Fuel cells and electrolysers in future energy systems - VBN

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Except when pure hydrogen is used, fuel processing removes impurities. Typically, this also involves steam‐reforming processes to ensure hydrogen‐rich fuels. All cells are intolerant to sulphur, and, depending on the type of fuel, the fuel cells must be fitted with a desulphur‐ iser. In lower temperature cells, CO, CO2 and NH3 must also be removed, depending on the type of cell and the type of fuel used. The fuel processing system must also provide fuel and air under the right conditions, i.e. temperature, pressure, moisture and mix, which involves air compressors or blowers as well as air filters. Many of the proposed systems re‐use the waste heat and water in the fuel processing, and they also include afterburners in order to utilise the unused fuel from the fuel cell. In HT‐PEMFCs, anode recirculation has proven to generate high efficiencies [44]. In integrated methanol‐reforming HT‐PEMFCs, purification measures can be avoided. The SOFC is still at the development stage and such systems as well as an integrated fuel‐reforming system still need to be developed. Fig. 8, Principle balance of plant scheme for SOFC. Based on Hansen (CHP) [53]. For all fuel cell systems, a careful management of the temperatures in the fuel cell stack is required. Water/steam is needed in some parts of the fuel cells. While water is a reaction product, a water management system is required in most fuel cells systems to avoid the feed‐in of water in addition to fuel and to ensure a smooth operation of the cell. Large dif‐ ferences can be seen between the specific designs of the fuel cells in terms of fuel and oxi‐ dant handling. For high temperature fuel cells, such as SOFCs, this processing typically also helps to ensure a constant stack temperature as well as longer fuel cell lifetimes by smoothly distributing the different gasses through the cell. In high temperature fuel cells, such as MCFC and SOFC, the fuel processing system may be integrated with a fuel‐reforming system, enabling the use of high temperature heat for re‐ forming e.g. biogas or natural gas to H2. Lately, also HT‐PEMFCs have been developed with integrated fuel processing, leading to improved total efficiencies [29]. For high temperature 44
fuel cells, namely MCFC and SOFC, the system may also be integrated with gas and/or steam turbines, in which the high grade heat is used to increase electricity efficiency. This process integration poses a major challenge to fuel cells at the system level. These issues are intensively researched in order to improve the performance of fuel cell systems. [26;38] In order to be able to integrate the fuel cell unit into the electricity grid, an inverter must change the current from DC to AC. Like other parts of the systems surrounding the cells, this is associated with losses. Additional power electronics and integrated system control can provide the fuel cells with the same abilities as other traditional power supply units in terms of grid stability, i.e. ancillary services enabling them to contribute to maintaining the voltage and frequency stability of the grid [25]. Recent studies show that the feedback from the inverters to the cells may have negative effects on the lifetime of stacks; these are chal‐ lenges that will have to be dealt with in the power conditioning supply. The balance of plant equipment uses a part of the electricity from the cell. Even though the cell itself is scalable for all types of fuel cells, the energy consumed in order to improve the balance of the plant increases with lower cell capacities, especially in the case of high tem‐ perature fuel cells. These effects differ from one cell type to another. The higher the pres‐ sures used in the cell, the more losses result from the balance of the plant. This is especially a challenge to the SOFCs, which are operated at high pressures, and makes the application of hybrid SOFC gas turbines to small‐scale systems unlikely. 4.5 Start‐up, operation and regulation abilities of grid‐connected fuel cells The operation and regulation abilities of fuel cells have to be addressed from a system per‐ spective, since factors such as electrochemical reactions, current and voltage change, gas flow controls, fuel processing, pressure, and water management interact with changing loads. Demands are made on fuel cells in order to meet certain requirements for power quality. In general, all types of fuel cells can respond quickly to an experienced load change; however, differences exist in the start‐up performances of the fuel cells. While stacking the cells increases the voltage of the direct current from the fuel cell; voltage decreases as the amount of power drawn from the cell increases. This is solved by use of appropriate power electronics. A DC/DC converter, and possibly also a DC/AC inverter, can convert the output voltage DC to the voltage DC or AC required for the specific application. When converting output DC to AC, the voltage peaks of the cell as well as the voltage and current relation can be regulated. The grid‐connected fuel cells have to meet certain requirements if they are to support the electricity grid stability. A battery can supply start‐up power and assist in the power conditioning. Furthermore, a transformer can convert lower voltage power into higher voltages, if needed for the supply to the electricity grid, at the distribution or trans‐ mission level. An example of the principle of such a grid‐connected system is illustrated in Fig. 9. Stand‐alone systems also have to meet the requirements of the applications which 45
Page 1: Fuel cells and electrolysers in fut
Page 5 and 6: Tilegnet mine forældre Karl Kristi
Page 7 and 8: Abstract Efficient fuel cells and e
Page 9 and 10: Dansk resumé Effektive brændselsc
Page 11 and 12: Contents ABSTRACT .................
Page 13: Appendices I. B. V. Mathiesen and M
Page 16 and 17: In this dissertation, fuel cells an
Page 18 and 19: Nomenclature Power generation and r
Page 20 and 21: Fuel cells and electrolysers have t
Page 22 and 23: In December 2006, a plan for how an
Page 24 and 25: a) Fuel 107 units b) Fuel 87 units
Page 26 and 27: In the current energy system, elect
Page 29 and 30: 2 The energy system analysis method
Page 31 and 32: taxes. Output consists of annual en
Page 33 and 34: 3 Reference systems and the design
Page 35 and 36: the IDA 2030 system, and, in an upd
Page 37: gies to improve the integration of
Page 40 and 41: Fuel cells AFC PEMFC PAFC MCFC SOFC
Page 42 and 43: PEMFCs are characterised by a rathe
Page 44 and 45: tion time in portable devices [25].
