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So far, the size of industrial energy and recovery boilers has been increased continuously. This development has led to a situation where the middle parts of the large boilers are extremely difficult to reach with traditional measurement methods. Due to this, our research group has studied possibilities to develop a mobile sensor ball propagating freely also in the center parts of combustion chambers. The sensor ball will consist of sensor electronics with sensor elements and a protective cover or envelope. The duty of the envelope is to delay the heating of sensor electronics inside the ball. This article focuses on studying the thermal protection issues of the sensor ball and its operation times in flames. [ABSTRACT FROM AUTHOR]

Electrical discharge machining bearing currents that may occur within electric machines of variable-speed-drive motor systems have been recognized for a long time. One key influential factor, the machine's capacitive voltage divider “bearing-voltage-ratio” (BVR) strongly depends on the rotor-to-frame and the stator winding-to-rotor capacitances; these are, in turn, affected by the design of the machine's stator slot. This paper presents an approach to improve the accuracy with which these capacitances can be estimated. It is based on the well-known plate capacitance equation which is then corrected by normalization functions. The functions are defined by extensive parameter studies using electrostatic finite element method (FEM) simulations. The final expressions not only allow for the prediction of the stator-winding-to-rotor and rotor-to-frame capacitances, they are also readily applicable. Thereby, they facilitate, for example, the clear-cut study of the sensitivity of the BVR towards changes in the different stator slot parameters. [ABSTRACT FROM AUTHOR]

The authors' research group is developing a mobile sensor for operation inside combustion chambers of big industrial power plants. The aim of developing the ball-formed sensor is to measure process information inside big combustion chambers (heat power over 100 MW), hopefully mainly from places which cannot be reached by ordinary measurement equipment outside the chamber. The sensor ball needs means for communication during operation. In order to provide a reliable communication link through the extreme harsh conditions, one must clarify the basic phenomena inside combustors, especially electromagnetic noise and attenuation. According to measurements, attenuation at frequency band 2-18 GHz is ~10 dB/m. [ABSTRACT FROM AUTHOR]

Microwave‐based measurement can provide new methods and practical solutions for the challenging task of measurement inside large industrial combustion chambers. In order to measure or communicate inside a combustion chamber using microwaves, the spectrum of background noise at microwave frequencies must be known. This study investigates the basic electromagnetic spectrum in flames, concentrating on microwave frequencies from 0.1 to 19 GHz. The study introduces, as reference values, known results from forest flames and flames in controlled environments. The focus of the work is the level of background noise at microwave frequencies and the impact of this noise on radio communication inside the combustion chamber. The effects of the microwave radiation levels are compared with the requirements of practical communication systems such as Bluetooth and narrowband ISM (industrial, scientific, medical) systems at 800–950 MHz. [ABSTRACT FROM AUTHOR]

In this paper, a novel communication concept for sensors at an inverter-fed electric motor is proposed. The concept utilizes power-line communication and a motor cable in data transmission. The signal used in communication is inductively coupled to the motor cable. The supply power for sensing and communication at the electric motor is harvested from the motor-phase conductor with a current-transformer-based power supply. The proposed concept has numerous advantages, such as no galvanic connection to the motor power circuit, an opportunity to implement the concept afterwards without electrical installation, and reliable and battery-free operation. The operation of the concept is analyzed, simulated, and verified by laboratory measurements. [ABSTRACT FROM PUBLISHER]

• A sensorless method for minimizing the life-cycle cost of air filters is presented. • Aside from a variable-speed drive, no extra equipment is required by the method. • The method's feasibility is evaluated with simulations and laboratory measurements. • Lower cost of filtering than with fixed filter replacement schedules is achieved. The flow resistance of air filters accounts for a significant share of the electric energy consumed by fan systems. Due to their inevitable fouling, filters must be replaced periodically. This paper presents a novel variable-speed-drive-based method for online determination of the cost-optimal time to replace the filter of a fan system. The total cost of filtering per filtered volume of air is continuously calculated and when its minimum is reached, filter replacement is recommended. As part of the calculation, the energy cost related to the pressure drop of the filter is estimated using a variable-speed-drive-based filter pressure drop soft sensor. In addition to a variable-speed-drive and manufacturers' specifications for the fan and filter, no extra equipment is required. As such, the method can be implemented as a programmed feature in a variable-speed drive or in a remote control and monitoring system. Feasibility of the method is verified with simulations and laboratory measurements, and the results suggest that it can realize a lower life-cycle cost of air filtering than the so far prevalent practices of filter replacement timing. [ABSTRACT FROM AUTHOR]

Industrial water electrolyzers mainly use old thyristor-based rectifiers to obtain the DC current required to run because of the low voltage level and high current requirements of the processes. These rectifiers cause significant ripple in the electrolyzer input current, leading to dynamic operation of the electrolyzer. Even though industrial-scale water electrolyzers are operated under such dynamic conditions, the effect on the electrolyzer performance is not well explored. In this study, current measurements from an industrial alkaline electrolyzer plant were used to define the common current ripple amplitude and frequency caused by the thyristor-based rectification. Based on the parameters obtained, laboratory measurements were conducted using an alkaline water electrolyzer to define the power losses incurred at various ripple amplitudes and frequencies. Additionally, the linearization of the electrolyzer current–voltage behavior as a function of frequency was studied using two electrode sets made of different materials. The laboratory measurements carried out in the study show that the ripple amplitude has a significant effect on increasing the losses, whereas the ripple frequency counteracts this. Thus, dynamic operation can have a large impact on losses, especially at partial loads, where the ripple current amplitudes increase significantly when using thyristor rectifiers. Lastly, the frequencies where the electrolyzer starts to behave linearly were observed to be at 68 Hz with the first electrode set and at 5 Hz with the second one. The considerable difference between the electrode sets indicates that the electrode materials and microstructure play a significant role in defining the electrolyzer frequency behavior. Because common thyristor-based power delivery systems operate at 300 Hz or 600 Hz, the results also imply that when modeling these systems, a linear model can be used for the electrolyzer to simplify the simulation. [Display omitted] • Large amplitude current ripple on alkaline electrolyzers is studied. • Ripple amplitude increases power losses, while frequency counteracts it. • As ripple frequency is increased, the electrolyzer starts to behave linearly. • The linear slope is determined purely based on the impedance. • At high frequencies, power usage can be determined from EIS measurement. [ABSTRACT FROM AUTHOR]

