Renewable energy is going to play an immensely important role in the coming decades. Hence, the bulk manufacturing of solar panels has seen a renewed interest. For this purpose, it is imperatively important to assess the techniques that can be employed on automated production lines for evaluating the quality of solar wafers and cells. To-date many non-destructive testing methods to access the micro-defects in solar wafers and cells have been developed around the globe; however, not all of them can be applied on a fast-paced production line. In this regard, this study details all the non-destructive evaluating techniques that can be employed on an automated production line. Using a multi-attribute decision-making method, a strategic evaluation procedure is developed that can be adopted for the optimum selection of evaluation tools currently available in the market. This study is aimed at young researchers, graduate students and practitioners who want to come up-to-speed regarding the various defects that occur in solar wafers and cells along with the techniques that are currently being adopted to evaluate those defects. Also, future trends in research are highlighted regarding the development of assessment techniques.

This study performs an extensive review on distributed economic dispatch method for the power system based on consensus. It covers the comparison of centralised and distributed economic dispatch method in terms of system structure, performance requirement and solution process. The key links in the process of solving economic dispatch problem are summarised, and the advantages and disadvantages of the existing distributed economic dispatch algorithm are reviewed. Furthermore, the possible research directions, from the authors’ point of view, are also provided in this study.

Maximum power extraction from the photovoltaic (PV) system plays a critical role in increasing efficiency during partial shading conditions (PSC's). The higher cost and low conversion efficiency of the PV panel necessitate the extraction of the maximum power point (MPP). So, a suitable maximum power point tracking (MPPT) technique to track the MPP is of high need, even under PSC's. This study gives an extensive review of 23 MPPT techniques present in literature along with recent publications on various hardware design methodologies. MPPT classification is done into three categories, i.e. Classical, Intelligent and Optimisation depending on the tracking algorithm utilised. During uniform insolation, classical methods are highly preferred as there is only one peak in the P–V curve. However, under PSC's, the P–V curve exhibits multiple peaks, one global MPP (GMPP) and the remaining are local MPPs. Hence, Intelligent and Optimisation techniques came into limelight to differentiate the GMPP out of all LMPPs. Every MPPT technique has its advantages and limits, but a streamlined MPPT is drafted in numerous parameters like sensors required, hardware implementation, tracking in PSC's, cost, tracking speed and tracking efficiency. This present study aimed to address the advancement in this area for further research.

This study presents development of a modified leaky least mean square (MLLMS)-based control strategy for a single-stage three-phase grid-tied photovoltaic (PV) system. In the proposed MLLMS-based control scheme, the authors employ an incremental conductance maximum power point tracking algorithm for maximum power extraction, MLLMS algorithm for extraction of fundamental active and reactive components of the load current, delivering PV power to the grid, balancing the grid current and compensating harmonics of the connected loads at the point of common coupling. By virtue of a leakage factor and selection of sum of the exponential of the adaptation error in the cost function, the MLLMS algorithm overcomes the problems of drifting, low convergence and oscillations in weights encountered by some popular adaptive algorithms, e.g. least mean square (LMS) and least mean fourth (LMF) algorithms. The proposed control scheme is simulated in MATLAB/Simulink environment under different load and environmental conditions. Subsequently, the proposed control scheme is realised on a prototype grid-tied PV system developed in the laboratory. From both the simulation and experimental results, it is observed that the proposed MLLMS algorithm outperforms LMS and LMF algorithms in terms of mean square error, oscillation in weights and total harmonic distortions of the grid currents.

As the energy demand is increasing every day, the environmental pollution has been a main concern. To reduce environmental pollution while satisfying the energy demand, renewable energy is a good solution and attracted many researchers not only to produce clean energy but also to find sustainable energy solution. Among renewable energy, geothermal energy is one of promising renewable sources and is recently given a high consideration. The tectonic position of Rwanda and volcanism show that Rwanda may have promising geothermal resources. One of the evidences is the hot springs originated from tectonic. Gisenyi hot spring is located in Northern Province nearest to the Kivu Lac on the base of volcanoes with surface water temperature of 71°C. In this paper, the conceptual and numerical models were made on Gisenyi hot spring based on geological, geochemical, hydrochemistry and geophysical data to estimate the temperature profile of the spring. This paper assesses the reservoir temperature of Gisenyi hot spring by using various geothermometers along with existing data and information using MATLAB software. The electrical power potential using Organic Rankine Cycle and Carbon dioxide as a working fluid have been assessed together with the optimum depth by considering the dominant mode of heat transfer.

