PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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generated than there is demand for), in order to avoid wastage [2,3]. This electricity may be stored, using various means, depending on the scale of storage required. This stored electricity would then be available for use at times when there is not enough being generated to meet demand. This type of storage system is useful when the overall amount of excess electricity is equal to the overall demand that cannot be met by generation over a given length of time. The sizing and type of storage system required depends on the relationship between the supply and demand profiles. This type of system, however, only addresses the demand for electricity, and not those for heat, hot water and transport. If large amounts of excess electricity are being produced (much more than is needed overall to meet the electricity demand), this could be used to make hydrogen via the electrolysis of water [4]. This hydrogen could then be stored, used in heaters or vehicles, or converted back into electricity via a fuel cell later as required. Using excess electricity, this hydrogen could be produced centrally and piped to users, produced at vehicle filling stations, or at individual homes or business premises [5]. Alternatively, excess electricity could be used directly to fuel electric vehicles, recharging at times of low electricity demand, or to produce heat for space and water heating for immediate use, or to be stored as hot water or in storage heaters. When there is an electricity demand that cannot be met by the intermittent generators, a small amount of storage, or generators fuelled with biomass, waste or derived fuels could be used in the system to meet this. The same derived fuels can also be used to fuel vehicles. If large amounts of excess electricity are not desired, or if there is a low percentage of intermittent generation available in the system, the bulk of the electricity generated will need to come from engines or turbines fuelled with biomass, waste or derived fuels [2]. If this is the case, the use of combined heat and power (CHP) generation should be considered, as this provides much better fuel utilisation and can also help meet the heat demand [6]. When considering CHP, it is important to bear in mind the heat to electricity ratio. This ratio states 30
the amount of usable heat that is generated in comparison to the electricity output, and can vary between 1 and 5 times the electricity output, depending on the type of plant being considered. In a system using CHP, it is important to get the balance between heat and electricity demand as close to the heat to electricity ratio as possible to avoid wastage. This may be achieved by using intermittent supplies to meet some of the electricity demand, by using heat and electricity storage, and/or by using supplementary electrical heating. This optimum balance can be difficult to find, especially where there is a large seasonal variation in heat demand. Where technologies that are best run continuously (e.g. nuclear power stations or slow response energy limited plant), or supplies with predictable but intermittent outputs (e.g. tidal barrages) are run, the same problem of excess electricity occurs at times of low demand. If CHP is being considered, there is also the problem of excess heat. Again, suitable use should be made of these excesses, and this may be achieved using the various methods described previously. These examples highlight the complex nature of sustainable energy supply systems, especially when considering the total energy needs of an area and the use of intermittent sources of electricity. The integration and control strategies for all of these components must be carefully considered and implemented, and this complexity has been seen as a barrier to renewable energy system deployment. There are many possible supply combinations that can be employed, and the optimum combination for a given area depends on many factors. The balances being considered can be complex, and this highlights the need for a decision support framework through which the relative merits of many different scenarios and control strategies for a chosen area can be quickly and easily analysed. This chapter describes the technologies currently available to enable the realisation of the systems described above. Alternative transportation fuels and vehicles, and alternatively fuelled technologies for CHP generation are discussed. The production and storage of heat, and other uses for excess 31
Page 1 and 2: Decision Support for New and Renewa
Page 3 and 4: Abstract The global requirement for
Page 5 and 6: CONTENTS 1 ENERGY SYSTEMS FOR SUSTA
Page 7 and 8: 5.5 Steam Turbine Model 149 5.6 Fue
Page 9 and 10: FIGURES Figure 1.1 Final Energy Con
Page 11 and 12: Figure 7.30 Following Electricity a
Page 13 and 14: on the use of fossil fuels, energy
Page 15 and 16: The general increase in energy cons
Page 17 and 18: supply is reduced or eliminated, lo
Page 19 and 20: Figure 1.3 The Electricity Supply G
Page 21 and 22: on different generation mixes depen
Page 23 and 24: Various studies have been carried o
Page 25 and 26: provision for smaller areas, and he
Page 27 and 28: 1.7 References [1] The Internationa
Page 29: 2 Options for New and Renewable Ene
Page 33 and 34: the conversion of petrol cars; howe
Page 35 and 36: set times, producing a constant ele
Page 37 and 38: partial load. Fast response and sta
Page 39 and 40: 2.3 The Production and Storage of H
Page 41 and 42: dedicated boiler, which runs contin
Page 43 and 44: Figure 2.3 A Typical Hydrogen Filli
Page 45 and 46: part of the natural carbon cycle (a
Page 47 and 48: Figure 2.4 Layout of a Gasification
Page 49 and 50: met by process integration and the
Page 51 and 52: Figure 2.5 The Inputs and Outputs o
Page 53 and 54: 1. Scale for measuring out lye and
Page 55 and 56: feedstock being used. Sugary feedst
Page 57 and 58: carbon dioxide via steam reforming.
