The future energy: Hydrogen versus electricity

Abstract

Theoretically there can be different ways of the green (carbon-free) energy development aimed at providing sustainable development of humankind in the future, in particular hydrogen economy or electricity economy. In this paper the processes of hydrogen and electricity production, conversion and storage are compared in terms of energy and economic expenditure for each stage of these technologies. The assessment shows that the electricity economy proves more preferable in the case of short-term energy storage, whereas the use of hydrogen is more beneficial in the case of long-term storage. This is indicative of the fact that the hydrogen economy and electricity economy can coexist in the energy of the future and each energy carrier can find its application area.

Full text

Short Communication
The future energy: Hydrogen versus electricity
O.V. Marchenko, S.V. Solomin
*
Energy Systems Institute of Russian Academy of Sciences, 130 Lermontov Street, 664033 Irkutsk, Russia
article info
Article history:
Received 9 December 2014
Received in revised form
20 January 2015
Accepted 22 January 2015
Available online 14 February 2015
Keywords:
Carbon-free energy technologies
Hydrogen
Electricity
Energy storage
Energy cost
abstract
Theoretically there can be different ways of the green (carbon-free) energy development
aimed at providing sustainable development of humankind in the future, in particular
hydrogen economy or electricity economy. In this paper the processes of hydrogen and
electricity production, conversion and storage are compared in terms of energy and eco-
nomic expenditure for each stage of these technologies. The assessment shows that the
electricity economy proves more preferable in the case of short-term energy storage,
whereas the use of hydrogen is more beneficial in the case of long-term storage. This is
indicative of the fact that the hydrogen economy and electricity economy can coexist in the
energy of the future and each energy carrier can find its application area.
Copyright ©2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights
reserved.
Introduction
Transition to the sustainable development of the human
civilization will inevitably require some change in the energy
mix, development and implementation of new energy tech-
nologies including those carbon-free to reduce greenhouse
gas emissions and restrain the global climate change caused
by the human impact on the environment [1e5].
The wide use of hydrogen, a universal, environmentally
clean energy carrier that has virtually unlimited resources for
its production can become one of the possible avenues for the
future energy development [1,5e13]. Long-term forecasts of
the world energy development [1e4] show that depending on
the expected level of energy consumption as well as other
conditions, especially constraints on the greenhouse gas
emissions, the production and energy-related consumption of
hydrogen by 2050e2100 may exceed the current level by tens
or even hundreds of times.
According to the concept of hydrogen economy, hydrogen
produced from water will gradually replace fossil fuels and
become the main energy carrier in the second half of the 21st
century [5,7]. To this end, it is necessary to solve many tech-
nical problems, which will ensure the safety of hydrogen
technologies, and improve the methods for hydrogen pro-
duction, storage and transportation.
The electricity economy concept represents an alternative
to the hydrogen energy [2,14]. According to this concept
virtually all demand for energy will be met by the single,
environmentally friendly and easy-to-use energy carrier, i.e.
electrical energy. The electricity economy concept suggests
the development of systems for electricity storage and trans-
portation, i.e. storage batteries, supercapacitors and super-
conductors. As in the case of hydrogen economy, it combines
*Corresponding author. Tel.: þ7 3952 500646 448; fax: þ7 3952 426796.
E-mail addresses: marchenko@isem.sei.irk.ru (O.V. Marchenko), solomin@isem.sei.irk.ru (S.V. Solomin).
Available online at www.sciencedirect.com
ScienceDirect
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international journal of hydrogen energy 40 (2015) 3801e3805
http://dx.doi.org/10.1016/j.ijhydene.2015.01.132
0360-3199/Copyright ©2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