Self-sustaining off-grid energy systems may require both short-term and seasonal energy storage for year-around operation, especially in northern climates where the intermittency in both solar irradiation and energy consumption throughout the year is extreme. This paper examines the technical feasibility of an off-grid energy system with short-term battery storage and seasonal hydrogen storage, comprising a water electrolyzer and a fuel cell. The study is based on data from a currently grid-connected residential single-family house in Finland with an existing 21 kWp photovoltaic (PV) installation and a ground source heat pump based heating system. Energy system performance is simulated using real PV power generation data as well as data on grid electricity import and export from the house over a three-year period to find the minimum combination of battery and hydrogen storage system capacities capable of year-round off-grid operation. It is concluded that technically feasible solutions are available for the proposed setup. The most significant factor affecting the system dimensioning is found to be high peak electric power demand during times of low PV power generation, indicating a need for smart power control. Demand for battery storage capacity is found to be significant only to about 20 kWh. Fuel cell and electrolyzer nominal powers of at least 4 kW and 5 kW to 7 kW, respectively, were found to be sufficient for off-grid operation with the studied system. The storage capacity demand for 170–190 kg of hydrogen annually is, however, impractically large for residential houses. [ABSTRACT FROM AUTHOR]

Nowadays, electric motors and frequency converters have a great variety of applications. In motor feedback systems, communication is performed over separate sensor cables, which are notable for their high cost. Power line communication (PLC) over the motor cable is a promising and cost effective alternative. In this paper, a communication concept based on PLC and direct sequence spread spectrum (DSSS) channel access method is presented for motor cable communication. The channel characteristics and noise in the channel of a laboratory test setup are studied. Effect of the frequency converter output and switching frequencies on the channel noise are investigated. Capacitive and inductive signal coupling methods are evaluated and compared first theoretically by measurements and analysis of channel characteristics, and then practically by data transmission tests carried out in the laboratory test setup. Software-defined radios (SDRs) are used as the data transmission devices for the communication concept evaluation. Concept's performance against variation of a signal-to-noise ratio (SNR) and switching frequency of the converter are evaluated. The concept applicability limits and optimal settings are presented. It can be stated that the concept provides a wider application range, than available solutions and can be effective for motor monitoring and speed data transmission. [ABSTRACT FROM AUTHOR]

Nowadays, electric motors and frequency converters have a great variety of applications. In motor feedback systems, communication is performed over separate sensor cables, which are notable for their high cost. Power line communication (PLC) over the motor cable is a promising and cost effective alternative. In this paper, a communication concept based on PLC and direct sequence spread spectrum (DSSS) channel access method is presented for motor cable communication. The channel characteristics and noise in the channel of a laboratory test setup are studied. Effect of the frequency converter output and switching frequencies on the channel noise are investigated. Capacitive and inductive signal coupling methods are evaluated and compared first theoretically by measurements and analysis of channel characteristics, and then practically by data transmission tests carried out in the laboratory test setup. Software‐defined radios (SDRs) are used as the data transmission devices for the communication concept evaluation. Concept's performance against variation of a signal‐to‐noise ratio (SNR) and switching frequency of the converter are evaluated. The concept applicability limits and optimal settings are presented. It can be stated that the concept provides a wider application range, than available solutions and can be effective for motor monitoring and speed data transmission. [ABSTRACT FROM AUTHOR]

Due to their notable share of the total energy consumption of industries, pumps hold particular significance in industrial energy audits. In industrial facilities, pumps exist in large numbers, which leads to only the pumps most critical to the process being monitored. Meanwhile, many old or poorly sized pumps may operate inefficiently without attention. To determine the energy efficiency of a pump, information on the pump's flow rate is required. To this end, flow meters are often used to determine the flow rate produced by a pump, which can be used in determining the pump's specific energy consumption. However, flow meters tend to be costly and impractical for some applications and are laborious for energy auditing, if no preexisting metering can be found in the audited process setup. Thus, soft sensor approaches to estimate flow rate are suggested by several authors. However, the use of model-based flow rate estimators is still uncommon, because they require detailed information on the pump characteristic curves and manual configuration of the device employing the flow rate estimator. This paper introduces a novel flow rate estimator tuned with only four variables: the nominal flow rate, head, shaft power and rotational speed of a centrifugal pump. The estimator operation is based on the expected characteristic performance curves of the centrifugal pump according to its specific speed. Due to a small number of required input parameters, and no need for manufacturer's pump curves, the proposed estimator is easier to commission than existing solutions available both in fixed speed systems and commercial variable-speed drives. The performance and accuracy of the presented estimator are studied by comparing it with the basic QP and QH-curve-based estimation methods through simulations with four different centrifugal pumps and through measurements with two different centrifugal pumps in a test laboratory. In the experimental evaluation, the suggested estimator estimated the flow rate produced by centrifugal pump with an error of 7–15% of the nominal flow rate through a flow rate range of 60–100% of the nominal flow rate. Thus, the presented method is accurate enough to be used in continuous large-scale energy auditing, for example to highlight inefficiently running pumps from large pump populations. [ABSTRACT FROM AUTHOR]

• Using 1-s data instead of 1-h data is beneficial. • Nordic conditions increase the optimal sizing ratio. • We find an optimal array-to-inverter sizing ratio of 1.6–2.17. • The ratio is higher on smaller system sizes. The amount of installed solar power in Finland is increasing as a result of decreasing photovoltaic (PV) system component prices. The growth is especially noticeable in residential systems, and ways to make PV electricity a more competitive choice for Finnish residents are studied. One of these ways is to decrease the solar PV electricity production costs by decreasing the investment costs by undersizing the inverter of the PV system. The objective of undersizing is to find the optimal array-to-inverter sizing ratio (AISR) where the ratio of the economic loss from the clipped energy to the economic gain from the decreased system investment achieved by an undersized inverter is lowest. In this paper, the economically most optimal AISRs are determined for different residential array sizes, orientations, and inclinations when operating in Finnish locations and conditions. Calculations for each inverter size are carried out by using recorded Finnish meteorological data and the current Finnish PV system cost distribution, and by analyzing existing 1-s resolution production measurement data of a Finnish PV system. It is concluded that it is necessary to use 1-s resolution data as the use of 1-h resolution production data would lead to more significant undersizing caused by the power clipping occurring within an hour. The optimal AISRs presented in this study are higher than the optimal ratios reported in previous studies for locations further south than Finland. This can be explained by the northern location of Finland, where the irradiance above Standard Test Conditions (STC) is lower than in central Europe, for example. This allows more significant undersizing as less energy is clipped even at higher ratios. In the case of south-oriented arrays in a 30° installation angle, the optimal AISRs for the 10 kW, 6 kW, and 3 kW inverters were 1.6, 1.8, and 2.08, respectively. Again, the AISRs for the southwest-southeast facade installations were 1.8, 1.9, and 2.17 for the inverters under study. They do not clip the produced energy as much as rooftop systems because their production is more evenly distributed throughout the day, yet they do not achieve as low production costs either. It is pointed out that if the PV self-consumption is optimized by using PV to heat water or batteries as a storage, limitation of the PV generation might not be the correct solution. [ABSTRACT FROM AUTHOR]

