Penetration Limit Research Articles

Modelling and optimisation of a hydrogen-based energy storage system in an autonomous electrical network

The European Union’s 2020 climate and energy package (known as “20–20–20” targets) requests, among other key objectives, 40% of the electricity production in Greece to be supplied from Renewable Energy Sources by 2020. The main barriers for reaching this target is the intermittency of renewable energy sources combined with the penetration limits in the local electrical grids and the high seasonal demand fluctuations. In this context, the introduction of energy storage systems, comprises one of the main solutions for coping with this situation. One of the most promising technologies for storing the excess energy, that would be otherwise lost, is the production and storage of hydrogen through water electrolysis. Hydrogen can be used for supporting the electricity grid during periods of high demand but also as transportation fuel for hydrogen-based automobiles (e.g. fuel cell vehicles). For this purpose, a simulation algorithm has been developed, able to assess the specifications of the optimum sizing of hydrogen production storage systems. For the application of the algorithm, the area of the Aegean Sea has been selected, owed to the considerable renewable energy sources curtailments recorded in the various non-interconnected islands in the region. More specifically, the developed algorithm is applied to an autonomous electricity network of 9 islands, located at the SE area of the Aegean Sea and known as the “Kos-Kalymnos” electricity system. The results obtained designate the optimum size of the hydrogen-based configuration, aiming to maximize the recovery of otherwise curtailed renewable energy production.

Photocatalytic water disinfection under solar irradiation by Ag@TiO2 core-shell structured nanoparticles

Abstract The Ag core-TiO 2 shell structured (Ag@TiO 2 ) nanoparticles were found to be efficient in the disinfection of water under solar light irradiation both in free and immobilized form. Complete disinfection of 40 ∗ 10 8 CFU/mL Escherchia coli cells was achieved in 15 min by solar photocatalysis with 0.4 g/L Ag@TiO 2 catalyst loading. Ag@TiO 2 nanoparticles were found to be superior to TiO 2 nanoparticles in solar disinfection. Photocatalysis rate was found to increase with increase in catalyst loading and with decrease in cell concentration. Ag@TiO 2 nanoparticles showed their efficacy in the degradation of endotoxin, a harmful disinfection byproduct. Kinetics of solar disinfection with Ag@TiO 2 nanoparticles followed Chick’s law. The kinetics of endotoxin degradation followed zero order kinetics at high concentrations of endotoxin. However at lower concentrations, rate followed a nth order model with n = 6.99. A lower rate of photocatalytic disinfection with Ag@TiO 2 nanoparticles immobilized on cellulose acetate as compared to that in their free form was observed, owing to diffusional and light penetration limitations. The re-growth of cells after photocatalytic disinfection was below the detectable limits, thus proving the potential of the process to produce safe drinking water. Ag@TiO 2 nanoparticles can find potential application in solar water disinfection and the process which harnesses the solar energy may prove to be energy efficient and economical, thus can be easily adopted for large scale applications and portable drinking water treatment units for domestic applications.

Hemispherical nosed steel projectile high-speed penetration into aluminum target

Terminal ballistic performance of high-strength projectiles penetrating into metallic targets is mostly concerned by both weapon and armor designers. Most existing works are concentrated on the rigid-eroding penetration regime, and limited studies have addressed the rigid-deforming-eroding penetration regime. In this paper, nineteen shots of hemispherical nosed D6A steel projectiles penetration test on 5A06-H112 aluminum targets is conducted with a wide range of velocities (696m/s–1870m/s). The non-monotonic dependence of depth of penetration (DOP) on the impact velocity is observed, which successively corresponds to the three penetration stages, i.e., rigid projectile penetration, deforming projectile penetration without eroding and eroding projectile penetration. Then, for the non-monotonic rigid-deforming-eroding projectile penetration regime, the applicability of the existing six classical theoretical models for both rigid and eroding projectile penetrations is evaluated. Furthermore, the transition velocities (the upper limit of rigid penetration and the lower limit of eroding penetration) are discussed and an empirical judgement criterion for the occurrence of non-monotonic dependence is proposed. Finally, by conducting the dynamic compression test, quasi-static tension test under varying temperature, etc., the Johnson-Cook model parameters for the present target and projectile are calibrated and validated by numerically simulating the present test.

