Renewable Power System Research Articles

Hybrid off-grid renewable power system for sustainable rural electrification in Benin

Providing power to rural communities, which are far from the grid and suffer from lack of energy access in Africa, especially in Benin, in a sustainable manner requires the adoption of appropriate technology. This paper aims at analysing the techno-economic feasibility of hybrid renewable energy system (HRES) for sustainable rural electrification in Benin, using a case study of Fouay village. HOMER software is used to perform optimization, simulation and sensitivity analysis. The analysis showed that hybrid solar photovoltaics (PV)/diesel generator (DG)/battery (of 150 kW/62.5 kVA/637 kWh) is the least cost optimal system. This system ensures a reliable power supply, reduces battery requirements by 70% compared to PV/battery system and achieves 97% CO2 emissions reduction compared to a conventional DG. Moreover, the study demonstrated that the most economical HRES depends strongly on the potential energy sources available at a location and power plant's remoteness from the beneficiary. In summary, as solar radiation is an abundant resource across the country, this hybrid PV/DG/battery system can be a suitable model to power remote areas in Benin, and we recommend it for future electrification projects in the country in place of the current widely deployed PV/battery system.

Flexible, reliable, and renewable power system resource expansion planning considering energy storage systems and demand response programs

This study presents a flexible, reliable, and renewable power system resource planning approach to coordinate generation, transmission, and energy storage (ES) expansion planning in the presence of demand response (DR). The flexibility and reliability of the optimal resource expansion planning are ensured by means of appropriate constraints incorporated into the proposed planning tool where thermal generation units, ES systems, and DR programs are considered as flexibility resources. The proposed planning tool is a mixed-integer non-linear programming (MINLP) problem due to the non-linear and non-convex constraints of AC power flow equations. Accordingly, to linearise the proposed MINLP problem, the AC nodal power balance constraints are linearised by means of the first-order expansion of Taylor's series and the line flow equations are linearised by means of a polygon. Additionally, the stochastic programming is used to characterise the uncertainty of loads, a maximum available power of wind farms, forecasted energy price, and availability/unavailability of generation units and transmission lines by means of a sufficient number of scenarios. The proposed planning tool is implemented on the IEEE 6-bus and the IEEE 30-bus test systems under different conditions. Case studies illustrate the effectiveness of the proposed approach based on both flexibility and reliability criteria.

Optimization of the Fuel Cell Renewable Hybrid Power System Using the Control Mode of the Required Load Power on the DC Bus

In this paper, a systematic analysis of seven control topologies is performed, based on three possible control variables of the power generated by the Fuel Cell (FC) system: the reference input of the controller for the FC boost converter, and the two reference inputs used by the air regulator and the fuel regulator. The FC system will generate power based on the Required-Power-Following (RPF) control mode in order to ensure the load demand, operating as the main energy source in an FC hybrid power system. The FC system will operate as a backup energy source in an FC renewable Hybrid Power System (by ensuring the lack of power on the DC bus, which is given by the load power minus the renewable power). Thus, power requested from the batteries’ stack will be almost zero during operation of the FC hybrid power system based on RPF-control mode. If the FC hybrid power system operates with a variable load demand, then the lack or excess of power on the DC bus will be dynamically ensured by the hybrid battery/ultracapacitor energy storage system for a safe transition of the FC system under the RPF-control mode. The RPF-control mode will ensure a fair comparison of the seven control topologies based on the same optimization function to improve the fuel savings. The main objective of this paper is to compare the fuel economy obtained by using each strategy under different load cycles in order to identify which is the best strategy operating across entire loading or the best switching strategy using two strategies: one strategy for high load and the other on the rest of the load range. Based on the preliminary results, the fuel consumption using these best strategies can be reduced by more than 15%, compared to commercial strategies.

