Mean Power Density Research Articles

Evaluation of wind energy potential in the south-south geopolitical zone of Nigeria

This study examined wind energy potential of six selected locations the South-South geopolitical zone of Nigeria using 10 year wind data obtained at a height of 10m as a possible location for energy generation from wind. The obtained data showed that the annual mean wind speed for Asaba, Benin, Calabar, Port Harcourt, Uyo, and Warri were 3.3m/s, 3.3m/s, 4.4m/s, 3.4m/s, 3.5m/s and 3.7m/s respectively, with corresponding mean power density of 21.8W/m 2 , 21.4W/m 2 , 35.8W/m 2 , 23W/m 2 , 25.2W/m 2 , and 30.8W/m 2 .. The mean energy output of 183.4KWh/m 2 , 205.4KWh/m 2 , 311.7KWh/m 2 , 200.9KWh/m 2 , 220.9KWh/m2, and 274.3KWh/m2 were found for the respective locations. The corresponding annual mean wind speed with maximum energy ranged from 4.1m/s to 4.4m/s with Calabar station found to be the most suitable site for the installation of wind turbine for power generation. The overall mean wind power densities and the annual mean power densities were under class 1 of wind classification scheme indicating that, the mean wind speed fell short of required standard of 6m/s for large-scale installation of wind energy generation. Nevertheless, the power generated could be improved using suitable wind turbines at reasonable heights. Keywords: Mean wind speed, Wind power density, Wind energy, Renewable energy

Feasibility of electricity generation using WECS in the selected locations of Tigray region (Ethiopia)

This paper presents the feasibility of electricity generation using WECS in the selected locations of Tigray region in Ethiopia. Weibull parameters were obtained using the energy pattern factor method (EPFM). A linear agreement was observed between mean wind speed and power density. Analysis of the present value of cost per kilowatt hour was estimated for selected wind turbines at different hub heights. In addition, regardless of the location, power law curve fit provides higher regression than the linear curve fit. From the analysis of results and discussion, it is revealed that (WECS)III has the least progressive ratio when compared with (WECS)IV. Finally, the average specific cost per unit for all chosen turbines at Mekele and Chercher is comparable to the cost per kWh charged by EEPCo, except for a few turbines in this study.

Numerical investigation of wave energy resources and hotspots in the surrounding waters of Taiwan

Abstract A state-of-the-art, third-generation, spectral wind wave model was implemented for the surrounding waters of Taiwan. The model was driven by 10-m winds above sea level from ERA-Interim reanalysis data. Medium-term (ten-year) hindcasts covering the period from 2007 to 2016 were conducted to assess the wave power resources in Taiwanese waters. The lowest monthly mean wave power density occurs in May and June, while the most energetic month is December. The sea area with the highest wave power density was observed near Lanyu. Four energetic areas located off the northern coast (H1), the southeastern coast (H2 and H3), and the southern coast (H4) of Taiwan serve as the appropriate sites (hotspots) for deploying wave energy converters. The annual mean wave power densities over ten years are approximately 8.72 kW/m, 10.97 kW/m, 13.72 kW/m, and 13.02 kW/m for H1, H2, H3, and H4, respectively. The annual total wave energy outputs were estimated to be 48.80 MWh/m, 76.59 MWh/m, 94.20 MWh/m, and 92.56 MWh/m at H1, H2, H3, and H4, respectively. The wave power is primarily driven by the northeast monsoon and the bulk of the wave energy appears to be generated by local wind waves in the surrounding waters of Taiwan.

Evaluation of an automated pipeline for large-scale EEG spectral analysis: the National Sleep Research Resource