VOCs photocatalytic abatement using nanostructured titania-silica catalysts

In this work, different quantities of TiO2 incorporated into TiO2-KIT6 nanostructured catalysts were considered to improve the photocatalytic abatement of volatile organic compounds (VOCs; ethylene, propylene) at ambient temperature. The best optimized activity and stability of the catalysts toward(s) ethylene and propylene degradation has been shown for 30wt% TiO2, while the worst conversion has been observed for a 90wt% TiO2 loading. This was likely due to the dispersion and stabilization of the anatase TiO2 with 30wt% on KIT-6, which in turn allowed more VOCs adsorption and better light penetration than 90% TiO2/KIT-6 in which it showed a bulk phase and large agglomerates with light penetration limitations. VOC abatement has been found to be not only influenced directly by the dispersed TiO2 contents but also by the calcination temperatures, and 500°C has been found to be the best calcination condition to achieve the highest propylene conversion. The optimized nanostructured photocatalyst developed for ethylene and propylene, could also be promising candidate for other VOCs and different applications.

Fabrication and Characterization of a 20-MHz Microlinear Phased-Array Transducer for Intervention Guidance.

This paper describes the design and fabrication of a miniature ultrasonic phased-array transducer used for intervention guidance. Currently, ultrasound probes are often placed at the body surface of the patients, leading to several drawbacks including the limitation of penetration and image quality. In order to improve the reliability of the guiding process, we propose a miniature phased-array transducer that can be placed adjacent to the intervention device during the interventional procedure. In this paper, we report the work that has been carried out on the development of this miniature phased-array transducer. It comprised 48 elements housed in a 3-mm-diameter needle. A specially designed flexible circuit was used for accommodating the transducer array in the long, thin needle housing. The center frequency and the fractional bandwidth were approximately 20 MHz and 42%, respectively, with an average crosstalk lower than -30 dB. The axial and azimuth resolutions were approximately 80 and [Formula: see text], respectively. The imaging capability of the transducer was further evaluated by acquiring the B-mode images of a needle in a cow liver. The performance of the proposed phased-array transducer demonstrates the feasibility of such an approach for interventional guidance.

Analytical Hydrogen Production and Storage Simulation for the “Kos-Kalymnos” System

The European Union's 2020 climate and energy package (known as “20-20-20” targets) requests, among other key objectives, 40% of the electricity production in Greece to be supplied from Renewable Energy Sources (RES) by 2020. The main barriers for reaching this target is the intermittency of RES combined with the penetration limits in the local electrical grids and the high seasonal demand fluctuations. In this context, the introduction of energy storage systems (ESSs), comprises one of the main solutions for coping with this situation. One of the most promising technologies for storing the excess energy, that would be otherwise lost, is the production and storage of hydrogen through water electrolysis. Hydrogen can be used for supporting the electricity grid during periods of high demand and as transportation fuel for H2-based automobiles (e.g. fuel cell vehicles). For this purpose, a simulation algorithm has been developed, able to assess the specifications of the optimum sizing of hydrogen production storage systems. For the application of the algorithm, the area of the Aegean Sea has been selected, owed to the considerable RES curtailments recorded in the various non-interconnected islands in the region. More specifically, the developed algorithm is applied to an autonomous electricity network of 9 islands, located at the SE area of the Aegean Sea and known as the “Kos-Kalymnos” electricity system. The results obtained designate the optimum size of the hydrogen-based configuration, aiming to maximize the recovery of otherwise curtailed RES production.

Harmonic impedance measurement based on short time current injections

This work presents an alternative method of measuring the equivalent impedance of an electric power network by injecting a short time current waveform based on Modulated Gaussian Signal. The frequency domain measurement of the equivalent impedance of an electric network is an important issue to correctly design harmonic filters and capacitor banks, detect resonance and antiresonance frequencies and evaluate the harmonic penetration and emission limits. The method proposed in this paper uses the Sliding Window Recursive Discrete Fourier Transform (SWRDFT) to extract the harmonic components of the measured voltage due to the injection of the short time current into the network. The proposed method was tested with different electric system topologies and the estimated impedance was compared with the impedance estimated by other methods found in the literature. Real time simulation using Hardware-in-the-Loop (HIL) methodology, as well as experimental results are presented in this paper.

