Optimal scheduling for distributed hybrid system with pumped hydro storage

Published ArticlePhotovoltaic and wind power generations are currently seen as sustainable options of in rural electrification, particularly in standalone applications. However the variable character of solar and wind resources as well as the variable load demand prevent these generation systems from being totally reliable without suitable energy storage system. Several research works have been conducted on the use of photovoltaic and wind systems in rural electrification; however most of these works have not considered other ways of storing energy except for conventional battery storage systems. In this paper, an energy dispatch model that satisfies the load demand, taking into account the intermittent nature of the solar and wind energy sources and variations in demand, is presented for a hybrid system consisting of a photovoltaic unit, a wind unit, a pumped hydro storage system and a diesel generator. The main purpose of the developed model is to minimize the hybrid system’s operation cost while optimizing the system’s power flow considering the different component’s operational constraints. The simulations have been performed using ‘‘fmincon” implemented in Matlab. The model have been applied to two test examples; the simulation results are analyzed and compared to the case where the diesel generator is used alone to supply the given load demand. The results show that using the developed control model for the proposed hybrid system, fuel saving can be achieved compared to the case where the diesel is used alone to supply the same load patters

Optimization of the daily operation of a hydrokinetic–diesel hybrid system with pumped hydro storage

Published ArticleThe present paper develops a model to optimize the daily operation of a hybrid energy system consisting of a hydrokinetic, a pumped hydro storage system and diesel generator. The optimization approach is aimed at minimizing the cost function subject to the availability of water resource, the variable load requirements, and operational constraints of the hybrid system’s components. The main purpose of the developed model is to minimize the daily amount of diesel fuel consumed to supply the load while maximizing the use of the hydrokinetic operating in conjunction with the pumped hydro storage. For simulation purposes, the hourly load demand, resource data for a selected rural area in South Africa have been collected and used as an input to the developed model. The economic analysis has resulted in the calculation of optimized daily operation cost of the proposed hybrid system in summer and winter conditions. The obtained results demonstrate that a substantial reduction in the daily operation cost can be achieved (88% in summer and 97% in winter) using the hybrid system compare to the case where the diesel generator is used alone

Optimal operation control of a grid-connected photovoltaic-battery hybrid system

Published Conference ProceedingsIn this work, the optimal power scheduling for a grid-connected photovoltaic-battery hybrid system is proposed to sufficiently explore solar energy and to benefit customers at demand side. The developed model for the hybrid system’s optimal power flow management aims to minimize electricity cost subject to the power balance, photovoltaic and battery storage outputs as well as other operational constraints. With respect to demand side management, an optimal control method is developed to schedule the power flow of hybrid system over 24-h period. Simulation are performed using MATLAB, and the results demonstrate that operating the proposed hybrid system under the developed optimal energy management model can reduce the operation cost and allow consumers to generate substantial income by selling power to the grid

Energy management of a grid-connected hydrokinetic system under Time of Use tariff

Published ArticleIn this work, the optimal power scheduling for a grid-connected hydrokinetic-battery hybrid system is proposed to sufficiently explore hydrokinetic energy and to benefit customers at demand side. The developed model for the hybrid system’s optimal power flow management aims to minimize electricity cost subject to the power balance, hydrokinetic and battery storage outputs as well as other operational constraints. With respect to demand side management, an optimal control method is developed to schedule the power flow of hybrid system over 24-h. Simulations are performed using MATLAB (R2016a), and the results demonstrate that operating the proposed hybrid system under the developed optimal energy management model can reduce the operation cost and allow consumers to generate substantial income by selling power to the grid

Operation cost minimization of photovoltaicedieselebattery hybrid systems

Published ArticleIn this paper, two control strategies involving “continuous” and “ON/OFF” operation of the diesel generator in the solar photovoltaicedieselebattery hybrid systems are modeled. The main purpose of these developed models is to minimize the hybrid system's operation cost while finding the optimal power flow considering the intermittent solar resource, the battery state of charge and the fluctuating load demand. The non-linearity of the load demand, the non-linearity of the diesel generator fuel consumption curve as well as the battery operation limits have been considered in the development of the models. The simulations have been performed using “fmincon” for the continuous operation and “intlinprog” for the ON/OFF operation strategy implemented in Matlab. These models have been applied to two test examples; the simulation results are analyzed and compared to the case where the diesel generator is used alone to supply the given load demand. The results show that using the developed photovoltaicedieselebattery optimal operation control models, significant fuel saving can be achieved compared to the case where the diesel is used alone to supply the same load requirements