This research work is concerned with maximum power point tracking (MPPT) in photovoltaic (PV) systems under partially shaded conditions (PSCs) through an improved particle swarm optimisation (PSO). The traditional PSO is investigated toward MPPT and the reasons for delayed convergence characteristics are investigated. Then, a modified PSO is proposed, in which population is reduced sequentially by eliminating less-promising particles. The new concept is applied to a 30 kW PV plant situated in a school building and the results are analysed. The new methodology is also experimentally verified on a 400 W prototype PV system in the laboratory. Enhanced energy harvesting from the existing 30 kW PV plant is highlighted considering realistic shading patterns and full bright conditions of solar insolation. The computed and measured results clearly demonstrate that the new PSO is a promising candidate for MPPT in PV systems under PSC.

The sudden voltage drop may upsurge the current level and trigger the self-protective system to disconnect the wind turbines that are detrimental for grid constancy. A novel structure of a modified switch type fault current limiter (M-STFCL) is proposed that protects the doubly-fed induction generator wind turbine (DFIG-WT) during the symmetrical and asymmetrical grid faults. The M-STFCL is cost-effective and requires little maintenance during operation. The proposed system maintains the rotor current and DC-link voltage below the maximum acceptable limits, thus, fortify the back-back converters. The M-STFCL is tested with both the sliding-mode control (SMC) and proportional–integral (PI) controller and their results are compared. From the simulation results, it is obvious that SMC has edged over the PI controller and demonstrated superior control over the critical parameters. The performance of M-STFCL is also compared with the conventional switch type fault current limiter and the analytical results clearly validate the significance of the proposed system.

Microgrids and modern bulk power systems usually have multiple time scale dynamics, such as slow and fast dynamics. In this study, the stability of a wind–diesel hybrid microgrid is investigated to show a mechanism of system collapse caused by the interaction between fast dynamics of interface converters and slow electromechanical dynamics. This mechanism leads to a Hopf bifurcation of the fast subsystem due to slow changes in the variables of the slow subsystem and is completely understood by decomposing the stability analysis of the microgrid into the stability assessment of two simpler subsystems: the slow and the fast subsystems. The time-scale method proposed in this study for stability analysis of the microgrid extends the existing proposals in the literature and is able to detect this kind of instability scenario, where the interaction between fast and slow subsystems is the cause of collapse, while the existing approaches, such as quasi-steady-state analysis, fail in detecting instability.

Electric power systems have undergone substantial changes in their operation. The higher penetration of renewable resources, demand response capability, and generators operating via droop control at the distribution level are the main features resulting in the microgrid concept. Microgrids must operate connected or islanded from the main grid, ensuring reliability and quality in the supply of energy in both operating scenarios. In this sense, the secondary control becomes essential in the system's resilience, since it is responsible for restoring the frequency and voltage within acceptable values. This study proposes a unified frequency and voltage secondary controls for microgrids operating in islanded mode. For this sake, a modification in the load flow algorithm considering a Jacobian matrix takes place, enabling a sensitivity analysis to give the adjustments in the set point of generators. The help of the Levenberg–Marquardt method improves the convergence in the modified load flow. All generators are continuously considered in this process, regarding their capabilities and relative control sensitivities concerning the operation point restoration. The proposed methodology is validated in a modified IEEE-37 node test feeder, showing the efficacy of the centralised secondary control under different scenarios of renewable generation penetration and load levels.

Ocean waves are an important renewable energy resource and several fields of are concurrently working to improve technologies for harnessing their power. In that context, this study presents a control to optimise the performance of oscillating water column systems. As a first contribution, a novel criterion to attain maximum wave energy extraction is developed, resulting in an enhancement of the global power efficiency of the system. Then, taking advantage of the proposed criterion, a second-order sliding mode control set-up is designed, with power extraction maximisation the primary objective and reactive power regulation a secondary one. Simulation results confirm the highly satisfactory performance of the proposed controller and its robustness in the presence of the inherent uncertainties and disturbances in the non-linear system.