Design and implementation of a test bed for building controls

Advanced controls play an essential role toward the improvement of building operational efficiency and the integration of responsive loads in buildings for grid services. Ideally, control algorithms must be sufficiently tested and validated before they are applied on real systems. This paper presents the development and current state of such an evolving test bed to support and enable experiments on advanced controls for buildings. The test bed presented in this paper consists of nine operating buildings—which possess various types of equipment and systems having different control systems and communication mechanisms (e.g., media and protocols) used in building automation systems—on the Pacific Northwest National Laboratory campus. The test bed architecture is developed in such a way that (1) it supports interactions among the buildings and heterogeneous building components and systems, including both virtual and physical devices, e.g., heating, ventilating, and air-conditioning and lighting systems; (2) it can be easily reconfigured for different control topologies and methodologies, e.g., centralized and distributed; (3) it allows selection of communication protocols, communication media, and computation resources; and (4) it is part of a larger cyber-physical test bed that includes both physical and virtual assets on distributed renewable generation, energy storage, and power system assets. Practical application: The test bed presented in this paper can be used by industry to develop and evaluate the performance of advanced control algorithms on real systems for buildings and buildings-to-grid applications. This provides practitioners an opportunity to test the applications and modify them accordingly based on their use cases and selection criteria, e.g., a controller modulating the temperature in a hospital will have different criterion as compared to an office building.

The impact of climatic extreme events on the feasibility of fully renewable power systems: A case study for Sweden

Long term time series of variable renewable energy (VRE) generation and electricity demand (load) provide important insights into the feasibility of fully renewable power systems. The coverage of energy statistics is usually too short or the temporal resolution too low to study effects related to interannual variability or the impact of climatic extreme events. We use time series simulated from climate data to assess the frequency, duration, and magnitude of extreme residual load events of two fully renewable power scenarios with a share of VRE generation (wind and solar PV) of about 50% for the case of Sweden. We define residual load as load – wind – PV – nuclear generation. Extreme residual load events are events that exceed the balancing or ramping capacities of the current power system. For our analysis, we use 29 years of simulated river runoff and wind and PV generation. Hourly load is derived from MERRA reanalysis temperature data by applying statistical models. Those time series are used along with historic capacity and ramping restrictions of hydro and thermal power plants in an optimization model to minimize extreme residual load events. Our analysis shows that even highly flexible power systems, as the Swedish one, are affected by climatic extreme events if they increase their VRE shares. Replacing current nuclear power capacities by wind power results on average in three extreme residual load events per year that exceed the current power system's flexibility. Additional PV generation capacities instead of wind increase the number of extreme residual load events by about 4%, as most events occur during the winter month when solar generation is close to zero and thus not able to counterbalance low wind events. Contrarily, overproduction and the need to curtail VRE generation become more pressing with higher shares of PV. In the discussion we highlight measures that could provide additional balancing capabilities to cope with the more frequent and severe residual load events in a fully renewable power system with high shares of VRE generation.

Optimal utilization of renewable energy sources in MG connected system with integrated converters: an AGONN Approach

This paper proposes an efficient converter for the usage of hybrid renewable energy sources and reduced switching loss in the Micro Grid associated frameworks. The work resulted in a DC–DC converter for module integration and maximum power point tracking with an efficient adaptive control scheme. The proposed control scheme is a combined execution of both the adaptive grasshopper optimization algorithm (AGOA) and artificial neural network (ANN) named as AGONN strategy. In the proposed strategy, the AGOA plays out the evaluation technique to set up the correct control signals for the system and develops the control signals database for the offline way subject to the power exchange between source side and the load side. Moreover, to train the ANN system for the online way, the achieved dataset is utilized and it drives the control method in less execution time. Also, the objective function is characterized by the system data subject to equality and inequality constraints. The constraints are the accessibility of the renewable energy sources, power demand and the state of charge of storage elements. Batteries are used as an energy source, to balance out and allow the renewable power system units to continue running at a steady and stable output power. By then, the proposed show is executed in MATLAB/Simulink working platform and the execution is surveyed with the current methods.

Enhanced load frequency control: incorporating locational information for temporal enhancement

With the increasing penetration of renewables in power systems, frequency regulation is proving to be a major challenge for system operators using slower conventional generation, and alternative means to provide faster regulation are being actively sought. The participation of demand side management in ancillary service provision is proven in some energy markets, yet its full potential to benefit frequency regulation, including the exploitation of fast power ramping capability of some devices, is still undergoing research. In this study, a novel approach to improve the speed of response of load frequency control, a secondary frequency control approach is proposed. The proposed control is enabled by an effective location identification technique, is highly resilient to anticipated system changes such as reduction of inertia, and enables fully decentralised power system architectures. The effectiveness of the approach is demonstrated and compared to that of present day regulation control, by means of real-time simulations incorporating appropriate time delays conducted on a five-area reduced model of the Great Britain power system. The applicability of the method is further proven under realistic communications delays and measurements experimentally using a controller and power hardware-in-the-loop setup, demonstrating its critical support for enabling the stable operation of future power systems.

