Showing papers on "Electricity generation published in 2019"

Integrated charge excitation triboelectric nanogenerator.

Abstract: Performance of triboelectric nanogenerators is limited by low and unstable charge density on tribo-layers. An external-charge pumping method was recently developed and presents a promising and efficient strategy towards high-output triboelectric nanogenerators. However, integratibility and charge accumulation efficiency of the system is rather low. Inspired by the historical development of electromagnetic generators, here, we propose and realize a self-charge excitation triboelectric nanogenerator system towards high and stable output in analogy to the principle of traditional magnetic excitation generators. By rational design of the voltage-multiplying circuits, the completed external and self-charge excitation modes with stable and tailorable output over 1.25 mC m−2 in contact-separation mode have been realized in ambient condition. The realization of the charge excitation system in this work may provide a promising strategy for achieving high-output triboelectric nanogenerators towards practical applications. Triboelectric nanogenerators may benefit Internet-of-Things era energy demands, but application is hindered by low charge density. Here the authors maximize charge density in ambient conditions and achieve stable power generation in a triboelectric nanogenerator that can realize external and self-excitation.

A new prediction model of battery and wind-solar output in hybrid power system

Abstract: In this paper short term power forecast of wind and solar power is proposed to evaluate the available output power of each production component. In this model, lead acid batteries used in proposed hybrid power system based on wind-solar power system. So, before the predicting of power output, a simple mathematical approach to simulate the lead–acid battery behaviors in stand-alone hybrid wind-solar power generation systems will be introduced. Then, the proposed forecast problem will be evaluated which is taken as constraint status through state of charge (SOC) of the batteries. The proposed forecast model includes a feature selection filter and hybrid forecast engine based on neural network (NN) and an intelligent evolutionary algorithm. This method not only could maintain the SOC of batteries in suitable range, but also could decrease the on-or-off switching number of wind turbines and PV modules. Effectiveness of the proposed method has been applied over real world engineering data. Obtained numerical analysis, demonstrate the validity of proposed method.

Shape Conformal and Thermal Insulative Organic Solar Absorber Sponge for Photothermal Water Evaporation and Thermoelectric Power Generation

Abstract: DOI: 10.1002/aenm.201900250 can attain the highest achievable conversion efficiency and enable a broad range of applications, including domestic heating, brine desalination, wastewater purification, steam sterilization, and power generation.[1–7] One actualization of solarto-thermal technology, solar-driven water evaporation can directly transfer heat to drive evaporation using sunlight as the only power input.[8–15] Compared with the conventional solar-driven steam generation system which requires high optical devices and large footprints investment, the emerging interfacial photothermal water evaporation based on nanostructured solar receiver materials restrict the solar heat at the water–air interface to suppress the heat losses and enhance the conversion efficiency. To date, significant progress in preparation of solar absorber materials, including semiconductors,[16–18] metallic,[19–21] and carbonaceous nanomaterials,[22–25] alongside with prudent system designs, e.g., environmental enhancement,[26–28] optical,[28–30] and thermal management[31–33] have been made to improve solar energy conversion efficiency. However, extended and collaborative utilization of nonconcentrated solar energy conversion for practical applications is making a little headway due to inconsequential/conflicting outcomes. On one hand, the heat losses from the solar absorber to bulk water and surrounding air for water vaporization are inevitable. On the other hand, constructive low-grade solar heat harvesting during evaporation are rarely reported. Therefore, effective thermal management and synergic utilization of the solar steam generation are essential. Another major roadblock toward photothermal technological advancement is the accessibility to a robust and practical material structure for practical deployment. As such, lightweight, load bearing, weather resistant, and uncommonly shape adaptive solar absorber materials are long sought after for durable outdoor application. Herein, we report a 3D organic bucky sponge that is collectively elastic, broadband light absorbing, and heat insulative that enables desired combination of efficient solar thermal conversion and mechanical stability. The 3D cellular truss is highly compressible and elastic which assumes excellent shape conformity and recovery, particularly beneficial to maximize space usage as well as for flexible, resilient outdoor purposes. Importantly, a rational integration of efficient solar water Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air–water interface has attracted tremendous attention due to its high conversion efficiency for water purification, desalination, energy generation, etc. However, ineffective integration of hybrid solar thermal devices and poor material compliance undermine extensive solar energy exploitation and practical outdoor use. Herein, a 3D organic bucky sponge that has a combination of desired chemical and physical properties, i.e., broadband light absorbing, heat insulative, and shape-conforming abilities that render efficient photothermic vaporization and energy generation with improved operational durability is reported. The highly compressible and readily reconfigurable solar absorber sponge not only places less constraints on footprint and shape defined fabrication process but more importantly remarkably improves the solar-to-vapor conversion efficiency. Notably, synergetic coupling of solar-steam and solar-electricity technologies is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas.