This study proposes a composite generation and transmission expansion planning (CGTEP) with high renewable penetration in Iran power grid. The goal is to minimise the generation and transmission investment and operation costs, start-up/shut-down costs, and the cost of energy not served during a 10-year planning horizon. The problem is formulated in a mixed-integer linear format, considering power flow limits, ramping rate limits, minimum up/down times of the generation units, uncertainty of wind and solar generations, and deterministic and probabilistic reliability constrains including reserve margins for generation capacities and expected energy not supplied boundary. In addition, according to the specific geographic characteristics of Iran, import and export of the electricity, as well as the limitation of water resources for power generation, is modelled in the CGTEP problem. The proposed CGTEP method is implemented in business as usual and renewable target cases without considering the uncertainty, and RT case with uncertainty considerations. In RT cases, 30% renewable penetration is targeted to reduce the CO₂ emission by 10%. In addition, the capability of Iran power grid in providing green energy for the neighbouring countries is investigated in this study.

This study proposes a technique for the enhancement of the stability of microgrids during unsymmetrical temporary faults in the distribution network. In order to enhance the transient stability and the quality of voltage in the microgrid during different disturbances caused by faults in the distribution network, this study proposes a concept with a centralised battery energy storage system. The battery is connected to the network through single-phase converter units which are to be implemented in every phase so that they can inject independently both the active and reactive power in certain phases. The proposed technique enhances the transient stability of microgrids and provides symmetrical operating conditions for consumers and generators in it during all temporary symmetrical and unsymmetrical faults in the distribution network. An innovative concept has been proposed for managing the balance of active and reactive power that uses, as control variables, magnitude and voltage phase angle at the point of connection of the microgrid to the distribution system. The proposed concept and technique have been tested on the IEEE 33 BUS system with additional sources. The dynamic simulations of disturbances and the verification of the proposed technique have been performed in DIgSILENT PowerFactory software.

Half-bridge modular multilevel converter-based high-voltage direct-current (MMC-HVDC) grids are technically and economically viable solutions to transmit bulk electrical energy generated from geographically dispersed and remote renewable resources. However, due to the half-bridge converter's inability to control fault currents, these grids need specialised protection schemes to increase reliability and equipment safety. This study proposes a non-unit non-differential protection scheme founded on a comparative orientation measure of fault components for buses of half-bridge MMC-HVDC grids. Considering the selected protection strategy, the protection zone of this scheme can also cover a part of the converter station's ac side; in which severe short-circuit faults should be quickly detected and isolated as well since they may cause the entire grid outage. This scheme can be used as the main protection or a backup of the conventional differential current protection, and subsequently, increase the protection system dependability by increasing the functional diversity. The test results disclose that the proposed scheme has superior sensitivity to identify single-pole and double-pole faults with resistances up to 1500 and 2000 Ω, respectively, at the protected dc bus with the maximum delay of 1 ms, while it is robust against all ac and dc faults outside the designated protection zone.

Large hydro generators are usually overloaded at various situations such as the period when excess water is available and when excess inflow is to be discharged. The period may have extended to many weeks under exigent conditions e.g. six weeks in case of a 1000 MW hydropower plant (HPP) located at northern region, India at 20% overload. All the performance related parameters including vibrations were observed during commissioning except runaway speed test at load rejection. At overloads, if there is a sudden load rejection the vibration transients will be even more severe due to drop in current and internal impedance. Hence this paper aims to analyze the vibration signature of large synchronous generator (SG) when operated at overloads and subjected to sudden load rejection. The substantiation of the factual model of 250 MW hydro generating units (HGU) replicating the case plant has been simulated using SIMSEN software. Apart from case report and simulative validation an experimental verification is also conducted with a prototype model of 2.2 kW SG. This paper provides the feasibility to operate the SG's 20% beyond its rated load as designed with proper maintenance and safety carried out by plant operators.

The fluctuating nature of solar energy necessitates suitable energy storage systems. Compared to typical battery banks, supercapacitors offer longer cycle life eliminating the need to replace them regularly. However, compared to a typical maximum power point tracking controller, where the battery bank and resistive load fed by a switch-mode DC–DC converter allows impedance matching for maximum power transfer, a supercapacitor bank's significantly large capacitive load does not permit the typical impedance matching for maximum power transfer. This study compares the theoretical difference between battery versus supercapacitor energy storage, and highlights of the supercapacitor-assisted LED converter technique in achieving high-efficiency renewable energy-based DC-microgrid systems.

Assessment and enhancement of transmission network capability have been one of the prime interests of power system monitoring, operation and control. Conventionally, the issue of available transfer capability (ATC) assessment has been tackled considering the transmission and distribution networks as segregated entities because they had little or no influence on each other's performance owing to the unidirectional flow of power from the transmission to distribution networks. Now, with increasing interest in smart transmission and distribution in amalgamation with a paradigm shift in sources of generation from centralised to decentralised even at distribution levels mandating the analysis of power grid while inculcating both the hierarchies simultaneously. In this study, a platform for quasi-static operation of power transmission and distribution networks, employing a multi-agent based system has been developed. The developed multi-agent systembased system has been utilised for assessment of ATC considering active distribution network (ADN) whereby Modified IEEE 24 bus system at transmission and Modified IEEE 123 node system at distribution level has been considered as a test system. It has been observed that the presence of ADN considerably affects the ATC of the system.