Page 59 and 60: • Where CHP is used, the balance
Page 61 and 62: [22] Vehicle Certification Agency (
Page 63 and 64: [55] M. A. Paisley, J. M. Irving, R
Page 65 and 66: 3 Approaches to Renewable Energy Sy
Page 67 and 68: Because of the intermittent nature
Page 69 and 70: A renewable energy supply evaluatio
Page 71 and 72: the system are kept. The output of
Page 73 and 74: There are various models available
Page 75 and 76: When the use of climate dependant i
Page 77 and 78: 3.5 References [1] M. Muselli, G. N
Page 79 and 80: 4 A Procedure for Demand and Supply
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pumped storage and flywheels), a ba
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for the agricultural vehicle use re
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Figure 4.4 Combining Demands to Tak
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ates for vehicles, engines and othe
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Figure 4.5 Derived Fuel Production
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together if desired, and taken forw
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profiles are output from this part
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dividing the production rate at eac
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As it would be too confusing to sho
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Figure 4.12 Output of the Matching
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However, when more than one transpo
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considered, this amount is added to
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users are alerted if there is not e
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at the matching stage, along with t
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vehicles if they are increased by 1
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If biogas is being considered, the
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The number of timesteps per hour wi
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After the algorithm has been follow
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• Float Charge - once the battery
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Discharge No tank = tank fuel used
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equired (kW) = maxkWh x bulk% (5.16
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An example of the output graph prod
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5.2.1 Required Power Specifically d
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5.2.3 Engine Performance in the Con
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used for gas powered ICEs, but the
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and five times, depending on the nu
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Is PL < Min ? No Is PL = 0 ? No Is
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where Max = maximum energy availabl
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where Ratiopart = heat to electrici
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(including following heat demand wh
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where SFC = specific fuel consumpti
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engines running respectively). If t
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(continued) Is Fuel Available > (4
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of the definition window for a Stir
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and continuous operation. Again, mu
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The performance of a fuel cell is n
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percentage loading, rather than usi
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Is Min = 0 ? No Is Min = PC1 ? No I
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5.6.4 If Fuel Availability is Less
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5.7 Electrolyser Model An electroly
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original calculation of the amount
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5.8 Regenerative Fuel Cell Model A
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following the heat demand. To follo
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C:\ My Documents\ Nic\ Thesis\ Old\
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As 1 kWh = 3610.3 kJ, and using lit
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Add Heat to Water Storage Tank Usin
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Use Stored Hot Water to Supply Heat
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information is given about the over
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[23] K. Foger, B. Godfrey, “Syste
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the gasification and pyrolysis defi
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eing used each day for a continuous
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Where Biogas = Biogas production ra
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6.1.3 Use of Biogas Various options
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The amount of hydrogen that can be
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direct proportion, and the weight o
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produce in total (Nm 3 per tonne fe
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Electricity (kW) = Elec x Feed (6.1
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3. Make hydrogen via steam reformin
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Where Methane = Methane Production
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(continued) Keep as medium heating
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Yes Feed1 = Yield1 x Land1 / No. of
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production and energy use profiles
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If it is the last timestep of the p
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For each process, the process chara
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At the end of the simulation, graph
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As the time required for one batch
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Ethanol = Factor1 x Eth x Timesteps
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6.5 Electrolysis As it is sometimes
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6.7 Landfill Gas Processing As the
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Demand Profile Design & Profile Dat
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Figure 7.2 Degree-Days Versus Month
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Stage 1 - Sustainable Fuel Supply S
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The different profile of use graphs
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Figure 7.3 Fermentation System Inpu
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Figure 7.7 Fermentation System Info
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Figure 7.10 Fermentation System Out
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The output obtained when a second h
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Figure 7.16 Anaerobic Digestion Par
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Figure 7.19 Fermentation System Inp
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clarity. A constant supply rate of
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Figure 7.25 Heat Demand Profile Fig
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Figure 7.28 Effect of Minimum Load
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esidual heat demand as this would r
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Figure 7.35 Second Engine: Followin
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This chapter described how the over
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heat and electricity during the tou
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Figure 8.2: Overall Yearly Heat Dem
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to allow for efficient operation du
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would be incurred, and the scale of
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Figure 8.5: Electricity Supply and
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heat demand or both, or run at cons
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ut with 30% less land being require
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9 Conclusions and Recommendations T
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through these, technically viable p
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considered. The introduction of coo
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When considering larger geographica
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Appendix 1: Program Windows Figure
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Figure A1.5 CreateClimate.exe Figur
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Figure A1.9: Demand Profile Designe
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Figure A1.13: Derived Fuel Supply W
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Figure A1.17: Fermentation System D
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Figure A1.21: PV Electrolysis Syste
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Figure A1.25: Fuel Supply Profile D
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Figure A1.29: Auxilliary Supply Def
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Figure A1.33: Stirling Engine Syste
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Figure A1.37: Fuel Cell System Defi
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Figure A1.41: Electric Vehicle Syst
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Figure A1.45: Vehicle Conversion Fa
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Figure A1.49: Heating System Defini
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Figure A1.53: Pumped Hydro System D
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Figure A1.57: Auto Search Evaluatio
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PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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