Arnaud ETE MSc in Energy System and the Environment Optimization of the HARI stand-alone energy system with TRNSYS Individual Project nd Friday 22 September 2006 Copyright Declaration The copyright of this dissertation belongs to the author under the terms of the United Kingdom Copyright Acts as qualified by University of Strathclyde Regulation 3.49. Due acknowledgement must always be made of the use of any material contained in, or derived from, this dissertation. 2 Abstract The project aims to assess the viability of a stand-alone hydrogen-based energy system. This will be achieved using software models that could be applied in the design of similar hydrogen and renewables systems. The suitability of the selected tools for this tasks will also be assessed. The assessment will be based around the case study of the Hydrogen and Renewables Integration (HARI) project at West Beacon Farm in Leicestershire. This project investigates methods of storing the energy generated by intermittent renewable sources using hydrogen. A hydrogen system comprising an electrolyzer, a pressurised gas store and fuel cells has been added to an existing renewable energy system which includes wind turbines, PV arrays and micro-hydro generators to feed commercial and domestic loads on a local mini-grid. The local electricity distribution network is centred around a 620V DC bus. The HARI project illustrates the concept of “Hydrogen Economy” with the ultimate objective of achieving grid independence for West Beacon Farm once become self-sufficient. In this project the HARI system is modelled and simulated with the program TRNSYS, developed by the University of Massachusetts, in parallel with another modeling and optimization software (HOMER). The specific objectives of the work are as follows. The first objective was simply to evaluate the ability of TRNSYS to model the HARI system. The second objective was to use HOMER and TRNSYS in parallel to compare the operation of both programs and to optimize the size of the HARI system components and thereby improve its performance. Thirdly, a methodology was established from the modelling process. This methodology was finally applied in a different context: the HARI system relocated into a more Northerly climate (Glasgow); this was undertaken to determine the impact of weather changes on the optimal configuration of the system. The main outcome of the project was that the optimization process developed and applied to the HARI system predicted the potential for a significant reduction in the size of the system components, thereby reducing the system cost and improving its performance. The geographic relocation of the project indicated that the optimization process was applicable on different scenarios. 3 Table of contents A. Introduction and objectives 8 1. Aims and objectives of the project......................................................................................8 2. The Hydrogen Economy......................................................................................................9 B. Description of the HARI project 10 1. West Beacon Farm.............................................................................................................10 2. The installed system at WBF.............................................................................................11 a. Installed generators 11 b. Hydrogen system 12 c. Summary of HARY components and WBF layout 15 3. Electrolysis from renewables.............................................................................................17 4. WBF infrastructure............................................................................................................17 5. Components integration and electrical network at WBF...................................................19 a. Central DC bus 20 b. Power-electronic converters 21 c. Power conditioning model in TRNSYS 22 6. System of control...............................................................................................................23 a. Power supply control 23 b. Control parameters and description of the control strategy 24 c. Optimisation of the control strategy 27 7. The HARI project and the hydrogen economy..................................................................30 8. Conclusion: knowledge gained so far and further plans....................................................31 C. Simulation with TRNSYS 34 1. Definitions.........................................................................................................................34 a. What is TRNSYS 34 b. What is HYDROGEMS 34 2. HARI model: control strategy based on the SOC of the hydrogen store..........................35 a. The Master Controller 35 b. HARI system modelling 38 D. Simulation with HOMER and combined modelling 41 1. What is HOMER...............................................................................................................41 2. Control strategy in HOMER..............................................................................................41 3. HARI system modelling....................................................................................................42 4. Load and resource data......................................................................................................43 5. Simulation of the HARI system by HOMER and TRNSYS.............................................47 E. Methodology for the