Off-grid Research Articles

Comparative study of off-grid and grid-connected hybrid power system: issues, future prospects and policy framework

A sustainable energy system is of utmost importance for any significant development in any nation.This work identified some obstacles inhibiting rapid renewable energy growth in Nigeria and recommended some policy measures in overcoming them. Moreover, a comparative study of off-grid (OG) and grid-connected (GC) small hydro-solar photovoltaic-diesel hybrid system was carried out using Oyan river, Abeokuta, Nigeria as a case study. The hybrid components were modeled with and without the grid. The hydro solar resources data of the area were collected and analyzed using hybrid optimization model for electric renewable (HOMER) software. The simulation results proved that the GC hybrid power system is better than the OG hybrid power system in technical and economic terms depending on the location. This paper, therefore, proposed the use of OG hybrid power system for electrification of distant villages especially where extending the grid seems infeasible and the use of GC hybrid power system in the urban areas. The work will assist power sector stakeholders in making informed decisions towards the growth of hybrid power system technology in Nigeria.

Business Model Proposal for Energy Transition towards Operational and Economic Sustainability for Rural Electrification: Colombian Case

This study focuses on strategic development for incorporating distributed energy resources into the electrical off-grid power system operator, or isolated microgrids, to guarantee sustainability and energy transition by an adapted business model. A business model canvas was adapted to allow sustainability in an off-grid Colombian microgrid by integrating distributed energy resources with voltage and frequency control as ancillary services; support services that maintain the stability and security of energy supply in isolated rural electrification. The business model canvas was studied with government funds, who cover all the costs associated with making the model attractive and sustainable in a Colombian context, and some proposed technical incentives to analyze the profitability and guarantee the sustainability of rural electrification. The proposed modified business model canvas offers a useful tool for supporting microgrid market scheme development to include distributed energy resources in a Colombian case. The model showed the importance of motivating investors and increasing profitability by including a value proposition based on technical contributions that benefit the microgrid operation; by around 80%. These benefits can solve some stability problems, including ancillary services, like frequency and voltage support, using distributed energy resources. Finally, integrating rural electrification in off-grid zones into the national energy regulation system is vital for incentivizing sustainable projects in rural zones, such as microgrids.

Techno-economic Assessment of Co-gasification of Rice Husk and Plastic Waste as an Off-grid Power Source for Small Scale Rice Milling - an Aspen Plus Model

Inadequate access to electricity has necessitated other alternative energy sources in Nigeria. As a result, small modern rice milling uses mainly energy from diesel-fired generator, while traditional milling still uses energy from the combustion of wood. Consequently, the cost of diesel as fuel has contributed to the high operating cost of the rice mills. Moreover, these sources of energy contribute hugely to CO2 emission. Also, rice husk (RH) generated as waste from the mill is not utilized properly in the country, thereby adding to the environmental issue due to open burning disposal. In addition, a large amount of sachet water plastic waste (SWPW) is also generated in Nigeria. This research therefore presents co-gasification of RH and SWPW in the presence of CaO with integrated combined heat and power (CHP) generation for small scale rice mills in Nigeria using Aspen plus model. Optimum operating conditions in the gasification section were determined as inputs to the CHP section. At 800 °C gasification temperature with feed capacity of 30 kg SWPW/hr and 70 kg RH/hr, the system showed a CHP efficiency of 70%, which is sufficient for the rice mill energy requirement. The economic assessment of the system showed promising economic feasibility with a net present value (NPV) value of $1.47 million over 15 years. While the levelized cost of electricity (LCOE) value of $0.07-0.11/kWh indicates the cost attractiveness of the system as compared to other sources of energy in Nigeria. The system demonstrated an alternative cost and GHG emission savings source of energy. The project will promote the UN’s sustainable development goals of affordable and clean energy.

Стратегии поведения промышленного предприятия на энергетических рынках как инструмент реализации принципа рационального поведения