well with large-scale development of nuclear energy and en-
ergy based on renewable energy sources, provides flexible
energy supply, high level of security and reliability of energy
systems, and possibility of unifying the technologies and
equipment in the sector of final energy consumption.
Which of the two concepts will be implemented in reality,
or do they both have a right to exist, and hydrogen and elec-
trical energy will occupy their specific niches?
Currently, along with the arguments in favor of transition
to the hydrogen economy [5,6] there is an opinion on its
obvious inefficiency [14e16]. The main argument is the
statement on its low total efficiency. In particular, the author
of [15] shows that the total efficiency of all the hydrogen
technology stages (hydrogen is produced through electrolysis
on the basis of renewable energy sources and is used as a fuel
for cars) is 19e23%, whereas the efficiency of similar electric
system (the same electrical energy production using renew-
able energy sources and charge of the electric car battery) is
69%.
In this connection, it is necessary to note that the efficiency
cannot always be used as a criterion for the comparison of
variants. In many cases (or rather in most cases) it is much
more important to have economic estimates which are not
presented in Refs. [14e16]. Besides, the indicated studies do
not consider the key parameter for the considered energy
carriers, i.e. the time necessary to store them. It is clear that
electrical energy can be used directly for the production of
final energy and energy services with very high efficiency. And
here it surpasses hydrogen. Such a situation, however, occurs
only in the case where we need the final energy at the time of
its production. Meanwhile, to provide the autonomous oper-
ation of energy customer, energy production and consump-
tion should not coincide in time. The difference can be tens of
hours as a minimum. In this case the question arises: what is
more profitable to produce, transport and store: hydrogen or
electrical energy? Even more energy storage time can be
required in the energy systems including renewable energy
sources with stochastic operating conditions (wind and solar
power plants). Normally, it is supposed that the autonomous
operation of such a system can be provided by accumulators
with a capacity allowing load supply during several days
[9,17].
The goal of the present research is to compare the eco-
nomic efficiency of production and storage of energy in the
form of hydrogen and electrical energy, i.e. in fact to compare
the hydrogen economy and the electricity economy. Consid-
eration is given to green (carbon-free) energy production
technologies which do not emit greenhouse gases into the
atmosphere (renewable energy sources and nuclear energy).
The calculation scheme
The research focuses on the hydrogen production from water
on the basis of green (carbon-free) electrical (electrolysis) or
thermal (thermochemical reactions) energy with subsequent
storage. Electrical energy can be generated by renewable en-
ergy sources of different types (wind turbines, solar, hydro, bio
power plants and others). Thermal energy can be produced by
a nuclear unit (high temperature gas cooled reactor). The
technology is compared with the system of electrical energy
conversion and storage (Fig. 1.) Energy carrier (electrical en-
ergy and hydrogen) successively passes through Icompo-
nents; power of the i-th component eN
i
, efficiency eh
i
(Fig. 2).
From the energy conservation law it follows the relation-
ship between the powers of the components
Niþ1¼hiþ1Ni;i¼1;2;…;I1 (1)
and the total efficiency
hS¼Y
I
i¼1
hi:(2)
Let us define the relationship between energy carrier cost
at the input of component p
i
and output from it p
iþ1
as follows.
Suppose that the system is created during a relatively short
time period and then is operated with the constant capacity
factor. Then, the cash flow E
i
(the difference of benefits and
costs for the i-th component per time unit) and net present
value (NPV
i
)will be equal [9] to
Ei¼piþ1pi
hiNihmikiNi;(3)
NPVi¼kiNiþZTi
0
EiexpðstÞdt;i¼1;2;…;I;(4)
respectively, where his the annual number of utilization
hours, k
i
is the specific capital investment (per power unit), m
i
is the specific constant costs (share of investments), T
i
is the
lifetime of components, s¼lnð1þdÞ,dis the annual discount
rate.
The condition for the project effectiveness is non-
negativity of the NPV value. In the case of a competitive
Electrolyzer
Compressor
Hydrogen tank
Electrical energy
АС/DC
converter
Fuel cells
Electric
accumulator
АС/DC
converter
Nuclear energy
Compressor
Fuel cells
Hydrogen tank
Fig. 1 eCompared variants.
international journal of hydrogen energy 40 (2015) 3801e38053802

