International Journal of Modern Engineering Sciences, 2013, 2(1): 28-38
International Journal of Modern Engineering Sciences
ISSN: 2167-1133
Florida, USA
Journal homepage:www.ModernScientificPress.com/Journals/IJMES.aspx
Article
Utilization of Excess Wind Energy for Electrolytic Hydrogen
Production
Umar Kangiwa Muhammad1, Sadik Umar1, Muazu Musa2, Muhammad Mahmud Garba2, Umar
Zangina2
1
Kebbi State University of Science and Technology Aliero
2
Sokoto Energy Research Centre (SERC), Usmanu Dan Fodio University Sokoto
*
Author to whom corresponding should be addressed; Email: [email protected]
Article history: Received 30January 2013, Received in revised form 13 March 2013, Accepted 20
March 2013, Published 26 March 2013.
Abstract: Since wind power is a clean source of energy and is widely available, scientists
have focused on finding ways to store wind power for energy use during times when there
is no wind present. Storing excess energy generated from wind power during times of high
wind and low demand can power an electrolyzer to generate hydrogen fuel. Utilizing the
stored hydrogen for re-electrification through the fuel cell, Internal Combustion Engines
(ICE) and domestic heating through burners declared hydrogen an alternative renewable
energy resource. In the present research, the diverted excess wind energy is stored in
auxiliary storage batteries and used for water electrolysis using potassium hydroxide
(electrolytes) and platinum electrodes. However, electrolyzers are connected in parallel and
series arrangements to the excess wind energy source and the effects of input voltage and
current on electrolyzer performance due to these connection modes are investigated. The
results show that electrolyzer voltage has highly effected the specific energy consumption,
the hydrogen volume flow rate and energy conversion efficiency for electrolyzers series
connection. Electrolyzer current has highly affected the performance of electrolyzer when
parallel connections are been considered. However, better performances were observed by
series connections of electrolyzers.
Keywords: Wind Energy, Electrolytic Hydrogen, Volume flow rate, Energy efficiency
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
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1. Introduction
Wind energy is a clean and useful renewable natural form of energy. It is converted into wind
power to generate electricity by using wind turbines. Wind turbines produce electricity only when the
wind is blowing. But due to the variability of wind speed, the wind energy becomes intermittent in
nature. Therefore, storage facilities need to be integrated to store the energy during the off- load and
low load demand periods. However, under these conditions, the storage batteries may be fully charged
and the excess energy generated would be dissipated through the dump load (heat sinks). Heating has
negative effects on batteries and usually electronics devices such as inverters and charge controllers
and therefore, the excess wind energy need to be stored in another form of energy carrier, which could
be utilized for other domestic uses or re-generation of electricity for maintaining the usability and
stability of the wind power systems.
Marco, (2012) suggested methods for storing excess wind energy as: Storage batteries, Pumped
storage, compressed air, Hydrogen and ammonia and others such as dump load for space heating, fan
for cooling and super- capacitors for storing large electricity for later use. He pointed out that
Hydrogen can be produced from electricity from wind turbines and it can also be supplied to a fuel cell
to produce electricity at a later time Marco (2012). Producing hydrogen with domestic RE sources will
reduce the impact of greenhouse gasses emitted into the atmosphere. Wind energy is currently the
lowest cost RE source, and is the leading near term candidate for renewably generated hydrogen
production. Katarzyna pointed out that the only mature and available technology for producing
hydrogen from renewable sources is water electrolysis, in which a molecule of water is split into
oxygen and hydrogen by applying electricity Katarzyna (2009). The limitations of intermittent wind
energy source are potentially overcome by hydrogen system. Excess power is converted and stored
inform of hydrogen gas in storage tank. Advances in hydrogen technology and equipment such as
electrolysers, fuel cells, hydrogen storage techniques in the recent years make the storage of excess
renewable energy a high-potential alternative, and also increase the possibility to make the remote
areas and isolated community self-sufficient (Karri et al.2008). Stiller and Michalski, pointed out that
the excess wind power could be utilized for the electrolytic production of hydrogen which can be
stored and used as a transportation fuel, as a feed stock for chemical industries, or even for power
production in times of low renewable generation (Stiller and Michalski, 2010). Anna (2011) pointed
out that, in order to stabilize energy production during the absence of wind or in the condition of light
wind, stored hydrogen could be re–used. Excess wind power is defined as the effect that the production
from the base load power plants and the wind power plants exceeds the electricity demand.(Gerard
and Marcel 2008).