To ensure the sustainability of their market, energy-intensive industrial companies need to address energy efficiency issues. Companies that are prepared for higher tariffs, structural changes in fuel and energy markets, and shortages of energy resources have a wider range of options for responding to new challenges posed by the external environment and reducing their risks. This challenge becomes especially relevant in the context of the development of closed-loop economy aimed at resource optimization, energy conservation, zero-waste production and business models based on maximum operational efficiency. This research aims to build a comprehensive view of the rational behavior of industrial energy consumers in an effort to maximize the benefits and potential of energy markets to reduce the cost of energy supply, increase the level of electrification of industrial production and use the opportunity of their own energy business, as well as identify the main strategies of manufacturing companies in the energy market and the conditions for their effective implementation. The article describes the basic principles of rational behavior, which serve as a basis for the effective implementation of various strategies (seller’s, buyer’s or combined strategy) for industrial enterprises. The connection between rational behavior and management of the energy market potential in the company, as a combination of technological, economic and organizational actions, performed by the energy consumer in the competitive market, and effective management of market risks is shown. Forms of off-grid power supply and conditions of their application in production were analyzed on the example of mini-CHP. The offered classification of behavior strategies of an enterprise at the power market allows making a rational choice among various variants of behavior corresponding to concrete marketing purposes of the company. The choice can be made by analyzing the technological features of production processes, determining the marketing goals of the company, checking the volume of demand and the structure of demand (supply) for the main products of the company, as well as the amount of energy needed for production. It has been shown that as smallscale generation technologies become more advanced, having an on-site energy source becomes a more attractive option. Along with the penetration of smart technologies into core production practices and the transition to a new energy paradigm, conditions are created for the integrated use of various resource reserves.

Mathematical programming for optimal design of hybrid power systems with uncertainties

The hybrid power system (HPS) is an application variant of distributed generation, defined as a system utilising two or more energy sources, such that the power generation is more efficient, reliable and cost-effective, offering a better option than single-source systems. HPSs can be used in urban, rural and remote areas. HPS research has focused on sizing and optimisation, which requires efficient and effective methodologies to ensure reliable power supply and a cost-effective system. This paper presents a mathematical programming technique for the design of off-grid HPSs, taking into account uncertainties in renewable energy resources. The basic model formulation is based on a comprehensive superstructure that includes all possible connections for power allocation. Chance-constrained programming is applied in determining the optimal capacities of power generation and energy storage with a specified system reliability level. A case study is presented to demonstrate the application of the proposed approach.

A Review of Smart Off-Grid Power Systems Optimization Models for the Oil and Gas Industry

The article discusses current issues of using alternative energy sources for electricity supply of consumers in the oil and gas industry. Examples of off-grid power systems used for the electrification of different facilities of oil and gas production are shown. This paper introduces a review of mathematical optimization models of modes in micro-energy systems with different distributed generation resources. Optimization methods based on mathematical programming in game theory are studied in details. It is concluded that the use of adaptive-game modelling is perspective in solving optimization problems.

Off-grid rural electrification using integrated renewable energy sources

Presented in this study is an economic and technical evaluation to determine the optimal system combination for off-grid power generation based on solar, wind and biodiesel renewable energy resource. Nsukka being endowed with high intensity solar radiation, adequate wind speed and sufficient bioresource is a prospective candidate for a hybrid system. The monthly average daily global radiation ranges from 3.91kWh/m2 to 5.74kWh/m2 and the average wind speed is about 2.64m/s. This system was designed to meet the load requirement of the school with annual electrical demand of 10,163 MWh. Sensitivity analysis was carried out based on the effect of change in biodiesel fuel price and interest rates on the economic performance criteria of the optimal configuration. The optimum hybrid system is composed of 1kW capacity PV system, auto sized biodiesel generator and battery bank of 820h of autonomy. The Levelized Cost of Energy from the optimal system was found to be $0.0898/kWh based on sensitivity results. These results obtained shows that an integrated system with combination of PV, biodiesel generator and battery bank is a cost-effective alternative to grid extension which cost $0.126/kWh. The system life span is for 25years and it is sustainable, economical, technically feasible and environmentally friendly.

Grid Island Energy Transition Scenarios Assessment Through Network Reliability and Power Flow Analysis

This paper presents a methodology for the reliability and power flow analysis of islands or off-grid power networks for situations of scarce data and information. It offers a new and pragmatic approach to derive the required power network information, including the power cable parameters and the load at each power node. The paper aims to present the developed methodology, and to illustrate its application, using Ushant Island as a case study. The assessment of the current power network status and the reliability analysis are presented. Grid performance parameters are further compared for conventional diesel generator operation and renewable energy generation scenarios, demonstrating the advantages of replacing the existing diesel units with renewable energy sources in terms of system reliability. The analysis shows that by introducing renewable energy systems to the island’s grid, the reliability of the grid increases by up to 50% and cable capacity usage reduces by up to 30%. Furthermore, this work suggests that it would not be necessary to modify the grid cables when substituting the diesel generator. The paper will be of interest to network planners, community stakeholders, project developers and decision-makers concerned with renewable energy investment on islands and in remote rural areas.

