Stand-alone Power System Research Articles

Sustainable Cooling with Hybrid Concentrated Photovoltaic Thermal (CPVT) System and Hydrogen Energy Storage

Standalone power systems have vital importance as energy source for remote area. On the other hand, a significant portion of such power production is used for cooling purposes. In this scenario, renewable energy sources provide sustainable solution, especially solar energy due to its global availability. Concentrated photovoltaic (CPV) system provides highest efficiency photovoltaic technology, which can operate at x1000 concentration ratio. However, such high concentration ratio requires heat dissipation from the cell area to maintain optimum temperature. This paper discusses the size optimization algorithm of sustainable cooling system using CPVT. Based upon the CPV which is operating at x1000 concentration with back plate liquid cooling, the CPVT system size is optimized to drive a hybrid mechanical vapor compression (MVC) chiller and adsorption chiller, by utilizing both electricity and heat obtained from the solar system. The electrolysis based hydrogen is used as primary energy storage system along with the hot water storage tanks. The micro genetic algorithm (micro-GA) based optimization algorithm is developed to find the optimum size of each component of CPVT-Cooling system with uninterrupted power supply and minimum cost, according to the developed operational strategy. The hybrid system is operated with solar energy system efficiency of 71%.

Sizing a stand-alone off-grid wind turbine-battery power system for a remote house in Catalca Istanbul Turkey

Abstract- For remote houses with no connection to the grid, if the site is suitable for wind energy, an off-grid wind turbine-battery power system is a good alternative for supplying the energy need of the house. If the reliability of the power supply is crucial then sizing of the components, wind turbine and the battery bank, is very important. In the market there are many wind turbines with different ratings and power curves. For an off-grid turbine-battery power system, for every different chosen wind turbine the minimum required number of batteries in the battery bank would be different for reliable and continuous power supply to the house. It is the usual case in practice that either the battery bank is chosen as undersized such that the consumer suffers from no power from time to time or the battery bank is chosen as oversized without any calculation and this results in high initial costs for the consumer. In this study, for a remote house in Catalca Turkey, a stand-alone wind turbine-battery system will be sized using wind data of the site and consumption data of the house. Our results show that the minimum number of batteries needed in the battery bank for an uninterrupted electrical energy supply changes very much according to the chosen wind turbine and the minimum required number of batteries depends on the power curve of the chosen wind turbine rather than the rated power of the wind turbine.

Optimisation of Hybrid Energy System Production Parameters for Electricity Power Generation in Nigeria

Solar and wind energy are two of the most viable and sustainable sources of energy due to the tendency of renewal. The power generating supplies in Nigeria appear unreliable, rapidly diminishing and expensive. Researches are sparse on operating both energy sources alongside fossil fuel for power generation in order to take advantage of their complementary characters. The aim of this study is to explore renewable sources combined with non-renewable source to generate electricity with the objective of establishing an optimal design for a hybrid solar-wind-diesel energy plant that minimizes cost. The capacity factor of the standalone system was determined for the study area. The cost of energy for the hybrid optimal mix was determined. Levelised cost of energy was also used to determine the cost of energy for standalone power system. The result shows that the energy generated 200 MW hybrid system is 392 GWh with a cost of energy of $0.24/kWh (47.8/kWh). The energy produced can power 39,200 homes in a year. The optimisation shows that the number of solar system, wind and diesel are 699, 1 and 300 respectively. The cost of energy for the standalone system was $0.06/kWh, $0.08/kWh and $0.27/kWh for wind, solar and diesel system. The capacity factor was 56%, 21% and 80% for wind, solar and diesel system. There is a reduction in the amount of greenhouse gases released to the environment alongside with cost of energy generation. Hybrid power generation system is good and effective solution for power generation than conventional energy resources.

