Improved Evaluation of The Wind Power Potential of a Large Offshore Wind Farm Using Four Analytical Wake Models

The objective of this paper is to investigate the ability of analytical wake models to estimate the wake effects between wind turbines (WTs). The interaction of multiple wakes reduces the total power output produced by a large offshore wind farm (LOFWF). This power loss is due to the effect of turbine spacing (WTS), if the WTs are too close, the power loss is very significant. Therefore, the optimization of turbine positions within the offshore wind farm requires an understanding of the interaction of wakes inside the wind farm. To better understand the wake effect, the Horns Rev 1 offshore wind farm has been studied with four wake models, Jensen, Larsen, Ishihara, and Frandsen. A comparative study of the wake models has been performed in several situations and configurations, single and multiple wakes are taken into consideration. Results from the Horns Rev1 offshore wind farm case have been evaluated and compared to observational data, and also with the previous studies. The power output of a row of WTs is sensitive to the wind direction. For example, if a row of ten turbines is aligned with the 270° wind direction, the full wake condition of WTs is reached and the power deficit limit predicted by Jensen model exceeds 70%. When a wind direction changes only of 10° (260° and 280°), the deficit limit reduces to 30%. The obtained results show that a significant power deficit occurs when the turbines are arranged in an aligned manner. The findings also showed that all four models gave acceptable predictions of the total power output. The comparison between the calculated and reported power output of Horns Revs 1 showed that the differences ranged from - 8.27 MW (12.49%) to 15.27 MW (23.06%) for the Larsen and Frandsen models, respectively.

Impacts of electricity generation on air pollution: evidence from data on air quality index and six criteria pollutants

We estimate impacts of electricity generation (total power output and thermal power output) on air pollution (air quality index (AQI) and six criteria air pollutants), with a particular emphasis on industry and city heterogeneity. To identify this relationship, we combine detailed monthly data on electricity production, air pollution, economy and weather for a six-year period in four biggest cities in China. Our fundamental identification strategy employs Ordinary Least Squares Regression of panel data with city–month fixed effects and addresses confounding variations between electricity generation and economy or weather conditions. We find that one unit (100 million kwh) increase in power output is associated with a 0.3-unit (representing value) increase in AQI, nearly all of which is driven by increases in thermal power output. We notice a robust positive impact of increased electricity generation (specifically thermal power output) on PM2.5 and PM10, also positive relationships between increases in other power output (total power output minus thermal power output) and SO2, NO2, while changes in power output have no statistically significant effect on CO and O3. The heterogeneous pollution effects of electricity generation are present in specific cities with different weather conditions. The results indicate that a reduction policy in power industry differentiating among cities might enhance effectiveness by considering each city’s particular backgrounds, a previously overlooked aspect associated with pollution reduction policies.

Multirotor Systems Using Three Shrouded Wind Turbines for Power Output Increase

Brimmed-diffuser augmented wind turbines (B-DAWTs) can significantly increase the performance of the rotor. Multirotor systems (MRSs) have a lot of merits such as significant saving mass and overall cost of the wind turbine system. In the present research, B-DAWTs are studied in a MRS. In wind tunnel experiments, the power output and aerodynamics of three B-DAWTs placed in close vicinity have been investigated. The results show a significant increase of up to 12% in total power output of the MRS with B-DAWTs compared to the sum of the stand-alone (SA) same turbines. The accelerated gap flows between B-DAWTs in a MRS cause lowered pressure regions due to vortex interaction behind the brimmed diffusers and draw more wind into turbines.

Performance assessment of a four-air cathode membraneless microbial fuel cell stack for wastewater treatment and energy extraction

A stack of two identical single chamber microbial fuel cells (MFCs) was assessed during using fermentable house hold extract as substrate. The design of the MFC units was based on the single chamber membrane-less technology using four cathode electrodes. The total power output was 492 mW either in series or parallel connection considering a total anolyte volume of 240 cm3. During continuous operation, the COD removal was 80% for each cell and for both operation modes (series and parallel). The electrochemical profiles provided significant information on the behaviour of the stack. During continuous operation, parallel connection is preferred over series connection, as it results to the same power output values, and COD removal but it provides lower internal resistances leading to more stable electrochemical performance behaviour.