Study objectivesWe present an automated sleep electroencephalogram (EEG) spectral analysis pipeline that includes an automated artifact detection step, and we test the hypothesis that spectral power density estimates computed with this pipeline are comparable to those computed with a commercial method preceded by visual artifact detection by a sleep expert (standard approach). MethodsEEG data were analyzed from the C3-A2 lead in a sample of polysomnograms from 161 older women participants in a community-based cohort study. We calculated the sensitivity, specificity, accuracy, and Cohen's kappa measures from epoch-by-epoch comparisons of automated to visual-based artifact detection results; then we computed the average EEG spectral power densities in six commonly used EEG frequency bands and compared results from the two methods using correlation analysis and Bland–Altman plots. ResultsAssessment of automated artifact detection showed high specificity [96.8%–99.4% in non-rapid eye movement (NREM), 96.9%–99.1% in rapid eye movement (REM) sleep] but low sensitivity (26.7%–38.1% in NREM, 9.1–27.4% in REM sleep). However, large artifacts (total power > 99th percentile) were removed with sensitivity up to 87.7% in NREM and 90.9% in REM, with specificities of 96.9% and 96.6%, respectively. Mean power densities computed with the two approaches for all EEG frequency bands showed very high correlation (≥0.99). The automated pipeline allowed for a 100-fold reduction in analysis time with regard to the standard approach. ConclusionDespite low sensitivity for artifact rejection, the automated pipeline generated results comparable to those obtained with a standard method that included manual artifact detection. Automated pipelines can enable practical analyses of recordings from thousands of individuals, allowing for use in genetics and epidemiological research requiring large samples.

Effect of various strategies of soc-dependent operating current on performance of a vanadium redox flow battery

A two-dimensional quasi-steady-state model is applied to investigate charge/discharge behavior and performance of a VRFB. Emphasis is focused on exploring the influences of various strategies of soc-dependent operating current density on battery performance. For constant-current operation, with the increase of current density, although the system mean power density is significantly boosted, the system capacity and net discharge energy in a cycle are obviously decreased. It is quite difficult to give consideration to both the system capacity and system power simultaneously such that overall battery performance can be improved. Applying the strategy of soc-dependent operating current (i.e., low current at the end of charge/discharge process while high current for the rest time), the system capacity, power density and net discharge energy in a cycle can be simultaneously boosted while comparable efficiencies can be achieved. Optimally, at the mean operating current density of about 70 mA cm−2, the system capacity is maximally improved by 9.3% and the net discharge energy is maximally increased by 7.9% as compared with that under constant-current operation. As the same time, the energy-based system efficiency can be maintained over 78%, which is comparable with that for constant-current operation.

Statistical analysis of wind energy characteristics in Santiago island, Cape Verde

As a volcanic archipelago, the Republic of Cape Verde relies dominantly on diesel to power its electricity supply. Recognizing the financial and environmental burden of diesel generation and risk of energy security, the government of Cape Verde has launched an ambitious goal of 50% electricity from renewables by 2020, since the country is endowed with high potential of renewable energy resources such as wind and solar. Although the annual average penetration rate of wind power has reached 24% of total electricity production generated in Cape Verde, raising the wind energy penetration level in future will pose numerous challenges for the operation and control of the power system because of wind's inherent intermittency and unpredictability. In this study, a statistical analysis of the wind characteristics in Santiago island, is presented by using historical wind speed and power data of the Santiago wind farm in 2014. A two-parameter Weibull distribution is first applied to model the wind speeds on various timescales and to determine wind energy potential in Santiago island, Cape Verde. The annual average wind speed was 8.57 m/s with a standard deviation close to 3.29 m/s. The monthly Weibull scale parameters varied from 5.64 m/s to 13.7 m/s, while the monthly Weibull shape parameters varied from 1.97 to 9.13. Although the monthly mean power density of the rainy season from August to September was low, the annual mean power density shows that Santiago has good wind potential. Then, an approach to modeling the equivalent power curve based on available wind speed and power output data from the wind farm is proposed. By utilizing the estimated power curve, the uncertainty set of wind power generation, resulted from the uncertainty of wind speed forecast, can be obtained to quantify the power system reserve requirements. A statistical analysis of wind power ramp is also given for estimating the power capacity requirement of the energy storage system that can be considered as a reasonable way to mitigate the wind intermittency and minimize curtailment of wind. Results of this study contribute to assess the wind energy potential of Cape Verde for investors, and can be used to quantify the uncertainties of wind power generation for the power system operator.