Demand response integrated day-ahead energy management strategy for remote off-grid hybrid renewable energy systems

With the anticipated future price reductions in renewable technologies, hybrid renewable energy systems have emerged as a feasible retrofit to the primarily diesel-based remote off-grid power systems. However, in the presence of many supply/storage systems along with high penetration of intermittent renewable energy, energy management becomes a decisive step to achieve a stable and reliable power system operation. The intended benefits can be further maximized when the energy management framework is unified with demand response strategies. This paper presents a novel demand response integrated day-ahead energy management framework subjecting remote off-grid power systems. Several measures are taken to enhance the consumer acceptance and practical implementation of the demand response platform. Responsiveness of the customers to price-based incentives is estimated using a probabilistic fuzzy inference system to accurately model the stochastic human nature. Results are demonstrated for an isolated remote community in Northern Canada for both summer and winter seasons. The results confirm the applicability of the proposed method in achieving the intended objectives of day-ahead energy management.

The off-grid catch-22: Effective institutions as a prerequisite for the global deployment of distributed renewable power

Off-grid electric systems powered by renewable sources are appealing because they could reduce energy poverty in a sustainable manner. Yet their deployment has been uneven across the world. In this article, I argue that the deployment of such technology pre-requires effective institutions. This is because the off-grid power industry faces two problems: governments (who may reverse policies on short notice) and customers (who may fail to pay their bills). More democratic regimes, which tend to uphold the rule of law, can mitigate these risks and facilitate long-term investments. Empirically, I show that countries that are democratic deployed considerably more off-grid renewable energy capacity. An increase in the democratic score by one standard deviation leads to an increase in deployed capacity by 40% (95% CI: [20%, 63%]). Further, I show that this effect operates through supply-side institutions, such as the protection of the rule of law. I find little evidence for a competing interpretation of my main results based on the demand side: democracies do not provide more off-grid power in countries with stronger demand for it. These results suggest that institutions are a prerequisite for a successful growth of the off-grid renewable energy industry and raise concerns over the ability of its technologies to penetrate the most destitute regions.

Photovoltaic Off-Grid Inverter and Maximum Power Point Tracking Technology

The photovoltaic cells’ output characteristics and maximum power point tracking (MPPT) technology are studied to design a two-stage cascaded photovoltaic off-grid inverter, including the front-end Boost converter and the rear-end three-phase inverter. The state-space averaging method is adopted in front-end Boost converter modeling, and space vector pulse width modulation (SVPWM) technology is adopted in the rear-end three-phase inverter. The simulation drive model is obtained through research principles and algorithm realization. Based on the theoretical analysis and simulation, front-end Boost converter’s and the back-end inverter’s hardware are designed. The main circuit includes the front-end Direct Current (DC)-DC topology and the back-end DC-AC topology. The TMS320F28027 digital signal processor is the core of the front-end DC-DC topology’s control system, and LabView is the core of the back-end DC-AC topology’s control system. The front-end Boost converter’s analog output voltage is 32 V, stable at the maximum operating point in the test. The maximum power point can be effectively tracked in the proposed inverter. The rear-end three-phase inverter’s total harmonic distortion (THD) of phase voltage is less than 3%. Less harmonic wave meets the circuit harmonic distortion rate’s design requirements.

Shrouded wind turbine for low wind speed

The problem of electrification in Indonesia for remote areas is difficult to access and far away from the grid of PLN, so an alternative is needed to overcome this problem. One alternative to this problem is to build off-grid power plants by utilizing natural potential in an area such as wind energy, but not all regions have sufficient wind speed to use wind turbines, so the wind turbine must operate at low wind speeds with good efficiency. Shrouded can be used to increase the efficiency of conventional wind turbines, even at low wind speeds. In this study, the shrouded wind turbine can increase power output by up to 92.71%, with an average of 62.91% compared to conventional wind turbines under wind speed conditions of 2 m s−1 - 6 m s−1.