Synchronous DG Planning for Simultaneous Improvement of Technical, Overcurrent, and Timely Anti-Islanding Protection Indices of the Network to Preserve Protection Coordination

The deployment of the distributed generation (DG), especially the synchronous distributed generation (SDG), as the energy infrastructure of smart grid in the distribution systems has drawn the attention of the distribution utilities to improve system performance through DG planning. In this paper, a methodology has been proposed for the planning of SDG units in the distribution system in an attempt to optimize a multiobjective index including the active energy losses during the planning period, the active and reactive power losses at the peak demand, voltage deviations from a reference value, the network investment deferral, the overcurrent protection system speed, and the anti-islanding protection speed. The constraints include the feeders' capacity, the maximum penetration limit due to anti-islanding protection requirements, the voltage limit, the preservation of the overcurrent protection system coordination, and the discrete size of SDG units. The proposed method has been applied to IEEE 14-bus test system with different cases including the different sets of weighting coefficients and the anti-islanding protections.

Deep-penetrating photodynamic therapy with KillerRed mediated by upconversion nanoparticles.

KillerRed is a protein photosensitizer that holds promise as an alternative for the existing hydrophobic photosensitizers that are widely used in clinical photodynamic therapy (PDT). However, applications of KillerRed to deep-seated tumours are limited by the insufficient penetration depth of the excitation light in highly scattering and absorbing biological tissues. Herein, we reported the deployment of upconversion nanoparticles (UCNPs) to enhance the treatment depth of KillerRed by converting the deep-penetrating near-infrared (NIR) light to upconversion photoluminescence and activating the PDT effect of KillerRed under deep tissues. This work demonstrated clear potential of UCNPs as the NIR-to-visible light converter to overcome the light penetration limit that has plagued PDT application for many years.

PV Penetration Limits in Low Voltage Networks and Voltage Variations

Photovoltaic embedded generation in low-voltage ac networks is quite popular; however, despite its benefits, there are some problems especially when photovoltaic (PV) penetration exceeds certain thresholds. Among others, voltage violation is of prime importance. Our review of the literature focused on PV penetration limits due to voltage violations in low-voltage (LV) networks. The review revealed that voltage violations can occur at a penetration level as low as 2.5% when a large distributed generator (DG) is installed at a single point. Alternatively, a LV network can host a large number of photovoltaic distributed generators (PVDGs), with a penetration level up to 110% if evenly distributed over shorter lengths. However, an LV network has no rules of thumb for safe penetration limits. Penetration-level calculations have been found that they used numerous approaches, which we have analyzed and discussed to adopt a more rational and unified approach. Our literature review revealed that, in LVs, a very high penetration level can be achieved as compared with medium-voltage (MV) networks. However, MV voltage-level control problems impose a limit for PV hosting in LV networks. There is a need to evolve strategies for robust voltage control at the MV level and to develop certain rules of thumb for PV penetration limits in LV networks independent of the MV level, to increase the PV hosting capacity.

Analysis of source-grid-load contribution to wind power accommodation

In recent years, China’s wind power is developing rapidly, but wind electricity curtailment becomes a serious problem. This paper evaluates wind power penetration limit from peak regulation, analyses relevant technical elements that impact wind power accommodation, coving the source side, the transmission side and the load side. By taking certain measures around the three aspects, for example, reducing the minimum technical output of conventional units, increasing outbound transmission capacity, or increasing the valley load, wind electricity curtailment will be effectively reduced. This paper quantitatively analyses wind power penetration limit under certain conditions and the source-grid-load contribution to wind power accommodation, and explores the important technical factors that affect wind power accommodation.

