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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]

Highlights • Direct air capture of carbon dioxide from ambient air demonstrated using temperature-vacuum swing adsorption cycles. • Effect of weather conditions to carbon dioxide and water capture presented. • Areas for improvement of operation are explored and demonstrated. Abstract Direct air capture (DAC) is a technology for collecting and concentrating carbon dioxide from ambient air. If driven with renewable power, DAC is potentially a negative CO 2 emissions technology that can compensate emissions from non-point sources such as aviation, shipping and land-use change. This study presents the results of 10 days capture campaign done between May and July 2018 plus a process control improvement test. The bench scale DAC device is composed of eight beds containing amine-functionalized adsorbent and follows a temperature and vacuum swing adsorption (TVSA) operation cycle. The outlet CO 2 concentration reached less than 100 ppm at the start of the adsorption. Dynamic atmospheric conditions (varying T , relative humidity) affect the capture profile of the beds. Desorption is accomplished by heating the bed up to around 80 °C coupled with vacuum. The product gas has purity range of 95-vol% to 100-vol% CO 2. Major impurities are O 2 , N 2 , and H 2 O. The DAC system also produced water at molar ratio of 3.9 moles H 2 O per mole of CO 2. Water production is affected by air humidity. Measurement-based process control increased the production to 3.4 kg CO 2 per cycle with specific energy requirement of 10 kW h kg−1. The thermal energy requirement accounted for 76% of the total energy input during the improvement test. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hydrocarbon production directly from water, solar energy, and air is demonstrated. • Pilot plant operated 300 h with production of oil and wax 6.2 kg per day. • A conceptual plant can achieve energy and carbon efficiencies of 47% and 94%. Abstract This work demonstrates hydrocarbon production directly from water, solar energy, and air—called SOLETAIR. The plant includes direct air capture (DAC) of carbon dioxide, hydrogen production by water electrolysis, and two-step synthesis bench-scale units that operate using grid-connected solar photovoltaic (PV) electricity. In addition, co-feeding of hydrogen and carbon monoxide from gas bundles are utilized to enable scaling between units. This pilot plant achieved a total operating time of approx. 300 h with a combined production of oil and wax of 6.2 kg per day. The mass and energy balances in integration of the units are studied. According to the experiments and studies, potential and bottlenecks to improve the individual units and their integration are found. Finally, a conceptual Power-to-X plant is presented, which can achieve energy and carbon efficiencies of 47% and 94%, respectively, considering liquid and solid hydrocarbons as products. [ABSTRACT FROM AUTHOR]

High-temperature molten salt electrolysis is suitable for the production of carbon morphologies such as carbon nanotubes and nano-onions. In this study, CO 2 was electrochemically reduced to solid carbon by molten lithium carbonate electrolysis in an Inconel 625 vessel at a fixed temperature of 750∘C. Four different cathodes (clean nickel, used nickel, stainless steel, and galvanized steel) were used to determine the effect of the electrode material on the morphology produced. The carbonaceous products obtained were analyzed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Raman microscopy, and X-ray diffraction (XRD). With nickel cathodes, the dominant forms of carbon were spherical, whereas tubular structures dominated with steel-based cathodes. Nano-onion was the structure of carbon with the least metal impurities. Iron was discovered to promote carbon nanotube growth. In the presence of iron, nanotube wool was also found. A greater number of different morphologies were observed when the amount of metal impurities increased. The correlation found between XRD results and sample masses suggests that the amount of metal impurities in the sample varied more than the carbon content. Thus, the yield of the process can be expected to be fairly similar between parallel experiments. • The effect of cathode material was systematically investigated for the first time. • Detailed literature review on analysis methods to determine suitable analytics. • Comprehensive and detailed elemental and structural analysis of the carbon produced. • Iron promotes tubular structures, while without metal impurities nano-onions were observed. • A high amount of metal impurities leads to a mixture of various carbon structures. [ABSTRACT FROM AUTHOR]

