CHAPTER 7 CONCLUSION AND SCOPE FOR FUTURE WORK

Transcription

1 CHAPTER 7 CONCLUSION AND SCOPE FOR FUTURE WORK 7.1 CONCLUSION Microgrid is an extension of main grid providing on-site generation capable of fulfilling its local load demand. A microgrid architecture requires to be added to the main grid to increase the reliability, improve power quality, avoid the use of depleting fossil fuels, improve the technical performance and reduce the green house gases emissions. The microgrid can be connected in an islanded or isolated or autonomous and grid connected modes. Depending on the requirement these renewable energy sources are connected in the main grid or operate separately. Because of these reasons, operation, control and grid integration of renewable resources is a task of fundamental importance in modern power system. Microgrid operating modes and dispatch strategies must be studied. Furthermore, as renewable energy sources are intermittent in nature, energy storage schemes are required to store the energy and retrieve the energy at times required. Thus, it is desirable to develop reliable microgrid operation and effective energy storage algorithms which would enhance the performance of hybrid power systems. This thesis is devoted to the development of techno-economic analysis algorithms, different dispatch strategies algorithms and life cycle cost benefit analysis of energy storage schemes algorithms for different hybrid power system configurations in grid connected and islanded modes. In addition, the thesis also includes development of algorithm for flywheel energy storage system and compares the performance of battery and flywheel energy storage systems. Following are the major conclusions of the research work carried out in this thesis: 1. The work in this thesis was started with an objective to overcome the limitations of the existing schemes and further to develop a new techno-economic analysis of isolated and grid connected hybrid power systems. Initially, a scheme for Wind-Diesel Hybrid Power System has been developed. The simulation was carried out using various combinations of optimization and sensitivity variables developed in HOMER. The proposed configurations have been tested for feasibility condition using an algorithm proposed. The economic parameters play central role of deciding the dimension, feasibility and optimization of a proposed system. Hence, it is required to 172

2 optimize the proposed system for various combinations of system components to get least Net Present Cost. In order to achieve lowest NPC, comparison of Diesel Only, Diesel Battery and Wind-Diesel-Battery systems were compared for (i) economic (ii) technical and (iii) environmental parameters. On the basis of simulation and optimized results it was found that Wind-Diesel-Battery hybrid system outperform compare to Diesel Only and Diesel Battery systems. This justifies the use of renewable sources in the main grid. To illustrate the effectiveness of the proposed scheme, thousands of simulation cases have been generated with different combinations and system conditions. Later the proposed scheme was connected to grid and different simulation cases were generated and the optimized combination was selected. It has been observed from the performance of the proposed scheme that the Wind-Diesel Battery system is best and grid connected hybrid systems prove to be better option compared to isolated hybrid systems. Furthermore, considering different sizes of components, it has been found that the addition of PV in the proposed scheme increases the renewable energy penetration and reduces the effect of green house gases. Hence, the size of PV shall be effectively optimized for better system performance. The application of proposed technoeconomic based algorithm is further extended for variations in different parameters like wind speed, solar radiation, diesel fuel prices, cost of components and load demand. In this scheme, the variation in parameter is compared with the base case of Wind-Diesel System. With the increase in wind speed, NPC and COE decreases, RF increases and GHG emissions reduces. Whereas increase in load causes very less variation in all economic, technical and environmental parameters. Increase in diesel fuel prices increase the renewable penetration, NPC and COE, whereas emissions due to gases reduces. The selection of renewable components with 30% cost reduction causes NPC, COE, GHG emissions to come down. Due to increase in fuel price the renewable penetration increases. Further, it provides promising results in all cases. 2. Promising results given by the proposed Wind-Diesel Battery hybrid system with the inclusion of PV system in it, generates an idea of adopting a new PV-Wind- Diesel based hybrid system that can be applicable with high load demand is proposed and economic, technical and environmental aspects were studied for the proposed scheme. Therefore, a new scheme is designed in such a way that operation of it in isolated and grid connected modes gives better clarification of feasibility of the proposed scheme. Depending upon the application of microgrid, specific 173

