The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

Solar Engineering Of Thermal Processes

Hybrid energy systems are being utilized for supplying electrical energy in urban, rural and remote areas to overcome the intermittence of solar and wind resources. A hybrid renewable energy system incorporates two or more electricity generation options based on renewable energy or fossil fuel unit. The techno-economic analysis of the hybrid system is essential for the efficient utilization of renewable energy resources. Due to multiple generation systems, hybrid system analysis, is quite complex and requires to be analyzed thoroughly. This requires software tools for the design, analysis, optimization, and economic viability of the systems. In this paper, 19 softwares with their main features and current status are presented. The softwares studied are HOMER, Hybrid2, RETScreen, iHOGA, INSEL, TRNSYS, iGRHYSO, HYBRIDS, RAPSIM, SOMES, SOLSTOR, HySim, HybSim, IPSYS, HySys, Dymola/Modelica, ARES, SOLSIM, and HYBRID DESIGNER. The research work related to hybrid systems carried out using these softwares at different locations worldwide is also reviewed. The main objective of the paper is to provide the current status of these softwares to provide basic insight for a researcher to identify and utilize suitable tool for research and development studies of hybrid systems. The capabilities of different softwares are also highlighted. The limitations, availability and areas of further research have also been identified.

Review of software tools for hybrid renewable energy systems

Public awareness of the need to reduce global warming and the significant increase in the prices of conventional energy sources have encouraged many countries to provide new energy policies that promote the renewable energy applications. Such renewable energy sources like wind, solar, hydro based energies, etc. are environment friendly and have potential to be more widely used. Combining these renewable energy sources with back-up units to form a hybrid system can provide a more economic, environment friendly and reliable supply of electricity in all load demand conditions compared to single-use of such systems. One of the most important issues in this type of hybrid system is to optimally size the hybrid system components as sufficient enough to meet all load requirements with possible minimum investment and operating costs. There are many studies about the optimization and sizing of hybrid renewable energy systems since the recent popular utilization of renewable energy sources. In this concept, this paper provides a detailed analysis of such optimum sizing approaches in the literature that can make significant contributions to wider renewable energy penetration by enhancing the system applicability in terms of economy.

Optimum design of hybrid renewable energy systems: Overview of different approaches

Renewable energy becomes a key contributor to our modern society, but their integration to power grid poses significant technical challenges. Power quality is an important aspect of renewable energy integration. The major power quality concerns are: 1) Voltage and frequency fluctuations, which are caused by noncontrollable variability of renewable energy resources. The intermittent nature of renewable energy resources due to ever-changing weather conditions leads to voltage and frequency fluctuations at the interconnected power grid. 2) Harmonics, which are introduced by power electronic devices utilized in renewable energy generation. When penetration level of renewable energy is high, the influence of harmonics could be significant. In this paper, an extensive literature review is conducted on emerging power quality challenges due to renewable energy integration. This paper consists of two sections: 1) Power quality problem definition. Wind turbines and solar photovoltaic systems and their power quality issues are summarized. 2) Existing approaches to improve power quality. Various methods are reviewed, and the control-technology-based power quality improvement is the major focus of this paper. The future research directions for emerging power quality challenges for renewable energy integration are recommended.

Emerging Power Quality Challenges Due to Integration of Renewable Energy Sources

In recent times renewable energy sources have become an integral part of the modern power grid. As a result, the overall system inertia of the grid has been reduced, thus leading to frequency instability issues such as fast rate of change of frequency. Thus, to compensate for the declining inertia, it is important to carefully select renewable energy generators (REGs) and energy storage systems (ESS) in order to ensure the stability of the power grid, while also controlling greenhouse gases emissions in line with environmental standards. Therefore, this paper proposes an optimal planning model of REGs and ESS, considering the inertia requirement of the grid. The objective function is formulated to minimize the cost of operation, emissions, and investment in new REGs and energy storage units while maximizing the system inertia. The model was developed as a mixed integer linear programming problem and solved using CPLEX solver in GAMS. Finally, the model was validated using a modified IEEE 9-bus system and compared under three scenarios. The results show that in scenario 3 where system inertia is considered in the presence of REGs and ESS, higher system inertia of 8.776 s was achieved at minimal emission and cost, which justifies the aim of the study. 