optimization process 50 1. Optimization process.........................................................................................................50 a. Methodology 50 b. HOMER optimal system 51 c. TRNSYS optimal system 52 d. Summary 52 2. Operation of the optimal systems found by HOMER and TRNSYS................................52 3. Conclusion on the HARI optimal system..........................................................................57 4. Relocation of the model in Glasgow.................................................................................58 a. Glasgow weather data 58 b. Optimal system in Glasgow 60 4 c. Impact of the weather changes on the optimal system size 63 F. Conclusion 65 Acknowledgments.....................................................................................................................67 References .................................................................................................................................68 5 Table of figures and tables Figure 1: Hydrogen used as a load-balancing mechanism [2].........................................................9 Figure 2: The installed system at West Beacon Farm [2]..............................................................11 Figure 3: PV arrays at West Beacon Farm [4]...............................................................................12 Figure 4: The electrolyzer used at WBF [2]..................................................................................13 Figure 5: The hydrogen store at WBF [2].....................................................................................14 Figure 6: Intelligent Energy 2kW FC [1]......................................................................................14 Figure 7: Plug Power Gencore® 5kW FC [1]...............................................................................14 Figure 8: The 2kW nickel sodium chloride Zebra battery [1].......................................................15 Table 1: Summary of HARI sub-systems [1]................................................................................15 Figure 9: Map of the HARI project site [1]...................................................................................16 Figure 10: View of the hydrogen building at WBF [1].................................................................18 Figure 11: Layout of the WBF hydrogen building [1]..................................................................19 Figure 12: The West Beacon Farm stand-alone power supply [6]................................................20 Figure 13: The bespoke DC/DC converters [6].............................................................................21 Figure 14: Two-transistor forward converter diagram [6].............................................................22 Figure 15: State of charge control [6]............................................................................................24 Figure 16: Control strategy for the electrolyzer and the FC based on the battery SOC [14].......25 Figure 17: Cost of cycling energy [25]..........................................................................................28 Figure 18: Costs of supplying energy in the discharge process [15].............................................29 Figure 19: The Hydrogen Economy model [2].............................................................................31 Figure 20: HYDROGEMS components [10]................................................................................35 Figure 21: Control strategy based on the SOC of the hydrogen store...........................................36 Figure 22: HARI modeling with TRNSYS, including printers and plotters.................................38 Figure 23: HARI modeling with TRNSYS...................................................................................39 Figure 24: Alkaline electrolyzer model (EES executable developed by Øystein Ulleberg).........40 Figure 25: Parameters of the electrolyzer required by TRNSYS..................................................40 Figure 26: Model of the HARI system with HOMER...................................................................43 Figure 27: Copy of the TRNSYS model with HOMER................................................................43 Figure 28: Load data for HOMER and TRNSYS simulations......................................................44 Figure 29: Solar data for HOMER and TRNSYS simulations......................................................45 Figure 30: The NCEP reanalysis data download page..................................................................46 Table 2: Reanalysis data used to define the wind resource at WBF..............................................46 Figure 31: Wind data for HOMER and TRNSYS simulations.....................................................47 Table 3: Comparison of HOMER and TRNSYS simulations for the HARI system.....................48 Figure 32: SOC of the hydrogen store simulated by HOMER and TRNSYS...............................49 Figure 33: Energy balance simulated by TRNSYS and HOMER.................................................49 Figure 34: Methodology for the optimization process..................................................................51 Figure 35: Optimal system found by HOMER..............................................................................51 Table 4: Summary of HOMER and TRNSYS