Wind energy potential and economic assessment of four locations in Sistan and Balouchestan province in Iran

Utilization of wind turbines to produce energy has been increasing in recent years, due to technology advancement, cost stability and environmental issues. In this paper, the wind resource and economic feasibility have been studied to avoid investment risk in cites of Zabol, Zahak, Zahedan and Mirjaveh in Sistan and Balouchestan province of Iran. The Weibull distribution function has been applied to estimate the wind power and energy density, using meteorological data. Determination of coefficient, root mean square error, mean bias error and mean bias absolute error are also calculated to ensure the accuracy of the statistical analysis of fitted distribution. Windographer software has been employed to investigate the prevailing wind direction. The estimated annual energy densities are 2495.36, 2355.69, 1265.24 and 1214.01 kWh/m2/year, and the annual mean power densities are 284.97, 269.02, 144.49 and 138.64 W/m2. It is found that Zabol and Zahedan are suitable for large scale power generation. The results indicate that using DW61-900 kW wind turbines are highly beneficial for Zabol and Zahak, while for Zahedan, DW52/54-250 kW wind turbine is more appropriate for generating electricity. However, Mirjaveh is suitable for off-grid applications. It should be noted that in this analysis, monetary units are presented in 2016 U.S. dollar.

Electrical Guidance Efficiency of Downstream‐Migrating Juvenile Sea Lampreys Decreases with Increasing Water Velocity

AbstractWe tested the efficacy of a vertically oriented field of pulsed direct current (VEPDC) created by an array of vertical electrodes for guiding downstream‐moving juvenile Sea Lampreys Petromyzon marinus to a bypass channel in an artificial flume at water velocities of 10–50 cm/s. Sea Lampreys were more likely to be captured in the bypass channel than in other sections of the flume regardless of electric field status (on or off) or water velocity. Additionally, Sea Lampreys were more likely to be captured in the bypass channel when the VEPDC was active; however, an interaction between the effects of VEPDC and water velocity was observed, as the likelihood of capture decreased with increases in water velocity. The distribution of Sea Lampreys shifted from right to left across the width of the flume toward the bypass channel when the VEPDC was active at water velocities less than 25 cm/s. The VEPDC appeared to have no effect on Sea Lamprey distribution in the flume at water velocities greater than 25 cm/s. We also conducted separate tests to determine the threshold at which Sea Lampreys would become paralyzed. Individuals were paralyzed at a mean power density of 37.0 µW/cm3. Future research should investigate the ability of juvenile Sea Lampreys to detect electric fields and their specific behavioral responses to electric field characteristics so as to optimize the use of this technology as a nonphysical guidance tool across variable water velocities.Received April 26, 2016; accepted November 1, 2016 Published online February 13, 2017

The ant and the elephant: ambient RF harvesting from the uplink

This work investigates the available ambient radio frequency (RF) power density in dynamic, outdoor environments with a specific focus in the uplink. A spectrum survey was carried out around Bristol, UK between 500 MHz and 3 GHz using a handheld spectrum analyser and an omnidirectional broadband discone antenna. Measurements were performed while walking, travelling in a car and on a train. The results are compared with baseline indoors measurements, and as expected, ambient RF power densities in the outdoor environments were significantly higher. Interestingly, in some cases the power contained in the uplink of cellular communication networks is shown to be a better energy source than the downlink. It was found that in a train during rush hour, there is 17 times the mean power density and 45 times the peak power density in the uplink compared with the downlink. This shows that there is scope for ambient energy harvesting in environments with a large density of user equipment. Finally, by accounting for the rectifier efficiency it is estimated that during the train commute between Bristol and Bath in the UK a total of 27.2 mJ of energy could be collected.