Energy management algorithm for optimum control of an off-battery autonomous DG/DFIG based WECS

A new management algorithm to improve performance and reliability of an off-battery autonomous energy system consisting of DFIG based wind energy converter (WEC) and diesel generator (DG) is proposed in this paper. Among its several constraints, the most significant ones are the limitation of wind power penetration and rotor side converter safety due to both the load demand variation and wind speed fluctuation. The proposed algorithm consists in maximizing load connection to the DFIG-based WECS and limiting the use of DG to only priority load taking into account some criteria to respect. A decision is made up with reference to specific rules on the basis of the measured wind speed and the predicted load demand. A stator flux-oriented technique for rotor side converter is presented to regulate voltage and frequency at stator/load terminals. Different possible case studies are presented to show the effectiveness of the proposed algorithm. Simulation results obtained from a 250 KW DFIG based wind power system are given and discussed in this paper.

Histological evaluation of follicular delivery of arginine via nanostructured lipid carriers: a novel potential approach for the treatment of alopecia

The use of lipidic nanoparticles can overcome the limitations of skin penetration of hydrophilic charged materials. Oleic acid as an ion pairing agent was used to enhance the encapsulation of positively charged arginine into lipophilic nanostructured lipid carrier (NLC). Histological study on the male hamsters was performed to assess the efficiency of drug delivery on hair growth. The accumulation of NLCs in the hair follicles was verified and in vivo studies showed more new hair follicle growth by utilizing arginine-loaded NLCs than arginine aqueous solution. It was concluded that employing ion pairing agent could enhance drug encapsulation into NLCs structure.

Voltage modelling of LV feeders with dispersed generation: Limits of penetration of randomly connected photovoltaic generation

Conditions on feeders with dispersed generation vary between voltage drop when there is no generation, and voltage rise when the generation exceeds the load. The utility is responsible for keeping the voltage variation within regulatory limits while the location of generation could be determined by investing customers without regard to feeder performance. Therefore, utilities must estimate as a general case how much generation can be connected randomly to a stochastically-loaded LV feeder before the risk of violating voltage limits becomes high enough to require detailed location specific studies. A fast probabilistic analytical core for voltage calculations on a feeder with loads and generation, described in a companion paper, enables Monte Carlo simulation of thousands of scenarios with randomly located generation and low loads to be done quickly, and gives a visual representation of the probable voltage conditions. The implications of choosing various levels of risk are discussed. The results can be used to set indicative penetration limits for photovoltaic generation in grid codes for low voltage feeders.

An Analysis of Wind Curtailment and Constraint at a Nodal Level

Many countries have set challenging wind power targets to achieve by 2020. This paper implements a realistic analysis of curtailment and constraint of wind energy at a nodal level using a unit commitment and economic dispatch model of the Irish Single Electricity Market in 2020. The key findings show that significant reduction in curtailment can be achieved when the system nonsynchronous penetration limit increases from 65% to 75%. For the period analyzed, this results in a decreased total generation cost and a reduction in the dispatch-down of wind. However, some nodes experience significant dispatch-down of wind, which can be in the order of 40%. This work illustrates the importance of implementing analysis at the nodal level for the purpose of power system planning.

Stochastic-based resource expansion planning for a grid-connected microgrid using interval linear programming

This paper represents a stochastic approach for long-term optimal resource expansion planning of a grid-connected microgrid (MG) containing different technologies as intermittent renewable energy resources, energy storage systems and thermal resources. Maximizing profit and reliability, along with minimizing investment and operation costs, are major objectives which have been considered in this model. Also, the impacts of intermittency and uncertainty in renewable energy resources were investigated. The interval linear programming (ILP) was applied for modelling inherent stochastic nature of the renewable energy resources. ILP presents some superiority in modelling of uncertainties in MG planning. The problem was formulated as a mixed-integer linear programming. It has been demonstrated previously that the benders decomposition (BD) served as an effective tool for solving such problems. BD divides the original problem into a master (investment) problem and operation and reliability subproblems. In this paper a multiperiod MG planning is presented, considering life time, maximum penetration limit of each technology, interest rate, capital recovery factor and investment fund. Real-time energy exchange with the utility is covered, with a consideration of variable tariffs at different load blocks. The presented approach can help MG planners to adopt best decision under various uncertainty levels based on their budgetary policies.

