Small-scale Generation Research Articles

Construction and testing of small-scale thermoacoustic electricity generator with different heating power

The necessity of renewable energy is indispensable. Nowadays, researchers focus on converting waste or solar heat into advantageous energy, such as electric energy, using thermoacoustic scientific knowledge. The thermoacoustic machine converts the heat energy into sound energy and conversely. Then, using a linear alternator, it converts into electric energy. In this study, we focus on the construction and testing of small-scale thermoacoustic electricity generators with different heating temperatures. The heat is converted into acoustic energy employing the thermoacoustic engine, and the acoustic energy is converted into electrical energy using the linear alternator. In this investigation, the heating power varies from 226-389 W. The result shows that 32.2 mW of electricity was found as the thermal power at 389 W. Moreover, the onset heating temperature span is 316?C.

Design guidelines for HAWT / VAWT decision-making in the context of underserved communities

Underserved communities in rural areas often lack access to appropriate technologies that provide sustainable and reliable energy sources vital to their well-being and economic activities. In this context, the potential of small-scale wind turbine generators (WTGs) as a renewable energy source is investigated, as they can provide enough energy while being relatively easy to operate and maintain. Nevertheless, limited research is carried out about the comparative advantages of vertical axis wind turbines (VAWTs) and horizontal axis wind turbines (HAWTs) for these resource-limited conditions. The research approach includes a literature review, a field study in Kenya, and a multi-criteria decision analysis (MCDA) tailored to local wind conditions and humanitarian engineering design principles. Structural, operational, and performance differences between HAWTs and VAWTs are explored as well as the local needs of underserved communities. The MCDA results highlight design principles for the deployment of small wind turbines in rural areas and provide useful design guidelines for WTG development in underserved regions.

Renewable energy sources in small-scale generation systems

A number of issues related to renewable energy sources are considered, and various technologies for their application are briefly described.

Design and Optimization of an Alkaline Electrolysis System for Small-Scale Hydropower Integration

Alkaline electrolysis systems are currently considered to be suitable for large-scale hydrogen production. Previous research has primarily focused on integrating renewable energy sources such as solar and wind into water electrolysis systems. However, intermittent issues stemming from the sporadic nature of renewable energy sources have led to the introduction of energy storage systems (ESSs) to address these intermittent challenges. Extensive research has been conducted on the efficiency and operational aspects of these systems. In contrast to other renewable energy sources, hydropower offers the advantages of stable output and high utilization, making it a promising solution for overcoming intermittent issues. In this study, we propose the design of an optimized alkaline electrolysis system tailored for small-scale hydropower generation. This approach allowed us to confirm the efficiency of a small-scale hydropower-based hydrogen production facility and the analysis of hydrogen production costs under diverse scenarios. Notably, the optimal selling price per kilogram of hydrogen was determined to be USD 15.6 when the operational time exceeded 20 h, albeit indicating a challenging market supply. Under the consideration of various scenarios and government subsidies, this study revealed that a USD 10/kgH2 subsidy or 24 h of continuous operation achieved break-even points in the sixth and eighth years, respectively. Ultimately, the findings underscore the necessity for essential measures, including government backing and technological advancements in small-scale hydropower facilities, to enhance the economic viability of the green hydrogen market in South Korea.

Generation of microbubbles at high gas concentrations via cavitation

A novel method of continuous microbubble generation is proposed in which an air–water mixture is pressurized in a chamber (up to 47 atm), leading to complete gas dissolution, before being expelled through a restriction to induce bubble nucleation. This approach differs from existing methods for small-scale bubble generation due to the high pressure gas–liquid mixture, nucleation approach, and large gas concentrations, which range from saturation ratios of 2.85 to 9.56 at normal temperature and pressure. The flow of bubbles produced by the system is characterized through optical microscopy to determine the influence of various operating parameters on the volumetric bubble size distributions (VBSDs) at a fixed flow rate. In particular, the gas concentration, compressor pressure, restriction diameter, and restriction length are varied for two classes of restrictions: capillaries with large length-to-diameter ratios, and orifices with comparatively low ratios. VBSDs are modestly polydisperse under all conditions, but with tunable distributions in the 10–70 μm diameter range. The VBSDs for each configuration collapse when non-dimensionalized by the Sauter mean diameter, which provides an opportunity to describe bubble size distributions using a predictor model for this reduced order quantity. The coefficients from the predictor model reveal a low sensitivity of the Sauter mean diameter to the gas concentration and a reduction of bubble diameters when the residence time of solution in the restriction is decreased. Analysis of the technique of bubble generation yields an energy balance to quantify the relative energy ratio of the bubble generation process, which is presently less than 0.2%. Insight from the energy balance suggests that the process could be optimized to generate smaller bubbles.