This paper investigates conversion of a Nordic oil-heated townhouse into carbon-neutral by different energy efficiency (EE) improvements and an off-grid system including solar photovoltaics (PV), wind power, and battery and hydrogen energy storage systems (BESS and HESS). A heat-pump-based heating system including waste heat recovery (WHR) from the HESS and an off-grid electrical system are dimensioned for the building by applying models developed in MATLAB and Microsoft Excel to study the life cycle costs (LCC). The work uses a measured electrical load profile, and the heat generation of the new heating system and the power generation are simulated by commercial software. It is shown that the EE improvements and WHR from the HESS have a positive effect on the dimensioning of the off-grid system, and the LCC can be reduced by up to €2 million. With the EE improvements and WHR, the component dimensioning can be reduced by 22%–41% and 13%–51% on average, respectively. WHR can cover up to 57% of the building's annual heat demand, and full-power dimensioning of the heat pump is not reasonable when WHR is applied. Wind power was found to be very relevant in the Nordic conditions, reducing the LCC by 32%. [Display omitted] • Energy efficiency improvements notably reduce dimensioning of system components. • Waste heat from FC and electrolyzer covers up to 57% of the annual heat demand. • A full-power-dimensioned GSHP does not reduce the fuel cell dimensioning. • Seasonal storage on a small scale makes the system not economically viable. • Small-scale wind power is expensive, but it significantly reduces the system LCC. [ABSTRACT FROM AUTHOR]

Power-electronic-converter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machine's parts provide a path for leakage currents, which finally harm metallic ball bearings. Remembering that end-windings have a significant contribution in building up stray capacitances, a countermeasure affecting both the lamination stack and end-winding areas is needed. This article focuses on a countermeasure against the noncirculating bearing currents in the cluster of solutions at the motor side. The electrostatic shielding approach, which is a known principle to reduce capacitive couplings, is applied in electrical machines every now and then. In this article, the principle of slot-embedded grounded electrodes is extended to cover also the end-windings. Thus, the electrodes provide a better shaft-to-ground voltage mitigating effect compared to the case where electrodes are applied only in the lamination stack area. The feasibility and effectiveness of such a countermeasure are investigated. Different options in terms of scaling of both the machine size and diameter of the electrodes were analyzed and corresponding conclusions were pointed out. [ABSTRACT FROM AUTHOR]

Inverter-induced high-frequency bearing currents are a recognized cause of bearing failure in frequency converter-fed electric machines. Mechanical bearing faults are generally identified by vibration measurements. In this work, we submit bearings to electric discharge machining bearing currents, measure the electrical stress placed on the bearings, the resulting vibration signal and operating temperature, and apply time- and frequency-domain signal processing techniques for feature extraction. Experiments are run for 940 h of operation, so as to study the incipient bearing failure behavior. After the end of the test run, the bearing surfaces are inspected using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Bearing faults may significantly reduce the useful life of electric machines. With the advent of modern fast-switching frequency converters, electric currents induced by the high-frequency common-mode voltage of these converters have been recognized as additional, sometimes severe, contributors to bearing degradation. The degradation is understood to progress both by damaging the bearing surfaces and by altering the chemical composition of the lubrication greases, which can lead to ineffective lubrication and reduction in permissible mechanical bearing load. This paper studies the effect of grease degradation due to discharge currents on the grease dielectric strength and chemical composition of several greases typically used with electric drives. From this, conclusions on the grease selection for variable-speed drive applications are drawn. [ABSTRACT FROM AUTHOR]

The basis for smart grids is the implementation of active functionalities that interconnect the power system stakeholders, such as electricity end users (customers), producers, retailers, and system operators in a novel manner. Not only electric energy but also data flows are required between all the actors involved. A communication network between components and actuators is needed for functionalities such as grid operation, monitoring, and protection. This article studies powerline communication for a low-voltage direct current distribution system. An LVDC system is considered as part of future smart grids. The channel characteristic measurements carried out for an LVDC laboratory setup and the subsequent theoretical and practical analysis show that the studied LVDC distribution system provides a suitable medium for the high frequency band PLC between 5 and 20 MHz when an inductive PLC signal coupling method is used. Moreover, the article proposes an IP-based PLC network concept for the LVDC system; the concept is based on commercial industrial compliant HF band PLC modems. [ABSTRACT FROM PUBLISHER]

A comprehensive literature review of current water electrolyzer modelling research was conducted and presented models critically evaluated. Based on the literature review this paper presents an open-source MATLAB toolbox for water electrolyzer polarisation curve parametrization and modelling. The modelling capabilities of the tooling were verified using measured PEM and alkaline water electrolyzer polarisation data. As real-world measurement data is rarely ideal, tests were also conducted using suboptimal data, first with data sets that have a low number of measurement points and secondly with data sets that have low or high current densities missing. The tooling is shown to work with a wide variety of use cases and provides an automated method for modelling and parametrization of electrolyzer polarisation curves. • Critical review of the water electrolyzer polarisation curve modelling is conducted. • Open source MATLAB toolbox for automated parametrization of models is presented. • Measured alkaline and PEM water electrolyzer data is used to verify fit accuracy. • Data sets of variable quality are used to verify fitting robustness. [ABSTRACT FROM AUTHOR]

Energy costs are typically the largest cost element in the life-cycle of a compressed-air system (CAS). Real-time usage information as well as historical data can help identify whether the CAS is functioning properly. To this end, modern variable-speed drives are able to provide this information as well as produce soft-sensor estimates of volume flow rate production and specific energy consumption of a CAS. In this paper, an identification (ID) run sequence for a twin rotary screw compressor-operated system is proposed to identify the total system volume, to improve the estimation accuracy of a volume flow rate soft sensor, and to create a specific energy consumption map for the CAS performance monitoring. Laboratory measurements are carried out to evaluate the feasibility of the proposed ID run and related estimations. Moreover, possible usage applications of the proposed methods are discussed. [ABSTRACT FROM PUBLISHER]