The thermal effect of 2.45 GHz microwave radiation on rat testes

The study focused on the effect of microwave radiation at a dose which commonly does not lead to tissue heating, however, in the rat testes it resulted in accumulation of heat. Adult rats were exposed to whole body pulse radiation at a frequency of 2.45 GHz and mean power density of 28 W/m2, for 3 h a day for the duration of 3 weeks. Immediately after each irradiation, the body temperature and the testicular temperature were measured in the control and experimental animals. Samples for histological and immunohistochemical analysis were taken after the last irradiation and processed for light and transmission electron microscopy. An evaluation of spermatozoa motility was performed using computer-assisted sperm analysis. Although the body temperature of the rats was not elevated after the irradiations, the testicular temperature was significantly increased (P < 0.004). Testes of the experimental animals had considerably dilated and congested blood vessels and the seminiferous epithelium showed degenerative changes. The Leydig cells showed no obvious structural abnormalities. Transmission electron microscopy revealed ultrastructural changes in developing sex cells, Sertoli cells, and endothelial cells. An intensified immunoreactivity to superoxide dismutase 1 was found in spermatogonia and Leydig cells in the experimental animals. Results of the present study revealed a distinctly adverse effect of microwave radiation on the thermoregulatory capability and histological structure of rat testes as well as an oxidative damage of the tissue. The scientific knowledge confirming or denying the thermal effect of microwave radiation on living tissue is scarce and thus the present study may be regarded as unique and helpful to clarify the issue.

Wind Energy Potentials and Its Trend in the South China Sea

Using a 30year (1976-2005) daily high-resolution reanalysis wind field dataset assimilated from several meteorological data sources, the wind speed and power characteristics of the South China Sea (SCS) were investigated using the Weibull shape and scale parameters. The region in general showed good wind characteristics. This is shown by high annual mean wind speed and power density values which are 5.93 m/s and 273.84 W/m2 respectively. The calculated annual mean wind power resource attributes the region to a relatively high potential site for large- scale grid connected wind turbine applications. The wind power ranged between 96.27 W/m2 in May and 527.03 W/m2 in December. Furthermore, spatio-temporal variations showed that strong trends in wind power exist in Luzon strait in the northern SCS and Xisha, Zhongsha, Luzon, Liyue bank in the central SCS which are evaluated as high wind potential regions and may be rated as locations excellent for installation of large wind turbines for electrical energy generation. Non-significant and negative trends dominate the southern SCS and may therefore, be suitable for small wind applications. The wind power density exhibited a significant increasing trend of 1.4 W/m2 yr-1 in the SCS as a whole throughout the study period. The trend is strongest (2.8 W/m2 yr-1) in winter.

Piezoelectric materials for bistable energy harvester: A comparative study

ABSTRACTThis paper deals with the potential of various lead-free piezoelectric materials for energy harvesting. The performance of these materials is simulated for unimorph bistable piezoelectric energy harvester. The finite element method considering first-order shear deformation theory is used to model the system. The energy harvesting potential of bistable system (Non-linear) is compared with its linear counterpart. The results depict that the mean power density is almost 100% higher in case of bistable system. K0.5Na0.5NbO3-LiSbO3 (KNN-LS) family exhibited better performance than the conventional lead-based piezoelectric material lead zirconate titanate (PZT). The mean power density of K0.5Na0.5NbO3-LiSbO3-CaTiO3 (2 wt.%) is reported to be 65% higher than PZT.

Wind energy potential assessment of Cameroon's coastal regions for the installation of an onshore wind farm.

For the future installation of a wind farm in Cameroon, the wind energy potentials of three of Cameroon’s coastal cities (Kribi, Douala and Limbe) are assessed using NASA average monthly wind data for 31 years (1983–2013) and compared through Weibull statistics. The Weibull parameters are estimated by the method of maximum likelihood, the mean power densities, the maximum energy carrying wind speeds and the most probable wind speeds are also calculated and compared over these three cities. Finally, the cumulative wind speed distributions over the wet and dry seasons are also analyzed. The results show that the shape and scale parameters for Kribi, Douala and Limbe are 2.9 and 2.8, 3.9 and 1.8 and 3.08 and 2.58, respectively. The mean power densities through Weibull analysis for Kribi, Douala and Limbe are 33.7 W/m2, 8.0 W/m2 and 25.42 W/m2, respectively. Kribi’s most probable wind speed and maximum energy carrying wind speed was found to be 2.42 m/s and 3.35 m/s, 2.27 m/s and 3.03 m/s for Limbe and 1.67 m/s and 2.0 m/s for Douala, respectively. Analysis of the wind speed and hence power distribution over the wet and dry seasons shows that in the wet season, August is the windiest month for Douala and Limbe while September is the windiest month for Kribi while in the dry season, March is the windiest month for Douala and Limbe while February is the windiest month for Kribi. In terms of mean power density, most probable wind speed and wind speed carrying maximum energy, Kribi shows to be the best site for the installation of a wind farm. Generally, the wind speeds at all three locations seem quite low, average wind speeds of all the three studied locations fall below 4.0m/s which is far below the cut-in wind speed of many modern wind turbines. However we recommend the use of low cut-in speed wind turbines like the Savonius for stand alone low energy needs

