- Email: [email protected]
Development of a photovoltaic energy conversion system with hydrogen energy storage
ht. .J. Hydrogen Energy, Vol. 20, No. 3, pp. 23’4-243. 199’ ” 1995 International Association for Hydrqzen Energ) Eisevier Science Ltd Printed in Great Britain. All rights reserved 036&3199(94)EOO26U 0360 3199’95 w50 i 000
Pergamon
DEVELOPMENT
Copyright
OF A PHOTOVOLTAIC ENERGY CONVERSION WITH HYDROGEN ENERGY STORAGE
SYSTEM
J. W. HOLLENBERG, E. N. CHEN, K. LAKERAM and D. MODROUKAS The
Cooper
(Received
Union,
New
York,
for publication
NY
10003. U.S.A.
29 March
1994)
Abstract-This paper describes an ongoing project to develop an integrated solar-hydrogen energy production, storage and utilization system consisting of a photovoltaic array, SPE electrolysers, metal alloy hydride tanks, an SPE fuel cell and an automatic control system.The hydrogen production and storage portions of the system,described herein, have been completed, successfullytested and typical performance data presented for a test run which occupied 2 h on the afternoon of 2 November 1993,producing and storing 26.5 1 of hydrogen, for isolation ranging between 200 and 800 Wm - ‘. A computer simulation, useful for sizing studies on systems of this type, was developed and a typical output from it is shown, The program code may be obtained from the referencesat the end of the paper
NOMENCLATURE El E2 AHa H/M LCB MR seem
ing system for an energy autonomous home design, it started out as a wind energy-based hydrogen energy system,where the wind turbine was subsequently replaced by a photovoltaic array for safety and rehability reasons [ 16-203. Design, testing and debugging work on individual components of the system during the 19% led to the construction of an integrated PECS system, whose hydrogen generation and storage modules were operated for the first time in April 1992 [21-241.
Electrolyser no. 1 Electrolyser no. 2 Change in enthalpy (kJ gmol- ‘) Hydrogen to metal atoms ratio Linear Current Booster Electrical resistance Flow rate INTRODUCTION
Recent work on photovoltaic energy conversion systems with hydrogen energy storage has been carried out at Brookhaven National Laboratories [l, 23, Humboldt State University [3, 41, in Germany and Saudi Arabia (Solar Wasserstoff Bayern, kFA and HYSOLAR) [S-lo], in Finland [l l-141, as well as other countries [is]. These efforts have included computer simulations, design work, construction and testing of pilot systemsof varying sizes of up to several hundred kilowatt output. However, none of these solar hydrogen energy projects have the particular configuration described in this paper, combining unsteady solar energy conversion, passive load conditioning between the photovoltaic array and SPE electrolysers, and a metal hydride storage tank system operating at sufficiently low pressures to eliminate the need for a compressor.Such an approach involves many advantages and it is the purpose of this paper to describe the design and initial testing of our photovoltaic energy conversion system (PECS) constructed along these lines. At The Cooper Union, the PECS has been an ongoing project for more than a decade,developed over the years by senior mechanical engineering students and masters degreecandidates. Initially conceived as a power generat-
DESCRIPTION OF SYSTEM Figure 1shows a schematicdiagram of our Photovoltaic Energy Conversion System(PECS). As it currently exists, the PECS is composed of three main modules (outlined in Fig. 1): a photovoltaic module, an etectrofyser (generation) module and a hydrogen storagemodule. The fourth and final module of the PECS is the hydrogen utihzation module, which will consist of a solid polymer electrolyte (SPE) hydrogen-air fuel ceil, and is currently in its design and implementation phase, as is the automatic control system for the entire PECS. All modtrIes of the PECS were developed with the additional capabihty of independent operation for testing and debu Sunlight incident upon a photovoltaic array is the power input to the PECS. The array’s power, totaling 150 W maximum, is derived from two Solartwst Ekctric ASIand two Arco M-73 panels. The direct current output from the array is then conditioned through a passive load matching device (Bobber LCB-28) which couples the photovoltaic array to the SPE e#ectrolysers. The load matching device converts excess voltage to current, resulting in a greater production of hydrogen from the electrolyser array.
