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 operation of a hybrid multisource energy system considering grid load shedding

Optimal switching control of an air to air heat pump operating under variable time-based electricity pricing

The study focused on the evaluation of the energy cost saving and greenhouse gas emission reduction when a 3.0 kW electric geyser is replaced by a 1.2 kW split type ASHP water heater. Both hot water devices were of 150 L capacity and are set up to operate simultaneously under specific volumes of hot water drawn off (150, 50 and 100 L) in the morning, afternoon and evening each day over a year. The data acquisition system comprising of flow meters, temperature sensors, power meters, ambient temperature and relative humidity sensor and a data logger. The data acquisition system was built and installed to monitor the performance of the hot water devices. The results depicted that the average monthly energy saving and CO2 reduction achieve with the ASHP system due to the 300 L of daily volume of hot water drawn off was 203.67 kWh and 201.63 kg, respectively for the summer season. The average monthly cost saving for the summer period based on the flat rate tariff (FR) and the time of use (TOU) tariff was R25S.66 and R 296.35. In addition, the average monthly energy and CO2 impact of the ASHP water heater due to the daily 300 L of hot water drawn off was 249.24 kWh and 246.74 kg, respectively for the winter season. The corresponding average monthly flat rate and time of use cost saving for the winter season was R 378.84 and R 719.26. The average month-day COP for both the summer and winter seasons was 2.90 and 2.49, respectively. A firm conclusion can be established that the time of use cost saving is higher than the flat rate cost saving due to the relatively higher electricity tariff structure attributed to the time of use electricity plan especially during the peak periods. Despite, the low average month-day COP experienced by the ASHP water heater in the winter as opposed to the COP for the average month-day in the summer period, the electrical energy saving of the ASHP water heater was higher due to the lowered makeup water temperature. These lowered makeup water temperature is associated with a greater electrical energy consumed and thermal energy gained before hot water set point temperature is attained after the hot water drawers.

The economic and environmental impact of replacing geyser with air source heat pump water heater

The aim of this paper is to provide an integrated optimization and control algorithm in order to solve the residential load demand uncertainty problem as encountered in a grid-interactive hydrokinetic river (GHR) system. The proposed GHR system is incorporated with a pumped hydro-storage system (PHS) to store excess energy. The proposed algorithm aims to resolve the load demand uncertainty in order to minimize the electricity bills of the consumer and to maximize the energy sales into the grid, under time-of-use (TOU) tariff scheme. Therefore, the maximization of load demand satisfaction is not compromised. The traditional open loop optimization approach cannot cater for load demand uncertainty. It becomes more challenging to adequately meet the uncertain load demand. Within this context, the rule-based control algorithm is developed to manage power flow during uncertain load demand. The obtained results demonstrated that the load demand is adequately met at a reduced grid consumption cost, through the application of the rule-based control algorithm. This confirmed that the proposed algorithm benefits the user, by reliably and economically satisfying the load demand at a minimal grid energy cost.

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Managing residential demand uncertainty in a smart grid-interactive hydrokinetic river system

The current study focused on developing a simulation tool that can be used for conduit hydropower generation. Hence, this paper presents the modelling and performance analysis of a small conduit hydropower system using MATLAB/Simulink software. This will assist the conduit hydropower developers to quantify the available energy and evaluate the viability of the conduit hydropower projects.Furthermore, the performance of the modelled conduit hydropower system is also compared to the performance of a prototype set up in a laboratory environment. The main findings revealed that the developed model responded effectively under variable pressure. The conduit hydropower was only active when the excess pressure was available, this is due to the pressure difference between pressure reducing valve (PRV) pre-set pressure and the system pressure. The performance can be studied using any generator including BPMDCG. Further research is required to address factors not covered by this work. This can include the evaluation of different turbine and generator technology, to validate the model as a universal conduit hydropower model, application of different configuration of the pipeline system and incorporating it to the simulation model and a thorough analysis of the physical losses in the pipeline, in order to accurately match the measured and simulated outputs.

Kanzumba Kusakana

Papers

Optimal operation of a hybrid multisource energy system considering grid load shedding

Optimal switching control of an air to air heat pump operating under variable time-based electricity pricing

The economic and environmental impact of replacing geyser with air source heat pump water heater

Managing residential demand uncertainty in a smart grid-interactive hydrokinetic river system

Experimental analysis of small conduit pressure hydropower systems