PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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All of these different possible fuel, intermittent electricity and auxiliary supplies and storage technologies could be used in a variety of combinations to fully satisfy the total energy demands for this island, but a technically attractive range of potential mixes of technologies and processes emerge from the analysis carried out using MERIT, and are discussed in Section 8.3. The final, most suitable solution, however, would depend on a variety of other factors, which might include available land, local geography, positioning of buildings, existing plant, cost of equipment, available subsidies, and projected future demand. 8.3 Analysis Results MERIT has been used to study a variety of different demand scenarios, to ascertain the most technically attractive use of the available local supplies. When considering seasonal fuel supplies such as biodiesel or ethanol from energy crops, it is necessary to consider the half-hourly demand and supply profiles over a whole year. The required plant types and sizes, and the amount of fuel production and storage necessary to allow all the energy requirements (for electricity, heat and transportation) to be met are ascertained for these different possible supply mixes, and the results are discussed below. 8.3.1 Intermittent Electricity Supply The use of an all-intermittent electrical supply was considered, where all the electricity was generated via wind turbines, and electrical storage heaters and electric vehicles were used to meet the heat and transportation demands respectively. Despite the fact that the storage heaters and vehicles provide some storage of excess electricity, a substantial amount of other electrical storage would still be required. In particular, the co-relation between the electricity supply and the overnight re-charging requirements of the vehicles was not good, as this created too large a demand overnight. The electrical storage necessary would be required for periods of one or two months at some times, and would require rapid switching at other times. This pattern of use and the required scale of storage make batteries unsuitable due to the equipment costs and losses which 256
would be incurred, and the scale of the demands being considered are too small for pumped storage to be a viable option. The required installed wind turbine capacity would vary with the inclusion of suitable storage, but would be in the order of 300 to 400 kW to allow all demands to be satisfactorily met within the limitations of currently available storage devices. The introduction of a small amount of photovoltaic generated electricity made little difference to the overall supply pattern due to limited available insolation and areas to site panels. 8.3.2 Intermittent Electricity Supply with Hydrogen Storage Hydrogen has the advantage that it can be used for both long and short term storage as necessary, without significant loss of the energy potential of the stored fuel, and has been considered here, not only as a form of electrical storage, but also for direct use as a fuel for transportation and heating. Any excess electricity is converted into hydrogen via the electrolysis of water (subject to a minimum electrolyser load of 10% of its rated capacity), and can then be used directly in vehicles, in fuel cells for CHP production, and in catalytic hydrogen heaters. For this example, the production of electricity and heat would be carried out centrally, and transmitted to households via an electricity network and district-heating scheme. Figures 8.4 to 8.7 present the results given by the matching procedure in MERIT. These show that all the energy requirements for this area can be met, with minimal losses, by 210 kW of installed wind capacity, a 50Nm 3 (150kW) electrolyser, hydrogen fuelled vehicles, two 20kW proton exchange membrane (low temperature) fuel cells, and a 100kW catalytic hydrogen heater. The excess electricity shown on the residual graph is due to the minimum load requirement of the electrolyser, but the use of this excess electricity in electric storage heaters makes no difference to the required rated capacity of wind turbines. The small amount of excess heat generated is due to excess heat production by the fuel cell CHP plant that is following the electricity demand. The use of the fuel cell CHP plant is considered before the use of the heaters to 257
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Decision Support for New and Renewa
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Abstract The global requirement for
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CONTENTS 1 ENERGY SYSTEMS FOR SUSTA
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5.5 Steam Turbine Model 149 5.6 Fue
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FIGURES Figure 1.1 Final Energy Con
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Figure 7.30 Following Electricity a
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on the use of fossil fuels, energy
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The general increase in energy cons
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supply is reduced or eliminated, lo
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Figure 1.3 The Electricity Supply G
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on different generation mixes depen
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Various studies have been carried o
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provision for smaller areas, and he
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1.7 References [1] The Internationa
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2 Options for New and Renewable Ene
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the amount of usable heat that is g
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the conversion of petrol cars; howe
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set times, producing a constant ele
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partial load. Fast response and sta
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2.3 The Production and Storage of H
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dedicated boiler, which runs contin
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Figure 2.3 A Typical Hydrogen Filli
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part of the natural carbon cycle (a
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Figure 2.4 Layout of a Gasification
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met by process integration and the
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Figure 2.5 The Inputs and Outputs o
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1. Scale for measuring out lye and
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feedstock being used. Sugary feedst
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carbon dioxide via steam reforming.