Influence of climatological data records on design of a standalone hybrid PV-hydroelectric power system

Climatological data records have a critical role in the design of renewable power systems. Various data sampling approaches were employed by literature. However, to the authors’ knowledge, there is no work comparing them. This paper compares the results of four commonly used data records sampling scenarios (scenario 1:“15th July”, scenario 2: “a single yearly-averaged day”, scenario 3: “12 monthly-averaged days”, and scenario 4: “full yearly data”) for the multi-objective optimal design of a standalone hybrid PV-hydroelectric system by using NSGA-II. Investment cost and Loss of Power Supply Probability (LPSP) constitute the objective functions of the problem. The results will reveal that scenario 4 is the only scenario that fully satisfies the demanded power profile over the year, whereas scenarios 1 to 3 are not able to satisfy more than 95.3%, 72.3%, and 92.4% of the yearly demanded power profile, respectively. The currently employed optimization procedure, which combines NSGAII with a simple operational strategy, allows for the implementation of all the mentioned scenarios with tractable computation time (35–4150 min on an Intel (R) Core (TM) i7 4 GHz processor). This study can help designers to select a suitable data records through making a trade-off among data availability, computation time, and power supply probability.

Predictive back-to-back SCHVC for renewable wind power system for scrutinizing quality and reliability

ABSTRACTIn recent days, power electronic conversion system on wind energy system is employed to reinforce and improve the quality of the power, reliability and to avoid harmonic distortion. Here, in order to transmute the power from generator to grid, high voltage is exploited. Sometimes this may lead to cascading failures. In order to rectify these pitfalls, this paper proposes a new predictive control over synchronize magnetic generator (SMG) with the back-to-back series connected H-bridge voltage converter (SCHVC). It is opportune to utilize SCHVC that is directly connected to the grid without transformer that paves the way to reduce the cost. Moreover, SCHVC is feasible for high-level voltage convertor to meet the power demand. By increasing the level of converter SCHVC, the output voltage will be enhanced. This SCHVC offers decreased voltage for switches, low harmonic distortion, and good dynamic response of the AC current. The predictive control schemes in this paper include a proportional integral to control the DC-link voltage and the speed controller to control the variable speed generated by the wind power. SMG in combination with SCHVC improves reliability and reduces harmonic distortion. In order to prove the proposed model and the control scheme, simulations with MATLAB Simulink software have been exploited. Simulation results show the quality and reliability of power for high voltage convertor.

Optimal Coordination of Aggregated Hydro-Storage with Residential Demand Response in Highly Renewable Generation Power System: The Case Study of Finland

Current energy policy-driven targets have led to increasing deployment of renewable energy sources in electrical grids. However, due to the limited flexibility of current power systems, the rapidly growing number of installations of renewable energy systems has resulted in rising levels of generation curtailments. This paper probes the benefits of simultaneously coordinating aggregated hydro-reservoir storage with residential demand response (DR) for mitigating both load and generation curtailments in highly renewable generation power systems. DR services are provided by electric water heaters, thermal storages, electric vehicles, and heating, ventilation and air-conditioning (HVAC) loads. Accordingly, an optimization model is presented to minimize the mismatch between demand and supply in the Finnish power system. The model considers proportions of base-load generation comprising nuclear, and combined heat and power (CHP) plants (both CHP-city and CHP-industry), as well as future penetration scenarios of solar and wind power that are constructed, reflecting the present generation structure in Finland. The findings show that DR coordinated with hydropower is an efficient curtailment mitigation tool given the uncertainty in renewable generation. A comprehensive sensitivity analysis is also carried out to depict how higher penetration can reduce carbon emissions from electricity co-generation in the near future.