With carbon capture and utilization (CCU) technologies, it is possible to take CO 2 from air and transform it into valuable carbon products, such as graphene and nanotubes. In this study, CO 2 was reduced to solid carbon by molten lithium carbonate salt electrolysis. The reactor used for the electrolysis was a coaxial-type unit, where a cylindrical nickel cathode was placed inside a cylindrical stainless steel vessel; such a coaxial-type reactor has not been used before for molten salt electrochemical reduction of CO 2. This reactor design allows studies of voltage-current characteristics, which have previously not been conducted for this specific process. As a result, voltage efficiency of this process could be determined along with effect of temperature to cell voltage. Based on these results it is evident that accurate temperature control is crucial in terms of energy efficiency of the process. Data monitoring revealed a high accuracy of temporal temperature control. Great temperature differences were observed spatially. Thermoneutral voltage from the process was determined to be 1.02 V. For this electrochemical process studied, carbon nano-onions (CNOs) were obtained as a main product. Identification of the product was carried out based on Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses. Results also showed that iron, chromium and nickel metals are released during electrolysis. Iron and chromium can only be released from the stainless steel anode, as nickel can come from anode or cathode. [Display omitted] • New, coaxial type, reactor is used for electrochemical reduction of CO 2 to solid carbon. • This new setup allowed studies concerning voltage behaviour and determination of thermoneutral voltage and voltage efficiency. • Detailed description of procedure and experimental setup is provided. • Main product obtained was spherical carbon nano-onion. [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]

• 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]

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]

• 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 expected extensive production of hydrogen through water electrolysis will generate a substantial quantity of industrial waste heat. Waste heat recovery from electrolyzer facilities would provide significant potential for renewable heat generation into district heating (DH) networks. This paper investigates the techno-economic potential for recovering waste heat from an off-grid alkaline water electrolyzer (AWE) plant and using the heat in a DH network under Nordic conditions. A waste heat recovery system that includes heat pumps, a pit thermal energy storage (PTES) and an electric boiler is modeled and component capacities are cost-optimized for four different scenarios with varying DH demand coverage rates. The waste heat generation of the AWE plant and the DH demand are based on measurements conducted in southeastern Finland. It was found that even with 100 % DH demand coverage rate, the levelized cost of heat (LCOH) would be 44 €/MWh. Heat pumps constitute the largest single cost while the share of the PTES in the LCOH varies between 11 % and 19 %. The results were compared with the estimated renewable hydrogen production capacity of Finland, leading to the conclusion that by 2040, there could be potential to fulfill the DH demand of the entire country. • Levelized cost of heat (LCOH) was optimized in 5-min resolution for four scenarios. • Measured district heat demand data from a medium-sized city in Finland was used. • The proposed heat recovery system includes PTES, heat pumps, and an electric boiler. • Depending on the scenario, LCOH in the range of 16–44 €/MWh was achieved. • The estimated waste heat potential could meet Finland's district heat demand in 2040. [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]

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]

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]

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]

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]

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]

• 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]

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]

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]

The worldwide spread of the SARS-CoV-2 virus has continued to accelerate, putting a considerable burden on public health, safety, and the global economy. Taking into consideration that the main route of virus transmission is via respiratory particles, the face mask represents a simple and efficient barrier between potentially infected and healthy individuals, thus reducing transmissibility per contact by reducing transmission of infected respiratory particles. However, long-term usage of a face mask leads to the accumulation of significant amounts of different pathogens and viruses onto the surface of the mask and can result in dangerous bacterial and viral co-infections. Zeolite imidazolate framework-8 (ZIF-8) has recently emerged as an efficient water-stable photocatalyst capable of generating reactive oxygen species under light irradiation destroying dangerous microbial pathogens. The present study investigates the potential of using ZIF-8 as a coating for face masks to prevent the adherence of microbial/viral entities. The results show that after 2 h of UV irradiation, a polypropylene mask coated with ZIF-8 nanostructures is capable of eliminating S. Aureus and bacteriophage MS2 with 99.99% and 95.4% efficiencies, respectively. Furthermore, low-pathogenic HCoV-OC43 coronavirus was eliminated by a ZIF-8-modified mask with 100% efficiency already after 1 h of UV irradiation. As bacteriophage MS2 and HCoV-OC43 coronavirus are commonly used surrogates of the SARS-CoV-2 virus, the revealed antiviral properties of ZIF-8 can represent an important step in designing efficient protective equipment for controlling and fighting the current COVID-19 pandemic. [Display omitted] • ZIF-8 is applied as a coating to different face masks. • ZIF-8-based coating exhibited good stability in boiling water. • ZIF-8-based coating exhibited high antimicrobial properties against S. Aureus. • ZIF-8-based coating exhibited high antiviral properties against SARS-CoV-2's surrogates including Bacteriophage MS2 and HCoV-OC43. [ABSTRACT FROM AUTHOR]