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
30
This study investigates the characteristics of excess wind power and the conversion of this
excess wind power to hydrogen by electrolysis. The 2.5kW wind turbine is connected to 472W load
and two storage batteries of 200Ah each. Another two auxiliary storage batteries of 92Ah each are
connected to the dump load terminals for storing the excess wind energy. The excess wind energy is
converted to hydrogen and oxygen through alkaline water electrolysis. The excess wind energy
utilized, the hydrogen produced and efficiency energy conversion of electrolyzer are investigated.
2. Methodology
2.1. System Description
The 2.5 kW WestWind turbine is a three bladed, three phase 24V Alternating Current (AC)
generator. In this research, it is connected to charge two 12V/200Ah deep batteries under off-load or
low demand or high wind speed. Two auxiliary, 12V/92Ah storage batteries are also connected to the
dump load source, to store the excess wind energy if the following conditions arise. For the purpose of
energy utilization, the AC converter, converters the three phase to single phase AC, the rectifier
converts the AC to direct current (DC) and the diversion charge controller controls the battery charging
and diverts the excess energy if they are fully charged to the auxiliary storage batteries. The diversion
of excess wind energy by the charge controller protects the batteries from damage and the turbine
against over spinning. However, an inverter model Radiant 2000, 2000VA, 1200W rated of 24V DC
input and 220V AC single phase of 10A max output is connected to serve 472 Watts load. The load
consist four 100W incandescent lamps and two 36W compact lamps for illuminating the inner and
outer sides of the control room. As the turbine operates under load and no load conditions in the nigh
and daily hours respectively, under variable wind speed, the auxiliary storage batteries would be able
to show an increase in stored energy which determine the excess wind energy generated. The excess
wind energy being stored in the auxiliary storage batteries is used to power electrolyzers for hydrogen
production. The figure 1.0 shows the inverter and excess storage battery bank connections.
The electrical energy derived by the electrolyzer from the auxiliary storage batteries in joules is
the excess energy generated. The electrolysis was conducted under atmospheric pressure and 250C
room temperature, using platinum electrodes and 35wt% potassium hydroxide solution as electrolytes.
Electrolyzers performances under different currents and voltages input based on parallel, series
connections of electrolyzers to the battery and direct connection to the dump load source are
investigated. The figure 2.0 shows series connection of two Hoffman Voltameter (electrolyzers) to the
auxiliary storage batteries.
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
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EXCESS ENERGYBATTERY BANK
SYSTEM POWER INVERTER
Figure 1: The auxiliary storage batteries
Figure 2: Electrolyzers series connections to the excess energy source
2.2. Systems Operation
Despite the 472W load connected to the system is small proportion compared to the 2.5kW
rated output power of the turbine and the experiments was conducted in early month of February when
dry wind is at high speed especially in Sokoto Nigeria, the excess wind energy is expected even under
load condition. Five experiments were conducted using the same electrolytes, the same electrodes but
different modes of connections in different days. The following are modes of electrolyzer’s
connections.
I.
Single cell connection
II.
Double cell connection in parallel
III.
Double cell connection in series(i)
IV.
Double cell connection in series (ii)
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
V.
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Double cell connection in series connection directly to the dump load terminals.
The 35wt% potassium hydroxide (KOH) solution is poured through the central limbs of the
electrolyzers with taps open and switch closed. The switch is on as the taps is closed, this allow current
to pass through the electrolytes. Water can be split into its constituent elements, hydrogen and oxygen,
by passing an electric current through it. This process is called electrolysis. Water molecules naturally
dissociate into H+ and OH− ions, which are attracted toward the cathode and anode, respectively. At the
cathode, two H+ ions pick up electrons and form H2 gas. At the anode, four OH− ions combine and
release O2 gas, molecular water, and four electrons. The gases produced bubble to the surface, where
they can be collected. Reduction occurs at the cathode, at this electrode hydrogen gas and hydroxyl
ions are formed. The electrons required for this reduction comes from the electrical power source.
4H2O + 4e-→2H2 + 4OH-
(1)
Oxidation occurs at the anode, producing oxygen and hydrogen ions. The electrons that are produce
returns to the power source.