Performance analysis of thermoelectric system based on radiative cooling and greenhouse effects

Electricity power has served as an essential source in our daily life. However, some remote areas that are difficult to be covered by the power grid, are still facing a serious shortage of electricity for outdoor equipment such as field monitors. Off-grid power is the alternative power in such areas, but there arise apparently economic and environmental problems. Therefore, the development of portable, pollution-free and sustainable power supply equipment has vital research significance. In this paper, based on the radiative cooling and greenhouse effects, a passive thermoelectric system without any active energy input is proposed. A square copper plate coated with a thin film of acrylic acid doped with SiO<sub>2</sub> particles, with an average emissivity value of 0.937, is selected as a radiative cooling material. The commercial polyolefin film with a thickness of 0.12 mm is selected as a greenhouse material. The radiative cooling effect cools the cold end of the thermoelectric generator (TEG) during the nighttime, the greenhouse effect during the daytime is utilized to increase the temperature of the hot end of the TEG. The radiative cooling effect and the greenhouse effect both result in the increase of the temperature difference between the cold and hot ends, and thus obtaining the output power. During the period of time from June 17 to June 21, 2020, the performance of the designed system at the location of Shaanxi, China was evaluated experimentally, and the weather condition effects were also studied. The experimental results show that a stable temperature drop of ～1.1 ℃ of the cold end is achieved via the radiative cooling effect at night. Owing to the greenhouse effect, the temperature increase of the hot end reaches a maximum value of 13.9 ℃. When the average ambient humidity decreases from 45% to 20%, the average temperature difference between the hot end and cold end of the thermoelectric module increased from 1.6 to 1.9 ℃ throughout the day, and the average power increased from 47.8 to 67.3 mW/m<sup>2</sup>, indicating that the equipment can have better power generation performance under the condition of 20% ambient humidity. The device developed in this work realizes all-day passive output and shows that it has potential applications in off-grid power supplies.

Wind-Solar Hybrid Power System Configuration Planning Using a Bi-Objective Optimization Model

This paper presents a decision model of planning the optimal configuration of hybrid wind/solar off-grid power systems. The proposed decision model is utilized to evaluate the effectiveness of reducing the hourly power supply variability through integrating the wind and solar power generation. In addition, the tradeoff between the cost minimization and power supply variability reduction is analyzed. The decision variables are composed of the number of installed wind turbines and solar panels. A multi-objective particle swarm optimization algorithm is applied to solve the proposed model. The computational results provide the optimal configurations of the hybrid wind/solar power systems due to various preferences of cost and power supply variability to meet the load requirements.

Dependability Impact in the Smart Solar Power Systems: An Analysis of Smart Buildings

The Internet has been going through significant transformations and changing the world around us. We can also see the Internet to be used in many areas, for innumerable purposes, and, currently, it is even used by objects. This evolution leads to the Internet of Things (IoT) paradigm. This new concept can be defined as a system composed of storage resources, sensor devices, controllers, applications, and network infrastructure, in order to provide specific services to its users. Since IoT comprises heterogeneous components, the creation of these systems, the communication, and maintenance of their components became a complex task. In this paper, we present a dependability model to evaluate an IoT system. Amid different systems, we chose to assess availability in a smart building. The proposed models allow us to calculate estimations of other measures besides steady-state availability, such as reliability. Thus, it was possible to notice that there was no considerable gain of availability in the system when applying grid-tie solar power or off-grid solar power. The grid-tie solar power system is cheaper than the off-grid solar power system, even though it produces more energy. However, in our research, we were able to observe that the off-grid solar power system recovers the applied financial investment in smaller interval of time.

Off-grid PV/URFC power plant fueled with biogas from food waste: An energetic and economic analysis

This paper presents the design, energy management and economic analysis of an off-grid power plant for a strip mall. The main goal is to achieve a 100% renewable operation, by using a photovoltaic panel array coupled to a battery and a unitized regenerative solid oxide fuel cell fed both with self-generated hydrogen and biogas produced from food waste in an on-site anaerobic digester. The power plant has been modeled by means of a self-made Matlab/Simulink® simulator and the plant operation has been simulated against different radiation and load demand scenarios. Results are compared both in terms of energetic and economic performance. In particular, it is observed that the annualized capital costs for unitized regenerative solid oxide fuel cell cover from 50% up to 58% of the total investment cost and from 71% up to 75% of the total replacement costs. Depending on the scenario and the specific tipping fee, tipping costs vary from a minimum of 9,793 $/y to a maximum 47,335 $/y. For all the analyzed scenarios, the cost of energy is higher than the grid electricity price, but the 100% renewable operation of the plant and the on-site waste conversion to biogas make this solution worth of investigation.