Class of high step‐up switched Z‐source inverters: steady state analysis and objective function

In this study, high step-up switched Z-source inverters (HSZSIs) with two main groups namely types I and II are proposed. Each of these groups includes several proposed structures. Owing to the features of the proposed structures such as high boost factor ( β ) , continuous input current, and low voltage stress; they can be used in different applications such as renewable power systems. By using the same numbers of the passive elements in comparison with a conventional Z-source inverter (ZSI), quasi-ZSI, and series ZSI (SZSI), the proposed structures produce a higher boost factor. A new objective function is defined so that all compared parameters can be investigated with each other simultaneously. The power losses and efficiency analyses for all of the proposed structures are done and compared with the conventional structures. It is shown that for P out ≃ 200 W , the measured efficiencies for basic HSZSI type I, quasi-HSZSI type I, basic HSZSI type II and quasi-HSZSI type II are 91, 85, 96, and 92%, respectively. In addition, the total harmonic distortion calculation, dynamic performance and designing a closed-loop control method for the proposed structures are shown. Finally, the experimental results are indicated for a 500 W prototype.

Power Control of Grid-Connected Photovoltaic-Wind Turbin-Bouy Conversion Energy Wave Hybrid System

Problems in the provision of electrical energy in the coastal areas, such as electricity installation networks do not exist and the cost of making the system. This paper presents the results of design, optimization, and control of hybrid energy system of wave energy and wind energy and solar power. The ultimate goal is to design clean energy systems to meet the demand for electrical energy on the coast. The actual power system results from two renewable power systems: (1) Grid solar power system: Solar PV / wave energy / battery / inventer system; and (2) wind turbine / wave energy / battery / inventer system. The results show that Solar PV power systems / wave energy / battery / inventer systems offer better performance. The total energy generated by the solar power system can meet the AC load for the electricity needs of the household scale with almost no power shortage. The recommended system for coastal homes is economically and environmentally friendly with excess power (0.10%) and zero noise level.

Fault analysis for renewable energy power system in micro-grid distributed generation

<span>In distribution system, wind power plants are becoming popular renewable energy sources. It employs Doubly Fed Induction Generator (DFIG) to generate power based on wind conversion. Short and long transmission lines, presence of faults and presence of Static Synchronous Compensator (STATCOM) are highlighted issues in this paper. Basically, this research develops investigations on some electrical variables such as voltage and current to control them. Distribution Static Synchronous Compensator (DSTATCOM) is proposed in this paper. Wind farm acts as a source while DSTATCOM is connected to the distribution system with a DFIG based wind farm. The controller proposed is DSTATCOM is modeled and simulated in MATLAB/SIMULINK and the results are given. A microgrid based small signal analysis is performed in the laboratory using MATLAB and different comparisons are made and simulation case studies are presented and validated.</span>

Renewable power systems dynamic security using a new coordination of frequency control strategy based on virtual synchronous generator and digital frequency protection

The renewable power systems have become more susceptible to the system insecure than traditional power systems due to reducing of the total inertia and damping properties that result from replacing the conventional generators with Renewable Energy Sources (RESs) as well as decoupling of the RESs from the AC grid using power converters. Therefore, maintaining the dynamic security of renewable power systems is the key challenge for integrating more RESs. This paper addresses a new strategy of frequency control including virtual inertia control based on Virtual Synchronous Generator (VSG), which emulates the behavior of conventional synchronous generators in large power systems, thus adding some inertia to the system control loop virtually and accordingly stabilizing the system frequency during high penetration of RESs. Moreover, the proposed virtual inertia control system-based VSG is coordinated with digital frequency protection for improvement the frequency stability and preservation the power system dynamic security because of the high integration level of the RESs. The effectiveness of the proposed coordination scheme is tested and verified through small and large scales of power systems, Microgrid (µG) and real hybrid power system in Egypt, respectively. System modelling and simulation results are carried out using Matlab/Simulink® software. The simulation results validated that the proposed coordination scheme can effectively regulate the system frequency and ensure robust performance to maintain the dynamic system security with high share of RESs for different contingencies.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Market value of PV battery systems for autonomous rural energy supply

Abstract Solar photovoltaics (PV) panels in combination with batteries are often proposed as a solution to provide stable power supply in rural areas. PV generation is mostly dominated by the solar diurnal cycle and has, in some countries, already started to have influence on the daily price distribution on the electricity market. In this work, we study the performance and optimisation of rural PV-battery hybrid systems in a future renewable Polish power system. We use data on generation potentials to study PV and battery deployment. Together with a power system optimisation and dispatch model for the Polish power system, we study market values when selling at the national market for different CO2 price scenarios. We show that optimal orientations with respect to tilt/azimuth are subject to change as the PV share grows and that the benefit from batteries grows for higher shares of renewables.