Solar Energy on Demand: A Review on High Temperature Thermochemical Heat Storage Systems and Materials.

Abstract: Among renewable energies, wind and solar are inherently intermittent and therefore both require efficient energy storage systems to facilitate a round-the-clock electricity production at a global scale. In this context, concentrated solar power (CSP) stands out among other sustainable technologies because it offers the interesting possibility of storing energy collected from the sun as heat by sensible, latent, or thermochemical means. Accordingly, continuous electricity generation in the power block is possible even during off-sun periods, providing CSP plants with a remarkable dispatchability. Sensible heat storage has been already incorporated to commercial CSP plants. However, because of its potentially higher energy storage density, thermochemical heat storage (TCS) systems emerge as an attractive alternative for the design of next-generation power plants, which are expected to operate at higher temperatures. Through these systems, thermal energy is used to drive endothermic chemical reactions, which can subsequently release the stored energy when needed through a reversible exothermic step. This review analyzes the status of this prominent energy storage technology, its major challenges, and future perspectives, covering in detail the numerous strategies proposed for the improvement of materials and thermochemical reactors. Thermodynamic calculations allow selecting high energy density systems, but experimental findings indicate that sufficiently rapid kinetics and long-term stability trough continuous cycles of chemical transformation are also necessary for practical implementation. In addition, selecting easy-to-handle materials with reduced cost and limited toxicity is crucial for large-scale deployment of this technology. In this work, the possible utilization of materials as diverse as metal hydrides, hydroxides, or carbonates for thermochemical storage is discussed. Furthermore, special attention is paid to the development of redox metal oxides, such as Co3O4/CoO, Mn2O3/Mn3O4, and perovskites of different compositions, as an auspicious new class of TCS materials due to the advantage of working with atmospheric air as reactant, avoiding the need of gas storage tanks. Current knowledge about the structural, morphological, and chemical modifications of these solids, either caused during redox transformations or induced wittingly as a way to improve their properties, is revised in detail. In addition, the design of new reactor concepts proposed for the most efficient use of TCS in concentrated solar facilities is also critically considered. Finally, strategies for the harmonic integration of these units in functioning solar power plants as well as the economic aspects are also briefly assessed.

Silicon solar cells: toward the efficiency limits

Abstract: Photovoltaic (PV) conversion of solar energy starts to give an appreciable contribution to power generation in many countries, with more than 90% of the global PV market relying on solar cells base...

Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation

Abstract: The energy shortage and clean water scarcity are two key challenges for global sustainable development. Near half of the total global water withdrawals is consumed by power generation plants while water desalination consumes lots of electricity. Here, we demonstrate a photovoltaics-membrane distillation (PV-MD) device that can stably produce clean water (>1.64 kg·m−2·h−1) from seawater while simultaneously having uncompromised electricity generation performance (>11%) under one Sun irradiation. Its high clean water production rate is realized by constructing multi stage membrane distillation (MSMD) device at the backside of the solar cell to recycle the latent heat of water vapor condensation in each distillation stage. This composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system and thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a fresh water producer. The increasing demand for energy and clean water has become a grand global challenge. Here the authors develop a membrane-distillation device that exploits sunlight and the heat dissipated by an integrated solar cell unit, enabling simultaneous efficient production of electricity and drinkable water.