239
J. W. HOLLENBERG et al.
240
PHOTOVOLTAICMODULE r------ -----------------------~ I c& q,o q,o c& 1I PHOTOVOLTAIC
I1 /
I I
HYDROGENSTORAGE MODULE
~--------------------------~~~-----------~~~~~
VACUUM
PUMP
__._
CULLI
WATER
DEIONIZER WATER FROM -A&&& NYC t WATER TANK
MAIN LINE
GAS MANIFOLD
~~
HOT WATER
1
PURIFICATION
SUBSYSTEM t ELECTROLYZERS (3)
i WATER TO DRAIN
ELECTROLYZER MODULE LEGEND SYMBOL RI cd
DESCRIPTION DIAPHRAGM CHECK
VALVE
THROTTLING z
PRESSURE
&
RELIEF
B
FLOWMETER
SYMBOL
VALVE VALVE REGULATOR
VALVE
f T @ 8
DESCRIPTION PRESSURE
TRANSDUCER
PRESSURE
GAUGE
HYDROGEN UTILIZATION MODULE
(PROPOSED)
VOLTMETER AMMETER TYPE
T THERMOCOUPLE
P
Fig. 1. Schematiclayout of the PECSat The CooperUnion.
Three multi-cell SPE (perfluorinated sulfonic acid) electrolysers wired in parallel make up the generation module. The electrolysers are Aadco units, each rated at a maximum voltage of 6.8 V and a maximum current of 14 A, and each has a maximum hydrogen production rate of 225 seem.The hydrogen flow rate from the array is directly dependent on the current and hence an increase in hydrogen production is a result of the current-boosting capability of the power conditioning device. Deionized water (resistance greater than 1 MQ) is supplied to the electrolysers whose output is oxygen gas, which is safely vented, and hydrogen gas, which can be stored in the hydride tanks for future use. The electrolytically generated hydrogen is first dried of its water vapor content, then purified by a Matheson PFH2 Purifilter to less than 10 ppm impurities. Once purified, the hydrogen gas can be sent to the hydrogen storage module at pressures in the range of O-100 psig, produced by the electrolysers. The hydrogen storage module is composed of two Ergenics ST-45 hydride tanks, each with a maximum storage capacity of 1274 standard liters of hydrogen gas.
Each tank contains 10.5 kg of a mischmetal-nickelaluminum hydriding alloy whose chemical composition is given by Mn0,9,Ni4,5A10.5, commercially known as HYSTOR-208. The hydriding alloy is stored in six stainless steel tubes, surrounded by a water jacket that facilitates heat exchange during absorption and desorption of hydrogen gas in and out of the metal hydride. These tanks are oversized in comparison to the electrolysers, so the heat of reaction during hydriding from the electrolyser output results in a negligible cooling water temperature rise using normal water flow rates. Hydrogen gas reacts with the metal alloy granules in the tank at a specific temperature and pressureaccording to the Van? Hoff equation, liberating heat in the process (for HYSTOR-208, this is - 6.7 kcal mol - ’ H,) [25]. Heat, in the form of hot water, can be supplied to the metal alloy via the heat exchanger to discharge the hydrogen gasfor utilization as required by the load. These hydriding and dehydriding reactions occur at convenient temperatures and at pressures deliberately matched to the specifications of the electrolysers, eliminating the need for a compressor.