Page 48 and 49: they supply. In transport applicati
Page 50 and 51: Thus, when in operation, all types
Page 52 and 53: CHP, and under four ancillary servi
Page 54 and 55: Grid‐stabilising plants 30 per ce
Page 56 and 57: In the IDA 2030 energy system, a sh
Page 58 and 59: PES excl. wind power (TWh) PES excl
Page 61 and 62: 6 Applications of solid oxide fuel
Page 63 and 64: tion of power plants and improve th
Page 65 and 66: hydrogen Central and Local FC‐CHP
Page 67 and 68: The combinations of seven different
Page 69 and 70: when fuel prices are high, especial
Page 71 and 72: 6.4 Socio‐economic consequences I
Page 73 and 74: 7 Individual household heating syst
Page 75 and 76: kW/kW‐average 3 2 1 0 Heat Demand
Page 77 and 78: Fig. 19, Annual fuel consumption of
Page 79 and 80: Fuel (TWh/year) 14 12 10 8 6 4 2 0
Page 81 and 82: M. EUR/year 800 700 600 500 400 300
Page 83 and 84: Fuel (TWh/year) 18 16 14 12 10 8 6
Page 85 and 86: d) Compared with other fossil fuel
Page 87 and 88: systems are installed, such low tax
Page 89: given heat production. A system is
Page 92 and 93: energy systems in the coming years,
Page 94 and 95: The second of the two types of ener
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Wind power Fuel Power plant CHP Boi
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has been used for identifying the n
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In Fig. 37, the effects of using th
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In the energy system analyses, HP p
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M€/TWh fuel saved 120 100 80 60 4
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For all alternatives, doubling the
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9 Life cycle screening of solid oxi
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chromium alloy used in the intercon
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In terms of primary energy consumpt
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ures on the path towards future 100
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plemented first. The socio‐econom
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socio‐economic calculations)," Da
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[40] M. C. Tucker, G. Y. Lau, C. P.
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[69] H. Lund, "Excess electricity d
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Appendix I 3
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2 Fuel cell types In most countries
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transport or smaller devices. DMFCs
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combined with the water management
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While interconnectors diffuse the g
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the systems are less sensitive to p
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Annex I. AFC Technology (2008‐pri
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Annex III. LT‐PEMFC Technology (2
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Annex V. MCFC Technology MCFC‐sys
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References [1] B. V. Mathiesen and
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[32] J. R. Selman, "Molten‐salt f
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[64] L. Blum, H. P. Buchkremer, S.
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Abstract Solid oxide fuel cells and
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West Denmark Norway Germany 31 Swed
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2 Ancillary service requirements An
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have been identified. For SOFCs, me
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As a reference for the analyses, a
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• Wind turbines and locally dispa
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In the first ancillary service scen
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10 Acknowledgements This paper is p
Page 169:
[34] M. C. Tucker, G. Y. Lau, C. P.
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Research Signpost 37/661 (2), Fort
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Energy system analysis of fuel cell
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Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189:
Page 193 and 194:
Solid oxide fuel cells in renewable
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now, the changes in the Danish ener
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In the next step, a market exchange
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Extensive investments have to be ma
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2.4 Costs of fuels, fuel handling,
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Input: BAU 2030 Electricity system
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potential for producing heat in FC
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cies do not increase due to larger
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In dry years, FC‐CHPs generate pr
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4 Conclusion SOFC can improve the f
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[23] Danish Energy Authority, "Frem
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Comparative energy system analysis
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2 Methodology In the methodology, t
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to fuel at households of 72 per cen
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listed in table 5 are from the Dani
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Fig. 4, Annual fuel consumption of
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enables a heat supply for at least
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The COP of both HP systems have to
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operated simultaneously; that the C
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The HP systems analysed for 300,000
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M. EUR/year 1,300 1,100 900 700 500
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[11] B. V. Mathiesen and H. Lund, "
Page 241 and 242:
Comparative analyses of seven techn
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energy system analysed. Outputs are
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illustrates the excess electricity
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Input: DEA 2030 (market) 123 Refere
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Wind power Fuel Power plant CHP Boi
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of driving at full capacity. The di
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Open energy system, 25 TWh annual w
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Marginal PES excl. wind (TWh) 0,0 -
Page 257 and 258:
educes excess production and fuel s
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M€/TWh fuel saved 120 100 80 60 4
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[8] M. Little, M. Thomson, and D. I
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[37] Danish Energy Authority, Elkra
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Long term perspective for balancing
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Contents 1 Technology Description .
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7.2.1 Fuel cell types In Table 7-2
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In the SOFCs the electrolyte allows
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In the same energy system SOFC CHP
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400$/kW before 2015 also for SOFC s
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unning temperature is lowered to 55
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[12] B. V. Mathiesen and H. Lund, "
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Abstract Integrated transport and r
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phase. The detailed energy system a
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The increase in the international a
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2030, this results in 28.56 PJ net
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ate to 6 per cent. The result is th
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Appendix IX 171
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2 The design of 100% renewable ener
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4 documentation of the model can be
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6 1.000 900 800 700 600 500 400 300
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8 combined in order to reach the ta
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Uncertainties related to the identi
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tion of one marginal technology is
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policies for changes and a projecti
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The policy from 1996 [24] built on
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tial LCA studies should include sev
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6 Case study of the affected electr
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adding waste to the BAU energy syst
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fected; thus, reinvestments are aff
Page 323 and 324:
Appendix A LCA‐Study Miljømæssi
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LCA‐Study LCA of Danish fish prod
Page 328 and 329:
[16] G. Finnveden, J. Johansson, P.
Page 330:
[46] N. Mattsson, T. Unger, and T.
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Fuel cells and electrolysers in future energy systems - VBN

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