Design and Optimization of Standalone Photovoltaic Power System for Ethiopian Rural School Electrification

Power is one of the basic need of the Ethiopian society and organization for cooking, lighting and to run different office or other place electrical devices like TV, radio, computer, fans etc. In Ethiopia grid electrical power supply is still not supplied to rural communities or organization due to the geographical topography difficulty as well as the shortage of grid power and Ethiopia has enough potential of solar energy resource. This paper presents a renewable standalone photo voltaic power system to electrify the selected rural school which are far from grid power supply for ceiling fan, office phone, lighting, computer, printer, radio and TV consumption. Therefore, this study focused on the design and optimization of the power system components by using homer software. The solar resource of the for the school site is collected. The electrical energy demand of the selected school, number of PV modules, payback period and other corresponding components as well as the initial cost estimation of the power system components and optimization of the standalone power system is done by homer software. There are 42 solar photo voltaic modules needed for the estimation energy demand of school with the energy cost of the power generated 0.13$/kwh and cash inflow 3431.1$/year for the payback period of 6.5 years.

Assisted power management of a stand-alone renewable multi-source system

The work presented in this paper deals with an assisted management of a standalone multi-source power system. The proposed structure consists of a wind turbine (WT) and a photovoltaic generator (PV) used as renewable sources, a super-capacitor (SC) as an energy storage system and a diesel generator (DG) as an emergency power supply. The aim of this work was to develop an assisted management strategy in order to control the power flow in the system operation with the highest reliability. Four limits of the SC state of charge (SOC) were defined states for the power control strategy. The main advantage of the used strategy was to protect the storage system from the deep charge and discharge and then increase its lifespan. The proposed energy management concept was tested in simulation by applying all possible cases. The obtained results confirm its efficiency and harmony between production and consumption was guaranteed.

Techno-economic role of PV tracking technology in a hybrid PV-hydroelectric standalone power system

The main aim of this study is to evaluate the techno-economic role of the PV tracking technology in a hybrid photovoltaic-pump storage hydroelectric (PV-PSH) standalone power system. In this regard, a multi-objective optimization procedure is developed for the optimal design of a PV-PSH system and the developed procedure is separately implemented for the different types of PV tracking technologies such as horizontal and fixed-tilt panels (without any sun tracker), East-West oriented single-axis tracking, fixed-tilt azimuth tracking and dual-axis tracking systems. A coastal area in the south of Iran is considered as the case study; investment cost and loss of power supply probability (LPSP) are considered as the objective functions. Moreover, number of PV modules, turbine capacity, pipes diameters, and the volume, installation height and depth to diameter ratio of reservoir constitute the set of design variables and NSGAII is employed as the optimization algorithm. The results show that for the present case study, the fixed-tilt azimuth tracking technology leads to the minimum system cost with a suitable certainty under different LPSP values. Moreover, it results in the greatest match between the demanded and supplied power profiles. The results also illustrate that the appropriate selection of sun tracking technology in a hybrid PV-PSH system can lead to a savings of up to 18.2%. Finally, the economic superiority of the PV-PSH system over the common PV-battery system is investigated and proved for the case study.

Sustainable mini-grid

Paper summarized the research done in min-grid field. Mini-grid is small, stand-alone power system, which role is to provide constant and affordable electricity in remote places, where the connection with main grid is unprofitable. Mini-grids are important tools in fight with power-poverty in developing countries. The economics of power technologies is widely analyzed in different studies. The paper presents the advantages of application of integrated sustainable assessment for analyzing different power technologies for mini-grids. The paper highlight the importance of environmental and social aspects and its influence on local community.

Modeling, size optimization and sensitivity analysis of a remote hybrid renewable energy system

Hybrid energy system based on solar and wind power coupled with energy storage unit provides a reliable and cost effective energy alternative above the commonly used diesel based standalone power system. Various methodologies are adopted for modeling hybrid energy system component. They are modeled either by deterministic or probabilistic methods. The current study considers the hardware failure of photovoltaic panels while modeling. A probability distribution (PD) represents the various capacity states due to hardware failure of photovoltaic panels and corresponding probabilities. A concept based on random number generation is adopted to calculate the actual hourly available photovoltaic power. Wind turbine power output modeling incorporate force outage rate of the turbine. A new meta-heuristic algorithm called Cuckoo Search is applied for solving the hybrid energy system optimization problem. Photovoltaic-Battery, Wind-Battery and Photovoltaic-Wind-Battery system applicable to a remote area located in Almora district of Uttarakhand, India are considered. The effectiveness of Cuckoo Search in solving hybrid system design problem is investigated and its performance is compared with other well known optimization algorithms like Genetic Algorithm and Particle Swarm Optimization algorithm. Furthermore, this paper investigates the sensitivity of various input parameters like solar, wind resources and capital cost on the cost of energy.