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Assessment of wind resources in two parts of Northeast Brazil with the use of numerical models

Tidal stream resource assessment in the Dover Strait (eastern English Channel)

A methodology of tidal flow resource assessment in the Dover Strait is presented. The resource assessment is performed using surface velocity time series recorded by Very High Frequency Radars (VHFR) and ADCP velocity measurements. Following the EMEC guideline, the major parameters of tidal flow conventionally used for tidal energy site screening are estimated and mapped. The combination of two sources of data allowed to characterize the current velocity variation in three spatial dimensions and in time, which increased confidence in hydrokinetic resource assessment from the radar data. Current velocities provided by the radars show strong spatial variation and fortnightly modulation. The most energetic area was found west of the Cape Gris Nez with the peak velocity of 2.5m/s, mean velocity of 1m/s, and spring tide average velocity of 1.4m/s. Velocities exceeding 1m/s are observed more than 50% of time there. Averaged velocity profiles derived from ADCP data were obtained for different stages of the tidal cycle and then approximated by a power law function. Using velocity time series provided by the radars and the power law velocity profiles, the power density time series in the surface and bottom layers were generated. The analysis of these data show that west of the Cape Gris Nez, the mean power density attains its maximum value 0.9kW/m2 in the surface layer and a peak value 5kW/m2. In the rest of the domain, the mean power density varies from 0.1 to 0.6kW/m2. The power density is found three times lower in the bottom layer. A three dimensional hydrodynamic model MARS-3D is used for comparison with experimental data. The model results are in good agreement with observations thus allowing the use of the model for assessing tidal stream resource in extended area.

On the Use of Wind Energy at Tlemcen, North-Western Region of Algeria

In this work, ten years of wind data from Tlemcen meteorological station have been used to evaluate the potential of wind power on the North occidental region of Algeria. The WAsP program was used to analyse the wind Atlas of the region to find the windiest areas. The study proposes to assess the wind energy produced and the cost per kWh of electricity produced by a wind farm of 18.4 MW rated capacity installed at the southern part of Tlemcen. Despite a relatively low potential assessed at the meteorological station, it was possible to delineate a favourable zone for the use of wind energy. Thus, the investigation at 10 m above ground at the location of the airport shows a low wind potential, with an annual mean wind speed equal to 2.42 m/s and an annual mean power density of 49W/m2 while, the temporal study gives the hottest months as the windiest. However, the windiest area received 23 wind turbines of 800kW rated capacity and gives an annual energy production equal to 25.3 GWh. Concerning the economic analysis, it gives 0.0587 $ per kWh produced for a wind farm expected to cost about 30 million $ (US Dollar) for 20 years.