market, producers will have to decrease the price of their
product to the minimum value providing the project effec-
tiveness, i.e. the price under which the NPV is close to zero. By
equating NPV
i
to zero we find the cost of energy carrier
(minimum price) at the output of the i-th component
piþ1¼pi
hi
þki
hðCRFiþmiÞ;i¼1;2;…;I;(5)
where
CRFi¼s
1expðsTiÞ(6)
is the capital recovery factor [9]. Equation (5) makes it possible
to successively estimate a rise in the cost of the energy carrier
as it passes through the system components and compare the
final cost of energy for different variants.
The calculation of some components has specific features.
In literature, the specific capital investment in electrolyzer k
is usually given per unit of the consumed (electric) power. To
reduce the investment to the unit of the output power N,it
should be recalculated by the equation
k¼k=h:(7)
Specific capital investment in the hydrogen tank b
kis given
in US dollars per cubic meter of its actual volume. To reduce
this value to the dimension US$/kW required for equation (5),
we assume that the hydrogen tank volume should be such
that power Ncan be supplied during qhours (the value qwill
be called power supply period). Then
k¼k
∧
q=C1P0
P1;(8)
where C
1
¼3,56 kWh/m
3
is an energy equivalent of a cubic
meter of gaseous hydrogen under normal pressure P
0
,P
1
is
pressure in the tank.
Capital investment in the electric accumulator k*(US$/
kWh) is converted to the dimension US$/kW by the equation
k¼k*q:(9)
Technical and economic indices of the
technologies
Table 1 presents the characteristics of the hydrogen and
electrical energy production and storage technologies for two
scenarios by the data from Refs. [2,9,18e26]. The
characteristics of the basic scenario approximately corre-
spond to the best modern types of the respective technology,
optimistic eto the forecast for the coming 15e20 years.
The specific capital investment in the modern electrolyzers
with power consumption above 100 kW lies in the range
1500e3500 US$/kW [9,18,19]. For the prospective electrolyzers
the value used in some publications is 740 US$/kW [9,20].
Specific capital investment in the voltage transformers (con-
verters) correspond to the data from Refs. [18], in compressors
eto the data from Refs. [20], fuel cells e[9,18,22e24], electric
accumulators e[24,25]. The assumed values of operating costs
and service life are in line with the recommendations from
Refs. [9,18e24], the efficiency values correspond to those
presented in Refs. [9,15,18,26].
It was supposed that the process of electrolysis consumes
electrical energy generated by some conditional power plant
with an efficiency of 37 percent and cost of 7 cent/kWh (basic
scenario) and 5 cent/kWh (optimistic scenario), whereas the
hydrogen cost at its production using nuclear energy is
5 US$/kg (basic scenario) and 2 US$/kg (optimistic scenario).
The total number of capacity utilization hours h¼6000 h/
year.
Fig. 2 eThe i-th component of the energy conversion
scheme (i¼1, 2, …,I).
Table 1 eIndices of technologies.
Specific
investment,
$/kW
Specific fixed
costs, % of
investment
Efficiency,
%
Lifetime,
years
Business-as-usual (BAU) scenario
Converter 300 2 95 10
Electrolyzer 1500 3 70 10
Compressor 1000 2 90 10
Hydrogen tank 880
a
19510
Fuel cells 2000 2.5 50 10
Accumulator 150
b
58510
Optimistic (OPT) scenario
Converter 250 2 95 10
Electrolyzer 740 3 77 20
Compressor 1000 2 90 10
Hydrogen tank 600
a
19820
Fuel cells 800 2.5 60 10
Accumulator 100
b
39015
a
$/m
3
.
b
$/kWh.
Table 2 eEfficiency, costs in accordance with energy
conversion stages and energy cost (electrolytic hydrogen,
optimistic scenario, power supply period e12 h).
Energy
conversion
stage
Overall
efficiency,
%
Cost,
cent/kWh
Energy cost
Cent/kWh $/toe $/kg
Power plant
a
37.0 5.0 5.0 583
Converter 35.2 1.0 6.0 698
Electrolyzer 27.1 4.1 10.1 1173 4.0
Compressor 24.4 3.5 13.5 1577 5.3
Hydrogen tank 23.9 0.7 14.2 1657 5.6
Fuel cells 14.3 11.9 26.1 3042
a
Renewable energy source.
international journal of hydrogen energy 40 (2015) 3801e3805 3803