The capacity of each component in an off-grid water electrolyzer hydrogen production plant integrated with solar photovoltaics and a battery energy storage system represents a significant factor affecting the viability and reliability of the system. This paper describes a novel method that optimizes simultaneously the component capacities and finite-state machine based control of the system to minimize the cost of green hydrogen production. The components and control in the system are referenced to a proton exchange membrane water electrolyzer stack with a fixed nominal power of 4.5 kW. The end results are thus scalable by changing the nominal power of the electrolyzer. Simulations are carried out based on data collected from a residential solar photovoltaic installation with 300 s time resolution. Optimization of the system is performed with particle swarm optimization algorithm. A sensitivity analysis performed over the prices of the different components reveals that the price of the water electrolyzer has the greatest impact on the green hydrogen production cost. It is found that the price of the battery has to be below 0.3 €/Wh to become a feasible solution as overnight energy storage. • System components and control are optimized simultaneously using PSO algorithm. • Simulations are based on data collected from an existing solar PV installation. • Electrolyzer price has the strongest effect on off-grid hydrogen production cost. • Overnight hydrogen production becomes economic below 0.3 €/Wh battery system price. [ABSTRACT FROM AUTHOR]

Abstract: Centrifugal pumps often operate inefficiently because of their incorrect dimensioning and inefficient control. The economic potential of improving the pumping efficiency has generated a wide market for energy auditing products and services, which determine the prevailing energy efficiency of pump operation. Energy audits are commonly based on additional measurements that might be carried out for a short period of time, covering only a fraction of the pump operation cycle. Often the most feasible solution would be to use the existing measurements in the pumping system to determine its typical operation. Then, the correctness of pump dimensioning and the efficiency of the applied flow control method could be determined simultaneously for a large group of pumps, as there would be no requirements for additional measurement sensors on each device. In this paper, a current measurement-based approach to monitor centrifugal pump operation and its energy efficiency is studied. This approach allows a simple realization of energy audits for fixed-speed pumping systems, where only current consumption of the electric motor is measured. Approach is based on adjustable models for motor and pump operation, which in this case are configured for a laboratory pumping system. Factors affecting the estimation accuracy of the motor operation are also analyzed in the paper. According to the conducted tests with the laboratory setup, the motor shaft power can be estimated with the accuracy of 3.2%, and the pump flow rate with the accuracy of 16%. This accuracy class can be considered sufficient for energy auditing and monitoring purposes, since it allows detection of inefficiently operating pumps. After this, more accurate measurements with separate measurement instrumentation and more detailed pumping system energy efficiency analysis can be carried out. [Copyright &y& Elsevier]

Anthropogenic emissions of CO 2 and other greenhouse gases have increased since the pre-industrial era, driven largely by economic and population growth, and are now higher than ever. In this scope, hybrid biological–inorganic systems represent a sustainable and versatile chemical synthesis platform using CO 2 as a feedstock which realizes the idea of 'Cleaner Production'. Practical implementation of hybrid biological–inorganic systems for the production of value-added chemical products requires development of scalable and robust electrobioreactors with a high energy efficiency and an adequate size. This work reports an in situ water electrolyzer stack design as part of an electrobioreactor system required for the pilot-scale operation of the hybrid biological–inorganic process approaching the aforementioned requirements. The electrolyzer is designed by applying fluid dynamics simulation tools to model the electrolyte flow. The design takes into consideration the problem of leakage currents, reported in the previous works, which is tackled by applying an electrically insulating coating. Different electrode surface modification approaches, such as coating with electrocatalysts and etching, are used to further enhance the performance and energy efficiency of the electrolyzer. The performance of the electrolyzer stack was evaluated in a pH-neutral solution required for the hybrid biological–inorganic processes. The in situ water electrolyzer developed in this study showed a high Faraday efficiency close to 90% and acceptable specific energy consumption below 90 kWh kg H2 −1. The obtained energy-efficiency values are the highest reported for similar applications with a similar scale which emphasizes the successful design of the in situ water electrolyzer stack. All data collected during experimental work might be applied to further investigation, simulation, and optimization of electrobioreactors operating at neutral pH. Overall, the results achieved in this study are promising and represent a crucial step toward the industrial implementation of hybrid biological–inorganic systems. • Novel pilot-scale in situ water electrolyzer for electrobioreactor is presented. • Fluid dynamics simulation tools are used to model and improve the electrolyte flow. • Leakage currents are tackled by insulating Teflon coating. • Performance of the electrolyzer is further improved by Co–Fe–P-based electrocatalysts. [ABSTRACT FROM AUTHOR]

