With the development of micro-grids including PV production and storage, the need for efficient energy management strategies arises. One of their key components is the forecast of the energy production from very short to long term. The forecast time-step is an important parameter affecting not only its accuracy but also the optimal control time discretization, hence its efficiency and computational burden. To quantify this trade-off, four machine learning forecast models are tested on two geographical locations for time-steps varying from 2 to 60 min and horizons from 10 min to 6 h, on global irradiance horizontal and tilted when data was available. The results are similar for all the models and indicate that the error metric can be reduced up to 0.8% per minute on the time-step for forecasts below one hour and up to 1.7% per ten minutes for forecasts between one and six hours. In addition, it is shown that for short term horizons, it may be advantageous to forecast with a high resolut... [more]

The article presents methods of securing mining excavations using wooden cribs. For the underground room and pillar method used to excavate zinc and lead ore body in the Olkusz-Pomorzany mine in Poland, model tests for the replacement of rock pillars by wooden cribs are presented. In the first stage of research, the results of laboratory strength tests carried out on models of four-point, six-point and eight-point cribs made of wooden beech beams at a 1:28 scale arranged horizontally were determined. For the first time, a concave round notch connection was used to connect the beams of the wooden cribs. The maximal capacity of cribs consisting only of beams and filled with waste rocks taken from underground mining excavations was determined. In addition, the vertical deformations of the cribs at maximal loading force and their specific deformations are presented. Additionally, on the basis of load-displacement characteristics, the range in variability of the stiffness of empty cribs and... [more]

Grid operators are now considering using distributed energy resources (DERs) to provide distribution voltage regulation rather than installing costly voltage regulation hardware. DER devices include multiple adjustable reactive power control functions, so grid operators have the difficult decision of selecting the best operating mode and settings for the DER. In this work, we develop a novel state estimation-based particle swarm optimization (PSO) for distribution voltage regulation using DER-reactive power setpoints and establish a methodology to validate and compare it against alternative DER control technologies (volt−VAR (VV), extremum seeking control (ESC)) in increasingly higher fidelity environments. Distribution system real-time simulations with virtualized and power hardware-in-the-loop (PHIL)-interfaced DER equipment were run to evaluate the implementations and select the best voltage regulation technique. Each method improved the distribution system voltage profile; VV did n... [more]

Recently, a growing demand for geothermal applications has led to the exploitation of energy efficiently by developing grouting materials in the borehole between pipes and the ground. Therefore, the current study developed newly formulated cementitious grouts by the integration of expanded graphite (EG)-based hybrid additives synthesized by building chemical bridges between silica particles and EG in the presence of amino functional silane coupling agents. These produced hybrid additives with controlled EG and silica ratios were utilized in grout mixtures used in borehole heat exchangers to enhance the thermal conductivity. According to the optimization study on the formulation development of grout mixtures with bentonite, silica sands, cement, and superplasticizer by adding neat EG and EG-based hybrids, the relationship between the carbon amount and water demand was found to have a significant impact on thermal conductivity. The highest thermal conductivity value of 2.656 W/mK was ach... [more]

A selective fault clearing scheme is proposed for a hybrid voltage source converter (VSC)-line commutated converter (LCC) multi-terminal high voltage direct current (HVdc) transmission structure in which two small capacity VSC stations tap into the main transmission line of a high capacity LCC-HVdc link. The use of dc circuit breakers (dc CBs) on the branches connecting to VSCs at the tapping points is explored to minimize the impact of tapping on the reliability of the main LCC link. This arrangement allows clearing of temporary faults on the main LCC line as usual by force retardation of the LCC rectifier. The faults on the branches connecting to VSC stations can be cleared by blocking insulated gate bipolar transistors (IGBTs) and opening ac circuit breakers (ac CB), without affecting the main line’s performance. A local voltage and current measurement based fault discrimination scheme is developed to identify the faulted sections and pole(s), and trigger appropriate fault recovery... [more]

In this paper, a novel two-stage dish concentrator (TSD) with a rotary secondary mirror (SM) is presented for solar thermal water/CO2 splitting. An in-house code for ray-tracing simulation of the concentrator was developed and validated. Among all feasible geometries, a hyperboloid with an upper sheet is the most popular option and is widely used as a secondary reflector, which is mainly discussed here. All para-hyperboloid geometric combinations can be categorized into three typical patterns (φ1 < π/2, φ1 = π/2, φ1 > π/2, φ1 = field angle of PM). The initial designs of the TSD, respective to different off-axis levels for each combination, were first designed. Then a new mathematical model was introduced to reshape the SM to reach optimal truncated designs. Finally, a new concept of an off-axis primary mirror (PM) combined with the truncated SM was evaluated by using the in-house ray-tracing code. The results include the optical efficiency, concentration ratio and intercepted radiant f... [more]