Ventilation systems are responsible for the thermal comfort and air quality of indoor spaces. The adjustment of ventilation systems is a time-consuming task that may need multiple iterations. Incorrect adjustments of a ventilation system can reduce the quality of working and living conditions and degrade the energy efficiency of the ventilation. In this paper, a testing, adjusting, and balancing method for a ventilation system is presented that uses only the knowledge of the fan total flow rate and pressure. The method does not need additional instrumentation for the ventilation adjustment as the fan operating point can be estimated with the variable-speed drive. The method is noniterative, thereby saving time, and the ventilation system is adjusted to its minimum energy consumption setting without compromise in system operation. The proposed method is assessed with a laboratory test setup to verify the correct operation of the method in practice. [ABSTRACT FROM AUTHOR]

The aim of this paper is to analyze through simulation how the energy efficiency of a single electrolysis stack at various loads is affected by shunt currents and to determine the energy-optimal load distribution between lines in a multiline electrolysis system under various magnitudes of shunt current losses. A dynamic energy and mass balance model of an industrial 3 MW , 16 bar alkaline water electrolyzer (AWE) process was developed using MATLAB. The optimization goal is to determine the power supply for each AWE line so that it can meet any hydrogen demand while minimizing the global specific energy consumption (SEC). The Particle Swarm Optimization (PSO) algorithm is used to minimize the objective function. According to the results of the single stack investigation, shunt current reduction could significantly improve the energy efficiency of partial-load operation. In addition, the optimization study revealed that whenever two or more lines are required to run in order to satisfy the hydrogen demand, the global SEC is minimized when the lines operate at equal loads. [ABSTRACT FROM AUTHOR]

• Thirteen statistical customer class load profiles were used. • Orientation optimization based on a load profile may not be the most profitable. • Single-azimuth solar PV system is generally more profitable than dual-azimuth one. • Solar PV system revenue is not very sensitive to moderate changes in orientation. • Buildings should be designed from the perspective of solar PV. The profitability of a rooftop solar photovoltaic (PV) system depends on several factors, such as the retail price of electricity, the load profile of the building, and orientation of the solar PV modules. If there are consumption peaks in the morning, evening, or both, the solar PV modules can be oriented eastward, westward, or east–west, respectively, in order to increase self-consumption. However, the market price of electricity varies, which makes it challenging to evaluate the revenue of a solar PV system in advance. In this study, solar PV module orientation is considered based on profitability. The study uses hourly data of 13 different statistical customer class load profiles, historical electricity market price data for the years 2016–2020, and simulated solar PV yield from southern Finland. A comparison is made between single-azimuth and dual-azimuth systems, the latter of which having the orientation of half of the modules mirrored respective to the north–south axis. A single-azimuth system is usually more profitable when compensation is paid for surplus electricity. The optimal orientations are at azimuth angles of −15°–5° and at tilt angles of 35°–45° with both fixed and dynamic electricity purchase prices. However, if no compensation is paid for surplus electricity, it is usually more profitable to minimize the electricity purchase by orienting the solar PV modules in two azimuths between east and west with tilt angles of 10°–55° depending on the capacity of the solar PV system and the load profile. The revenue is not very sensitive to moderate changes in orientation. [ABSTRACT FROM AUTHOR]

The possibility of bearing damage caused by inverter-induced bearing currents in modern variable-speed drive systems has been well recognized. However, the breakdown and current conduction mechanisms have still not been well understood today. We present results on the HF impedance properties of rolling element bearings at 300-kHz and 1.5-MHz signals—frequencies taken from the typical spectra of HF circulating bearing currents. Different motor speeds, bearing temperatures, voltages across the bearing, and two different motor sizes are investigated. Notably, we analyze the frequency of transitions between ohmic and capacitive behavior (or vice versa)—the “mode transitions”—as a function of these operating parameters: For some operating conditions, the bearing impedance alternates between capacitive and ohmic behavior without any modification of the macroscopic conditions it is subjected to. [ABSTRACT FROM PUBLISHER]

An accurate measurement of power or heat losses of high-efficiency electrical devices is difficult with input and output powers. In the calorimetric method, these losses are measured directly. In this paper, a functional heat loss measurement concept with adequate data processing methods is suggested for heat losses up to 2 kW. Such a heat loss range can be applied to present-day power electronic converters with the rated power of up to 110 kW and motors up to 37 kW. The measurement system does not require a complex mechanical structure or a large footprint area on the measurement site. The concept is scalable to different sizes. New features to the balance type calorimeter data processing are introduced. These include a mass flow correction, a technique to detect the thermal equilibrium, and a method to correct measured heat losses to improve the measurement repeatability and reduce the measurement uncertainty. The measurement uncertainty of the proposed calorimetric concept is 0.4%. Laboratory measurements are carried out both for a commercial frequency converter and an electric motor. These are measured at the same time with two calorimeters. The losses of these devices are measured both by the input-output and calorimetric methods. [ABSTRACT FROM PUBLISHER]

The possibility of bearing damage caused by inverter-induced bearing currents in modern variable-speed drive systems has been well recognized today. Further research is needed to develop appropriate nonintrusive methods for detection and monitoring of such currents. A radio-frequency-based nondestructive method has been applied to detect discharge bearing currents. The method is understood to work on the energy that is radiated in the electric field during the bearing discharge event. We show that the method is also applicable to high-frequency circulating bearing currents that have so far been associated with ohmic bearing characteristics and no discharges occurring. The analysis and understanding of the applicability of the method to detect such currents also contributes to further understanding of the electric characteristics of the bearing, notably the moment the current conduction begins. [ABSTRACT FROM AUTHOR]

Fan systems are often responsible for the ventilation of contaminated air, such as exhaust gases. Contaminants can build up on the fan impeller eventually causing a mechanical imbalance, which may lead to the fan breakdown and shutdown of production processes. Usually, the contamination buildup can be detected by visual inspection or from increased vibrations caused by the imbalance on the fan impeller. If the contamination buildup could be detected before the imbalance occurs, the unscheduled maintenance or even the failure of the fan system could be avoided. In this paper, a novel method is presented that can be used to detect the contamination buildup on the fan impeller. The method uses the capability of the frequency converter controlling the fan motor to estimate the rotational speed of the motor and the capability to control the motor torque. The presented method is validated by laboratory measurements. [ABSTRACT FROM PUBLISHER]