Optimal operation control of hybrid renewable energy systems

Thesis (D. Tech. (Electrical Engineering)) -- Central University of Technology, Free State, 2014For a sustainable and clean electricity production in isolated rural areas, renewable energies appear to be the most suitable and usable supply options. Apart from all being renewable and sustainable, each of the renewable energy sources has its specific characteristics and advantages that make it well suited for specific applications and locations. Solar photovoltaic and wind turbines are well established and are currently the mostly used renewable energy sources for electricity generation in small-scale rural applications. However, for areas in which adequate water resources are available, micro-hydro is the best supply option compared to other renewable resources in terms of cost of energy produced. Apart from being capital-cost-intensive, the other main disadvantages of the renewable energy technologies are their resource-dependent output powers and their strong reliance on weather and climatic conditions. Therefore, they cannot continuously match the fluctuating load energy requirements each and every time. Standalone diesel generators, on the other hand, have low initial capital costs and can generate electricity on demand, but their operation and maintenance costs are very high, especially when they run at partial loads. In order for the renewable sources to respond reliably to the load energy requirements, they can be combined in a hybrid energy system with back-up diesel generator and energy storage systems. The most important feature of such a hybrid system is to generate energy at any time by optimally using all available energy sources. The fact that the renewable resources available at a given site are a function of the season of the year implies that the fraction of the energy provided to the load is not constant. This means that for hybrid systems comprising diesel generator, renewable sources and battery storage in their architecture, the renewable energy fraction and the energy storage capacity are projected to have a significant impact on the diesel generator fuel consumption, depending on the complex interaction between the daily variation of renewable resources and the non-linear load demand. V This was the context on which this research was based, aiming to develop a tool to minimize the daily operation costs of standalone hybrid systems. However, the complexity of this problem is of an extremely high mathematical degree due to the non-linearity of the load demand as well as the non-linearity of the renewable resources profiles. Unlike the algorithms already developed, the objective was to develop a tool that could minimize the diesel generator control variables while maximizing the hydro, wind, solar and battery control variables resulting in saving fuel and operation costs. An innovative and powerful optimization model was then developed capable of efficiently dealing with these types of problems. The hybrid system optimal operation control model has been simulated using fmincon interior-point in MATLAB. Using realistic and actual data for several case studies, the developed model has been successfully used to analyse the complex interaction between the daily non-linear load, the non-linear renewable resources as well as the battery dynamic, and their impact on the hybrid system’s daily operation cost minimization. The model developed, as well as the solver and algorithm used in this work, have low computational requirements for achieving results within a reasonable time, therefore this can be seen as a faster and more accurate optimization tool

Feasibility analysis of river off-grid hydrokinetic systems with pumped hydro storage in rural applications

Published ArticleHydrokinetic power generation is currently gaining interest as a cost effective way of supplying isolated areas where reasonable water resource is available. However the seasonal characteristic of the water resource as well as the intermittent fluctuating load demand prevents this power generation system from being entirely reliable without appropriate energy storage system. Few researchers have recently analyzed the use of hydrokinetic systems as standalone or combined with other energy source, however the authors of these researches did not explore other means of storing energy except for traditional battery storage systems. In this study, the most conventional and established storage technology, 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 operation principle of the system 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 studies to demonstrate the technical cost advantages as well as the cost effectiveness of the proposed supply option. The results reveal that the novel micro-pumped hydro storage based hydrokinetic system is a cost-effective, reliable and environmentally friendly solution to achieve 100% energy autonomy in remote and isolated communities

Impact of demand profiles on grid-interactive photovoltaic systems in Bloemfontein: A case study

Conference ProceedingsIn this paper the impact brought by different demand sector profiles on the daily operational cost and optimal scheduling of grid connected photovoltaic system with bidirectional power flow is analysed for the specific case of Bloemfontein in South Africa. For this purpose, residential, commercial and industrial daily load curves are used to estimate daily load demands. For comparison purposes, three load profiles representing the demands from the residential, commercial and industrial sectors, have been used and normalized to display the same daily energy consumption level with different demand patterns. The results of the simulations, obtained using Matlab 2016, have revealed that for the same energy consumption and renewable resources, the running expenses of any proposed scheme are mainly dependent on the demand sector. Consequently, it can be recommended that in Bloemfontein and South Africa in general more focus should be on implementing grid-connected renewable hybrid energy with storage system in the commercial and industrial sectors instead of in the residential sector

Energy dispatching of an isolated diesel-battery hybrid power system

Published Conference ProceedingsIn 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

Techno-economic analysis of multiple paralleled diesel generators for micro isolated applications

Conference ProceedingsThis paper analyses the key benefits of a multiple paralleled diesel generator system over a "Single" diesel generator system for supplying small remote and isolated loads. Even though having several small diesel generators in parallel instead of one larger one will certainly induce higher capital cost of the generating unit, the resulting cost of kWh generated as well as the system is life cycle cost can be significantly decreased . In this study, HOMER Pro software is used to compare the technical, economic and environmental performance of the two configurations. For the selected case study, the simulation results reveal that multiple connected small diesel generators instead on a single large one can be considered for rural and isolated electricity generation