Small-scale Distributed Generation Research Articles

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.

Expert System Integrating Rule-Based Reasoning to Voltage Control in Photovoltaic-Systems-Rich Low Voltage Electric Distribution Networks: A Review and Results of a Case Study

Nowadays, in low voltage electric distribution networks, the distribution network operators are encountering a high number of connected small-scale distributed generation units, mainly photovoltaic prosumers. The intermittent nature of the prosumers, together with the degree of uncertainty of the requested and injected powers associated with all end-users from low voltage electric distribution networks, can cause voltage variations that violate the allowable limits. In this context, this paper developed an efficient and resilient expert system integrating rule-based reasoning applied to the on-load tap changer-fitted transformer to improve the efficiency of the voltage control in the PV-rich LV EDNs. An in-depth analysis based on 75 scenarios, resulting from the combinations of three indicators—the penetration degree of the photovoltaic prosumers, the consumption evolution associated with the consumers, and the energy production of the photovoltaic systems—was performed to demonstrate the efficiency of the proposed expert system in a low voltage electric distribution network from a rural area belonging to a Romanian distribution network operator. The success rate of the expert system was 86.7% (65 out of 75 scenarios did not have voltage issues). All voltages were between the allowable limits in 100% of the time slots associated with the analysed period. For the other scenarios (representing 13.3%), voltages were inside the range [−10%, +10%] in at least 95% of the time slots.

Institutional structure of the energy industry in the Baikal region

The paper considers the conditions for solving the energy sector of the Baikal region problems related to the development of small-scale distributed energy generation and decentralization of energy supply within the expected energy transition. The institutional structure of energy production and transmission enterprises is analyzed, a group of companies and organizations associated with the local community is identified. A high degree of centralization and the prevalence of vertical ties in the industry management is highlighted, as well as dependency on structures external to the regions. Among the independent enterprises, organizations founded by the individuals prevail. Most of these companies have reduced their economic efficiency over the past five years. Difficulties are expected in the transition to a distributed architecture and horizontal principles of industry management due to the weakness of the sector that is not associated with vertically integrated companies, as well as the preservation of the industrial structure in the region, laid down in previous decades.

Optimal design of a 5th generation district heating and cooling network based on seawater heat pumps

This work presents the design and the thermo-economic optimization of a novel layout of a 5th generation district heating and cooling network, for a residential district located in the Pantelleria island (South of Italy). The research focuses on a novel arrangement based on two bidirectional low-temperature neutral rings. For both rings, the fluid temperature is controlled by means of two groups of heat pumps cooled by seawater. The investigated layout also includes wind turbines and photovoltaic panels for power production. This layout will be used as a driver to promote the transition from the present centralized energy paradigm to a novel one, based on small-scale distributed generation integrated with renewables. The paper aims at evaluating the energy, economic and environmental savings achieved by this novel layout. A thermo-economic optimization is also implemented in order to determine the set of design/operating variables, maximizing system economic profitability. To this scope, a detailed approach is implemented, developing a dynamic simulation model of the system in TRNSYS 17. The developed simulation tool is able to mimic the real time operation of the system, for whatever weather condition, boundary and/or design variable. The results of the simulations show that the proposed layout achieves significantly positive results, with a primary energy saving and avoided greenhouse gases emissions equal to 133% and 134%, respectively. The economic profitability of the system is limited with the payback period close to 15 years, due to the high capital cost of the plant. The renewable electric production of the plant meets 57% of the district demand, although only 37% of this amount is self-consumed by the district. The study also includes a sensitivity analysis suggesting to limit the capacities of solar and wind fields to reduce the electricity in excess sold to the grid.

