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

Optimal energy management of a grid-connected dual-tracking photovoltaic system with battery storage: Case of a microbrewery under demand response

In this study, a pumped hydro storage is proposed to be used in conjunction with a standalone hydrokinetic system in off-grid power supply. The techno-economic feasibility of such combination is analyzed and compared to the option where batteries are considered as storage system. The system working principle is presented; the mathematical model and simulation model are also developed. Simulations are performed using two different types of loads in rural South Africa as case study to demonstrate the technical advantages as well as the cost effectiveness of the proposed supply option. The results reveal that the novel combination is a cost-effective, reliable and environmentally friendly solution to achieve 100% energy autonomy in remote and isolated communities.

Pumped storage-based standalone hydrokinetic system: Feasibility and techno-economic study

Optimal energy management of a residential grid-interactive Wind Energy Conversion System with battery storage

In this paper, two control strategies involving "continuous" and "ON/OFF" operation of the diesel generator in the battery-integrated hybrid system are developed, implemented and compared. The main purpose of these modeled controlled strategies is to minimize the diesel generator operation cost in standalone electricity generation processes. The simulations have been performed using "fmincon" for the continuous operation and “intlinprog” for the ON/OFF operation strategy implemented in Matlab. A rural household and a base transceiver station have been used as case studies; and the daily operation cost obtained are compared to the scenario where the diesel generator is used alone to supply the same load demand. Sensitivity analyses have been conducted on the battery control settings as key parameters to find how changes in these parameters do impact the daily operation cost of the hybrid system. The results show that using the developed optimal energy dispatch models, significant fuel saving can be achieved compared to the case where the diesel is used alone to supply the same load requirements.

Energy dispatching of an isolated diesel-battery hybrid power system

In this work, an optimal energy management model for the grid-powered electric RTG, with a battery storage system, is developed. The aim of the model is to reduce the operation cost, by minimizing the component linked to the maximum demand charges from the grid, as well as the component linked to the Time of Use (ToU) pricing structure. As a case study, a RTG crane operating in South Africa has been selected. The load profile, size the battery storage system, ToU tariff, as well as the maximum demand charges, are used as input for the developed model. Simulations, for a complete RTG handling cycle, have been conducted to evaluate the techno-economic performances of the developed model, used to optimally dispatch the power flow in the system during the different phases of operation. Three main configurations have been simulated as energy sources for the RTG crane, namely, the exclusive supply from the grid, grid/battery hybrid system without energy recovery during the lowering phase and grid/battery hybrid with energy recovery, during the lowering phase. As compared to the baseline, the simulation results have shown that using the proposed model shows a possible 50.36, 60.6 and 64.4% cost reduction, per full handing cycle, are possible in off-peak standard and peak pricing period, for the selected winter day. The results also show that the maximum demand charges may be reduced by 45.20%. Further economic analyses have been conducted; and the results indicate that the proposed system successfully reduce electrical energy costs, the peak demand and outperforms each of the presented baselines.

Kanzumba Kusakana

Papers

Optimal energy management of a grid-connected dual-tracking photovoltaic system with battery storage: Case of a microbrewery under demand response

Pumped storage-based standalone hydrokinetic system: Feasibility and techno-economic study

Optimal energy management of a residential grid-interactive Wind Energy Conversion System with battery storage

Energy dispatching of an isolated diesel-battery hybrid power system

Optimal energy management of a retrofitted Rubber Tyred Gantry Crane with energy recovery capabilities