Bipolar configuration electrochemical stacks with a common or circulating electrolyte supply usually embody a high amount of shunt currents that escape from the main current path to the manifold nozzles. This paper suggests a novel and simplified semiempirical model to reasonably predict the total shunt currents in industrial alkaline water electrolyzers (AWE). The aim of the study is to perform a sensitivity analysis of the model parameters and the process conditions that affect the shunt currents and the plant's specific energy consumption (SEC), and to determine the most important ones by analyzing the thermodynamic and fluidic properties of the stack. An in-house MATLAB dynamic energy and mass balance model of an industrial 3 M W , 16 b a r AWE plant process was developed. The semiempirical dynamic process model is updated with the essential shunt currents and electrochemical, fluidic, and circulation impurity models. The study revealed the influence of the supplied current, the electrolyte temperature, the process pressure, the electrolyte flow rate, and the potassium hydroxide concentration on the shunt currents and the plant's SEC. • Simulation of a validated 3 MW industrial-scale AWE semi-empirical transient model. • Sensitivity analysis of the process conditions affecting the shunt currents in bipolar-configuration stacks. • Effect of the current supply, stack temperature, and electrolyte flow rate on the plant SEC. • Plant model parametrization and uncertainty analysis for the electrochemical model. • At partial loads, the shunt currents are the major source of energy loss in the system. [ABSTRACT FROM AUTHOR]

This paper proposes a parameter adjustable dynamic mass and energy balance simulation model for an industrial alkaline water electrolyzer plant that enables cost and energy efficiency optimization by means of system dimensioning and control. Thus, the simulation model is based on mathematical models and white box coding, and it uses a practicable number of fixed parameters. Zero-dimensional energy and mass balances of each unit operation of a 3 MW, and 16 bar plant process were solved in MATLAB functions connected via a Simulink environment. Verification of the model was accomplished using an analogous industrial plant of the same power and pressure range having the same operational systems design. The electrochemical, mass flow and thermal behavior of the simulation and the industrial plant were compared to ascertain the accuracy of the model and to enable modification and detailed representation of real case scenarios so that the model is suitable for use in future plant optimization studies. The thermal model dynamically predicted the real case with 98.7 % accuracy. Shunt currents were the main contributor to relative low Faraday efficiency of 86 % at nominal load and steady-state operation and heat loss to ambient from stack was only 2.6 % of the total power loss. [Display omitted] • Dynamic mass and energy balance simulation of a 3 MW industrial alkaline water electrolyzer. • Results are verified with measurements of an industrial plant. • Faraday efficiency at nominal operation was estimated at 86 %. • Contribution of each Faraday loss parameter was approximated. • 97 % of the stacks heat is extracted through the electrolyte circulation with heat exchangers. [ABSTRACT FROM AUTHOR]

Modern converter-supplied ac motors are exposed to bearing currents. Despite extensive research and development, the industry still does not have a final solution with acceptable cost and high efficiency. This article focuses on capacitive bearing currents. After a brief explanation of the phenomenon, an unconventional approach for effective mitigation of the capacitive bearing currents is proposed. The approach suggests using grounded electrodes in the slot openings to reduce the stator-winding-to-rotor-core capacitance and thereby the bearing currents. Different electrode diameters are considered and evaluated by a finite element method (FEM) analysis. The results are verified by laboratory tests. The bearing voltage ratios of the original and modified induction motor are compared. [ABSTRACT FROM AUTHOR]

Domestic hot water (DHW) heating is one of the most energy-consuming activities in a typical household. Photovoltaics (PV) connected with a ground source heat pump (GSHP) offers a low-emission method for DHW heating. This paper studies four different control methods for DHW heating in a building with a GSHP and a PV system. The main control method aims to minimize DHW heating costs by utilizing Nord Pool Spot market information together with a PV production output forecast. The results of this control method, implemented with a perfect PV output forecast and assessed over three years of hourly data, indicate that annual cost savings over other methods are achievable. Results with the real-world actual PV output forecast, evaluated between June–September 2020, demonstrate DHW heating cost savings up to 36–53%, even though forecasting errors are present. The heating costs are 9–11% higher compared against the perfect forecast case. The suggested control method thereby effectively reduces the costs when compared with all other methods, and its performance is not significantly affected even when an actual imperfect forecast is implemented. The results also indicate that minimizing energy consumption does not offer the lowest cost. • A solar PV production forecast is verified with measurements in a Nordic context. • A Cost optimal control method for domestic hot water heating is developed. • The control logic is based on PV forecast, electricity price, and COP curve data. • Clock control has 15–21% higher energy costs than the cost optimal control. [ABSTRACT FROM AUTHOR]

Research on utilization of a frequency converter and sensorless methods in the drive system diagnostics has been mostly limited to the motor and to the frequency converter itself. However, it has been shown that a frequency converter also allows the sensorless estimation of the operational state of a centrifugal pump providing new opportunities for the diagnostics and control of pumping systems. In this paper, a novel hybrid estimation method for the centrifugal pump operational state is proposed. It is based on the identification of the process by using those flow rate and head estimates produced by QP-curve-based method, which are known to be relatively accurate. After the identification phase, the process model can be used together with the estimates of the frequency converter for the sensorless operational state estimation of the pump. The method is evaluated by laboratory measurements, and its applicability to industrial pumping and fan systems is also discussed. [ABSTRACT FROM PUBLISHER]

While the cause-and-effect chains of inverter-induced bearing currents have been well understood today, not much is known about the damage mechanism inside the bearings. Research has suggested that the bearing degradation is approximately proportional to the frequency of occurrence of the bearing currents. For bearing currents that occur statistically distributed—such as discharge bearing currents—this parameter has not been thoroughly researched yet. In this paper, we present an analysis of the influence of different motor operating parameters on the frequency of occurrence (“discharge activity”) of discharge bearing currents, using a non-intrusive detection method. When analyzed individually, the motor speed, motor shaft temperature, inverter switching frequency, and inverter dc-link voltage influence the discharge activity. However, the overall running time of the motor, the state—steady-state versus instantaneous—and the “operating history” on the time-scale of several days have the strongest effect on the frequency of the discharge bearing current occurrence. [ABSTRACT FROM AUTHOR]

Abstract: Pumps are widely used in industry, and they account for 20% of the industrial electricity consumption. Since the speed variation is often the most energy-efficient method to control the head and flow rate of a centrifugal pump, frequency converters are used with induction motor-driven pumps. Although a frequency converter can estimate the operational state of an induction motor without external measurements, the state of a centrifugal pump or other load machine is not typically considered. The pump is, however, usually controlled on the basis of the required flow rate or output pressure. As the pump operational state can be estimated with a general model having adjustable parameters, external flow rate or pressure measurements are not necessary to determine the pump flow rate or output pressure. Hence, external measurements could be replaced with an adjustable model for the pump that uses estimates of the motor operational state. Besides control purposes, modelling the pump operation can provide useful information for energy auditing and optimization purposes. In this paper, two model-based methods for pump operation estimation are presented. Factors affecting the accuracy of the estimation methods are analyzed. The applicability of the methods is verified by laboratory measurements and tests in two pilot installations. Test results indicate that the estimation methods can be applied to the analysis and control of pump operation. The accuracy of the methods is sufficient for auditing purposes, and the methods can inform the user if the pump is driven inefficiently. [Copyright &y& Elsevier]