Technological, economic and environmental prospects of all-electric aircraft

Abstract: Ever since the Wright brothers’ first powered flight in 1903, commercial aircraft have relied on liquid hydrocarbon fuels. However, the need for greenhouse gas emission reductions along with recent progress in battery technology for automobiles has generated strong interest in electric propulsion in aviation. This Analysis provides a first-order assessment of the energy, economic and environmental implications of all-electric aircraft. We show that batteries with significantly higher specific energy and lower cost, coupled with further reductions of costs and CO2 intensity of electricity, are necessary for exploiting the full range of economic and environmental benefits provided by all-electric aircraft. A global fleet of all-electric aircraft serving all flights up to a distance of 400–600 nautical miles (741–1,111 km) would demand an equivalent of 0.6–1.7% of worldwide electricity consumption in 2015. Although lifecycle CO2 emissions of all-electric aircraft depend on the power generation mix, all direct combustion emissions and thus direct air pollutants and direct non-CO2 warming impacts would be eliminated. Electric aircraft offer an aviation decarbonization pathway and attract increasing attention owing to the rapid development of batteries. Here Andreas Schafer and colleagues analyse the potential technological, economic and environmental viability of battery-electric commercial aircraft.

2D materials as an emerging platform for nanopore-based power generation

Abstract: Osmotic power generation, the extraction of power from mixing salt solutions of different concentrations, can provide an efficient power source for both nanoscale and industrial-level applications. Power is generated using ion-selective channels or pores of nanometric dimensions in synthetic membrane materials. 2D materials such as graphene and MoS2 provide energy extraction efficiencies that are several orders of magnitude higher than those of more established bulky membranes. In this Review, we survey the current state of the art in power generation with both 2D materials and solid-state devices. We discuss the current understanding of the processes underlying power generation in boron nitride nanotubes and 2D materials, as well as the available fabrication methods and their impact on power generation. Finally, we overview future directions of research, which include increasing efficiency, upscaling single pores to porous membranes and solving other issues related to the potential practical application of 2D materials for osmotic power generation. Synthetic nanopores in 2D materials are an emerging platform for power harvesting from the controlled mixing of fresh and salty water. This Review surveys their physics and materials properties and the progress in the design of new, high-density, ion-selective membrane materials.

Comparative Study of Ramp-Rate Control Algorithms for PV with Energy Storage Systems

Abstract: The high variability of solar irradiance, originated by moving clouds, causes fluctuations in Photovoltaic (PV) power generation, and can negatively impact the grid stability. For this reason, grid codes have incorporated ramp-rate limitations for the injected PV power. Energy Storage Systems (ESS) coordinated by ramp-rate (RR) control algorithms are often applied for mitigating these power fluctuations to the grid. These algorithms generate a power reference to the ESS that opposes the PV fluctuations, reducing them to an acceptable value. Despite their common use, few performance comparisons between the different methods have been presented, especially from a battery status perspective. This is highly important, as different smoothing methods may require the battery to operate at different regimes (i.e., number of cycles and cycles deepness), which directly relates to the battery lifetime performance. This paper intends to fill this gap by analyzing the different methods under the same irradiance profile, and evaluating their capability to limit the RR and maintain the battery State of Charge (SOC) at the end of the day. Moreover, an analysis into the ESS capacity requirements for each of the methods is quantified. Finally, an analysis of the battery cycles and its deepness is performed based on the well-established rainflow cycle counting method.

