PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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The other main class of renewable energy sources are those that are intermittent in nature (e.g. wind, wave, solar, tidal, run-of-the-river hydro). With the exception of tidal energy, intermittent sources are unpredictable, have no storage capacity, and vary substantially with the local weather patterns. If a large percentage of this type of generator is used to feed an electricity supply grid, their intermittent and unpredictable nature is likely to make control of that grid difficult, due to problems with network balancing. Although it may be predicted from an area’s climate that the generators will supply enough electricity overall, this is no guarantee that this overall amount will be available, or when it will be available. Generators may not produce electricity when it is needed, or they may be generating when there is no demand. Variation of weather patterns and demand with the seasons also needs to be taken into consideration. Currently there are only a small number of these types of plant supplying electricity to the grid in the UK, however if an increasing number of intermittent generators are to be used, these problems will require further investigation. With the exception of large projects like tidal barrages, renewable energy power plant (both intermittent and energy limited) tend to be smaller than traditional capacity limited plant, and are generally spread throughout the network wherever the exploitable energy sources are located. This type of supply is known as distributed generation where there are a large number of smaller generators located throughout the network, often in more remote areas where the grid is weak. This, again, will have an important effect on the design of future electricity supply grids, and on the necessary intermediate planning decisions. 1.3.3 Increased Grid Penetration of Renewable Energy Generators A greater reliance on distributed renewable generating plants has interesting implications for the organisation of the electricity supply network. As more distributed sources start to be utilised, a more interconnected network should emerge. Having a larger number of minor generators throughout the network should allow many smaller areas of that network to become mainly selfsufficient, with the rest of the grid there only for backup. These areas will rely 20
on different generation mixes depending on the type of area, suitable sites, and available local resources. Distributed generation will also bring a number of other benefits. If electricity is generated closer to the end user by smaller plants it will not need to be transmitted as far, and at such large power densities. Transmission line and conversion losses will therefore be reduced, though remote networks containing generators may need to be upgraded. Also, if power transmission densities are reduced, it may allow more overhead lines to be economically replaced with underground cables, alleviating the health, safety and visual disturbance issues relating to overhead cables [11]. Although the exact effects need to be investigated, distributed generation should help strengthen the grid, and allow greater autonomy and a better security of supply, particularly in remote areas. Inevitably, the way the electricity supply grid is organised will change radically with the inclusion of increasing amounts of distributed renewable electricity generation. The situation will gradually change as individual thermal power plants reach the end of their lives and are replaced by increasing numbers of distributed renewable generators. Unfortunately, the intermittent nature of the most easily exploited sources (wind and solar) is likely to cause problems as ever-increasing amounts of these intermittent sources are used to supply the electricity network. This has implications for the management of this transitional period as the balance between supply and demand must be maintained as efficiently and reliably as possible while the system moves towards the ultimate goal of a 100% renewable energy supply over the next fifty to one hundred years. Opinion is divided as to the effect that a significant amount of intermittent electricity sources would have if integrated into a larger-scale electricity supply network. McLarnon and Cairns [8] state that energy storage is critical to systems supplied with intermittent energy, while Grubb [7] states that it should be possible to have large systems with well over half of their power from intermittent sources, provided that there is a large amount of fossil fuelled spinning reserve. This reserve, however, could be supplied by plant run on fuels 21
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: Figure 1.3 The Electricity Supply G
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 and 30: 2 Options for New and Renewable Ene
Page 31 and 32: the amount of usable heat that is g
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
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the system are kept. The output of
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There are various models available
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When the use of climate dependant i
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3.5 References [1] M. Muselli, G. N
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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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