2H2O → O2 + 4H+ + 4e-
(2)
Adding the two half reactions together, gives a net reaction of:
6H2O → 2H2 + O2 + 4H+ + 4OH-
(3)
The hydrogen and hydroxyl ions that are produced combines to form water.
6H2O → 2H2 +O2 + 4H2O
(4)
Finally we resolved at 2H2O (l) = 2H2 (g) + O2(g)
(5)
The parameters to be observe while electrolysis are the room temperature (K), average
electrolyzer voltage (V), average electrolyzer current (A) and the volume of hydrogen (millitre)
produced in 180seconds each.
2.3. Numerical Parameters
The following are parameters of calculation required from the experimental data collected in
section (2.2) above.
a) Excess wind energy: the input electrical energy utilized by the electrolyzer source by auxiliary
storage batteries, which is a product of electrolyzer current (I) and voltage(U) and the time(t)
taken for the operations. It is numerically given as:
(J)
(6)
b) Energy consumed (Ecc): the specific energy used by the electrolyzer in producing oe unit
volume of hydrogen (mill). It is numerically described as the ratio of total energy(J) used by the
electrolyzer to the total volume of hydrogen (mill.) as:
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
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(7)
c) Volume of hydrogen produced (
): this is the actual volume of hydrogen produced by the
electrolyzer. Thus when a H2 gas is collected by water displacement, the gas in the collection
bottle is actually a mixture of H2 and water vapor and the pressure in the test tube is from both
the hydrogen and the water. The total pressure in the collection bottle is equal to atmospheric
pressure and is a mixture of H2 and water vapour according to Delton’s law of partial pressure.
(8)
Where P room is the atmospheric pressure
P water is the water vapour partial pressure
PH2 is the pressure of hydrogen gas
The volume of hydrogen recorded is a mixture of hydrogen gas and water vapour, therefore, the exact
volume of hydrogen is obtained as:
{
Where
}
(9)
(mill): is the actual volume of hydrogen produced
: is the volume of hydrogen containing water vapour
d) Mass of hydrogen
density of hydrogen
(Kg): this is the product of actual volume of hydrogen
(m3) and
(Kg/m3). Numerically written as:
(10)
e) Hydrogen Volume Flow rate (Qt): this is the volume of hydrogen
produced by the
electrolyzer to the time (t) taken. It describes the quantity of hydrogen (mil) produced in a unit
time (min). It is numerically given as:
(11)
f) Hydrogen Energy (EH2): hydrogen energy is the resulted output energy (joule) produced by
the electrolyzer due to the electrical energy input. It is a product of mass of hydrogen (Kg) and
the Hydrogen Heating Value (HH2) MJ /Kg given as:
(Nyorka, 2008)
(12)
The hydrogen heating value of hydrogen was estimated at approximately 142 MJ/Kg as
(Harrison, et al. 2010), while the density of hydrogen is constant as 0.0998Kg/m3.
g) Energy Conversion Efficiency (ηe) :this is the efficiency of electrolyzer (%) for converting
the excess wind energy into hydrogen gas. It is therefore the ration of excess wind energy (J) to
hydrogen energy (J) as (Nyorka, 2008)
(13)
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
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3. Results and Discussion
The numerical equations in section (2.3) are used for estimating the excess wind energy, the
energy consumed, the volume of hydrogen produced, the mass of hydrogen produced, the hydrogen
volume flow rate, the hydrogen energy and the energy conversion efficiency of the electrolyzer using
the experimental data obtained in section (2.2).
For connection (I), the 2.5kW turbine supplied excess wind energy of 1005.73J, electrolyzer
consumed 43.27J/mil, produced 7.74mil/min and hydrogen energy of 330.008J at an efficiency of
32.8%. The electrolyzer connection (II) is supplied with 1563.85J of excess energy; it consumed
37.71J/mil and produced 13.91mil/min at energy efficiency of 37.9% when 592.708J of hydrogen is
produced. In connection (III), the turbine supplied 1998.43J of excess energy, utilized 41.79j/mil, and
generated15.94mil/min and produced 697.004J of hydrogen at efficiency of 34.87%. For connection
(IV), 2154.32J of excess energy is supplied to the electrolyzer, it consumed 38.84J/mil and produced
18.49mil/min at an efficiency of 36.56% when 787.674J of hydrogen is generated. The elecrolyzer
connection (V), is supplied with 2160J of excess energy, it consumed 46.22J/mil and generated
15.57mil/min and 663.566J of hydrogen at efficiency of 30.7%.
