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Objective of the studyComparison of two future energy systems
Hydrogen system (HS) vs.All electric system (AES)
Point 1: in terms of efficiency, not the cost
Point 2: primary energycase 1 fossil fuels
case 2 non-fossil fuels
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Fig.1 HS and AES
primary
energy
transportation
networkP.E.H2 FC E demand
electricity
wasteheat
power
generationtransportation
network
E demand
Heat demandHP
solar energy
COP
Hydrogen System(HS) Heat demand
electricity
H2
heat
exchangeable
All Electric System(AES)
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primary
energy
transportationnetwork
bombe
motor
power
generationmotor
ft fr fFC fm
hg ht hB h
electricity
fb
Hydrogen System (HS)
All Electric System (AES)
Fig.2 transportation system
in case ofFCV and pure EV
batterytransportation
network
exchangeable
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Main elements
in efficiency assessment
1. Conversion from primary energy
to secondary energy ( H2, electricity )
2. Fuel cells
3. Heat pumps ( Coefficient of performance)
4. Battery ( charging and discharging )
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Conversion of primary energy
to hydrogen1. Primary energy = fossil fuels: present reformer
2. Primary energy = non fossil fuels
1) nuclear / biomassburning electric catalysis
P.E electric power H2
2) nuclear
high temp.gas reactor thermo-chemical conv.P.E. high temp.heat H2
3) biomass direct conversion to H2
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present future
Production cost
of H2
Conversion
efficiency
ConversionEfficiency
(with CO2 capture)
Table 1: Reformer efficiency
(ct. US academy of science, LHV)
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on fossil fuels H21. P.E. elec.power H2
not competable with AES
reason: elec.power H2 elec. Power
is less efficient than AES
2. Therefore the following two are candidates.
1) P.E. high temp. heat H2
2) direct conversion of biomass to H2
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Fig.3 production of H2 from nuclear power- thermo-chemical conversion ( IS method) -
High temp.
gas reactor
H2+I22HI
2HI+H2SO4
I2+H2O+S2O+H2O
H2SO4
SO2+H2O1/2O2
SO2+H2O
900
heat400
heat
HI H2SO4
I2
H2O
H2
hydrogen
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HIILFLHQF\
Temp. Fig.4 Efficiency of IS method
source national academies press, Hydrogen Economy 2004,p.215
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Within
Several years
Future
(2015-2020)
Stationary FC
HHV
Present situation
47 %
32 %
55 %
Mobile FC
LHV
58 % 65 %
Table 2. Efficiency Targets forFC
- government of Japan -
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Assumptions1. In HS heat demand canbe satisfiedby waste
heat ofFC and afterburning of H2 if necessary.
2. Time variability of demands is neglected. Inother words demands are assumed to be
constant throughout the period.
3. Loss in transportation of H2 is neglected.
No.2 and 3 are optimistic assumptions for HS.
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Primary energy demands for HS and AES
- in case of stationary demand -
Without after-burning
FHS =D
t FC(1)
FAES =
D+H/COP
g(2)
With after-burning
FHS
=t
1D/
FC
+HD/FC
(1-FC
) (3)
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Case A Case B Case D Case E
HS is alwayssuperior
HS is relativelysuperior
HS and AES in total efficiency5 cases
AES is relativelysuperior
AES is always
superior
F
F:primary energy demand
heat / electric power ratio of the demand
: Hydrogen system(HS)
: All Electric system(AES)
HS
AES
Case C
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Technologies stagnant case progress case
H2 reformer r 0.72 0.79
H2 transport t 1 1
Fuel cell FC 0.40 0.55
Heat utilization
Ratio
1 1
Power generation
g
0.50 0.55
Power transmission
t
0.90 0.90
COP of heat pump 3 3
Table.Efficiency values of system elements:fossil fuel case
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Hydrogen tech
stagnant case
Hydrogen tech
progress case
Power tech
stagnant case
Case E
AES is always
superior
Case D
AES is relatively
superior
Power tech
progress case
Case E
AES is always
superior
Case D
AES is relatively
superior
Table. Comparison of HS and AES: stationary demand
- fossil fuel case -
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Primary E
HS
AES
HS is better
in efficiency
Case D
HS
AES
AES is always better
in efficiency
Case E
Fig. Cases D and E
Hydrogen tech progress case Hydrogen tech stagnant case
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Technologies stagnant case progress case
H2 reformer r 0.50 0.60
H2 transport t 1 1
Fuel cell FC 0.40 0.55
Heat utilization
Ratio
1 1
Power generation
g
0.30 0.35
Power transmission
t
0.90 0.90
COP of heat pump 3 3
Table.Efficiency values of system elements:nuclear case
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Hydrogen tech
stagnant case
Hydrogen tech
progress case
Power tech
stagnant case
Case E
AES is always
superior
Case B
HS is relatively
superior
Power tech
progress case
Case E
AES is always
superior
Case B
HS is relatively
superior
Table. Comparison of HS and AES: stationary demand
- nuclear case -
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Primary E
HS is better
in efficiency
Case B
HS
AES
AES is always better
in efficiency
Case E
Fig. Cases B and E
AES
HS
Hydrogen tech stagnant caseHydrogen tech progress case
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Fuel charging of EV and FCV1. Charging the battery takes hours, while
charging H2 takes only several minutes.