A high-resolution geospatial assessment of the rooftop solar photovoltaic potential in the European Union

Abstract: Rooftop solar photovoltaic (PV) systems can make a significant contribution to Europe's energy transition. Realising this potential raises challenges at policy and electricity system planning level. To address this, the authors have developed a geospatially explicit methodology using up-to-date spatial information of the EU building stock to quantify the available rooftop area for PV systems. To do this, it combines satellite-based and statistical data sources with machine learning to provide a reliable assessment of the technical potential for rooftop PV electricity production with a spatial resolution of 100 m across the European Union (EU). It estimates the levelised cost of electricity (LCOE) using country-specific parameters and compares it to the latest household electricity prices. The results show that the EU rooftops could potentially produce 680 TWh of solar electricity annually (representing 24.4% of current electricity consumption), two thirds of which at a cost lower than the current residential tariffs. Country aggregated results illustrate existing barriers for cost-effective rooftop systems in countries with low electricity prices and high investment interest rates, as well as provide indications on how to address these.

The role of energy storage in deep decarbonization of electricity production

Abstract: Deep decarbonization of electricity production is a societal challenge that can be achieved with high penetrations of variable renewable energy. We investigate the potential of energy storage technologies to reduce renewable curtailment and CO2 emissions in California and Texas under varying emissions taxes. We show that without energy storage, adding 60 GW of renewables to California achieves 72% CO2 reductions (relative to a zero-renewables case) with close to one third of renewables being curtailed. Some energy storage technologies, on the other hand, allow 90% CO2 reductions from the same renewable penetrations with as little as 9% renewable curtailment. In Texas, the same renewable-deployment level leads to 54% emissions reductions with close to 3% renewable curtailment. Energy storage can allow 57% emissions reductions with as little as 0.3% renewable curtailment. We also find that generator flexibility can reduce curtailment and the amount of energy storage that is needed for renewable integration. Existing studies on the economic feasibility of energy storage are system-specific without considering the decarbonisation of electricity production or impacts of GHG taxes. Here the authors applied an optimization model to investigate the economic viability of nice selected energy storage technologies in California and found that renewable curtailment and GHG reductions highly depend on capital costs of energy storage.

Atomic Layer Tailoring Titanium Carbide MXene To Tune Transport and Polarization for Utilization of Electromagnetic Energy beyond Solar and Chemical Energy.

Abstract: The utilization of electromagnetic (EM) energy neither is affected by the weather nor produces harmful substances. How to utilize and convert EM energy is of practical concern. Herein, delaminated titanium carbide (D-Ti3C2Tx) MXene nanosheet (NS) was successfully fabricated by the modified Gogotsi's method. The choice of atomic layer processing allows tailoring of layer distance of Ti3C2Tx so as to improve polarization. High-performance EM wave absorption of D-Ti3C2Tx MXene NS composites was obtained, and their comprehensive performance is the best of all Ti3C2Tx-based composites. Due to the competition between conduction loss and polarization loss, the higher the concentration of D-Ti3C2Tx in composites, the more the conversion of EM energy to thermal energy will be. Based on the mechanism, a prototype of thermoelectric generator is designed, which can convert the EM energy into power energy effectively. This thermoelectric generator will be the energy source for low power electric devices. Our finding will provide new ideas for the utilization of EM energy.

Impact of distributed generation on protection and voltage regulation of distribution systems: A review

Abstract: During recent decades with the power system restructuring process, centralized energy sources are being replaced with decentralized ones. This phenomenon has resulted in a novel concept in electric power systems, particularly in distribution systems, known as Distributed Generation (DG). On one hand, utilizing DG is important for secure power generation and reducing power losses. On the other hand, widespread use of such technologies introduces new challenges to power systems such as their optimal location, protection devices' settings, voltage regulation, and Power Quality (PQ) issues. Another key point which needs to be considered relates to specific DG technologies based on Renewable Energy Sources (RESs), such as wind and solar, due to their uncertain power generation. In this regard, this paper provides a comprehensive review of different types of DG and investigates the newly emerging challenges arising in the presence of DG in electrical grids.