3 configuration, energy storage requirements and cost of various components, suitable philosophy can be employed for the hybrid power system. Feasibility of the proposed scheme has been tested by generating large number of possible configurations by modeling a hybrid configuration having different optimization and sensitivity variables. Further, the proposed scheme gives comparison of various parameters with respect to base case. The increase in wind speed causes reduction in NPC and COE, increase in RF and reduction in GHG emissions. Similar results have been found for increase in solar radiation. Moreover, it provides better performance in terms of COE and RF. The proposed scheme provides better results when the cost of renewable energy technologies (specially wind) reduces to 30% and technical and environmental parameters have been found unaffected.the proposed scheme employed for microgrid, can be proven to be more effective compared to the techniques commonly used in present scenario. 3. A technique based on the concept of dispatch strategies for isolated and grid connected hybrid systems has been developed for microgrid. This proposed scheme utilizes load following and cycle charging dispatch strategies for isolated and grid connected Wind-Diesel Hybrid power systems. The computed simulations phasors are used to calculate the economic, technical and environmental parameters of the proposed systems. Penetration based dispatch strategies algorithm is used to estimate the system performance. Both the dispatch strategies have given almost same results for gird connected Wind-Diesel hybrid system. Hence, the dispatch strategy has no impact on the performance of the grid tied hybrid systems. The Load Following dispatch strategy has been found a better option for the isolated Wind-Diesel hybrid system in all three aspects: (i) economic (ii) technical and (iii) environmental. The work has been extended further to see the effect of load following and cycle charging dispatch strategies on different types of hybrid power systems. With two different hybrid power systems (i) Wind-Diesel and (ii) PV-Diesel simulated, the annual diesel fuel consumption can be reduced and, at the same time, the level of pollution can be minimized. A proper control and dispatch strategy is developed to take full advantage of the renewable energy during the periods of time it is available and to minimize diesel fuel consumption. The paper compares two dispatch strategies (i) load following and (ii) cycle charging along with different system controls for two different hybrid systems based on renewable penetration in microgrid. A variety of combinations and system controls have been simulated to evaluate the optimization 174

4 and sensitivity of the proposed technique. The proposed scheme has been validated by performing numerous simulations on proposed system using HOMER software. Wind-Diesel hybrid systems gives better system performance with Load Following dispatch strategy. On the other end, the performance of the PV-Diesel system with the Cycle Charging Strategy proves better compared to load following dispatch. It has been observed from the renewable fraction, that for the same dispatch strategy PV penetrates less compared to wind. Thus, the proposed schemes can be efficiently employed for microgrid configurations for different parameters and also for any system topology which are commonly used in present scenario. 4. The application of Battery Energy Storage System (BESS) in the field of microgrid demands dedicated operation of energy storage during excessive energy generation by renewable resources and retrieve the energy during the period when PV, wind sources are not available. In order to optimize the economic performance of the system, the type of battery selection is a key factor. The hybrid systems with different configurations (i) Wind-Battery (ii) PV-Battery and (iii) Wind-PV-Battery are simulated with every time battery replaced by (i) Lead Acid Battery (ii) Zinc Bromine Battery (iii) Vanadium Redox Battery. The validation of the proposed algorithm is carried out by generating various simulation cases considering optimization and sensitivity variables in HOMER software package. These cases are generated by considering parameters such as wind speed and solar radiation. The proposed methodology includes Life Cycle Cost Benefit Analysis of batteries. Results obtained from the simulation indicate effectiveness of the proposed algorithm to select the type of battery. At the end, a comparative study of all types of batteries is also carried out. The results show that Zinc-Bromine Battery (ZBB) gives less Initial Cost (IC), Operation Cost (OC), Net Present Cost (NPC) and Cost Of Energy (COE). This shows that the life cycle cost of a hybrid system is less for ZBB than other types of batteries taken for simulation. 5. Flywheel Energy Storage Systems used for storing the energy during the transition period of renewable energy resources. The high penetration of renewable energy resources can cause instability of the main grid and the microgrid. Conversely, the less use of renewable resources may cause the environmental issues. In order to overcome the said problem, author has presented a methodology to incorporate 175