A Review: Various Designs of Radial Flux Permanent Magnet Generator Technologies

In a renewable energy system, the amount of power generated by a renewable energy source constantly evolves. Furthermore, with the smart energy approach, small distributed renewable energy can be included into an industrialized network, enabling real-time optimization, and enabling communication with other facilities. A magnetic generator is one of the renewable energies that use the permanent magnet. As a result, this generator generated magnetic flux power by using the permanent magnetic field. An overview of the radial flux permanent magnet generator for small industry is provided in this study. First, a categorization and in-depth description of radial permanent magnet generators are reviewed. The important features of the permanent magnets are presented, along with their advantages and disadvantages. Additionally, an overview of the most recent machine developments is also presented. Lastly, an overview of the conventional radial flux permanent magnet generator designs that have been used in the development of small-scale generators is as follows.

Overview of Axial Flux Permanent Magnet Generator for Small-Scale Industry

A magnetic generator is not like a conventional generator that is produced by the coil. Consequently, this generator used the permanent magnetic field to produce magnetic flux energy. Although, most of the permanent magnet designs produce less aggressive copper winding. This paper provides an overview of axial flux permanent magnet generators for small-scale industries. First of all, the classification and a detailed overview of permanent magnet generators are presented first. The main characteristics of the generators together with their benefits and drawbacks are highlighted. Additionally, an overview of the most recent machine developments is also presented. The design of convenient permanent magnet generators that have been used to create small-scale generator varieties is then reviewed to conclude the most suitable design among axial flux which is the sandwiched construction.

Conflict and uneven development in the multidecade distributed solar energy transition in the United States.

A longitudinal analysis of small-scale solar energy generation in the United States is used to demonstrate how transition studies can explain nonlinearity in multidecade changes of consumption-production systems. Nonlinearity involves uneven development of sustainability innovations with episodes of rapid growth but also periods of slow growth, stalling, or even collapse. Factors that affect the increasing feasibility and attractiveness of small-scale solar include technological improvements, declining costs, and changes in global energy markets. However, a more complete explanation of nonlinearity highlights the importance of a type of systems analysis that also includes strategic action and broader societal and policy changes. Specifically, efforts by the utilities constrained the growth of small-scale solar by weakening policy support because of the perceived threat, but the solar industry and advocates responded with countervailing action in a changing context. As the transition developed, strategic action (including goals, targets, tactics, and coalition partners) changed and became more conflictual. However, by the beginning of the 2020 decade, the development of microgrids, digital technologies, storage, and virtual power plants in combination with net-zero energy policies provided indications of potential for a reconfiguration of the relationship that could be less polarized and conflicted.

Dynamics of a Plasma Cloud Generated by a Compact Coaxial Gun upon Expansion into Vacuum and Large-Volume Background Plasma in an External Magnetic Field

Results of experiments on injection of dense plasma clouds created by a small-scale coaxial generator into vacuum and large-volume background plasma in an ambient magnetic field are presented. The regime of an “infinite” background medium that allows studying the plasma-cloud dynamics on the scale of about one meter in the directions perpendicular and parallel to a quasi-uniform magnetic field is realized on “Krot” plasma device. The dynamics of the diamagnetic cavity appearing upon magnetic-field expulsion by a plasma blob, the electromagnetic noise appearing in the cavity, along with the evolution of plasma-cloud structure during injection and at the stage of its decay, were studied. It is demonstrated that the key properties of the cloud dynamics that are typical of the active space and high-energy laboratory experiments, including complete expulsion of the magnetic field from the cloud and development of the flute instability at its boundary, are reproduced at low injection speed (below 30 km/s) and low plasma energy (on the order of 0.1 J).