Statistical evaluation of wind speed forecast models for microgrid distributed control

With the increasing needs to decarbonise existing energy systems, there is an effort to integrate small-scale distributed generation sources, such as wind generators, with the electric demand in circuits known as microgrids. The operation of distributed variable renewable resources is subject to an optimum operating regime, ahead of real-time, which relies on output forecast. However, many wind speed forecast models are designed for centralised controllers, which are vulnerable to control failures. A suitable wind forecast model for a distributed control system is, therefore, required for optimal and reliable use of renewable generation. This paper presents a comparison of wind speed forecast models suited for distributed control, evaluating them in terms of the statistical significant difference in accuracy and computational resource requirements. This is essential since computational resources are limited in distributed control schemes. The data used in this paper is the historical wind speed of the Auchencorth Moss Atmospheric Observatory from 2016 to the end of 2019. Two forecast model types based on Auto-regression and Artificial Neural Network (ANN) are compared using the Diebold-Mariano test. Results show that ANN models with parallel hidden layers have the highest accuracy with statistical significant difference, while remaining suitable for microgrid distributed control.

Dynamic MGs-based load restoration for resilient urban power distribution systems considering intermittent RESs and droop control

The large amount of small-scale distributed generation can provide emergency power supply to critical loads during blackouts and help build resilient urban power distribution systems. However, the uncertainty from intermittent renewable energy sources (RESs) and loads complicates the modeling and challenges the operation of resilient distribution systems. This paper first proposes a novel offline probabilistic modeling and online updating method to characterize the time-varying uncertainty of multiple RESs power outputs and loads. Then, a scenario-based stochastic optimization model is proposed for load restoration, which incorporates the new concept of dynamic microgrids (MGs) and also takes into account the effects of droop control and frequency regulation. The case study to the modified 37 and 123 node test feeders shows that the restoration with droop control and frequency regulation could simultaneously consider the importance and frequency requirement of loads, and the proposed uncertainty modeling and updating method as well as the dynamic MGs could increase the overall system resilience, where the served ratio of critical loads would be particularly improved. All of these factors should be considered in real applications for a more realistic and feasible decision of load restoration strategy.

Thermodynamic performance study of a novel cogeneration system combining solid oxide fuel cell, gas turbine, organic Rankine cycle with compressed air energy storage

Energy storage becomes increasingly significant for addressing imbalance of grid supply and demand. In this paper, a new cogeneration system based on combined compressed air energy storage (CAES), solid oxide fuel cell (SOFC), gas turbine (GT) and organic Rankine cycle (ORC) is proposed. SOFC-GT system replaces GT combustor of traditional CAES, and SOFC-GT can operate with high efficiency at peak time. At the same time, ORC is employed to recover the exhaust from GT. Especially, in the new system, the surplus electricity is utilized to compress air, thus eliminating power consumption of air compressor in conventional SOFC-GT. Additionally, the system can also provide heat and power for small-scale distributed generation application users. The combined system is simulated based on Aspen plus and embedded Fortran. The energy, exergy analysis and parametric sensitivity analysis are used to evaluate the system performance. The results revealed that the round-trip efficiency, exergetic round-trip efficiency and discharging electrical efficiency are 76.07%, 61.78% and 72.39%, respectively. Compared with an integrated SOFC-GT-ORC system without energy storage, the electrical efficiency of the new system increases by 17.07%. Overall, the combined system can achieve high efficiencies, which can provide important theoretical guidance for efficient energy utilization.

Vortex-in-cell simulation of the flow and performance of a Savonius hydraulic turbine with S-shaped blades

The volume penalization vortex-in-cell (VP-VIC) method, which combines the vortex-in-cell and vortex penalization methods, is a kind of immersed boundary method that has the advantage of accurately calculating the vorticity field near the boundary. It is expected to be used as a design tool for shape optimization. In this study, the flow and performance of a small Savonius turbine rotor (rotor diameter DR = 245 mm) with S-shaped blades, which is used for small-scale distributed power generation with output less than 100 kW, were analyzed by numerical simulation. The results were compared with those of previous experimental studies to examine the usefulness of the VP-VIC method for fluid analysis around the Savonius turbine. The Reynolds number (Re=U0DR/ν) based on the streamwise velocity U0 is 1.32×105. The volume penalization vortex-in-cell (VP-VIC) method is applied for flow simulation, and the rotational motion of the rotor is analyzed using the calculation method previously proposed by the authors for the fluid force acting on the solid boundary (blade surface). As a result, the relationship between the rotational speed of the rotor and the output coefficient obtained in this simulation is similar in the experimental results of Golecha et al. [Appl. Energy 88, 3027–3217 (2011)] using S-shaped blades. In particular, with an increase in the load torque, the rotational speed of the rotor decreases, and the rotor stops momentarily. When the rotor stops, the positive torque of clockwise rotation acts on the advancing blade, while the negative torque of counterclockwise rotation acting on the returning blade decreases; hence, the rotor restarts immediately after stopping. In addition, it is established that the rotor output can be accurately predicted. Based on the above, it is reconfirmed that the VP-VIC method is beneficial for predicting the performance of a Savonius turbine.

