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

The aim of this paper is to provide a survey of different innovative technologies that can be applied to the micro-hydropower system to make it cost effective for rural energy supply. Electrical, mechanical, civil or electronic technologies that can increase the viability of micro-hydropower as a cost-effective energy source for remote and isolated communities in rural South Africa are presented. The motivation behind this study is that there are a significant number of potential sites in South Africa where micro-hydropower is a viable energy option to provide reliable and low cost energy and where conventional schemes are not appropriate.

A survey of innovative technologies increasing the viability of micro-hydropower as a cost effective rural electrification option in South Africa

This paper proposes a model for the optimal Peer-to-Peer energy sharing of grid-connected Prosumers. Current models within available literature do not include the constraint which forbid small renewable energy producers to share their excess power through the national grids; this leads to prosumers dissipating their excess power generated or using costly energy storage systems. Additionally, most of these models look at the savings made by the Peer-to-Peer community, without computing the cost reduction or benefit of each prosumer taken individually. Thus, these models are not suitable or directly applicable to many countries such as South Africa. For these reasons, the main aim of this paper is to develop a Peer-to-Peer energy sharing model that considers the above mentioned gaps. The proposed system consists of two prosumers; a residential prosumer that employs a roof mounted photovoltaic system with energy storage capabilities, and commercial prosumer with a dual-tracking photovoltaic system. The prosumers are connected to each other by power lines for P2P operation. The developed model minimizes both prosumers’ operation costs by maximizing the use of the power from the renewable energy sources; optimally managing the internal power sharing between the prosumers; and minimizing the use of the electrical utility operating with the Time-of-Use rate. The study uses the dissimilarity and complementarity of the load patterns in the South African residential and commercial energy sectors as an asset to implement the Peer-to-Peer energy sharing between the prosumers operating in these two sectors. Using a case study in South Africa, the results have demonstrated that, as compare to using the grid as sole power source, the residential prosumer can achieve a total daily cost reduction of 62.71% in summer and 68.99% in winter; while the commercial can achieve 81.31% and 31.69% in winter. For a 20 years’ project, using the grid as baseline for the comparison, the lifecycle cost analysis have projected the residential prosumer to break-even after 16.35 years and save 19.5%; while the commercial prosumer can break-even after 5.3 years and save 55.2%. Moreover, this study shows the ability of the developed model to simulate systems with different components, demands, resources as well as costs. The model developed in this study may assist researchers and engineers interested in the optimal operation of prosumers in Peer-to-Peer energy sharing schemes.

Optimal peer-to-peer energy management between grid-connected prosumers with battery storage and photovoltaic systems

Developing nations around the world are facing energy deficit crisis due to an increasing energy demand and slow exploitation of renewable energy (RE) technologies. Among different RE technologies, hydrokinetic is a promising technology that has proved to generate electricity cheaper than solar and wind technologies. Among different energy storage devices, pumped hydro storage (PHS) has proved to be the most cost-effective option. Due to rising electricity price, domestic farm-houses situated in close proximity to the flowing water resource can make use of a hydrokinetic-PHS system to reduce the electricity cost and to sell excess energy into the grid through feed-in tariff (FIT) scheme. This paper introduces an optimal energy management model for power dispatching within a grid-interactive micro-hydrokinetic pumped hydro storage (MHK-PHS) system. The aim is to minimize the grid consumption costs and to maximize the energy sales revenue by considering the weekdays and weekend time-of-use (TOU) tariffs. The simulation results have shown the effectiveness of the model since it allows most of the load power demand to be met by the RE systems during expensive peak-period as a means of minimizing the grid consumption costs. Most of the energy sales took place during standard and expensive peak periods as a means of maximizing the energy sales revenue. Additionally, the simulation results have shown that an energy saving potential of 100.1% and 104.23% can be achieved during high demand and low demand seasons, respectively.

Optimal power dispatch of a grid-interactive micro-hydrokinetic-pumped hydro storage system

Micro-hydrokinetic river system modelling and analysis as compared to wind system for remote rural electrification

A model of electricity cost minimization is proposed which can be implemented in small farming activities where boreholes are present for water supply. In this case, a hybrid system composed of solar photovoltaic and pico hydro supplied by a pumped storage system are used minimize the electricity cost in a dynamic electricity pricing environment. The varying price of electricity, the load demand, the reservoir state of water stored as well as the solar resource at any instant determine the optimal power flow from the different power sources to the load; these are the control variables to be optimised with the aim of reducing the power consumed from the grid. The optimization problem can be solved using linear programming. The simulation results can be used to investigate the impact and benefit of the proposed model on the electricity cost reduction of small loads in the South African farming sector.

Kanzumba Kusakana

Papers

A survey of innovative technologies increasing the viability of micro-hydropower as a cost effective rural electrification option in South Africa

Optimal peer-to-peer energy management between grid-connected prosumers with battery storage and photovoltaic systems

Optimal power dispatch of a grid-interactive micro-hydrokinetic-pumped hydro storage system

Micro-hydrokinetic river system modelling and analysis as compared to wind system for remote rural electrification

Optimal operation scheduling of grid-connected PV with ground pumped hydro storage system for cost reduction in small farming activities