Small-scale Kazantsev-Kraichnan dynamo in a MHD shell approach

The small-scale magnetic energy generation in a turbulent velocity field is studied by two different approaches. One of them is based on the Kazantsev-Kraichnan model developed for turbulence with short-time velocity correlations, and the other uses the shell model of magnetohydrodynamic turbulence, describing the turbulent energy cascade on a finite number of spectral shells. We have found that the injection of weak magnetic field at the initial moment in both models leads to an exponential growth of magnetic energy and tried to determine whether these effects are of the same or different nature. The investigations have shown that the rates of growths and magnetic energy spectra in two approaches can be very much different, which can be attributed to the contradictions of the model assumptions and unknown correlation time. The discussion of these contradictions allows us to formulate a possible explanation, which is likely related to the fact that the small-scale magnetic field generation is under the influence of some spectral subrange, rather than the entire kinetic spectrum. Varying the correlation time of the velocity field and considering the spectral regions, we have determined the range of kinetic energy spectrum responsible for the small-scale dynamo generation.

Suppression of small-scale dynamo in time-irreversible turbulence

ABSTRACT The conventional theory of small-scale magnetic field generation in a turbulent flow considers time-reversible random flows. However, real turbulent flows are known to be time irreversible: the presence of energy cascade is an intrinsic property of turbulence. We generalize the ‘standard’ model to account for the irreversibility. We show that even small time asymmetry leads to significant suppression of the dynamo effect at low magnetic Prandtl numbers, increases the generation threshold, and may even make generation impossible for any magnetic Reynolds number. We calculate the magnetic energy growth rate as a function of the parameters of the flow.

Investigation of a helical Savonius turbine with a deflector system

The growing demand for renewable energy sources to meet electricity needs has underscored the importance of exploring new resources of renewable energy. Among the various alternatives, Helical Savonius rotors have emerged as one of the most widely used technologies for small-scale hydropower generation. Numerous studies have been conducted to investigate these types of rotors, particularly to enhance their power output. Despite existing research, there is still a need for modifications and proposals for new configurations of Savonius rotors. This paper presents a numerical study of a Savonius rotor equipped with a new design of a deflector. The results indicate that the highest power coefficient achieved is 0.1247 at a tip-speed ratio of 0.7 in the absence of a deflector system. The geometric parameters of the deflector are varied to identify the configuration that generates the highest power output. With the implementation of an optimal configuration for the new deflector system, the maximum power coefficient is improved to 0.168 at a tip-speed ratio of 0.7. Otherwise, the maximum power coefficient could be enhanced by 34% compared to the same configuration without a deflector. This significant improvement highlights the potential of the proposed design system.

Innovative Loss of Field Protection Algorithm for Small-Scale Synchronous Generators

Although conventional loss of field (LOF) protection schemes, especially impedance-based ones, are widely used for large-scale synchronous generators, they may not provide proper performance for small-scale synchronous generators (SSSGs) due to various concerns including, (i) large tripping time for unrecoverable LOF (ULOF) which may lead to severe voltage drop and stalling of nearby induction motors, (ii) LOF function maloperation during islanding events, and (iii) LOF function maloperation during recoverable LOF events. To resolve these issues, a new adaptive LOF protection logic is proposed for SSSGs. After ULOF events, the automatic voltage regulator (AVR) output gradually increases, while the SSSG internal voltage does not considerably increase. Based on this principle, some measurable or easily calculable parameters, including AVR output and SSSG internal voltage, are adopted to discriminate ULOF from other disturbances. Meanwhile, the proposed logic is wisely equipped with an adaptive time delay to prevent stalling of nearby induction motors and enhance operation speed during ULOF. Performance of the proposed algorithm is evaluated under various LOF and islanding events as well as short circuits. Obtained promising results confirm desirable performance of the proposed approach. Besides, compared to the impedance-based method, the proposed adaptive time delay considerably improves the security and reliability.

Performance evaluation of a liquid-sodium thermoacoustic engine with magnetohydrodynamic electricity generation based upon the Swift model.