Optimal Control and Switching Mechanism of a Power Station With Identical Generators

This paper proposes a novel approach for optimizing the total power output of a generalized power station with identical generators by analyzing the characteristics of the efficiency function. The introduced treatment yields the maximum total power supply and the maximum overall efficiency for the generalized power station. To achieve these, the input factor for each generator is kept the same, and the optimal switch points are selected to be the same efficiency points of two operating methods.

Brief communication: On the influence of vertical wind shear on the combined power output of two model wind turbines in yaw

The effect of vertical wind shear on the total power output of two aligned model wind turbines as a function of yaw misalignment of the upstream turbine is studied experimentally. It is shown that asymmetries of the power output of the downstream turbine and the combined power of both with respect to the upstream turbine's yaw misalignment angle can be linked to the vertical wind shear of the inflow.

Brief Communication: On the influence of vertical velocity profiles on the combined power output of two model wind turbines in yaw

The effect of vertical velocity gradients on the total power output of two aligned model wind turbines as a function of yaw misalignment of the upstream turbine is studied experimentally. It is shown that asymmetries of the power output of the downstream turbine and the combined power of both with respect to the upstream turbine's yaw misalignment angle can be linked to the vertical velocity gradient of the inflow.

Discussion of Some Myths/Features Associated With Gas Turbine Inlet Fogging and Wet Compression

Gas turbine (GT) inlet fogging and overspray (high-fogging) have been considered the most cost-effective means of boosting a GT's total power output, especially under hot or dry weather conditions. The result of employing fogging or overspray is indisputably clear—total power output is increased; however, development of the theory and explanation of the phenomena associated with fogging and overspray are not always consistent and are sometimes misleading and incorrect. This paper focuses on reviewing several interesting features and commonly discussed topics, including (a) entropy production of water evaporation, (b) the effect of centrifugal force on water droplets, and (c) whether water droplets can survive the journey in the compressor and enter the combustor. Furthermore, three turbine myths that fogging/overspray increases the air density in the compressor, reduces the compressor power consumption, and noticeably enhances the GT efficiency are examined and discussed. Some common mistakes in describing the compressor work are identified and corrected. A newly constructed multiphase T–s diagram is used to explain the physics of water droplet evaporation process and corresponding entropy production during wet compression.

Piezoelectric-Based Rotary Electrical Energy Generator for Harvesting Energy From Low and Highly Variable Rotary Motion

A class of piezoelectric-based rotary electrical-energy generator is presented in which a polygon-shaped gear is used to effectively couple the rotating shaft with multiple piezoelectric cantilevers. The relation between the input rotational speed and the output power production for a laboratory-scale device with an octagonal gear is systematically characterized both by experiments with DC-motor controlled rotation inputs and by finite-element analyses (FEA) with prescribed gear rotational speeds. The electric signals generated by each piezoelectric bimorph are shown in phase with each other as well as the total power output scales with the number of piezoelectric bimorphs. The generator outputs higher electric power over a significantly wider range of rotational frequencies than similar devices do using the piezoelectric transduction mechanism. The generated power increases almost linearly with the input rotational speed for input frequencies up to at least 300 RPM. The broadband feature of the present generator makes it ideal for power generation systems that operate with low frequent, broadband excitations like those that harvest energy from wind and tidal flows.

Experimental Investigation of Heat Transfer Across a Thermoelectric Generator for Waste Heat Recovery From Automobile Exhaust

The study investigates the temperature gradients achieved across a thermoelectric generator by using the exhaust gases from a vehicle as a heat source and the radiator coolant as the cold sink. Various heat transfer enhancement features are employed in order to achieve as high a temperature gradient as possible. Effect of flow Reynolds numbers and inlet temperatures are examined to create a body of data predicting total power output from the TEG. Data is normalized against results from baseline heat exchanger designs investigated in the past. The experiments are carried out at 1/5th scale of the previously examined geometry. Impingement geometry is employed on the coolant side to enhance heat transfer. The experimental test sections are fabricated using metal 3D printing. Water is used instead of radiator coolant and heated air is used for exhaust gases. The results from the experiments provide valuable data which can be used for system level optimization.