The pace at which the human population is growing raises serious concerns related to food security while at the same time conventional agriculture-based food production is becoming a major cause of environmental pollution and greenhouse gas emissions. Numerous solutions have been proposed to boost food production among which edible microbial biomass is considered a promising alternative to conventional sources of food and feed with lower environmental footprint. This work introduces the Neo-Carbon Food concept that is a pilot-scale hybrid biological–inorganic process suitable for the production of microbial biomass. The concept includes integrated hydrogen production by water electrolysis, direct air capture (DAC) of carbon dioxide, and its subsequent assimilation by autotrophic hydrogen-oxidizing bacteria (HOB). The hydrogen production with in situ electrolysis achieved specific energy consumption just below 100 kWh/kgH 2 while the specific energy consumption of DAC was around 20 kWh/kg CO 2. Image 1 • Microbial protein could be a sustainable source of protein. • A pilot-scale hybrid biological-inorganic system is presented. • Novel in situ water electrolysis stack is introduced. • Energy consumption of hydrogen production and direct air capture of CO2 is studied. [ABSTRACT FROM AUTHOR]

• The effect of current ripple on PEM water electrolysis is analyzed. • A semi empirical PEM electrolyzer cell model is presented. • Higher power quality lowers energy consumption for water electrolysis. • High power quality reduces cell area up to five times at the same efficiency. Water electrolyzer technologies may play a key role in the decarbonization of the fossil-fueled world economy. Electrolytic hydrogen production could bridge emission-free power generation and various energy end-use sectors to drive the energy system towards a net zero-emission level. In order to reduce the economic cost of the required energy transition, both the overall system efficiency in converting electrical energy into the chemical energy carried by hydrogen, and the material used to build electrolytic cell stacks, should be optimal. The effect of power quality on the specific energy consumption of proton exchange membrane (PEM) water electrolyzers is investigated with a semi-empirical cell model. An experimentally-defined polarization curve is applied to analyze cell-specific energy consumption as a function of time in the case of sinusoidal current ripples and ripples excited by an industrial 12-pulse thyristor bridge. The results show that the effective electrolyzer cell area should be up to five times as high as an ideal DC power supply when powered by the 12-pulse thyristor rectifier supply to match the specific energy consumption between the two power supply configurations. Therefore, the improvement of power quality is crucial for industrial PEM water electrolyzer systems. The presented approach is applicable to simulate the effect of power quality for different proton exchange membrane electolyzers. [ABSTRACT FROM AUTHOR]

Industrial water electrolyzers apply direct current in kiloampere ranges. Therefore, rectifiers are typically based on thyristors despite the high amplitude current fluctuation excited by the rectifier. This paper studies the effect of thyristor rectifiers on the power quality of the electrolyzer stack and the supplying AC grid. The thyristor bridge excites high current and power fluctuation causing additional losses in the electrolytic cells. Further, the both AC supply side and DC output power factors are low especially under partial load conditions. The reactive power is divided into phase shift and distortion components. In the case of thyristor rectifier without any passive filter components the distortion reactive power component is dominating. The simulated results are supported by the power factor measurements of an industrial alkaline water electrolyzer. It is proposed that electrolyzer stack manufacturers should give requirements for the DC power quality to maximize the stack energy efficiency and lifetime. • DC current harmonics increase the specific energy consumption of water electrolyzers. • Thyristor rectifier has poor input and output power factor at partial loads. • Thyristor rectifier has high distortion reactive power component. • High AC reactive power component indicates poor DC quality. [ABSTRACT FROM AUTHOR]

The ripple of the supplied direct current has a significant effect on the energy efficiency of the water electrolyzer cell. Hydrogen production is defined by the current mean value, but current harmonics generate additional losses in the electrolyzer cell. However, the direct measurement of the DC current in the kiloampere range may be a challenging task compared with the voltage, which is practically in the range of a few hundreds volts in the electrolyzer stack. The effect of current harmonics on the energy efficiency and the voltage mean and root-mean-square (RMS) values is analyzed analytically based on the measured polarization curve of the PEM electrolyzer cell. The results show that both in the case of a theoretical sinusoidal current ripple and a practical thyristor bridge supply, the voltage mean or RMS values do not give a reliable estimate of the power quality. Instead, the voltage waveform as a function of time or the difference between the current mean and RMS values should be monitored. • Current quality has significant effect on the energy efficiency of electrolytic cells. • Sinusoidal and thyristor rectifier-induced current ripples cause additional losses. • Current RMS value differing from the mean value indicates poor power quality. • Cell voltage mean or RMS values do not indicate power quality. [ABSTRACT FROM AUTHOR]