Liquid sodium is an attractive working fluid for thermoacoustic conversion. Herein, a numerical study on a standing-wave thermoacoustic electricity generation system with liquid sodium as the working fluid is presented, based upon the Swift model. The characteristics of the thermoacoustic conversion and the output performance of the system have been investigated. The results show that the sodium engine can reach a power density much higher than the classical gas engine. Due to the strong acoustic coupling between components, the electricity output is significantly affected by the input heating power, the magnetic flux density, and the load ratio. In a typical case, the thermal-to-electric efficiency and the relative Carnot efficiency can reach 4.6% and 7.8%, respectively, with a temperature difference of 563 K and an input heat of 5 kW. More importantly, the output electricity density reaches 150 kW/m3, higher than some commercially available technologies. These results demonstrate the potential of such technology for small-scale electricity generation. Its extremely simple structure without any mechanical moving part endows the system with high reliability and long lifetime, if risks of corrosion and exposure to air and water can be avoided.

Towards smart energy management for community microgrids: Leveraging deep learning in probabilistic forecasting of renewable energy sources

The intermittent nature of renewable resources like solar and wind presents challenges for small-scale energy markets and off-grid regions. Localized forecasting of these resources is crucial to incentives the attention of citizens and urban designers in adopting small-scale generation systems, i.e., hybrid or renewable energy-based microgrids, in their communities. This study employs Encoder–Decoder Sequence-to-Sequence (Seq2Seq) models with two different recurrent neural network architectures (RNN), long short-term memory (LSTM) and gated recurrent unit (GRU), to forecast wind speed and solar radiation on a location appointed to install microgrids. The models were trained using meteorological data obtained from weather stations while taking into account data on extreme weather events, such as wind gusts, to enhance the predictive accuracy of the models. Particularly relevant in the context of the increasing menace of climate change and the resulting rise in the frequency and severity of extreme weather events. An ensemble method is also employed to quantify uncertainty in the model’s prediction to increase the confidence that an end-user of a microgrid can deposit in the forecasting for decision-making. We compared the Seq2Seq-LSTM and Seq2Seq-GRU models using deterministic and probabilistic metrics. Both models showed satisfactory accuracy and confidence in wind speed and solar radiation forecasting. However, the Seq2Seq-GRU model stood out for its significantly faster computation times. On average, it achieved a 20% reduction in processing time for the same dataset. The models performed best for shorter prediction horizons (1-hour) and higher lookback periods (k = 720-hrs). We also analyzed the models’ performances according to the season. The results show that the seasonal variation significantly affects the accuracy and uncertainty of wind speed forecasting, with fall and summer demonstrating the highest accuracy and winter and spring the lowest. For solar radiation, the models show greater reliability, narrower prediction intervals, and higher accuracy during winter, with opposite trends observed during summer. The deep learning framework proposed in this study can help anticipate daily surpluses or shortfalls in energy generation across different seasons, contributing to the efficient operation of microgrids.

Sharing the grid: The key to equitable access for small-scale energy generation

Small-scale distributed generation (DG) installations, like rooftop solar photovoltaics, are adopted earlier in high-income households than in other portions of society. This can limit grid electricity export capacity for latecomers, causing inequitable access and slower renewables deployment. In search for an equitable solution, this work challenges current DG permissioning practices: instead of applying rules of thumb to assign DG, we propose a policy that represents grid limitations at all hierarchies of the grid (i.e., customer, distribution, sub-transmission and transmission levels). A method to predict interest in household DG installations over time based on demographic and socioeconomic variables is presented and validated. This is leveraged to test a novel policy for small-scale DG deployment: sharing the grid; and to explore its potential to improve equity in grid access and speed of renewables deployment. Proposed, current and alternative policy paths on small-scale DG adoption are tested to identify benefits and trade-offs. Using Ireland’s national utility as case study, we perform a long-term simulation of solar photovoltaic adoption. Sharing electricity export capacities increases participation from 77.9 % to 100 %, unlocking access to the grid for 364,064 electricity customers compared to current policy—without the need for infrastructure upgrades. Furthermore, the proposed policy achieves the same overall level of installed capacity as current policy 44 % faster, accelerating small-scale DG rollout, benefiting households and decarbonisation targets. Ultimately, to determine equitability, we connect these results to demographic variables and find that grid limits are not biased towards any demographic group studied, suggesting that policy can be tailored to prevent DG access inequity.