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• Where CHP is used, the balance
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[22] Vehicle Certification Agency (
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[55] M. A. Paisley, J. M. Irving, R
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3 Approaches to Renewable Energy Sy
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Because of the intermittent nature
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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
Page 205 and 206: If it is the last timestep of the p
Page 207 and 208: For each process, the process chara
Page 209 and 210: At the end of the simulation, graph
Page 211 and 212: As the time required for one batch
Page 213 and 214: Ethanol = Factor1 x Eth x Timesteps
Page 215 and 216: 6.5 Electrolysis As it is sometimes
Page 217 and 218: 6.7 Landfill Gas Processing As the
Page 219 and 220: Demand Profile Design & Profile Dat
Page 221 and 222: Figure 7.2 Degree-Days Versus Month
Page 223 and 224: Stage 1 - Sustainable Fuel Supply S
Page 225 and 226: The different profile of use graphs
Page 227 and 228: Figure 7.3 Fermentation System Inpu
Page 229 and 230: Figure 7.7 Fermentation System Info
Page 231 and 232: Figure 7.10 Fermentation System Out
Page 233 and 234: The output obtained when a second h
Page 235 and 236: Figure 7.16 Anaerobic Digestion Par
Page 237 and 238: Figure 7.19 Fermentation System Inp
Page 239 and 240: clarity. A constant supply rate of
Page 241 and 242: Figure 7.25 Heat Demand Profile Fig
Page 243 and 244: Figure 7.28 Effect of Minimum Load
Page 245 and 246: esidual heat demand as this would r
Page 247 and 248: Figure 7.35 Second Engine: Followin
Page 249 and 250: This chapter described how the over
Page 251 and 252: heat and electricity during the tou
Page 253 and 254: Figure 8.2: Overall Yearly Heat Dem
Page 255: to allow for efficient operation du
Page 259 and 260: Figure 8.5: Electricity Supply and
Page 261 and 262: heat demand or both, or run at cons
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Page 265 and 266: 9 Conclusions and Recommendations T
Page 267 and 268: through these, technically viable p
Page 269 and 270: considered. The introduction of coo
Page 271 and 272: When considering larger geographica
Page 273 and 274: Appendix 1: Program Windows Figure
Page 275 and 276: Figure A1.5 CreateClimate.exe Figur
Page 277 and 278: Figure A1.9: Demand Profile Designe
Page 279 and 280: Figure A1.13: Derived Fuel Supply W
Page 281 and 282: Figure A1.17: Fermentation System D
Page 283 and 284: Figure A1.21: PV Electrolysis Syste
Page 285 and 286: Figure A1.25: Fuel Supply Profile D
Page 287 and 288: Figure A1.29: Auxilliary Supply Def
Page 289 and 290: Figure A1.33: Stirling Engine Syste
Page 291 and 292: Figure A1.37: Fuel Cell System Defi
Page 293 and 294: Figure A1.41: Electric Vehicle Syst
Page 295 and 296: Figure A1.45: Vehicle Conversion Fa
Page 297 and 298: Figure A1.49: Heating System Defini
Page 299 and 300: Figure A1.53: Pumped Hydro System D
Page 301: Figure A1.57: Auto Search Evaluatio
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PhD Thesis - Energy Systems Research Unit - University of Strathclyde

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