Calculation results
Results of the calculation using equations (1)e(9) are pre-
sented in Tables 2e4for a short power supply period (q¼12 h)
and in Figs. 3 and 4 for q¼12 and q¼120 h. The total efficiency
of the hydrogen technology, when hydrogen is produced by
both electrolysis and using nuclear energy (14.3 and
19.6 percent, Tables 2 and 3), is considerably lower (by
1.5e2 times) than in the case of electrical energy technology
(31.6 percent, Table 4). Such a relationship takes place even
with prospective characteristics of hydrogen technology. This
confirms the conclusion made in Ref. [15] about its lower en-
ergy efficiency. Meanwhile, the conclusion on lower cost
effectiveness of the hydrogen technology can be made only for
a short-term power supply period (to the points of intersection
of curves in Figs. 3 and 4): less than 100e110 h for electrolytic
hydrogen (Fig. 3) and 50e80 h for nuclear hydrogen production
(Fig. 4). This can be explained by the fact that when the time of
energy storage rises, the costs of accumulator in the
electricity-based system increase much faster than the costs
of hydrogen tank.
Thus, in the case of short-term energy storage it turns out
to be more preferable to use the electricity-based system,
while in the case of long-term energy storage ethe hydrogen
one. This means that hydrogen economy and electricity
economy can apparently coexist, and each energy carrier will
find its niche of application. In short-term energy storage the
most effective energy carrier is electrical energy, and in long-
term energy storage ehydrogen (for instance, as a fuel for
peak power plants and heat supply systems and as an energy
carrier that will be stored in renewable energy system oper-
ating under stochastic conditions [9,17,27]). It should be noted
that the obtained results are true only for presently available
technical and economic indices of the technologies and their
further improvement may require more detailed research into
the said indices.
Conclusion
Presently, there is no consensus on the potential use of
hydrogen in the future. Along with the arguments for the
transition to hydrogen economy in prospect, there is an
opinion about its insufficient efficiency.
The paper presents a comparative economic analysis of
hydrogen and electricity production and storage (comparison
of hydrogen economy and electricity economy). The analysis
is based on the existing and projected technical and economic
indices of the competing variants.
The obtained estimates prove that the claims that the
hydrogen economy is ineffective due to its lower efficiency are
Тable 3 eEfficiency, costs in accordance with energy
conversion stages and energy cost (nuclear hydrogen
production, optimistic scenario, power supply period e12 h).
Energy
conversion
stage
Overall
efficiency,
%
Cost,
Cent/kWh
Energy cost
Cent/kWh $/toe $/kg
Nuclear
power plant
37.0 5.1 5.1 592 2.0
Compressor 33.3 3.3 8.3 971 3.3
Hydrogen 32.6 0.6 8.9 1040 3.5
Fuel cells 19.6 8.3 17.3 2012
Table 4 eEfficiency, costs in accordance with energy
conversion stages and energy cost (electrical energy,
optimistic scenario, power supply period e12 h).
Energy
conversion
stage
Overall
efficiency,
%
Cost,
cent/kWh
Energy cost
Cent/kWh $/toe
Power plant
a
37.0 5.0 5.0 583
Converter 35.2 1.0 6.0 698
Accumulator 31.6 3.8 9.8 1138
a
Renewable energy source.
0
25
50
75
0 20 40 60 80 100 120
Power supply period, ho urs
Energy cost, cent/kWh
H2-BAU
E-BAU
E-OPT
H2-OPT
Fig. 3 eRelationship between final electrical energy cost
and power supply period. Electrolytic hydrogen
production. Variants: Н
2
ehydrogen, E ¡electrical energy,
BAU ebusiness-as-usual scenario, ОPT eoptimistic
scenario.
0
25
50
75
0 20 40 60 80 100 120
Po wer supply period, ho urs
Energy cost, cent/kWh
H2-BAU
E-BAU
E-OPT
H2-O PT
Fig. 4 eRelationship between final electrical energy cost
and power supply period. Nuclear hydrogen production.
Variants: Н
2
ehydrogen, E ¡electrical energy, BAU e
business-as-usual scenario, ОPT eoptimistic scenario.
international journal of hydrogen energy 40 (2015) 3801e38053804

inadequate. Indeed, in the case of short-term energy storage
(less than 50e110 h) it is more preferable to use the electric
system, whereas in the long-term energy storage the
hydrogen system is more efficient. In this connection we can
suppose that the hydrogen economy and electricity economy
can coexist in the energy industry of the future. Moreover,
each energy carrier will find its niche of application.
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