Decentralized Emergency Control of AC Power Grid Modes with Distributed Generation

Large-scale development of small-scale generation, and facilities based on this, with their integration into existing distribution networks, qualitatively change the modes and tasks of network management and transform previously passive electric networks into active ones. Features of parameters and modes of small-scale generation, insufficient observability and manageability in centralized management determine the need to use a decentralized multi-agent control of the modes of such networks. First of all, this applies to emergency management, which includes automatic restoration of the integrity and normal operation of the network. This paper presents a set of specialized methods for emergency management of active power grid modes and the results of a study of their effectiveness on mathematical and physical models that confirm the feasibility of using decentralized emergency management and network recovery management. In particular, this includes: a method of emergency proactively balanced separation of grid energy districts along one of the a priori fixed network cross-sections in the event of disturbances with the transition to island mode, and a method for two-stage restoration of the integrity and normal network mode with decentralized synchronization of active parts on remote network switches. In the case of the decentralized remote synchronization of active parts, it is proposed to use special control of the excitation and speed of generators to create conditions for the successful operation of automatic reclosing devices with synchronization detection. It is essential for emergency management in active networks with small generation to reject the concept of ensuring the reliability of power supply through maintaining the integrity of the network in favor of the concept of an emergency-balanced breakdown of the network into balanced areas with the subsequent automatic restoration of integrity. To conduct research on the physical model, a prototype of distributed system emergency automation has been developed that does not use data transmission tools, which ensures its high cybersecurity and the feasibility of decentralized management.

Cost of small-scale dispatchable CO2 capture: Techno-economic comparison and case study evaluation

Dispatchable power sources are crucial for electricity system stability and security of supply. Currently, the United Kingdom uses small-scale (<50 MWe) gas turbines to provide this function. To ensure we reach Net-Zero emissions by 2050, these small-scale dispatchable generators will require CO2 abatement; however, limited studies focus on these forms of power generation.In this work, we use process models developed in our previous studies, to calculate the levelised cost of electricity (LCOE) for a small-scale gas turbine equipped with Carbon Capture and Storage (CCS). The results show that the inclusion of CCS for these dispatchable generators increases the LCOE from 172 £/MWh to 514 £/MWh, almost tripling the cost of electricity. This is due to economies of scale and the low capacity factor. As these generators operate for less than 20% of the year, the levelised cost is drastically higher than other forms of low-carbon power. Dispatchable power is usually more expensive due to the small plant size and transient operation, and including CCS exacerbates this issue. Future work should focus on alternative forms of CO2 capture (designed specifically for small-scale gas turbines) and different dispatchable power generation, i.e., hydrogen and energy storage.

One Network for Europe – Scalability and Replicability in View of Harmonised Electricity Markets

Renewable energy production is mentioned by many as one of the key factors in mitigating the effects of climate change. However, there may be several downsides to the spread of renewables, such as their impact on the balance of the electricity system and on receiving networks. The project OneNet (One Network for Europe) is funded through the EU’s eighth Framework Programme Horizon 2020. It is titled “TSO – DSO (TransmissionDistribution System Operator) Consumer: Large-scale demonstrations of innovative grid services through demand response, storage and small-scale (Renewable Energy Source) generation” and responds to the call “Building a low-carbon, climate resilient future”. While the electrical grid is moving from being a fully centralized to a highly decentralized system, grid operators must adapt to this changing environment and adjust their current business model to accommodate faster reactions and adaptive flexibility. This is an unprecedented challenge requiring an unprecedented solution. Thus, the two major associations of grid operators in Europe, the European Network of Transmission System Operators for Electricity (ENTSO-E) and European Distribution System Operators (EDSO), have activated their members to establish a unique consortium.

Process design and simulation study of an electricity generation plant utilizing low-grade wasted thermal energy using aspen Hysys software

An analysis of the operational parameters of a small-scale electrical generation facility that uses the thermal energy contained in the flue gases from rubbish waste incineration is the goal of this study. To assess this system, the organic Rankine cycle (ORC) thermodynamic system was used. Since the organic fluid has a lower boiling point than water and can be evaporated with less thermal energy, it was chosen as a heat transfer medium instead of water. Aspen Hysys was utilized as a simulation tool, while R11 was used as the working fluid. To maximize the amount of available electrical output power, the plant's operational temperature, working fluid flow rate, and pressure are all maximized. According to the simulation's findings, flue gas may generate electric power between the ranges of 3.12 – 29.71 kW at working pressures between 2.5 and 3.5 bar and working fluid flow rates between 3.600 and 7200 kg/h when the temperature is between 50 and 95 oC. The system reaches a thermal efficiency of about 8.30 at 350 kPa of working fluid pressure.