This article presents an original predictive strategy, based on a new mid-term forecasting model, to be used for trading physical electricity futures. The forecasting model is used to predict the average spot price, which is used to estimate the Risk Premium corresponding to electricity futures trade operations with a physical delivery. A feed-forward neural network trained with the extreme learning machine algorithm is used as the initial implementation of the forecasting model. The predictive strategy and the forecasting model only need information available from electricity derivatives and spot markets at the time of negotiation. In this paper, the predictive trading strategy has been applied successfully to the Iberian Electricity Market (MIBEL). The forecasting model was applied for the six types of maturities available for monthly futures in the MIBEL, from 1 to 6 months ahead. The forecasting model was trained with MIBEL price data corresponding to 44 months and the performances... [more]

Staged combustion is an effective technology to control NO emissions for coal-fired boilers. In this paper, the characteristics of NO emissions under a high temperature and strong reducing atmosphere conditions in staged air and O2/CO2 combustion were investigated by CHEMKIN. A methane flame doped with ammonia and hydrogen cyanide in a tandem-type tube furnace was simulated to detect the effects of combustion temperature and stoichiometric ratio on NO emissions. Mechanism analysis was performed to identify the elementary steps for NO formation and reduction at high temperatures. The results indicate that in both air and O2/CO2 staged combustion, the conversion ratios of fuel-N to NO at the main combustion zone exit increase as the stoichiometric ratio rises, and they are slightly affected by the combustion temperature. The conversion ratios at the burnout zone exit decrease with the increasing stoichiometric ratio at low temperatures, and they are much higher than those at the main com... [more]

Hospitals are very attractive for Combined Heat and Power (CHP) applications, due to their high and continuous demand for electric and thermal energy. However, both design and control strategies of CHP systems are usually based on an empiric and very simplified approach, and this may lead to non-optimal solutions. The paper presents a novel approach based on the dynamic simulation of a trigeneration system to be installed in a hospital located in Puglia (South Italy), with around 600 beds, aiming to investigate the energy and economic performance of the system, for a given control strategy (electric-load tracking). The system includes a natural gas fired reciprocating engine (with a rated power of 2.0 MW), a single-stage LiBr-H2O absorption chiller (with a cooling capacity of around 770 kW), auxiliary gas-fired boilers and steam generators, electric chillers, cooling towers, heat exchangers, storage tanks and several additional components (pipes, valves, etc.). Suitable control strateg... [more]

The paper aims at describing a model-based approach to design automation logics for fault location and supply restoration in medium voltage distribution networks. The application of automation functions along medium voltage feeders and, in particular, the installation of protection devices in secondary substations mandates the design and the implementation of complex logics to coordinate the operations of this hardware in case of fault occurrences. This synchronization is realized with the exchange of IEC 61850 GOOSE messages, but the correct usage of this information must be implemented in each protection device through dedicated logics, which are not in the common out-of-the-box system configurations. To support the introduction and the design of these logics, an automata-based approach has been proposed and successfully demonstrated in a real environment in the European research project IDE4L. This formal methodology has been introduced to simplify the design phase and to standardiz... [more]

Growing penetration of uncoordinated Distributed Energy Resources (DERs) in distribution systems is contributing to the increase of the load variability to be covered at the transmission system level. Forced, fast and substantial changes of power plants’ output powers increase the risk of their failures, which threatens the reliable and safe delivery of electricity to end users in the power system. The paper handles this issue with the use of DERs and proposes a bilevel coordination concept of day-ahead operation planning with new kind of bids to be submitted by Distribution System Operators (DSOs) to the Transmission System Operator (TSO). This concept includes the extension of the Unit Commitment problem solved by TSO and a new optimization model to be solved by DSO for planning a smoothed power profile at the Transmission−Distribution (T−D) interface. Both optimization models are described in the paper. As simulations show, the modified 24-h power profiles at T−D interfaces result i... [more]

The large-scale renewable energy power plants connected to a weak grid may cause bus voltage fluctuations in the renewable energy power plant and even power grid. Therefore, reactive power compensation is demanded to stabilize the bus voltage and reduce network loss. For this purpose, time-series characteristics of renewable energy power plants are firstly reflected using K-means++ clustering method. The time group behaviors of renewable energy power plants, spatial behaviors of renewable energy generation units, and a time-and-space grouping model of renewable energy power plants are thus established. Then, a mixed-integer optimization method for reactive power compensation in renewable energy power plants is developed based on the second-order cone programming (SOCP). Accordingly, power flow constraints can be simplified to achieve reactive power optimization more efficiently and quickly. Finally, the feasibility and economy for the proposed method are verified by actual renewable en... [more]