Electric Power Generation in small-scale distributed generation systems using bioenergy in Nicaragua

En este artículo se presentan los resultados de un estudio que indagó sobre la posibilidad de generar electricidad en sistemas de generación distribuida utilizando los residuos agrícolas a pequeña escala en la región del oeste de Nicaragua; se utilizaron sistemas de información geográfica (SIG) para evaluar el potencial de energía eléctrica de la biomasa realizando un análisis espacial que permitió determinar la cantidad de residuos disponibles. Además, se obtuvo un modelo conceptual de localización de biocentrales de generación y se calculó el potencial energético teórico disponible. Se utilizó el programa HOMER para simular la generación de energía eléctrica, considerando el potencial energético determinado de las regiones en estudio, y se determinó su posibiliad técnica; no obstante, se comprobó que el costo nivelado de la generación usando biomasa residual tiene un valor mayor al de la red, y, por lo tanto, su empleo para la generación de electricidad no es rentable en las condiciones actuales del mercado energético nicaraguense.

A novel trigeneration system based on solid oxide fuel cell-gas turbine integrated with compressed air and thermal energy storage concepts: Energy, exergy, and life cycle approaches

Energy storage technologies are considered as an available solution to improve the reliability of conventional energy systems as well as responding to the peak load. This paper offers a novel integrated system with remarkable potential to provide users’ electricity, heating, and cooling demand for small-scale distributed generation applications. The main objective of this research is improving thermodynamic efficiency as well as mitigating emissions of the conventional solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system with the option of peak-shaving. A compressed air energy storage and thermal energy storage are employed to store the surplus power and recover the waste heat of the prime mover, respectively. The proposed system operates with a round-trip efficiency of 76.8 % and exergy efficiency of 46 % under the design condition: 8 h of off-peak period with 97.5 kW power demand and 8 h of peak period with 305.6 kW power demand; 113.4 kW cooling capacity; 37.4 m3 hot water production. Furthermore, the evaluation of environmental impacts indicates that GHG emissions are low at 0.27 kgCO2e/kWh. Also, the life cycle assessment shows that well-to-production GHG emissions of the proposed integrated system during a round-trip of operation are 1890 kgCO2e which is 6.6 % lower than the conventional SOFC-GT.

A Methodological Framework to support Load Forecast Error Assessment in Local Energy Markets

Due to the expansion of small-scale distributed generation, residential consumers are evolving to active participants in energy markets. Concepts like Local Energy Markets (LEM) are designed to harvest flexibility of these prosumers and contribute to a stable power system operation. However, the stochastic nature of the consumption of households increases the difficulty of accurate forecasts and can lead to erroneous bids and penalty payments. State of the art load forecasting methods can reduce this error to a certain extend. Yet, for a systematic assessment of the implications of forecast errors, a method capable of generating forecast time series with defined errors is required. With this method, measures to decrease the implications of forecast errors (e.g., aggregation of participants) can be evaluated. In this paper, we introduce such a method based on nonlinear optimization. After an analysis of typically used error metrics and achieved forecast errors in the literature, the proposed method is evaluated using German household load profiles demonstrating similar statistical properties as found in the literature. Additionally, we show the application of the method to a LEM simulation case revealing that a participation of a household without flexible assets would only be profitable for forecast errors instead of accuracies below 30-40%.