Grid-tied and stand-alone hybrid solar power system for desalination plant

This paper presents results on simulation, optimization and control of hybrid solar based energy system to power a desalination plant. The principal objective is to design a clean energy system to meet the desired electric load of the desalination plant with high renewable fraction, low cost of energy, and low carbon dioxide gas emissions. Hourly simulations and optimization were performed to determine the performance and life cycle cost of the different hybrid power configurations. The results of the baseline or the actual power system from the grid are compared with two new renewable power systems: (1) grid tied solar system: solar PV/grid/inverter power system, and (2) Off grid solar power system: PV/diesel generator/battery/inverter power system. The results show that the solar PV/grid/inverter power system offers the best performance compared to PV/diesel generator/battery/inverter. The total energy from the hybrid grid tied solar system is used to meet the AC load of the desalination plant with almost no excess electricity and power shortage. The proposed hybrid power system for the desalination plant is sustainable, economically viable and environmentally friendly: high renewable fraction (47.3%), low excess power (0.15%), low levelized cost of energy (90$/MWh), and low CO2 gas emissions (264.25kgCO2/MWh).

Optimisation of stand-alone hybrid CHP systems meeting electric and heating loads

Most research published into stand-alone energy systems, hybridised by supplementing PV with combustion-based prime movers, considers meeting an electric load demand. This paper goes further by studying the role of both electric and heating loads on the optimisation of hybridised stand-alone Combined Heating and Power (CHP) systems. The role of both the load following strategy in these systems (electric only FEL, versus electric and thermal FEL/FTL) as well as the relative magnitude of the heating load is analysed on system cost and performance. The conceptual CHP systems modelled also consider waste system derived from either multiple Internal Combustion Engines (ICEs) or Micro Gas Turbines (MGTs). The research uses MATLAB-based Genetic Algorithm (GA) optimisation throughout and features detailed hardware characteristics as well as temporally fluctuating meteorological (solar irradiance, temperature) and load (electric, heating) data. The outcomes are also tested in relation to CHP systems sized whilst optimising either single (Cost of Energy-COE, $/kW h) or multiple functions (COE and overall system efficiency, ηCHP,%).Results indicate that whilst the power management strategy used in CHP systems (FEL or FEL/FTL) has minimal effects on the COE, it can appreciably affect other performance indicators. For example, in CHP systems sized based on FEL/FTL, whilst COE = ∼0.20 $/kW h the resulting ηCHP is 66% for PV/Bat/ICE and 44% for PV/Bat/MGT. This is compared to using a PMS of the FEL type which results in similar COE = ∼0.21 $/kW h but with ηCHP = 50% in PV/Bat/ICE systems and 34% in PV/Bat/MGT. In relation to overall environmental impact expressed though Life Cycle Emission-LCE (kg CO2-eq/yr) when heating demand is around 50% of the electric (Electric to Thermal Load Ratio = 60:40), a PMS of the FEL/FTL results in up to 30% lower LCE compared to those with FEL in some CHP systems.

A Blended SPS-ESPS Control DAB-IBDC Converter for a Standalone Solar Power System

In sustainable energy applications, standalone solar power systems are mostly preferred for self-powered energy zones. In all standalone renewable power systems, batteries are still preferred as the common energy storage device. On the other hand, batteries are not applicable for high peak power demand applications because of their low power density. A supercapacitor is a preferable high-power density energy storage device for high peak power applications. A 2 kW, 50 kHz digital control dual active bridge isolated bi-directional dc-dc converter (DAB-IBDC) was developed for interfacing the supercapacitor bank in standalone solar power system. This paper proposes a blended SPS-ESPS digital control algorithm for a DAB-IBDC converter instead of using a traditional single-phase shift (SPS) control algorithm, which is commonly used for large input to output voltage varying applications. This proposed blended SPS-ESPS control algorithm achieved high power conversion efficiency during a large input to output voltage variation, over a traditional phase shift control algorithm by reducing the back-power flow and current stress in a circuit. This system also achieved maximum power point for solar modules and enhanced rapid charging-discharging for a supercapacitor bank. Both SPS and the blended SPS-ESPS control algorithms were verified experimentally using 2 kW DAB-IBDC topology implemented with standalone power system that combination of 2000 W input solar module and 158 Wh supercapacitor bank.