5 various energy storage systems to discriminate between various economic and environmental parameters. To validate the proposed scheme, different component sizes, optimization variables and sensitivity variables have been generated with and without energy storage elements. Two types of energy storage systems have been proposed in this methodology (i) BESS and (ii) FESS. In order to check the performance of proposed scheme, various configurations have been generated with and without ESS. It has been observed from the said analysis that COE and NPC increases with the inclusion of FESS compared to BESS. The main aim of FESS is to limit the renewable penetration. The renewable fraction reduces from to 0.277, which shows the amount of renewable energy penetration has been reduced, if a FESS is added. The proposed scheme is capable to determine the impact of FESS on environment. As the renewable energy penetration is limited by FESS, the GHG emission increases by 8% compared to a schematic with no ESS and 18% compared to BESS. Thus, the proposed scheme can be effectively used for design and feasibility study of microgrids in present scenario. 7.2 SCOPE FOR FUTURE WORK It is almost impossible to have an algorithm suitable for all situations. It is, therefore, important to consider some of the situations for which the further study is required. Suggested below are the few areas which can be further explored to improve the microgrid operation and energy storage schemes: 1. To evaluate the practicality of the proposed (i) Wind-Diesel and (ii) PV- Wind-Diesel hybrid systems in isolated and grid connected modes, a number of pragmatic issues such as control and grid integration aspects can be taken into consideration for the microgrid and energy storage schemes. 2. In hybrid systems, depending upon the type of application, design and feasibility many different strategies other than cycle charging and load following, can be performed for enhancing the system performance by implementing it on hardware. However, the structure of algorithm includes a multiple optimization process; practical application of this scheme may demand high computational integrity. Hence, the hardware implementation of proposed hybrid configurations is a challenging task. Conversely, many other hybrid configurations with different microsources like fuel cell, Bio fuel and micro turbines have been introduced in the field of hybrid power systems. They can provide good results with various 176

6 combinations in real-time applications using these energy sources. Hence, there is a scope to implement the suggested hybrid power system configurations in real time application. 3. After modeling the HPS configuration in HOMER software, with different dispatch strategies like load following and cycle charging, a new algorithm can be developed based on relative phase angle comparison of sequence components was tested in laboratory environment. However, its validation can be done by real time implementation in the field. In addition, the algorithm can be modified for various configurations of HPS when connected to grid. This portion has not been taken up in the present work, and thus provides generous opportunities for further work. Furthermore, the proposed scheme can be customized with the renewable energy penetration and stability studies for large power system network. 4. The proposed Wind-Diesel and PV-Wind-Diesel hybrid configurations, have been modeled in the present work. These HPSs are simulated and analyzed for techno-economic and environmental impacts. The effect of temperature, different tracking mechanisms, wind gust, pitch angle control has not been modeled in the computer simulations used in the present work for its better performance. Consequently, the design parameters such as the characteristic of wind Low Voltage Ride Through capability, power quality and stability can be considered for future work. Hence inclusion of these parameters provide gray areas to be looked into for further research. Moreover, it is also necessary to develop schemes and algorithms for enhancing the system performance in grid connected mode. 5. The energy storage algorithm developed for battery and flywheel discrimination between implementation and application can be tested and modified if required for grid connected modes and hybrid AC/DC systems. Moreover, the proposed scheme has considered battery for DC load requirements and flywheel for AC/DC load requirements. It would be interesting to make experiments or simulations on larger networks that include small hydro, fuel cell and micro urbines along with the pumped hydro storage, magnetic storage elements and hydrogen storage and to find possible optimization configuration to implement the proposed scheme. Furthermore, the algorithm in this thesis is based on utilization of electrical, economical and environmental parameters, extension of this algorithm or addition of different technical parameters is required to make decisions of the feasibility, design and optimization condition. 177

7 Besides, primary load provided provided during simulation, the deferrable load and thermal load (i.e. Combined Heat and Power) applications for various HPSs configurations in islanded and grid connected mode aspect has not been considered in the proposed work, and can be further studied. 178