Model Predictive Control of Bidirectional DC–DC Converters and AC/DC Interlinking Converters—A New Control Method for PV-Wind-Battery Microgrids

Abstract: In renewable energy systems, fluctuating outputs from energy sources and variable power demand may deteriorate the voltage quality. In this paper, a model predictive control strategy without using any proportional–integral–derivative (PID) regulators is proposed. The proposed strategy consists of a model predictive current and power (MPCP) control scheme and a model predictive voltage and power (MPVP) control method. By controlling the bidirectional dc–dc converter of the battery energy storage system based on the MPCP algorithm, the fluctuating output from the renewable energy sources can be smoothed while stable dc-bus voltage can be maintained. Meanwhile, the ac/dc interlinking converter is controlled by using the MPVP scheme to ensure stable ac voltage supply and proper power flow between the microgrid and the utility grid. Then, a system-level energy management scheme is developed to ensure stable operation under different operation modes by considering fluctuating power generation, variable power demand, battery state of charge, and electricity price. Compared with the traditional cascade control, the proposed method is simpler and shows better performance, which is validated in simulation based on a 3.5-MW PV-wind-battery system with real-world solar and wind profiles.

A Rotation-Free Wireless Power Transfer System With Stable Output Power and Efficiency for Autonomous Underwater Vehicles

Abstract: This letter proposes a rotation-free wireless power transfer system based on a new coil structure to achieve stable output power and efficiency against rotational misalignments for charging autonomous underwater vehicles. The new coil structure has two decoupled receivers composed of two reversely wound receiver coils and the magnetic flux directions of the two receivers are perpendicular to each other, guaranteeing a relatively constant total mutual inductance and a decoupled characteristic under rotational misalignments. The proposed coil structure is verified via finite element analysis based on ANSYS Maxwell. A rotation-free LCC–LCC compensated WPT prototype is built and the experimental results verify the theoretical analysis and simulations. The system can deliver 664 W with a dc–dc efficiency of 92.26% under the best case and 485 W with a 92.10% dc–dc efficiency under the worst case.

High Power Density Tower-like Triboelectric Nanogenerator for Harvesting Arbitrary Directional Water Wave Energy

Abstract: Wave energy is one of the most available energy sources in oceans. In this work, a design of high power density triboelectric nanogenerator (TENG) based on a tower structure is proposed for harvesting wave energy from arbitrary directions. Such tower-like TENG (T-TENG) consists of multiple units made of polytetrafluoroethylene balls and three-dimensional printed arc surface coated with melt adhesive reticulation nylon film. The power generation model coupled with the kinetic model for the T-TENG is proposed and discussed. The T-TENG can effectively convert arbitrary directional wave energy into electrical energy by utilizing charged balls rolling on an optimized arc surface due to ocean wave excitation. In addition, it is found that the power density of the present T-TENG increases linearly from 1.03 W/m3 to 10.6 W/m3 by increasing the units from 1 to 10 in one block. This supports that the power density of the T-TENG increases proportionally with the number of units connected in parallel without rectifie...

Effective Scheduling of Reconfigurable Microgrids With Dynamic Thermal Line Rating

Abstract: This paper addresses the optimal operation and scheduling of reconfigurable microgrids incorporating the dynamic line rating limitations during the islanded and grid-connected mode operations. The incorporation of the dynamic line rating of overhead feeders can potentially improve the system security when providing economical and technical benefits for the microgrid. The proposed framework takes into account a realistic formulation to minimize the total microgrid costs in both grid-connected and multiperiod islanded modes. Also, a stochastic framework based on unscented transform is proposed to model the uncertainties associated with renewable energy sources output power, market energy price, and load demand, as well as the weather uncertain parameters such as solar radiation, wind speed, and ambient temperature. Due to the high nonlinearity and complexity of the proposed problem, an efficient optimization algorithm based on the collective decision optimization algorithm is proposed. A new two-stage modification method is also developed to improve the algorithm search ability and avoid premature convergence. The proposed problem is examined on the IEEE 32-bus microgrid test system. The simulation results show the effectiveness of the proposed model and verify its economic and reliability merits.