A virtual power plant optimal dispatch model with large and small-scale distributed renewable generation

Volatility and sharp increases in the price of electricity are serious economic problems in the primary sector because they affect modernization investments for irrigation systems in Spain. This paper presents a new virtual power plant (VPP) model that integrates all available full-scale distributed renewable generation technologies. The proposed VPP operates as a single plant in the wholesale electricity market and aims to maximize profit from its operation to meet demand. Two levels of renewable energy integration in the VPP were considered: first, a wind farm and six hydroelectric power plants that inject the generated electricity directly to the distribution network, and second, on-site photovoltaic plants associated with each of the electricity supply points in the system that are designed to prioritize self-consumption. The proposed technical-economic dispatch model was developed as a mixed-integer optimization problem that determines the hourly operation of distributed large-scale renewable generation plants and on-site generation plants. The model was applied to real data from an irrigation system comprising a number of water pumping stations in Aragon (Spain). The results of the VPP model demonstrate the importance of the technical and economic management of all production facilities to significantly reduce grid dependence and final electricity costs.

Dual‐loop control of transfer delay based PLL for fast dynamics in single‐phase AC power systems

Phase-locked loop (PLL) is commonly utilised for AC power systems to detect phase and frequency. With the increasing use of small-scale distributed power generation, the technique becomes widely available for grid interconnection of renewable power source into single-phase AC distribution network. Through comprehensive analysis and design, this study proposed a new approach that includes dual independent control loops to enhance the transfer delay-based PLL capability in terms of speed and accuracy. The effectiveness and advantages of the proposed PLL structure are demonstrated by numerical simulation and verified by experimental test.

Implementing triple helix through Listrik Kerakyatan initiative: community-based energy from waste

As depicted by its three components, A (academic), B (business), and G (government), the Triple Helix principle aims at narrowing the gap between the competencies of university graduates and those required by businesses or industries in the real world, under the corridor of government rules and regulations. The main issues that will be addressed by the triple helix concept is the national policy to attain 23% of renewable energy portion by the year 2025. However, the conventional electricity construction, which usually prefer a large-scale interconnected system, is currently facing serious delay due to difficulties in acquiring land and permit. Moreover, such large-scale power plants are not sufficient to serve consumers that are scattered in more than three thousand islands in Indonesia archipelago. In addition, such big projects are mostly owned by giant investors that depend on foreign fund and technology, leaving no opportunity for local people to contribute and have ownership over their energy needs. STT PLN proposes a simple small-scale distributed generation that can be owned and managed by local people by using renewable energy sources that are available around the communities. Waste is the most attractive resources because by converting waste to energy, the problem of waste can be solved at the same time. Based on the research and pilot project that had been conducted in three locations, Listrik Kerakyatan (Community-based Electricity) is technically simple so it can be applied and managed by local people. It is also economically viable as the required capital is relatively small and affordable by small enterprises. The commutative law of math also says that 1x1000 = 1000 x1. Therefore, going by that law, the total capacity generated by 1000 units of small LKs can be similar to one large unit of conventional model.

A Review of Technologies for Multistage Wood Biomass Gasification

Currently, small-scale distributed power generation is being intensively developed in Russia and abroad. Given the rise in the rates for the electric and thermal energy, the development of new territories, and the technical infeasible connection to the power supply system, one of the most promising variants of supplying isolated consumers with power is the application of wood biomass gasification technologies. Analysis of the studies in this sphere shows that considerable attention is paid to enhancing the gasification efficiency and ensuring the purity of the gas. These problems are solved using multistage gasification technology. This technology involves the pyrolysis and gasification in separated zones of the gasifier or individual interconnected reactors, which enables achieving the optimal conditions for the conversion of biomass at every separate stage. The major advantage of multistage gasifiers is the production of synthesis gas with a low content of tar. The article represents a review of technologies for multistage wood biomass gasification and comparison of the relevant gasifiers of various types; the basic single-stage and multistage wood biomass gasification technologies are examined and their technical characteristics and examples of their commercial implementation are provided. Analysis of the current situation shows that predominantly foreign multistage wood biomass gasification technologies/plants have found practical application. These technologies allow the produced syngas to be directly used in internal combustion engines and gas turbines without employing expensive auxiliary detarring plants.

