmission infrastructure, and all USSE installations average at most 7 and 5 km from protected areas, for PV and CSP, respectively. Where energy, food, and conservation goals intersect, environmental compatibility can be achieved when resource opportunities, constraints, and trade-offs are integrated into siting decisions.

Concepts: Sun, Solar cell, Photovoltaics, Solar energy, Solar power, Nuclear power, Solar thermal energy, Concentrating solar power


To realize the sustainable energy supply in smart city, it is essential to maximize energy scavenging from the city environments for achieving the self-powered functions of some intelligent devices and sensors. Although the solar energy can be well harvested by using existing technologies, the large amounts of wasted wind energy in the city cannot be effectively utilized since the conventional wind turbine generators can only be installed in remote areas due to the large volumes and the safety issues. Here, we rationally design a hybridized nanogenerator, including a solar cell (SC) and a triboelectric nanogenerator (TENG), that can individually/simultaneously scavenging solar and wind energies, which can be extensively installed on the roofs of the city buildings. Under the same device area of about 120 mm×22 mm, the SC can deliver a largest output power of about 8 mW, while the output power of the TENG can be up to 26 mW. Impedance matching between the SC and TENG has been achieved by using a transformer to decrease the impedance of the TENG. The hybridized nanogenerator has a larger output current and a better charging performance than that of the individual SC or TENG. This research presents a feasible approach to maximize solar and wind energies scavenging from the city environments with the aim to realize some self-powered functions in smart city.

Concepts: Sun, Renewable energy, Solar power, Nuclear power, Wind power, Energy development, World energy resources and consumption, Wind turbine


Quantum dot nanoscale semiconductor heterostructures (QDHs) are a class of materials potentially useful for integration into solar energy conversion devices. However, realizing the potential of these heterostructured systems requires the ability to identify and synthesize heterostructures with suitably designed materials, controlled size and morphology of each component, and structural control over their shared interface. In this review, we will present the case for the utility and advantages of chemically synthesized QDHs for solar energy conversion, beginning with an overview of various methods of heterostructured material synthesis and a survey of heretofore reported materials systems. The fundamental charge transfer properties of the resulting materials combinations and their basic design principles will be outlined. Finally, we will discuss representative solar photovoltaic and photoelectrochemical devices employing QDHs (including quantum dot sensitized solar cells, or QDSSCs) and examine how QDH synthesis and design impacts their performance.

Concepts: Energy, Sun, Solar cell, Photovoltaics, Solar energy, Solar power, Photovoltaic array, Solar thermal energy


Graphene not only possesses interesting electrochemical behavior but also has a remarkable surface area and mechanical strength and is naturally abundant, all advantageous properties for the design of tailored composite materials. Graphene-semiconductor or -metal nanoparticle composites have the potential to function as efficient, multifunctional materials for energy conversion and storage. These next-generation composite systems could possess the capability to integrate conversion and storage of solar energy, detection, and selective destruction of trace environmental contaminants or achieve single-substrate, multistep heterogeneous catalysis. These advanced materials may soon become a reality, based on encouraging results in the key areas of energy conversion and sensing using graphene oxide as a support structure. Through recent advances, chemists can now integrate such processes on a single substrate while using synthetic designs that combine simplicity with a high degree of structural and composition selectivity. This progress represents the beginning of a transformative movement leveraging the advancements of single-purpose chemistry toward the creation of composites designed to address whole-process applications. The promising field of graphene nanocomposites for sensing and energy applications is based on fundamental studies that explain the electronic interactions between semiconductor or metal nanoparticles and graphene. In particular, reduced graphene oxide is a suitable composite substrate because of its two-dimensional structure, outstanding surface area, and electrical conductivity. In this Account, we describe common assembly methods for graphene composite materials and examine key studies that characterize its excited state interactions. We also discuss strategies to develop graphene composites and control electron capture and transport through the 2D carbon network. In addition, we provide a brief overview of advances in sensing, energy conversion, and storage applications that incorporate graphene-based composites. With these results in mind, we can envision a new class of semiconductor- or metal-graphene composites sensibly tailored to address the pressing need for advanced energy conversion and storage devices.

Concepts: Nanoparticle, Sun, Nanomaterials, Composite material, Solar energy, Solar power, Boeing 787, Carbon fiber


It is highly desired to enhance the visible-excited charge separation of nano-sized BiVO4 for efficient solar utilization. Herein, different molar-ratio ZnO/BiVO4 nanocomposites are fabricated by simple wet-chemical processes, after nano-sized BiVO4 and ZnO are respectively synthesized by hydrothermal methods. It is shown by means of atmosphere-controlled steady-state surface photovoltage spectra (SS-SPS) and transient-state surface photovoltage (TS-SPV) responses that the photogenerated charges of resulting nanocomposite display longer lifetime and higher separation than those of BiVO4 alone. This leads to its superior photoactivities for water oxidation to produce O2 and for colorless pollutant degradation under visible irradiation, with about three times enhancement. Interestingly, it is suggested that the prolonged lifetime and promoted separation of photogenerated charges in the nanocomposite is attributed to the unusual spatial transfer of visible-excited high-energy electrons from BiVO4 to ZnO on the basis of the ultra-low-temperature EPR measurements and the photocurrent action spectra. Moreover, it is clearly demonstrated that the photogenerated charge separation of resulting ZnO/BiVO4 nanocomposite could be further enhanced after introducing the silicate bridges so as to improve the visible photoactivity greatly, attributed to the built bridge roles favorable to charge transfer. This work would provide a feasible way to enhance the solar energy utilization of visible-response semiconductor photocatalysts.