Start-up conditions largely dictate the performance longevity for solid oxide fuel cells (SOFCs). The SOFC anode is typically deposited as NiO-ceramic that is reduced to Ni-ceramic during start-up. Effective reduction is imperative to ensuring that the anode is electrochemically active and able to produce electronic and ionic current; the bi-polar plates (BPP) next to the anode allow the transport of current and gases, via land and channels, respectively. This study investigates a commercial SOFC stack that failed following a typical start-up procedure. The BPP design was found to substantially affect the spatiotemporal dynamics of the anode reduction; Raman spectroscopy detected electrochemically inactive NiO on the anode surface below the BPP land-contacts; X-ray computed tomography (CT) and scanning electron microscopy (SEM) identified associated contrasts in the electrode porosity, confirming the extension of heterogeneous features beyond the anode surface, towards the electrolyte-... [more]

The district heating operator Fortum and the city of Espoo have set a goal to abandon the use of coal in district heating production and increase the share of renewable sources to 95% by the year 2029. Among renewable fuels and heat pumps, waste heat utilization has an important role in Fortum’s plans for the decarbonization of district heating production, and Fortum is considering the possibility of utilizing waste heat from a large data center in its district heating network. The goal of this paper is to investigate the feasibility and required amount of waste heat to achieve this goal. Two different operation strategies are introduced—an operation strategy based on marginal costs and an operation strategy prioritizing waste heat utilization. Each strategy is modeled with three different electricity price scenarios. Because the low temperature waste heat from a data center must be primed by heat pumps, the electricity price has a significant impact on the feasibility of waste heat ut... [more]

A spark plug calorimeter is introduced for quantifying the thermal energy delivered to unreactive gas surrounding the spark gap during spark ignition. Unlike other calorimeters, which measure the small pressure rise of the gas above the relatively high gauge pressure or relative to an internal reference, the present calorimeter measured the differential rise in pressure relative to the initial pressure in the calorimeter chamber. By using a large portion of the dynamic range of the chip-based pressure sensor, a high signal to noise ratio is possible; this can be advantageous, particularly for high initial pressures. Using this calorimeter, a parametric study was carried out, measuring the thermal energy deposition in the gas and the electrical-to-thermal energy conversion efficiency over a larger range of initial pressures than has been carried out previously (1−24 bar absolute at 298 K). The spark plug and inductive ignition circuit used gave arc-type rather than glow-type discharges.... [more]

If electric vehicles have to be truly sustainable, it is essential to charge them from sustainable sources of electricity, such as solar or wind energy. In this paper, the design of solar powered e-bike charging station that provides AC, DC and wireless charging of e-bikes is investigated. The charging station has integrated battery storage that enables for both grid-connected and off-grid operation. The DC charging uses the DC power from the photovoltaic panels directly for charging the e-bike battery without the use of an AC charging adapter. For the wireless charging, the e-bike can be charged through inductive power transfer via the bike kickstand (receiver) and a specially designed tile (transmitter) at the charging station, which provides maximum convenience to the user.

The importance and urgency of energy efficiency in sustainable development are increasing. Accurate assessment of energy efficiency is of considerable significance and necessity. The data envelopment analysis (DEA) method has been widely used to study energy efficiency as a total factor efficiency assessment method. In order to summarize the latest research on DEA in the field of energy efficiency, this article first analyzes the overall situation of related literature published in 2011−2019. Subsequently, the definition, measurement and evaluation variables of energy efficiency are introduced. After that, this article reviews the current DEA model and its extension models and applications based on different scenarios. Finally, considering the shortcomings of the existing DEA model, possible future research topics are proposed.