Capacity Fade Analysis and Direct, Efficient, and Real-Time Simulation of Physics-Based Battery Models for Stand-Alone PV-Battery Microgrids

Accurate and economical sizing of stand-alone power system components, including batteries, has been an active area of microgrid research, but current control methods do not make them economically feasible.1 Typically, batteries are treated as a black box that does not account for their internal states in current microgrid simulation and control algorithms.2 This might lead to under-utilization and over-stacking of batteries. In contrast, detailed physics-based battery models, accounting for internal states, can save a significant amount of energy and cost, utilizing batteries with maximized life and usability. We have previously shown the implementation of the optimization and benefits of using the MPPT controller algorithm and physics-based battery model along with other microgrid components.3 In this talk, we will discuss some simple examples for microgrids as well as consider the model of battery as a pack, i.e. a set of cells in series and parallel with slight inherent variation in SoC and SoH. The results of the proposed approach are compared with the conventional control strategies and improvements in performance and speed are reported. Acknowledgements This work was supported by the Clean Energy Institute located in University of Washington, Seattle and Washington Research Foundation. The battery modeling work has been supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U. S. Department of Energy through the Advanced Battery Material Research (BMR) Program (Battery500 Consortium).

Experimental characterization and comparison of performance parameters of S-rotors for standalone wind power system

An open wind flow test of seven Savonius models was conducted to explore the influence of design parameters on the performance and starting characteristics. The seven rotors are coded as Model 1 to Model 7, with various blade designs, number of blades, and number of stages. Results demonstrated that Model 1, a modified two-blade single-stage conventional S-rotor, has the highest power coefficient of 0.26. Model 1 also exhibited an improved maximum power coefficient of about 47% than the previously reported in the literature due to increasing of the aspect ratio from 0.77 to 2.0. The power coefficient of double-stage Savonius-rotors was found to be lower by about 11%–20% than the identical design single-stage S-rotors. The static torque assessment exhibited that double-stage rotors and rotor with more than three blades do not have any negative torque angle position. Nonetheless, the single-stage Savonius-rotor, even with three blades, has few negative torque angles. The study suggests that Model 2, modified double-stage rotor and Model 5, conventional double stage rotor with overlap ratio of 0.2, are most suitable rotors for stand-alone wind power systems, where they have not shown any negative torque angle, in spite that the power coefficient can be sacrificed for the sake of improved starting ability.

A design methodology of stand-alone photovoltaic power systems for rural electrification

A promising way to electrify regions lacked to reliable access to electricity is the employment of stand-alone photovoltaic power systems (SPPSs). Recently, the cost of electricity from such systems has fallen, and it is expected that this tendency will continue in the future. Within this paper, a new design methodology of highly reliable and sustainable SPPSs is presented. The approach consists of the following processes: prediction of the load demand, characterization of the PV performance on site, sizing the SPPS considering different storage technologies, and forming the most effective design. On the other hand, a new dimensionless number will be introduced to characterize the PV performance at a particular location. In order to demonstrate the methodology, an intention to electrify 93 households in a rural community is given as an example. The results show that a SPPS configuration including compressed air energy storage and supercapacitor may be the most effective SPPS design.

Smooth Operation Transition Scheme for Stand-Alone Power System With EG and BESS-PV Panels

This letter proposes a new scheme of smooth operation transition for the stand-alone power system which is composed of engine generator and battery energy storage system (BESS) with photo voltaic panels. The proposed scheme offers smooth operation transition of BESS controller from the current control to the voltage control and vice versa. The feasibility of proposed scheme was verified through experiments with a scaled prototype.

Microcontroller based bidirectional buck–boost converter for photo-voltaic power plant

A common configuration for a stand-alone PV power system may consist of three converters: a buck converter for the PV panel to charge the battery, a boost converter for the battery to discharge to the load and one for the load voltage regulation. Such a system requires a coordinated control scheme for three converters which can be complicated. A simple structure for a stand-alone PV plant consists of a PV array, a battery unit, and its associated bidirectional converter which is a combination of a buck and boost converter. When controlled properly the system can provide uninterrupted power to the load, despite the intermittent availability of sunlight. In this paper complete design of the converter is carried out and the simulation has been performed using Psim. From the simulation, the graphs are presented to show the converter working in buck mode and boost mode. Controller is designed to take care of mode transition, buck to boost and boost to buck mode automatically based on source voltage. Hardware implementation has been done using microcontroller (8051).