Concepts: Electron, Electric charge, Photocatalysis, Fossil fuel, Photocatalytic water splitting, Solar energy, Solar power, Nanocomposite


We report an efficient approach to the synthesis of AgSbS2 nanocrystals (NCs) by colloidal chemistry. The size of the AgSbS2 NCs can be tuned from 5.3 to 58.3 nm with narrow size distributions by selection of appropriate precursors and fine control of the experimental conditions. Over 15 g of high-quality AgSbS2 NCs can be obtained from one single reaction, indicative of the up-scalability of the present synthesis. The resulting NCs display strong absorptions in the visible-to-NIR range and exceptional air stability. The photoelectrochemical measurements indicate that, although the pristine AgSbS2 NC electrodes generate a cathodic photocurrent with a relatively small photocurrent density and poor stability, both of them can be significantly improved subject to CdS surface modification, showing promise in solar energy conversion applications.

Concepts: Energy, Chemical reaction, Sun, Photovoltaics, Energy conversion, Solar energy, Solar power, Solar thermal energy


When wind or solar energy displace conventional generation, the reduction in emissions varies dramatically across the United States. Although the Southwest has the greatest solar resource, a solar panel in New Jersey displaces significantly more sulfur dioxide, nitrogen oxides, and particulate matter than a panel in Arizona, resulting in 15 times more health and environmental benefits. A wind turbine in West Virginia displaces twice as much carbon dioxide as the same turbine in California. Depending on location, we estimate that the combined health, environmental, and climate benefits from wind or solar range from $10/MWh to $100/MWh, and the sites with the highest energy output do not yield the greatest social benefits in many cases. We estimate that the social benefits from existing wind farms are roughly 60% higher than the cost of the Production Tax Credit, an important federal subsidy for wind energy. However, that same investment could achieve greater health, environmental, and climate benefits if it were differentiated by region.

Concepts: Oxygen, Carbon dioxide, Oxide, Solar power, Volcano, Wind power, Wind farm, Wind turbine


As wind and solar power provide a growing share of Europe’s electricity1, understanding and accommodating their variability on multiple timescales remains a critical problem. On weekly timescales, variability is related to long-lasting weather conditions, called weather regimes2-5, which can cause lulls with a loss of wind power across neighbouring countries6. Here we show that weather regimes provide a meteorological explanation for multi-day fluctuations in Europe’s wind power and can help guide new deployment pathways which minimise this variability. Mean generation during different regimes currently ranges from 22 GW to 44 GW and is expected to triple by 2030 with current planning strategies. However, balancing future wind capacity across regions with contrasting inter-regime behaviour - specifically deploying in the Balkans instead of the North Sea - would almost eliminate these output variations, maintain mean generation, and increase fleet-wide minimum output. Solar photovoltaics could balance low-wind regimes locally, but only by expanding current capacity tenfold. New deployment strategies based on an understanding of continent-scale wind patterns and pan-European collaboration could enable a high share of wind energy whilst minimising the negative impacts of output variability.

Concepts: Solar cell, Germany, Renewable energy, Wind, Solar energy, Solar power, Wind power, Pumped-storage hydroelectricity


We estimate the consumptive water footprint (WF) of electricity and heat in 2035 for the four energy scenarios of the International Energy Agency (IEA) and a fifth scenario with a larger percentage of solar energy. Counter-intuitively, the ‘greenest’ IEA scenario (with the smallest carbon footprint) shows the largest WF increase over time: an increase by a factor four over the period 2010-2035. In 2010, electricity from solar, wind, and geothermal contributed 1.8% to the total. The increase of this contribution to 19.6% in IEA’s ‘450 scenario’ contributes significantly to the decrease of the WF of the global electricity and heat sector, but is offset by the simultaneous increase of the use of firewood and hydropower. Only substantial growth in the fractions of energy sources with small WFs - solar, wind, and geothermal energy - can contribute to a lowering of the WF of the electricity and heat sector in the coming decades. The fifth energy scenario - adapted from the IEA 450 scenario but based on a quick transition to solar, wind and geothermal energy and a minimum in bio-energy - is the only scenario that shows a strong decline in both carbon footprint (-66%) and consumptive WF (-12%) in 2035 compared to the reference year 2010.

Concepts: Energy, Sun, Fossil fuel, Solar energy, Solar power, Wind power, Geothermal power, International Energy Agency


Many different photovoltaic technologies are being developed for large-scale solar energy conversion. The wafer-based first-generation photovoltaic devices have been followed by thin-film solid semiconductor absorber layers sandwiched between two charge-selective contacts and nanostructured (or mesostructured) solar cells that rely on a distributed heterojunction to generate charge and to transport positive and negative charges in spatially separated phases. Although many materials have been used in nanostructured devices, the goal of attaining high-efficiency thin-film solar cells in such a way has yet to be achieved. Organometal halide perovskites have recently emerged as a promising material for high-efficiency nanostructured devices. Here we show that nanostructuring is not necessary to achieve high efficiencies with this material: a simple planar heterojunction solar cell incorporating vapour-deposited perovskite as the absorbing layer can have solar-to-electrical power conversion efficiencies of over 15 per cent (as measured under simulated full sunlight). This demonstrates that perovskite absorbers can function at the highest efficiencies in simplified device architectures, without the need for complex nanostructures.

Concepts: Sun, Solar cell, Photovoltaics, Energy conversion, Dye-sensitized solar cell, Thin film solar cell, Solar power, Photovoltaic array