The parameters of the off-grid power system with a biomass gasifier engine for the autonomous power supply of forest harvesters

The paper analyses the results of the simulation modelling of autonomous power supply system of forest electric drive harvesters. MATLAB with the use of dynamic modelling Simulink tools was employed for the simulation modelling. The modelled system incorporates gasifier for solid fuelwood, a heat engine, an electric generator, a battery, and electric drive engines for the mechanisms of a mobile wood chipper. The authors determined that the minimum 12 A h Battery is required to ensure the uninterrupted operation of an off-grid power system with a gasifier, a 300 kW heat engine and a 200 kW engine wood chipper. The model allows for measuring the system performance indicators in various operating modes. The specific consumption of fuelwood was 2.217 kg/kW h in the specified mode.

Optimization of a PV-Wind Hybrid Power Supply Structure with Electrochemical Storage Intended for Supplying a Load with Known Characteristics

An important aspect of the off-grid utilization of hybrid generation systems is the integration of energy storage facilities into their structures, which allows for improved power supply reliability. However, this results in a significant increase in the cost of such systems. Therefore, it is justified to use optimization resulting in the minimization of the selected economic indicator taking into account the most important technical constraints. For this reason, this work proposes an algorithm to optimize the structure of a hybrid off-grid power distribution system (with electrochemical energy storage), designed to supply a load with known daily energy demand. The authors recommend genetic algorithm utilization as well as a modified criterion for evaluating the quality of solutions based on the Levelized Cost of Energy (LCOE) index. Several technical and economic analyses were presented, including unit costs, power distribution of the wind and solar sections, nominal battery capacity, SSSI index (System Self-Sufficiency Index), etc. The model of the system includes durability of the elements which have a significant impact on the periodic battery replacement. The tests were carried out for two types of loads and two types of electrochemical batteries (NMC—Lithium Nickel Manganese Cobalt Oxide; and PbO2—Lead-Acid Battery), taking into account the forecast of an increased lifetime of NMC type batteries and decreasing their price within five years. The proposed synthesis method of photovoltaic-wind (PV-wind) hybrid off-line systems leads to limiting the energy capacity of electrochemical storages. Based on the analyses, the authors proposed recommended methods to improve (reduce) the value of the criterion index (LCOE) for PV-wind off-grid systems while maintaining the assumed level of power supply reliability.

Powering Multiple Gas Condensate Wells in Russia’s Arctic: Power Supply Systems Based on Renewable Energy Sources

Using renewable energy off-grid power supply and choosing the right equipment that meets the operating conditions in the Arctic can provide companies with reliable power sources for producing gas at facilities located in remote areas and will reduce capital and operating costs associated with the construction of power transmission lines. For more than 15 years, a remote control system powered by renewable energy has been used in parallel with power transmission lines by Gazprom to operate its multiwell pads in Russia’s Far North, which validates the relevance of this study. The subject of the study is a group of gas condensate wells that consists of four multiwell pads operated by Wintershall Russland GmbH. The article discusses a stand-alone renewable-based power system as an option for powering remote oil and gas production facilities. The procedures used in the study include calculating such parameters as power output and power consumption, choosing equipment, describing the design features of a power supply system for a multiwell pad, conducting an economic assessment of the project, comparing different power supply options, analyzing project risks, and developing measures to mitigate these risks.

Economic analysis and optimization of a renewable energy based power supply system with different energy storages for a remote island

This study investigates and compares the various combinations of renewable energies (solar, wind) and storage technologies (battery, pumped hydro storage, hybrid storage) for an off-grid power supply system. Four configurations (i.e., single RE source system, double RE source system, single storage, and double storage system) based on two scenarios (self-discharge equal to 0% and 1%) are considered, and their operational performance is compared and analyzed. The energy management strategy created for the hybrid pumped battery storage (HPBS) considers that batteries cover low energy surplus/shortages while pumped hydro storage (PHS) is the primary energy storage device for serving high-energy generations/deficits. The developed mathematical model is optimized using Particle Swarm Optimization and the performance and results of the optimizer are discussed in particular detail. The results evidence that self-discharge has a significant impact on the cost of energy (13%–50%) for all configurations due to the substantial increase in renewable energy (RE) generators size compared to the energy storage capacity. Even though solar-wind-PHS is the cost-optimal arrangement, it exhibits lower reliability when compared to solar-wind-HPBS. The study reveals the significance of HPBS in the off-grid RE environment, allowing more flexible energy management, enabling to guarantee a 100% power supply with minimum cost and reducing energy curtailment. Additionally, this study presents and discuss the results of a sensitivity analysis conducted by varying load demand and energy balance of all considered configurations is performed, which reveals the effectiveness of the supplementary functionality of both storages in hybrid mode. Overall, the role of energy storage in hybrid mode improved, and the total energy covered by hybrid storage increased (48%), which reduced the direct dependency on variable RE generation.