It has been shown that an inverter-fed power line is a feasible medium for the transmission of modulated information. The communication channel includes the feeder cable terminated by two loads: the motor and the inverter. This link is a suitable alternative for the sensor cabling between motors and inverters in motor control and diagnostic applications. The use of the motor power cable in the speed feedback induction motor control application and the modelling of the formed communication channel are presented and discussed in this paper. [ABSTRACT FROM AUTHOR]

Solar photovoltaic systems have been growing in popularity in prosumer households as a means of increasing the share of renewable energy and decreasing electricity import. The available self-consumption is, however, limited by a temporal supply–demand imbalance. In this paper, options for improving the self-consumption of a prosumer household are studied by using three-year data sets of electricity import and export data from two distinct, real-life cases from Finland. Two separate approaches are analysed: the use of energy storages, physical or monetary, and changing of the electricity metering method. A switch of the electricity metering method from instant phasewise to hourly net metering was found to increase the self-sufficiency by about 3 to 5 percentage points and have an annual monetary benefit of a few tens of euros when a network storage was used. Considering the energy storage methods under study, the network energy storage was found to be more economically feasible than a physical or a virtual battery energy storage, even though a physical battery storage could increase the self-sufficiency as much as by 30 percentage points with a storage capacity of 20 kWh. The studied virtual battery concept was found to limit the profitable solar photovoltaic plant size if high enough storage capacity was not provided. When a physical battery energy storage is used, switching to hourly net metering does not add value to the system. A significant decrease in the system cost is required for a physical battery energy storage to be economically competitive in northern climate conditions. • Measured electricity flow is used to study energy storage concepts in Finland. • Change of electricity metering method can increase self-sufficiency up to 5 p.p. • Physical battery with 20 kWh capacity can increase self-sufficiency up to 30 p.p. • Network storage is currently the most profitable concept from the studied options. • The physical battery cycle rate will remain low even with small battery sizes. [ABSTRACT FROM AUTHOR]

Different mechanisms by which bearing currents flow inside the electrical machine are well studied. In contrast, investigation and development of different techniques to mitigate these currents remain a field for improvement, and the final common solution to the problem has not been provided yet. In pursuit of addressing the problem, this article deals with noncirculating (or capacitive) bearing currents. The circuit mechanism of capacitive currents is explained in brief, and an approach for their mitigation is introduced. This article studies the influence of the stator winding and the slot geometry and presents different geometries to modify the motor to reduce the capacitive bearing currents. The effectiveness of the proposed mitigation technique is shown by finite-element-based modeling and verified by laboratory tests with different induction motor designs, where the winding and magnetic circuit geometries are varied. The technique can be used, in particular, for the mitigation of noncirculating currents, but it also offers potential for further research. [ABSTRACT FROM AUTHOR]

The operating expenditures of electric vehicles (EVs) consist mainly of the electricity used to charge the EV battery and of the replacement of wearing parts. This paper aims to optimize the EV battery charging as cost-effectively as possible for a household with a small-scale photovoltaic (PV) power plant. The optimization is carried out by problem-based optimization to closely match the average Finnish user behavior. For reference, an optimization was also performed disregarding the user behavior to make EV charging as cost-effective as possible. Cost minimization was done by using Nord Pool Spot market data to find the cheapest grid electricity prices, employing a perfect PV forecast, and using only surplus PV electricity for EV charging. Six years' worth of data were analyzed, and it was found that the annual savings with average user behavior ranged between 25.4% and 51.9% when comparing optimized charging with uncontrolled charging. When disregarding the typical user behavior and having the EVs chargeable at all times, the annual savings ranged between 38.3% and 54.5%. The results show that the more the user uses the EV daily, the more cost-effective the optimization becomes compared with uncontrolled charging methods. The results also show that depending on daily fluctuations in the electricity prices, it is sometimes more beneficial to sell the produced PV power rather than use it to charge the EV and instead charge the EV with grid electricity at nighttime. • Benefits of solar photovoltaic use for electric vehicle charging are emphasized. • Over 50% cost reduction for electric vehicle charging can be achieved. • Methods of this study can be applied anywhere with fluctuating electricity market. • Multiple benefits of smart charging are presented. [ABSTRACT FROM AUTHOR]

Horizontal vacuum belt filters are used for continuous solid–liquid separation in a wide variety of industrial processes. Despite the low pressure difference (usually Δp < 0.8 bar), the high air pumping requirement to maintain the pressure difference results in considerable energy consumption. In this article, the specific energy consumption of vacuum filtration and air flow rates of a pilot-scale horizontal vacuum belt filter unit are investigated. The results show that a claw-type vacuum pump consumes only half the energy compared to a conventional liquid ring vacuum pump at corresponding operating points. A comparison between the specific energy consumption of vacuum filtration and thermal drying of the filter cake to zero moisture revealed that vacuum filtration accounted for less than half of the total energy consumption in the applied experimental conditions at Δp = 0.2–0.5 bar. The majority of the total pumping requirement of the pilot-scale filter resulted from leaks, and only 2–25% of the air flow found its way through the cake and the filter medium. The results suggest that there is a combination of the pressure difference level and the mass of solids deposited per filtration area that together with thermal drying consumes the least amount of energy per solids mass. [ABSTRACT FROM AUTHOR]

• An islanding can be detected by monitoring bit error rate, bit rate and latency. • System detects islanding within 33 ms, following IEEE Std. 929-2000 and 1547-2003. • The DSSS settings, providing the highest communication efficiency, were identified. • The bypass scheme improves efficiency and applicability range of the concept. As smart grid applications, distributed generation, and microgrid technologies have become more widespread, new safety-related issues have arisen. Unintentional islanding is an example of a grid fault that may result in damage to electrical equipment and severe personal injuries. In this paper, an anti-islanding system employing power line communication (PLC) and direct-sequence spread spectrum (DSSS) modulation implemented with software-defined radios for continuous signaling is tested in a laboratory test setup. A concept of a fault detection algorithm is evaluated. A DSSS sensitivity analysis is carried out to investigate system's performance against variation of a signal-to-noise ratio, and define optimal DSSS settings. The results of the analysis are interpreted, and conclusions are drawn. A transformer bypassing scheme allowing to increase the fault detection speed and throughput is introduced and tested, and the conditions of applicability are described. As a result of the study, recommendations for the system development are presented. [ABSTRACT FROM AUTHOR]