The graphs of electrolyzer average voltage and current and parameters such as specific energy
consumption, hydrogen volume flow rate and energy conversion efficiency against different
connections modes are plotted in figure
The results in figure 3.0 represent relationship between current and voltage due to different
electrolyzer connections mode. The result shows that, better performance of electrolyzer would be
realized for series connection when the electrolyzer voltage and current ranges (22 – 24V) and (0.48 –
0.508A) respectively.
The results in figures 4, 5 and 6 show the effects of electrolyzer voltage on energy
consumption, hydrogen flow rate and energy efficiency due to different electrolyzer connections mode.
The results in figure 4 shows that, for a parallel connection of electrolyzers, high specific energy is
consumed at low electrolyzer input voltage. While for a series connection,low specific energy is
consumed by the electrolyzer at high input voltage. The result in figure 5 shows that at low voltage,
low hydrogen volume flow rate is observed in the case of parallel connections. While for a series
connections, at high electrolyzer input voltage, high hydrogen volume flow rate is observed. The result
in figure 6.0 shows that direct connections resulted low energy efficiency and the parallel connections
resulted high efficiency at low voltage. But high efficiency is observed by the series connections at
high voltage.
The results in figures 7, 8 and 9 shows the effects of electrolyzer input current on energy
consumption, hydrogen volume flow rate and electrolyzer energy efficiency due to different
Copyright © 2013 by Modern Scientific Press Company, Florida, USA
Int. J. Modern Eng. Sci.2013, 2(1): 28-38
35
connections mode. The result in figure 7 shows that for parallel connections, low specific energy is
consumed at high electrolyzer input current. While for series connections, specific energy consumption
has decreased as a result of increased in electrolyzer current input. The result in figure 8 shows that for
parallel connections, at high current, low hydrogen volume flow rate is observed. While for series
connection of electrolyzers, high volume flow rate is observed at low current, but for a direct
connection, slight increase in electrolyzer current resulted a decreased in hydrogen volume flow rate
.The result in figure 9 shows that for parallel connections of two electrolyzers, high energy efficiency
is obtained at high electrolyzer current, but it has a disadvantage of high energy consumption and low
hydrogen volume flow rate, also increase in current resulted increase in energy efficiency. However,
generally, the direct connection shows a decrease in energy efficiency and volume flow rate and
increase in specific energy consumption as a result of increase in electrolyzer current, but a decrease in
electrolyzer voltage results an increase in specific energy consumption and a decrease in volume flow
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Figure 3: Graph of electrolyzer current and voltage for different electrolyzer connections
electrolyzer
average
voltage (V)
specific energy
consumed
(J/mil)
Figure 4: Graph of electrolyzer voltage and specific energy consumed for different connections
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Figure 5: Graph of electrolyzer voltage and volume flow rate for different electrolyzer connections
electrolyzer
average
voltage (V)
electrolyzer
energy
efficiency
(%)
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Figure 6: Graph of electrolyzer voltage and energy efficiency for different connections
electrolyzer
average
current (A)
specific
energy
consumed
(J/mil)
Figure 7: Graph of electrolyzer current and energy consumption for different electrolyzer connections
Copyright © 2013 by Modern Scientific Press Company, Florida, USA
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Figure 8: Graph of electrolyzer current and volume flow rate for different electrolyzer connections
electrolyzer
average
current (A)
electrolyzer
energy
efficiency
(%)
Figure 9: Graph of electrolyzer current and energy efficiency for different electrolyzer connections
4. Conclusions
The 2.5kW wind turbine while connected to 472W load was able to supply electrolyzers with
total excess wind energy of 8882.33J. Electrolyzers specifically consumed total 207.85J/mil and
produced about 71.56mil/min of hydrogen. While, electrolyzers produced a total of 3070.96J of
hydrogen it attains an overall energy efficiency of 34.56%. The best performance of electrolysis is
observed by series connections of electrolyzers, in which low energy consumption, high hydrogen
volume flow rate and high energy efficiency were realized at high voltage and low current.
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Int. J. Modern Eng. Sci.2013, 2(1): 28-38
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