optimal systems....................................................52 Table 5: Operation of the optimal systems obtained with HOMER and TRNSYS......................53 Figure 36: SOC of the H2 store for the optimal systems found by HOMER and TRNSYS.........53 Figure 37 (a), (b) and (c): Energy balance in the optimal systems found by HOMER and TRNSYS................................................................................................................................56 Figure 37 (d): Zoom of figure 36 (c) between days 250 and 350..................................................56 6 Figure 38: Correlation between the energy balances in the optimal systems found by HOMER and TRNSYS.........................................................................................................................57 Table 6: Comparison between the actual and optimal HARI systems..........................................58 Figure 39: Glasgow solar data for HOMER and TRNSYS simulations.......................................59 Table 7: Reanalysis data used to define the wind resource in Glasgow........................................59 Figure 40: Glasgow wind data for HOMER and TRNSYS simulations.......................................60 Table 8: Summary of HOMER and TRNSYS optimal systems in Glasgow................................61 Table 9: Comparison of the optimal systems in Glasgow obtained with HOMER and TRNSYS61 Figure 41: SOC of the H2 store in the optimal systems found by HOMER and TRNSYS in Glasgow.................................................................................................................................62 Figure 42: Energy balance in the optimal systems found by HOMER and TRNSYS in Glasgow62 Figure 43: Correlation between the energy balance in the optimal systems found by HOMER and TRNSYS in Glasgow.............................................................................................................63 Table 10: Comparison of the optimal systems found by TRNSYS in Loughborough and Glasgow ...............................................................................................................................................63 Table 11: Comparison of performances of the optimal systems in Loughborough and Glasgow 64 Figure 44: Comparison of the SOC of the H2 store in Loughborough and Glasgow...................64 7 A. Introduction and objectives 1. Aims and objectives of the project Stand-alone power systems are used by many communities around the world that have no access to grid electricity. But whereas most of these stand-alone systems are still based on fossil fuel power production, the use of renewable energy within these systems is growing as a consequence of rising fuel prices and environmental concerns. The integration of wind and solar energy system based on a long-term seasonal storage of hydrogen is considered as a promising solution to overcome the limitations associated with the intermittency of renewable sources. The Hydrogen and Renewables Integration (HARI) project at West Beacon Farm (WBF) in Leicestershire is part of the research program at CREST (Centre for Renewable Energy Systems Technology), at Loughborough University. This project aims at investigating methods of storing the energy generated by intermittent renewable sources such as wind and solar energy. The project, which was actually conceived with the ultimate objective of achieving grid independence for WBF once become self-sufficient, constitutes the first illustration of the concept of “Hydrogen Economy” in action within the UK. But this hydrogen-based technology is far from being mature, with only a few examples throughout the world. This is still an expensive technology and developing software models of these stand-alone power systems is therefore essential to simplify the design of future similar systems. The main objective of this project was therefore to model a stand-alone power system (the HARI project, described later), optimize the size of its components and evaluate its performances under different geographical and weather conditions. More specifically, this report presents two models of the HARI system developed on the TRNSYS and HOMER simulation platforms. The results of these models are analysed and compared in order to estimate the accuracy of the simulations. Both models can then be used complementarily using the strong points of each program to determine the optimal size of the system. HOMER is used to find a first approximation of the optimal system, and TRNSYS is then used to refine the previous results. The specific objectives of the work are therefore to evaluate the ability of TRNSYS to model the HARI system, to compare the operation of HOMER and TRNSYS, to establish a methodology using both programs in parallel to optimize the size of the HARI system components and thereby improve its performance, and finally to determine the impact of weather changes on the optimal configuration of the system. This report is organised in 6 parts. The next part describes the HARI project and the different elements that compose the power system. A crucial aspect of this project, the control strategy developed at WBF to control the HARI system, is part of this description. Parts C and D describe the models developed with HOMER and TRNSYS. The methodology for the optimization process and the results of the simulations are presented in part E. Finally, the effects of the relocation of the HARI system in Glasgow precede the conclusion of this report. 