• A novel soft sensor method has been developed and evaluated. • Evaporation of void space water cools vacuum filter cake and suction air. • Change in suction air temperature correlates with filter cake solids contents. • Temperature change information increases the accuracy of moisture content estimates. • Conditions for minimum specific energy consumption were identified. The moisture content of filter cakes is probably the most important characteristic that should be kept at a desired level in industrial cake filtration applications to maintain consistent product quality and minimize energy consumption. Most of the currently applied methods for contactless real-time monitoring of the moisture content are based for example on x-ray or microwave techniques, and therefore, the equipment for the purpose is highly specialized. This paper introduces a novel soft sensor for filter cake moisture estimation that uses machine learning algorithms and data collected with basic process instrumentation. The method is primarily based on the cooling effect observed in the cake and air, caused by evaporation of liquid from the cake during the dewatering period, and it can be supported by other process data. The specific energy consumption of vacuum filtration and the subsequent thermal drying to zero moisture is also analyzed. The results of pilot-scale experiments with calcite slurry and a horizontal belt vacuum filter show that in order to minimize the specific energy consumption of vacuum filtration, it is crucial to find the right combination of slurry concentration, vacuum level, and mass of filter cake per unit area. The proposed method for estimating the filter cake moisture content is especially suitable for real-time monitoring and control, enabling also considerable reduction in the energy consumption of the overall process. When applying the proposed soft sensor method in a pilot-scale process, the mean absolute error of the estimated moisture content of the filter cake is ∼0.4 percentage points when the temperature of air at the vacuum pump inlet and the vacuum pump air flow rate are included in the input variables. [ABSTRACT FROM AUTHOR]

• Five different energy efficiency alternatives for the building were studied. • A ground-source heat pump and solar PV usually provide the highest profitability. • A household battery has become profitable at the 2022 electricity price. • Dimensioning of a solar PV system massively depends on the electricity price level. • At the 2022 electricity price level, the array-to-inverter ratio can be up to 4.9. Buildings and the construction sector make up about a third of the final energy consumption and energy-related carbon dioxide emissions, offering a significant potential for emission reductions. This paper investigates the conversion of a Nordic oil-heated townhouse into a carbon-neutral one. Five different energy efficiency (EE) alternatives including, for example, different heat pump types and their dimensioning are studied. The electricity demand of the EE alternatives is aimed to be covered as cost-effectively as possible with an on-grid system based on solar photovoltaics (PV) and a battery energy storage system (BESS). The cost-optimal dimensioning of the components is based on the 30-year life cycle cost (LCC), and the work is carried out using an hourly level simulation model developed in MATLAB. To maximize the profitability of the BESS, an intelligent control algorithm based on linear programming is implemented based on a day-ahead electricity spot price for the years 2020–2022 and "perfectly" forecasted power demand and generation data. The data used in the simulation consist of measured electricity consumption, simulated heat generation based on annual oil consumption, and simulated solar PV power generation. It was observed that an about 60% partial-power-dimensioned ground source heat pump together with a solar PV system provides almost always the lowest LCC. However, the BESS was shown to be profitable at the current investment costs for the first time at the 2022 electricity prices, enabling a capacity of 210–230 kWh. On average, the cost-optimized on-grid electricity system was found to reduce the 30-year life cycle costs by 6%, 20%, and 85% with the electricity prices of 2020, 2021, and 2022, respectively. When the price of electricity is exceptionally high, it may be justified to implement more extensive energy efficiency improvements, such as additional insulation of the building envelope. Nevertheless, the impact on the life cycle costs is marginal. In addition, the cost-optimized solar PV capacity has increased more than sevenfold between 2020 and 2022. [ABSTRACT FROM AUTHOR]

Green hydrogen production systems will play an important role in the energy transition from fossil-based fuels to zero-carbon technologies. This paper investigates a concept of an off-grid alkaline water electrolyzer plant integrated with solar photovoltaic (PV), wind power, and a battery energy storage system (BESS). The operation of the plant is simulated over 30 years with 5 min time resolution based on measured power generation data collected from a solar photovoltaic installation and a wind farm located in southeastern Finland. Levelized cost of hydrogen (LCOH) is calculated based on the capital expenditures (CAPEX), the operating expenses (OPEX), and the respective learning curves for each of the components. Component degradation and replacements during the operational lifetime are included in the model, and the capacity of the components and the system control are simultaneously optimized to obtain the minimum LCOH. A sensitivity analysis performed over different installation years and discount rates reveals that for the off-grid alkaline system, the implementation of a wind farm as the sole power supply is the most economical solution until the installation years 2035–2040. Solar PV and a BESS are found to increase the full-load hours of the electrolyzer and reduce the electricity curtailed in the off-grid plant to less than 8%. However, with the current component prices and the climate in the studied region, they are not economically beneficial. It is found that the cost of hydrogen can be reduced to 2 €/kg by the year 2030. • Optimal control and component capacities for a green hydrogen production plant. • Simulations use measured power from a solar PV installation and a wind farm. • Levelized cost of hydrogen is less than 2 €/kg by the year 2030. • Purely wind based system is the most cost-effective solution until the years 2035–2040. [ABSTRACT FROM AUTHOR]

The interest in green hydrogen has been increasing in recent years for several applications, such as energy storage and different industrial sectors. The green hydrogen is produced from water electrolysis supplied by renewable electricity. The operation of industrial large-scale water electrolysis is characterized by a high DC current in the kiloampere range and a few hundred volts. Therefore, the rectifier unit plays an important role in converting AC current of the electricity grid into DC current supplied to the electrolyzer. The power electronic converters are also considered as one of the main cost components of the water electrolyzer system. The objective of this paper is to study whether the operation at a higher voltage than typical values (200 V–300 V) can be beneficial both for the cost and energy efficiency of the power converters in water electrolyzer systems. In this study, three different rectifier topologies considered for an industrial-scale electrolyzer are analyzed and compared in terms of energy efficiency and cost. The simulation models of each topology are carried out in the Matlab/Simulink environment. • The effect of voltage elevation on industrial water electrolyzer system is studied. • Thyristor and transistor-based rectifiers for water electrolyzers are analyzed. • Voltage elevation improves the energy efficiency and cost of rectifiers. • Buck-rectifier provides lowest specific energy consumption of electrolyzer stack. [ABSTRACT FROM AUTHOR]