With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stabil... [more]

The paper presents a comparative analysis of life-cycle energy consumption for three different types of 4 kW line-start motors used in a pump unit with throttling: the most widely used induction motor with IE3 efficiency class, line start permanent magnet synchronous motor with IE4 efficiency class and line start synchronous reluctance motor with IE4 efficiency class. The operating cycle for pump units with constant flow is considered for the above-mentioned types of motors taking into account not only the losses in the pump and motor, but also in the power supply cable. It is shown that the line start synchronous reluctance motor without magnets has the highest efficiency over the entire considered loading range. However, its power factor is lower than that of the synchronous motor with magnets and therefore it has more significant losses in power supply cable. Despite this disadvantage, the line-start reluctance motor is a good alternative to widespread induction motor since it allow... [more]

It is important to understand residential energy use as it is a large energy consumption sector and the potential for change is of great importance for global energy sustainability. A large energy-saving potential and emission reduction potential can be achieved, among others, by understanding energy consumption patterns in more detail. However, existing studies show that it requires many input parameters or disaggregated individual end-uses input data to generate the load profiles. Therefore, we have developed a simplified approach, called weighted proportion (Wepro) model, to synthesise the residential electricity load profile by proportionally matching the city’s main characteristics: Age group, labour force and gender structure with the representative households profiles provided in the load profile generator. The findings indicate that the synthetic load profiles can represent the local electricity consumption characteristics in the case city of Amsterdam based on time variation a... [more]

The next-generation performance-based building energy codes are focusing on minimizing building envelope air leakage. The quantification of air leakage in buildings is typically performed with a blower door test. However, this test does not provide information about the locations of air leakage. The aim of this study is to demonstrate a method involving qualitative and quantitative components that can be used to characterize locations of air leakage with infrared thermography. Since air leakage can have a significant impact on building energy consumption in cold climates, like in Canada, this approach can quickly inform where air barrier discontinuities occurred during construction or where to selectively target air sealing efforts in existing buildings. The observations from this study are presented, based on a thermographic image analysis during a depressurized blower door test at various pressures, in an attempt to quantify the relative rates of air leakage. The results from the inv... [more]

Non-invasive diagnostic methods for electric machines’ diagnostics, which can be used during their operation in a drive system, are needed in many branches of the production industry. For the reliable condition assessment of electric machines, especially those operating in drive systems, various tools and methods have been suggested. One diagnostic method that has not been fully recognized and documented is a diagnostic method based on zero-sequence voltage component (ZSV) applications for the condition assessment of induction machines. In this paper, the application of ZSV in induction machine diagnostics is proposed. A factor that speaks in favor of applying this signal in such diagnostics is the high sensitivity of the signal to damage occurrence, and the distinct change of extracted symptoms in the case of asymmetry. It is possible to obtain a high signal amplitude, which simplifies its processing and the elaboration of reliable diagnostic factors. This ZSV-based method is also abl... [more]

Smart energy transition efforts at the municipal level are gaining importance and go far beyond implementing single projects. Decarbonising cities involves complex strategic planning and needs system level thinking and changes. This has been increasingly realised at the municipal level, but challenges remain regarding the tools, involvement of stakeholders and on the development of policies. The focus of the research is on the use of participatory foresight for fostering smart energy transition on a municipal level, the key benefits and success factors that participatory foresight brings, and the replicability of this approach. Within the novel Cities4ZERO framework, an overarching methodology for a smart urban decarbonisation transition, guiding cities through the process of developing the most appropriate strategies, plans, projects, as well as looking for the commitment of key local stakeholders for an effective transition−foresight framework, was developed and tested in five pilot... [more]

Direct injection of H2 to an anaerobic reactor enables biological fixation of CO2 into CH4 (biomethanation) and consequently boosts methane content in the produced biogas. However, there has been only a small amount of literature reporting results on this technique in a continuous reactor framework to date. To fill this gap, the present study devoted an experimental work to direct H2 addition to a fed-batch semi-continuous reactor, where the injected H2 concentration increased gradually (~3−30 mmol), spanning a moderate operational period of about 70 days. As the results revealed, the reactor continued anaerobic operation for each level of H2 dosing and produced an average methane content in the biogas ranging between 65% and 72%. The exhibited biogas upgrading trend appeared to be under-developed, and thereby suggests the need for further research.

One potential opportunity for the decarbonisation of heat supply in the UK is the repurposing of onshore hydrocarbon wells for the production and/or storage of geothermal heat. This paper reports an investigation into the most favourable candidate sites for such repurposing, taking into consideration the available thermal energy outputs and technological options for heat use. A GIS mapping model was generated, combining public domain data on onshore wells and production data from onshore fields, provided by the UK Oil and Gas Authority, with available subsurface temperature data. This model has thus integrated information on location, depth, operational status, and bottom-hole temperature for onshore hydrocarbon wells with production rates from onshore fields in the UK. Of the 2242 onshore hydrocarbon wells thus reported, 560 have the potential to be repurposed, 292 of which are currently operating. Using aggregated water production data for all operating wells in each field, the field... [more]