/pdf/optimal-planning-of-renewable-energy-generators-in-modern-1bdvql50.pdf

Optimal planning of Renewable energy generators in modern power grid for enhanced system inertia

In this paper, the performance of the proposed off-grid wind-solar PV hybrid system powering the cathodic protection unit is simulated and analyzed using MATLAB/SIMULINK. Furthermore, the performance simulation for the battery energy storage system with PV-wind hybrid energy system under variable solar irradiance and wind speed respectively is also conducted. The hybrid system consists of a wind turbine which uses a permanent magnet synchronous generator driven directly from the turbine, a PV array and a battery bank. The simulated results reflect that the designed hybrid system of such capacity can adequately supply a cathodic protection unit with no power shortage at different weather conditions.

/pdf/modelling-and-simulation-of-a-hybrid-renewable-battery-1cm2p3h4on.pdf

Modelling and Simulation of a Hybrid Renewable/Battery System Powering a Cathodic Protection Unit

Hybrid renewable energy systems are economical off-grid methods of generating power to remote rural areas, where power lines are prohibited due to costs. However, South Africa's policies and regulations are not making it any easier for these systems to be more exposed and accessible in real time. Most of the research studies on renewable hybrid systems or microgrids in South Africa focused mainly on the optimal sizing and optimal control of different systems by making use of renewable energy simulation software's, but there is no research done on the implementation of these hybrid systems in real time. The aim of the study is to come up with the methodology to design, implement and control a hybrid system in South Africa conditions for small rural loads. However, further comprehensive research work have to be done on the study.

Practical Implementation of Hybrid Energy Systems for Small Loads in Rural South Africa

This paper is a survey of technologies that increase the viability of micro-hydropower as a cost-effective energy source for remote communities. These technologies (civil, electrical, mechanical or electronic.) have helped in the development of micro-hydropower industry all over the world. They can be applied in rural areas not sevred by the grid to provide reliable and low cost energy. The motivation has been that there are a significant number of viable potential sites in isolated areas where micro hydropower is a realistic energy option, and where conventional schemes are not appropriate, especially in rural parts of South Africa.

A survey of technologies increasing the viability of micro-hydropower as a cost-effective energy source for remote communities in South Africa

Water heating is the fourth largest energy consumer in the commercial building sector, accounting for >40 % of the energy consumed in South Africa. Traditional electric storage tank water heaters (ESTWHs) have been the most frequently used systems in the past, owing to their low electricity costs and implementation. It was low enough at that time that energy costs were not considered. These systems have grown increasingly hostile to consumers as power prices have risen, particularly to the undesirable high morning and afternoon peaks. The indirect-expansion solar-assisted heat pump water heater (IDX-SAHPWH), for the commercial sector, to reduce energy consumption of hot water production while maintaining the users' thermal comfort level, has been proposed in this paper. The system is operated under an optimal energy control scheme, integrated with the load shifting by time-of-use (TOU) pricing plan. The comparison of the performance of the proposed optimally controlled system and the electric storage tank water heater (ESTWH) was performed through the simulation approach using the Solving Constraint Integer Programs (SCIP) solver, in the MATLAB interface optimization toolbox. The simulations reveal that the proposed system operates during off-peak hours, when power prices are lower, as compared to ESTWH system. The techno-economic analysis was conducted and presented for a project lifespan of 20 years. The proposed optimally controlled system demonstrates the cost savings obtained from the winter and summer seasons, as well as annual, as 76.0 %, 75.6 % and 75.8 %, respectively. The break-even point of the project is during the 9th month of the first year of the project, with a possible savings of 71.5 % at the end of the project's lifetime. 

Kanzumba Kusakana

Papers

Optimal planning of Renewable energy generators in modern power grid for enhanced system inertia

Modelling and Simulation of a Hybrid Renewable/Battery System Powering a Cathodic Protection Unit

Practical Implementation of Hybrid Energy Systems for Small Loads in Rural South Africa

A survey of technologies increasing the viability of micro-hydropower as a cost-effective energy source for remote communities in South Africa

Optimal energy management of a solar-assisted heat pump water heating system with a storage system