Velocity measurements in whole blood using acoustic resolution photoacoustic Doppler.

Acoustic resolution photoacoustic Doppler velocimetry promises to overcome the spatial resolution and depth penetration limitations of current blood flow measuring methods. Despite successful implementation using blood-mimicking fluids, measurements in blood have proved challenging, thus preventing in vivo application. A common explanation for this difficulty is that whole blood is insufficiently heterogeneous relative to detector frequencies of tens of MHz compatible with deep tissue photoacoustic measurements. Through rigorous experimental measurements we provide new insight that refutes this assertion. We show for the first time that, by careful choice of the detector frequency and field-of-view, and by employing novel signal processing methods, it is possible to make velocity measurements in whole blood using transducers with frequencies in the tens of MHz range. These findings have important implications for the prospects of making deep tissue measurements of blood flow relevant to the study of microcirculatory abnormalities associated with cancer, diabetes, atherosclerosis and other conditions.

Study of the Maximum Penetration Rate of Wind Power in an Island Network

The Penghu islands have abundant wind resources; the capacity factor of local wind farms exceeds 47% and these wind farms are slated for expansion. However, wind turbine power output is unstable and excessive turbine installation may negatively affect system stability. This paper seeks to determine an upper limit of the wind power penetration in the Penghu region power system to minimize waste and optimize system safety.

Dynamic Positron Emission Tomography Imaging of Renal Clearable Gold Nanoparticles.

Optical imaging has been the primary imaging modality for nearly all of the renal clearable nanoparticles since 2007. Due to the tissue depth penetration limitation, providing accurate organ kinetics non-invasively has long been a huge challenge. Although a more quantitative imaging technique has been developed by labeling nanoparticles with single-photon emission computed tomography (SPECT) isotopes, the low temporal resolution of SPECT still limits its potential for visualizing the rapid dynamic process of renal clearable nanoparticles in vivo. The dynamic positron emission tomography (PET) imaging of renal clearable gold (Au) nanoparticles by labeling them with copper-64 ((64) Cu) to form (64) Cu-NOTA-Au-GSH is reported. Systematic nanoparticle synthesis and characterizations are performed to demonstrate the efficient renal clearance of as-prepared nanoparticles. A rapid renal clearance of (64) Cu-NOTA-Au-GSH is observed (>75%ID at 24 h post-injection) with its elimination half-life calculated to be less than 6 min, over 130 times shorter than previously reported similar nanoparticles. Dynamic PET imaging not only addresses the current challenges in accurately and non-invasively acquiring the organ kinetics, but also potentially provides a highly useful tool for studying renal clearance mechanism of other ultra-small nanoparticles, as well as the diagnosis of kidney diseases in the near future.

Contrast enhanced ultrasound (CEUS) - an unique monitoring technique to assess microvascularization after buried flap transplantation.

Incidence of patients requiring complex soft tissue or osseous reconstruction has dramatically increased. However most of the monitoring systems have limitations in tissue penetration and are not able to detect microvascular complications after transplantation of so-called buried-flaps, that have no contact to the surface.Aim of the study was to assess contrast enhanced ultrasound (CEUS) as monitoring tool after buried flap transplantations. 20 patients were examined after buried flap transplantation using CEUS. Quantitative perfusion analysis (TIC) was performed with an integrated perfusion software using stored cine-loops. Two perfusion-parameters, time to PEAK (TtoPk) and area under the curve (Area), were evaluated using TIC analysis. Minor complications were observed in 3 patients. In these patients a delayed contrast agent wash-in and wash-out was observed. Additionally the perfusion values TtoPk (sec.) and Area (relative Units) were clearly different in the patients with minor complications: TtoPk: 32.0 sec; Area 425.5 rU (without complication), TtoPk: 38.6 sec.; Area: 18.3 rU (wound healing disturbance) and TtoPk: 14.4 sec.; Area: 105.9 rU (hematoma). As CEUS can assess microvascularization almost depth-independent, CEUS is an unique method to assess global flap perfusion after buried flap transplantation.