In this study, a single-phase multi-input photovoltaic (PV) inverter has been proposed for simultaneously achieving maximum power extraction and load voltage regulation under various operating scenarios involving weather intermittency and dynamic loading. This is achieved by maintaining the PV modules in series for similar atmospheric conditions and by allowing isolated operation of individual modules during mismatched atmospheric conditions among different modules. The weather-dependent operation of the modules allows efficient extraction of maximum power from all the modules by avoiding the modules to operate at the least maximum power point (MPP) among them, which has been a limitation of classical techniques aiming at MPP with multiple modules. A comprehensive analysis of the proposed inverter topology and its associated synchronous reference frame-based control scheme has been carried out by considering a wide range of operating scenarios in terms of (i) maintaining the operation closer to MPP under varying irradiance levels and temperature; (ii) regulated output voltage for load variation. The appropriateness of the scheme has been compared with the existing state-of-the-art topologies. In addition to the MATLAB simulation, validation has been carried out on a 300 W laboratory prototype.

Increasing discharge of sewage sludge is a threat to the ecological environment, and sludge treatment via combustion is the most feasible alternative. However, the low calorific value and high-water content of raw sludge results in poor firing performance and increases the risk of environmental pollution. Recently, co-combustion has emerged as a more environment-friendly technology. Herein, the combustion behaviours of sewage sludge, corn stalk and their mixture at four heating rates were studied via thermogravimetric experiments. Results yielded the division of weight loss into three stages for corn stalk: dehydration, combustion of volatiles and combustion of fixed carbon; four stages were identified for sewage sludge and the mixture of sludge and stalk: dehydration, combustion of volatiles, combustion of fixed carbon and thermal decomposition of a small amount of minerals. Synergistic analyses found that with a 60% blending ratio of sewage sludge, interaction between the components in the high-temperature range was greatly promoted. Gas emission characteristics showed that CO₂ was the main product during (co-)combustion, while the NO _x emissions at low (or high) temperatures for the blend were higher (or lower) than the theoretical values. Temperature had little effect on H₂S emissions, though it significantly affected SO₂ emissions during co-combustion.

Photovoltaic (PV) panel is subjected to high temperatures from solar radiation. The performance of the PV panel deteriorates as the PV's operating temperature increases. This study aims to examine the cooling method using a cold plate attached to the PV panel to lower its operating temperature. The cold plate consists of several guided channels or ribbed walls of thickness 0.015 m to direct the circulating water flow from its entrance to the exit point at the back of the PV panel. The experiment demonstrates a decrease of around 21.2°C in surface temperature and improves ∼2% in electrical efficiency, 8% in thermal efficiency and 1.6% in PV panel efficiency as compared to PV panel without a cooling system. The relationship between the average PV's surface temperature and output power is obtained. The uncertainty analysis shows that the average standard deviation in PVs, electrical and thermal efficiency is not more than 1.26% when subjected to differences in the day of measurements, mass flow rate, and pressure of the pump.

This work presents a generalised integrator-based control algorithm for power quality (PQ) amelioration of the grid in the presence of non-linear load enabling leakage current suppression feature. Owing to the presence of stray capacitance between solar photovoltaic (PV) array and the ground, the variation in common-mode voltage across stray capacitance leads to potential safety issues, electromagnetic interference, and distortion into the injected grid currents. Furthermore, the PQ of the grid is highly deteriorated under the existence of non-linear loads. To solve the aforementioned issues, the harmonic compensation controller is presented herein to ensure the unity power factor operation, harmonic compensation, leakage current suppression using the grid-connected solar PV array system. Simulated results show the effectiveness of the control strategy under various operating scenario. In contrast to the state-of-the-art techniques, the grid currents are attained sinusoidal and balanced even in the presence of unbalanced non-linear load. Furthermore, the leakage current is suppressed within 300 mA as per the VDE-00126-01 standard. The comparative performance explicitly validates the effectiveness of the presented harmonic compensating strategy over the conventional schemes. Test results manifest the response of the solar PV array system for various operating conditions and follows the revised IEEE-519–2014 sand VDE-00126-01 standards.