Design and Control of Stand-alone Combined Heat and Power Systems Using CO 2 /CH 4

Abstract The power plants use methane instead of coal to deal with the issue of global warming, but it will produce some problem about the concentration of carbon dioxide in flue gas that is too low to capture. In order to increase the concentration of carbon dioxide and ensure the more clear power from methane, this research develops a stand-alone combined head and power (CHP) system which combines SOFC/GT by consuming carbon dioxide and methane simultaneously. The simulation shows that a stand-alone combined and power system performs the electric efficiency up to 47.3% and enhances the concentration of carbon dioxide up to 4.7 times of conventional gas power plant. Finally, the dynamic operation including set point tracking control is successfully addressed.

Proposal and assessment of a new CCHP system integrating gas turbine and heat-driven cooling/power cogeneration

This paper proposes a new combined cooling, heating and power (CCHP) system and presents a comprehensive thermodynamic analysis. This system consists of a gas turbine, a heat-driven cooling and power cogeneration subsystem and a hot-water heat exchanger. Natural gas is burnt in the gas turbine to generate power and the surplus heat contained in the flue gas is recovered and utilized in a cascade way. The high-temperature surplus heat of the gas turbine is firstly recovered by the heat-driven cogeneration subsystem and converted into power through an ammonia-water turbine. Then the exhaust vapor of the ammonia-water turbine drives a single-double LiBr-H2O absorption refrigerator to generate cooling energy. At last the low-temperature surplus heat of the gas turbine is used to generate hot water. Since the efficient utilization of surplus energy, the proposed CCHP system can consume 31.7% less natural gas compared with the stand-alone power, cooling and heating generation systems. Furthermore, part or full power generated by the ammonia-water turbine can also be converted to cooling energy through a compression chiller. In this manner, the proposed CCHP system can adjust the output ratio of cooling and power in a large range from 1.28 to 3.32 to flexibly meet the customers’ variable requirements. The results of economic analyses show that the proposed system has well benefit in practice. This work might provide a new approach to enhance the thermodynamic performance of CCHP systems.

Analysis and optimization of hybrid excitation permanent magnet synchronous generator for stand-alone power system

In this paper, electromagnetic design and permanent magnet shape optimization for permanent magnet synchronous generator with hybrid excitation are investigated. Based on generator structure and principle, design outline is presented for obtaining high efficiency and low voltage fluctuation. In order to realize rapid design, equivalent magnetic circuits for permanent magnet and iron poles are developed. At the same time, finite element analysis is employed. Furthermore, by means of design of experiment (DOE) method, permanent magnet is optimized to reduce voltage waveform distortion. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

Direct and Efficient Simulation of Battery Models for Standalone PV-Battery Microgrids

With renewable energy based electrical systems becoming more prevalent in homes across the globe, microgrids are becoming widespread and could pave the way for future energy distribution. Accurate and economical sizing of a standalone power system components has been an active area of research, but current control methods do not make them economically feasible. Typically, batteries are treated as a black box that does not account for their internal states in current microgrid simulation and control algorithms.1 This might lead to under-utilization and over-stacking of batteries. In contrast, detailed physics-based battery models, accounting for internal states, can save a significant amount of energy and cost, utilizing batteries with maximized life and usability.2 However, typical microgrid controls including feedback algorithms cause a significant time-delay as detailed physics-based battery models are coupled to the entire microgrid system.3 It is important to identify how efficient physics-based models of batteries can be included and addressed in current grid control strategies. In this talk, we will show that perhaps the best way to integrate detailed battery models is to write the microgrid equations in mathematical form and then identify an efficient way to solve those models simultaneously with battery models, which gives better results. Implementation of the maximum power point tracking controller algorithm and physics-based battery model along with microgrid components as differential algebraic equations will be discussed. The results of the proposed approach will be compared with the conventional control strategies and improvements in performance and speed will be reported. Acknowledgements This work was supported by the Clean Energy Institute located in University of Washington, Seattle and Washington Research Foundation.