Adding Inertia to Isolated Power Systems for 100% Renewable Operation

Following time-constraining obligations under 2015 Paris Agreement, nations are racing to integrate more renewable energy generation into their power systems than ever before. While solutions for mitigation of renewable energy negative effects to power system stability exist, they are still complex and expensive. One of the most promising technologies, battery energy storage, is widely advocated, but is still unable to solve basic challenge of renewable energy integration – low inertia and provision of sufficient fault currents. This paper presents a practical enabling technology in a form of synergy between a battery energy system and a synchronous machine, which can support fully renewable power system while providing nominal power system inertia. For simplicity, the case for this technology is presented on an example of an Isolated Power System capable of 100% instantaneous renewable operation for prolonged periods of time. High-speed measurements during both steady-state operation and performance under fault conditions were recorded and presented in the paper.

A porous medium for all seasons

The answer to seasonal energy storage and security to support highly renewable power systems could lie deep under the seabed, where compressed air energy storage offers a route to long-term storage at large scales. Now, research models the potential for this in porous rock and finds a large capacity in saline aquifers offshore in the UK.

Grid-Tied Solar PV/Fuel Cell Hybrid Power System for University Building

The results of an optimized design of grid-connected renewable energy system for University building are presented in this paper. Integrated modelling, simulation, optimization and control strategies are used to test the performance and select the best hybrid renewable power system. The main objective is to design a grid connected renewable energy system to meet the electric load of the building with high penetration of renewable energy, low greenhouse gas emissions, and low cost of energy. Hourly simulations, modelling and optimization were performed to determine the performance and cost of the hybrid power system configurations using load following and cycle charging control strategies. The results show that the grid-tied solar PV/fuel cell hybrid power system offers a good performance for the tested system architectures. With a solar PV capacity of 500 kW and fuel cell capacity of 100 kW integrated with the grid, the total energy generated from grid-tied renewable energy system to meet the desired load is 26% from the grid (purchase), 42% produced from the solar PV, and 32% from the fuel cell. From the total annual power produced, 95% is used to meet the AC primary load of the building and 5% is the sellback to the grid. The daily performance and electricity generation from the proposed grid-tied solar PV/Fuel cell power system is also presented in this paper. The proposed grid-tied solar PV/fuel Cell hybrid power system with the sale of electricity back to the grid has a high renewable fraction (40.4 %), low levelized cost of energy (71 $/MWh), and low carbon dioxide emissions (133 kg CO2/MWh).

Inter-seasonal compressed-air energy storage using saline aquifers

Meeting inter-seasonal fluctuations in electricity production or demand in a system dominated by renewable energy requires the cheap, reliable and accessible storage of energy on a scale that is currently challenging to achieve. Commercially mature compressed-air energy storage could be applied to porous rocks in sedimentary basins worldwide, where legacy data from hydrocarbon exploration are available, and if geographically close to renewable energy sources. Here we present a modelling approach to predict the potential for compressed-air energy storage in porous rocks. By combining this with an extensive geological database, we provide a regional assessment of this potential for the United Kingdom. We find the potential storage capacity is equivalent to approximately 160% of the United Kingdom’s electricity consumption for January and February 2017 (77–96 TWh), with a roundtrip energy efficiency of 54–59%. This UK storage potential is achievable at costs in the range US$0.42–4.71 kWh−1. Compressed-air energy storage could be a useful inter-seasonal storage resource to support highly renewable power systems. This study presents a modelling approach to assess the potential for such storage in porous rocks and, applying it to the UK, finds availability of up to 96 TWh in offshore saline aquifers.