Water electrolysis will be used to produce renewable hydrogen for energy storage and Power-to-X applications in the future renewable-energy-based energy systems. Therefore, the energy efficiency of hydrogen production will probably become a major issue. In this study, the effect of practical supply power converters on the specific energy consumption of megawatt (MW)-scale alkaline electrolyzers is studied and compared with an ideal dc power supply. The current quality and the stack specific energy consumption are studied in the case of traditional thyristor rectifiers and a transistor-based converter. The stack specific energy consumption is analyzed based on the simulated current waveforms and the electrical equivalent circuit of the electrolyzer stack. It is found that the transistor-based converter offers up to 14% lower electrolyzer stack specific energy consumption than the 6-pulse thyristor rectifier and up to 9.2% lower electrolyzer stack specific energy consumption than the 12-pulse thyristor rectifier as the current varies between 5000 and 1000 A. The simulated change in the stack specific energy consumption of the MW-scale alkaline water electrolyzer outweighs the losses occurring in the rectifiers. Further, selection of the ac voltage level may have a more adverse effect on the stack specific energy consumption with the thyristor rectifier topologies compared with the transistor-based topologies. [ABSTRACT FROM AUTHOR]

The amount of installed solar power in Finland tripled in 2016, reaching 27 MWp. In Finland there are no feed-in tariffs, and with the low price of electricity together with the annual distribution of insolation concentrating on summer, the photovoltaic electricity production is economical only when used for self-consumption. When the produced electricity is used for self-consumption, optimization of the photovoltaic power system size is essential for the profitability of the investment. Usually when optimizing the size of the PV system, the electricity production is optimized so that the electricity sold to the grid is minimized. However, this can lead to undersizing of the PV power system. The PV power system size can for example be dimensioned by using methods such as the minimum energy consumption of the building, the maximum power consumption, or the net zero principle. In Finland, the smart meters provide hourly consumption data from the electricity consumers, which can be used to generate electrical load profiles. These smart meters have been installed on almost every real estate. In this paper, the profitability of a photovoltaic power system in the conditions of southern Finland is studied, simulated, and analyzed for self-consumption. Three cases, a grocery store, a dairy farm, and a domestic house with direct electric space heating, are presented and used in the simulation. Their electricity consumption is measured by hourly automatic meter reading (AMR) on a yearly basis. An Excel tool was used for the analysis of the electrical load profiles against the PV power system production at different system sizes. The profitability of the PV power system was studied by using internal interest rate, net present value, discounted payback period, and self-consumption rate. The effects of government subsidies on the profitability of a PV power system were also examined. The optimized system sizes for the grocery store, dairy farm, and domestic house with direct electric space heating were 89 kWp, 28 kWp, and 5.2 kWp, respectively. The solar modules of the grocery store and the domestic house were facing south whereas the optimal module orientation in the dairy farm was 50–50% east-west. It was found that in the case of the grocery store and the dairy farm, the PV system size could be increased without the internal rate of return decreasing significantly, and thus, a larger system could be justified. Using the self-consumption ratio to optimize the PV power system size leads to undersizing of the system. It was found that the subsidies for the PV power systems have a significant impact on profitability. In the cases of optimized sizes, the grocery store would be economically viable even if the electricity price decreased annually by 3.6% with subsidies and 1.0% without subsidies. The optimized PV power system of the dairy farm would be economically viable if the electricity price decreased by 3.3% annually; however, without subsidies the electricity price would have to increase by 1.0% annually to remain viable. Considering a residential house, the annual increase in electricity price should be 0.6% with subsidies and 1.9% without subsidies. [ABSTRACT FROM AUTHOR]

A modular power-hardware-in-loop (PHIL) simulator for water electrolyzers is developed to study the electrolyzer as part of a smart grid and to examine the characteristics of various electrolyzer power supply electronics. A PHIL simulator up to 405 A of continuous current is built using commercially available power electronic converters. The design and operating principle of the emulator are analyzed. The experimental dynamics tests are performed to verify the PHIL simulator operation and suitability for water electrolysis emulation considering the effect of supply power quality. Finally, the PEM stack model is implemented, and the PHIL simulator is used to emulate a commercial PEM electrolyzer following the measured solar photovoltaic (PV) output power. [ABSTRACT FROM AUTHOR]

The practical dynamic properties and operational limitations of a commercial differential pressure 1 Nm 3 h −1 proton exchange membrane (PEM) water electrolyzer are studied from the viewpoint of renewable power production. Measured values from a 5 kW p solar photovoltaic (PV) power plant and PEM electrolyzer are analyzed to study factors affecting the control of PEM water electrolyzers operating as a part of renewable power production systems. Specific energy consumption of the PEM stack as a function of stack hydrogen outlet pressure is estimated based on measured values from two different measurement systems. Electrical energy consumption of the stack does not show any notable increase as the hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. However, the stack specific energy consumption increases by a maximum of 0.2 kWh/Nm 3 when hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. The increase in specific energy consumption at high differential pressure operation is due to a decrease in Faraday efficiency. Selection and control of the hydrogen outlet pressure can minimize the specific energy consumption and maximize the real hydrogen production in dynamic PEM water electrolyzer operation. [ABSTRACT FROM AUTHOR]

Power-electronics-based power-hardware-in-loop (PHIL) simulator for water electrolyzer emulation with a nominal current of 405 A is developed to study the electrolyzer as part of a smart grid and to analyze the characteristics of various electrolyzer power supply electronics. A simplified model of a proton exchange membrane (PEM) electrolyzer is implemented into the PHIL simulator to describe the voltage and current characteristics of the electrolyzer stack. The model is verified comparing the current and the estimated hydrogen production of the PHIL simulator with the measured values of the commercial PEM electrolyzer following the measured solar photovoltaic (PV) system output power. [ABSTRACT FROM AUTHOR]

The energy consumption of vacuum filtration operations in cake filtration depends on the properties of the cake, the filtration conditions applied, and the progress of the cake dewatering process. Operating a vacuum filter at a high pressure difference requires a high air flow rate and thus has high energy consumption. By taking the filtered solids content into consideration together with the power demand and energy consumed at a certain pressure difference level, it is possible to investigate the specific power demand and energy consumption relative to the filtered cake solids content. When the mother liquor in the void space of the filter cake is replaced by air, the flow rate of air through the cake increases, which has a dramatic influence on the specific energy consumption. In this study, dewatering of calcite mine tailings is investigated with respect to the specific power demand and energy consumption of vacuum generation calculated using the assumption of an ideal isentropic process. The results of this study demonstrate clearly that both the air flow rate and the specific energy consumption in dewatering increase sharply after a certain solid content of the cake is reached. The results suggest that pumping costs in vacuum filtration can be reduced substantially by allowing a slight increase in the residual moisture content of the filter cake. [ABSTRACT FROM AUTHOR]