8 2. The Hydrogen Economy The term “Hydrogen Economy” has different definitions depending on people who use it, but in its purest sense, it represents an energy systems relying exclusively on renewable energies for its primary resource and hydrogen for energy storage. All hazards of greenhouse gases are therefore eliminated in this system where all the primary energy will come from renewables (and nuclear power potentially). But in a stand-alone renewable energy system where the primary energy resource is totally dependent upon the weather, the output of such a resource cannot be controlled and it is inevitable that the power supply rarely matches the fluctuating demand of the system’s loads. Some form of balancing mechanism is absolutely necessary, as well as some form of energy storage. Batteries are able to compensate this mismatch over short periods, but they become expensive, bulky and inefficient beyond a few days. Lead acid batteries for example suffer from self- discharge, limited charge rates, high maintenance requirements and short lifetimes. On the other hand, hydrogen offers long-term and large-scale capacity storage achievable at a lower cost. At times of surplus of electricity production from the renewables, hydrogen can be produced through electrolysis of water (electrical energy transformed into chemical energy) and stored for later use. When there is a shortage of power from the renewable sources to power the loads on the system, the stored hydrogen can be converted back to water via fuel cells, releasing electricity to match the demand. The production and consumption of hydrogen are actually used as a load balancing mechanism. Moreover, hydrogen presents both a means of storing grid power and of providing transport fuel. Vehicles will then be able to run without emitting any hazardous gas, while providing the performances we expect from conventional engines – something that batteries have never been able to achieve. Combining the needs of balancing supply and demand on the electricity grid with providing fuel for transportation, hydrogen produced from renewables is the energy medium that can offer a pollution-free energy system for the future. Figure 1: Hydrogen used as a load-balancing mechanism [2] 9 B. Description of the HARI project The Hydrogen and Renewables Integration (HARI) project, joint winner of the “Non-profit Organisations” category of the 2006 Eurosolar UK Awards, is a research initiative investigating a stand-alone energy system that associates a complete renewable system and a hydrogen energy storage system. It is part of the research program at CREST (Centre for Renewable Energy Systems Technology), at Loughborough University. It constitutes the first large scale illustration of the concept of “Hydrogen Economy” in action within the UK. 1. West Beacon Farm West Beacon Farm (WBF) in Leicestershire is a family home that has been converted to demonstrate an integrated sustainable energy generation network providing independence from fossil fuels. More accurately, what is generally refered to as the West Beacon Farm (WBF) system is, in fact, spread across two interconnected sites that are very close to each other: the West Beacon Farm site itself and the Beacon Energy (BE) offices at Whittle Hill Farm. In 1969, the land of West Beacon Farm was very bleak, with only few trees. The priority was therefore to plant thousands of trees, which has enhanced the farm, enriched the biodiversity and at the same time added to the capture of carbon dioxide in the atmosphere. When in the 1980’s the public awareness was being raised and the UK’s increasing reliance on imported energy was also being highlighted, it was decided to replace the oil fired boiler in the farmhouse with a ground source heat pump system. A 4kW wind turbine and 3kW of photovoltaic arrays were installed shortly after that to make the heat pump a self-sufficient system powered entirely by renewables. The site has now become one of the world’s best examples of renewable energy in practice. The technologies on site include: - two 25kW two-bladed wind turbines (now 17 years old), - a total of 13kWp of PV arrays spread across the two sites, - 3.05 kW of micro-hydro generators, - a hydrogen energy system, - a water conservation system where rainwater is the only source, - a sustainable transportation system with electric and hybrid cars. Heating - The farm is heated by a Biklim TOTEM CHP. This propane fuelled CHP unit is approximately 95% efficient and is rated to generate 15kW of electricity and 38kW of heat. Although LPG is a fossil fuel, its combustion is cleaner than standard fuels, with relatively low emissions of greenhouse gases. Gas from a biomass gassifier or hydrogen generated by an electrolyzer could also be used to fuel the unit. Additional heating is generated by a water sourced heat pump system using the water from the lake of the farm. About 4.5 units of useful heat are produced for each unit of electricity consumed by the heat pump and compressor. Since all the electricity required is produced by renewable sources, this heat pump is one of the cleanest and most efficient home heating systems possible. Water - West Beacon Farm is not connected to the mains water network. The only source of water on the site is the rain. The rainwater is collected from the rooftop and filtered before being 10