= Fundamental disadvantage of EV
2. However,with revolutionary change in charging
tech ( including those of capacitors ), EV will
obtain muchbetterposition in future.
At this moment FCV is much advantageous.
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primary
energy
transportationnetwork
bombe
motor
power
generationmotor
ft fr fFC fm
hg ht hB
electricity
fb
Hydrogen System (HS)
All Electric System (AES)
Fig.2 transportation system
in case ofFCV and pure EV
batterytransportation
network
exchangeable
hm
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HS vs. AES: automobile demand
- (1) efficiency data -1. reformers and fuel cells
power generation and transmission
the same as in case of stationary demand
2. automobilebattery
present: 0.80 future: 0.85
3. motorsame for EV and FCV
for convenience efficiency = 1
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Hydrogen tech
stagnant case
Hydrogen tech
progress case
Power tech
stagnant case
fFCV = 0.29
fEV = 0.36
EV is superior
fFCV = 0.43
fEV = 0.36
FCV is superior
Power tech
progress case
fFCV = 0.29
fEV = 0.42
EV is superior
fFCV = 0.43
fEV = 0.42
EV and FCV
compatible
Table. Comparison of HS and AES: automobile demand
- fossil fuel case -
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Hydrogen tech
stagnant case
Hydrogen tech
progress case
Power tech
stagnant case
fFCV = 0.20
fEV = 0.22
EV is relatively
superior
fFCV = 0.33
fEV = 0.22
FCV is superior
Power tech
progress case
fFCV = 0.20
fEV = 0.27
EV is superior
fFCV = 0.33
fEV = 0.27
FCV is superior
Table. Comparison of HS and AES: automobile demand
- nuclear case -
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Summary of findings
- stationary demand (1) -1. In case that primary energy is of fossil fuels hydrogen
system (HS) is superior
only with advancement of related technologies, ifrequired afterburning is less than a certain limit.
However several assumptions about efficiencies of relatedhydrogen system elements being rather optimistic we
should recognize that HS can survive only withdesperate efforts for substantial improvement ofsystem efficiency.
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Summary of findings
- stationary demand (2) -2. In case that primary energy is nuclear,
HS is superior again only with remarkable
improvement of efficiencies of related systemelements.
The position of HS is relatively better when
compared with the case of fossil fuels being
primary energy sources.
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Summary of findings
- in case of automobile demand -FCV is mostly superior in system efficiency to
pure EV if related system technologies
remarkably advance.
Taking into account that FCV has much less fuel
charge time than EV, we may say that use of
hydrogen will be more advantageous and
realistic in transport sector than in stationary
demand sector.
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Fig. Remaining Issue: How to transfer from
Present decentralized system to Future centralized system
Primary
Energy
Distribution
network
City gas
Petro productsCokes gas
Gas pipeline
Petro station network
Large scale
Hydrogen network
PE: fossil fuels PE: nuclear / biomass
Small scale
biomass
Large scale
biomass
Nuclear energy
Decentralized
system
Centralized
system
present future