THE WAYS TO OPTIMIZE CLINICAL OUTCOMES OF PHOTODYNAMIC THERAPY BY OPTICAL IMAGING TECHNIQUES

Background: Photodynamic therapy (PDT) is a modern minimally invasive technique for treatment of a wide range of diseases, including malignancies. One of directions for PDT development is the individualization of exposure modes that can be achieved with effective treatment monitoring. There are a number of approaches employing imaging techniques, the most promising of them being optical ones. Aim: To analyze factors affecting clinical outcomes of PDT in non-melanoma skin tumors, and to evaluate the prospects of optical imaging techniques for PDT planning and monitoring. Materials and methods: We retrospectively analyzed various aspects of the results PDT obtained in 855 patients with non-melanoma skin tumors. PDT was performed with systemic chlorine photosensitizers. As a source of irradiation, the laser at a wavelength of 662 nm was used following exposure modes: mean power density 0.3 W/cm², the laser irradiation dose of 200 J/cm² for basal cancer and 300 J/cm² for squamous cell carcinoma. Clinical evaluation was performed based on tumor response according to RECIST criteria, by the presence or absence of recurrence during long term follow up and by the presence or absence of cosmetic defects. Fluorescence imaging and optical coherence tomography were used as non-invasive imaging techniques. Results: It was found that clinical predictors of treatment failure included tumor recurrence, squamous type of tumor, and advanced exophytic or infiltrative component. Fluorescence imaging showed an association between clinical outcomes of PDT and fluorescence characteristics of the photosensitizer. The best clinical outcomes were achieved in 147 patients with a combination of high contrast fluorescence (FC>1.2) and a high degree of photobleaching of the agent (ΔIt/IN >25%): the number of complete tumor responses was 94% (138 of 147), with recurrence seen in 3 (2%) patients only with the follow up from 6 to 53 month duration. Clinical predictors of PDT cosmetic failures are tumor recurrence and tumor stage above T2. The most vulnerable zones are the outer ear and nose wings; this fact is related to an involvement of the cartilage located directly beneath the thin skin in the photodynamic reaction. This was demonstrated by optical coherence tomography. Conclusion: Presence of clinical predictors of PDT failure justifies correction of light exposure modes that can be optimally implemented with techniques for objective evaluation of the tumor borders, photosensitizer accumulation and photobleaching. Dynamic non-invasive monitoring of PDT procedure with fluorescence imaging and optical coherence tomography seems promising for implementation of an individual approach resulting in optimal oncological and functional outcomes.

Frequency-Selective Evaluation of Personal Exposure to Electromagnetic Fields of Wireless Communications and Broadcast Transmitters

We performed a frequency-selective measurement campaign using personal exposure meters with a three-axis E-field probe to assess the electric field strength and power density of wireless communication systems and broadcast transmitters in Kosovo. Mean exposure levels were compared among different microenvironments--outdoor urban, living room, office and bedroom microenvironments--in different geographical locations and different exposure time periods. Furthermore, typical exposure levels in European countries and Kosovo were compared. Measurement post-processing results show that the highest values of the mean power density in an outdoor urban microenvironment were 0.173 mW/m2 for Wi-Fi 5G, 0.137 mW/m2 for GSM 900 uplink, 0.128 mW/m2 for GSM 1800 uplink and 0.112 mW/m2 for Wi-Fi 2G. The maximal recorded value of the total electric field strength was 10.44 V/m. The highest exposure levels per frequency band in the living room were 0.042 mW/m2 for FM, 0.023 mW/m2 for GSM 900 uplink and 0.023 mW/m2 for GSM 900 downlink and Wi-Fi 2G. In office environments, the mean power density for 14 predefined frequency bands in the range 88---5850 MHz was 0.227 mW/m2 in total. The highest total electric field strength for office microenvironments was 5.439 V/m. Residential homes were mainly dominated by the GSM bands (GSM 900 downlink, 54 %; GSM 1800 downlink, 36 %). For the frequency bands FM, TETRA and TV4&5, the exposure was much higher on upper residential floors.

Wind energy resources on Phuquoc Island, Vietnam

ABSTRACTThis study analyzes the wind energy resources on Phuquoc Island, Vietnam. Daily wind data are collected from 2005 to 2011 in this study. The annual mean speed and power density are 6 m/s and 355 W/m2, respectively. Results show that more than 35% of the wind energy comes from the northwest. In this study, a 75 MW wind farm with 25 wind turbines is simulated by using the WAsP 10 program. The wind farm can produce over 189.636 GWh annually. In addition, the effects of wind disturbance and three-phase short circuit of the grid are analyzed using the ETAP 7.0 program.

Comparison of Some Estimation Methods of the two parameter Weibull Distribution for Unusual Wind Speed Data Cases

Since the Weibull distribution has been accepted reference distribution in wind energy field, topics on its parameter estimation methods have been attracted issue. In this context, the literature have generally focused on non-robust methods which may yield questionable results in the cases of unusual and contaminated wind speed data. This paper discusses some robust estimation methods of the Weibull distribution for unusual wind speed data cases. The considered robust methods are evaluated by using artificially generated unusual wind speed data cases. It was found that some of the considered robust methods provide reliable results compared classical ones. Also, the same results are observed for the estimation of mean power density error. As a result, analyzes performed shows that robust and efficient classical methods can be used together to check results.