Small-scale Distributed Power Generation Development in the Siberian Regions: Evaluation of Efficiency

<p>It is shown that topical issue is the solution of problems of enhancement of structure electro and heat generations in regions of Russia, including through synchronization of schemes electro and heat supplies. It causes the necessity of integration to municipal level power engineering into development plans for big power industry that causes gain of a role of the distributed power engineering (including the cogeneration installations). The carried-out serial calculations for comparative assessment of a row of technologies of the small-scale distributed power generation in the Novosibirsk and Kemerovo regions allowed to select the perspective directions of diversification of energetic branch. </p>

Mathematical modeling of mini-CHP based on biomass

One of the promising directions of small-scale distributed power generation for Russia is the use of biomass. The present work is devoted to studies of an mini-CHP based on multi-stage biomass gasification. Mathematical models of elements and mini-CHP in general based on technological schemes were constructed. The mathematical models were constructed with the software developed at Melentiev Energy Systems Institute of Siberian Branch of the Russian Academy of Sciences. The calculations were made for two sizes of internal combustion engines. Thus, we obtained the values of flow rates, temperatures of heat carriers at various points of flow charts of the plants.

Demand response under real‐time pricing for domestic households with renewable DGs and storage

With the increasing penetration of small-scale distributed generators (DGs) and storage units into the domestic areas and the emergence of real-time pricing (RTP) of electricity, residents have more opportunities to obtain a cost-effective energy management through the participation of demand side management. Unlike existing online solutions, this paper presents an alternative one-day-ahead energy dispatch solution to achieve the economic benefits of meeting the demand with minimised electricity purchase cost by optimising the DG and storage utilisation efficiency in the presence of RTP. The performance of the proposed solution is assessed through a comparative study by carrying out simulation experiments for a set of operational scenarios. The numerical result demonstrates that the proposed energy dispatch solution can well meet the demand requirement with significantly reduced electricity purchase cost. With the recognition that the prediction of RTP and DG output can often be inaccurate, the robustness of the solution is further verified under prediction errors.

Optimization control scheme utilizing small-scale distributed generators and OLTC distribution transformers

Abstract The traditional policy of installing small-scale distributed generators (SSDGs) has focused on connection, rather than integration, with a fit-and-forget approach, based on the legacy of a passive distribution grid. Under this regime, the high penetration of SSDGs in distribution networks is expected to cause several issues related to power quality, efficiency and reliability. This paper proposes an optimization scheme to control both voltage magnitudes and voltage unbalances of LV distribution grids, utilizing on-load tap-changer (OLTC) distribution transformers, photovoltaic (PV) inverters, and batteries. Both the technical and cost models are taken into account for each of the aforementioned components, while the total cost function is constructed from the perspective of both distribution system operators’ and domestic consumers’ cost. The performance of the proposed approach is investigated on a typical rural Flemish feeder. We examine the violations of both voltage and voltage unbalance statutory limits, as well as the OLTC positions and the power utilization of both PV inverters and batteries.

The effect of distributed electricity generation using natural gas on the electric and natural gas grids

The efficient and economical design and operation of individual small-scale distributed generation (DG) units has received considerable attention. It is now plausible to envision a future scenario where a large number of such units, spanning capacities from the kW to the MW scale, are deployed in a region. As distributed electricity generation using natural gas becomes more widespread, the dependency of the electric grid on the natural gas grid will increase. This concerns multiple interaction points along the two networks, and reaches beyond the natural gas demand of large-scale load following or baseload gas-fired powerplants. More specifically, a better understanding is required of the potential changes in the dynamic behavior and interaction of the electricity and natural gas grids at or close to residential use sites (neighborhoods), where the small-scale DG infrastructure is likely to be located. In this paper, an optimization-based framework is developed for analyzing the operation of an ensemble of small-scale natural gas fueled DG units, and quantify their ability to flatten the electric grid load (i.e., reduce the peak demand) of the neighborhood that they serve. Our analysis relies on realistic energy use data and takes into account capacity limitations of the current natural gas distribution infrastructure, centralized vs. decentralized control of the DG unit operation, equipment durability considerations, heating preferences of home users, and seasonal effects. There is a substantial increase in natural gas consumption near consumers for all scenarios considered, which has implications for the control of the natural gas grid. We demonstrate the importance of having a centralized decision-making scheme when multiple distributed generation resources are present, and make recommendations for the optimal sizing of generators.