241
A PHOTOVOLTAlCENERGYCONVERSlONSYSTEM
PECS
Time
II
Ptatio [Hrs 1 [degFl
: 112.000 : 70.470
Torap
PHOTOVOLTAICS Config : 1 x
: 829.000 : 14.059
In801
Volts
4 [ SXPI
7.145
Ampa voc
:
ISC
17.899 7.712
[W/M21 Woltl
[Amps1 [Volt] [Amps]
HYDRIDE TANK # of Tanks: Ii2 Stored in
1: 99.9 2: 3: 4:
5:
1.8
2 Tanks
#
Max
.DAT .DAT . CHG
Charging HS/Metal: Prees Stored
Discharg: Ha/Metal: Press Stored Moles Mass
2
1
[ [Psia
[% I [G-Mel] [Grams]
Flowi
1.787 7.926 15.978 2.000
[Gpm
Temp:
77.029
[deg
Moles
[%I [%I
8: 9:
[%I [%I [%I
Mass H20 H20
: .095 14.846
[%I
[%I 10:
Datafile:aolar3 Loadbile:loadZ Savefile:whatZ FUEL CELLS Load : 50.000 H2 Flow : .OOl Voltage : 16.715
7:
[%I
1
[Watts] [Watts]
ELECTROLYZERS # Cells : 8 I 1 Ii2 Prod : .036 [GMolMl Eng Eff : 84.289 [% Volt Eff: 69.935 1% ; V/Cell : 1.757 [Volts] 1 1
[%I [%I
6:
[%
: 99.996 : 100.452 : 100.456
Act
: :
:
1
1 Fl
Current
H20
:
2.991
[Watts]
IQXolMl [Volts] [Amps i i
I
1 : : :
Flow:
Ii20 Temp :
.799 75.367 99.906 66.464 134.019 2.000 127.183
1
[ [Psia 1%
I I
[G-Mall
[Grams]
[Gpm [deg
1 Fl
Fig. 2. Output screenof PECScomputermodel “PECS-II”.
At the present time, the PECS is operated manually, with an automatic control system under development. Several safety interlocks have already been installed, including a hydrogen gas leak detection system, which can automatically shut down the entire PECS in the event of a major gas leak. COMPUTER
SIMULATION
A computer model, PECS-II, was developed by DeBernard0 [23]. It is a quasi-steady model of a PECS configuration operating for extended periods of time, which simulates performance characteristics and aids in sizing components. The main purpose of the model is to size the components of a PECS configuration to satisfy a power load. Given an input of load and insolation data on an hourly basis, the program can be used to determine the optimum number and size of PV arrays, electrolysers and hydride storage tanks, and model their performance as hourly output data. The program reads in the following user-specifiedinput quantities: l
l l l
These are displayed on an output screen generated by the program, as shown in Fig. 2.
24
t
Q 1nmoIation Q Current
before
LGB
900
The number and arrangement (series or parallel) of PV panels in the array, and the temperatures and insolation dependent characteristic (I-V) curve information. Hourly temperature and insolation data. The number of hydride tanks. The power load, to determine the hydrogen output flow rate and therefore define the discharging parameters of the hydride tanks.
The program then calculates, for each hourly time step, the following quantities: l
calculated optimum operating point. The amount and flow rate of hydrogen produced from the electrolysers. The pressure, H/M and amount of hydrogen stored for each hydride tank, and the water temperature for charging or discharging each tank. The voltage, current and H, gas flow rate required to drive a fuel cell to power the specified hourly load.
The voltage, current and power generated by the PV array, both at the maximum power point and a
Time
of Day(PM)
Fig. 3. Current before and after load matching device
J. W. HOLLENBERG et al.
242
z
7
A t
InAolAtion 0 Voltrp aitar l VoltA@o bdoro
I LCB LCB
-
500
-
700
-
600
-
500
-
400
-300 -
5 44100 2:30
ol^ Ei \ P z .d z z ; c(
7 250 $240 0
2m 230 f k
220
=
9
210
200
F
-
q
D
InAolAtion 0 Tank Promuro l Pi promrura
200 3:oo
3:30
Time
4:oo
4:30
14 12
0.10 0 Curront Current
v Ii,
in in
Clolrratr
02:; Time
El P2
3:30
4:oo
4:30
of Day(PM)
Fig. 6. Electrolyserand storagetank pressures.
RESULTS
The first unsteady operation of the PECS was conducted on 9 April 1992. Following this date, more than 24 h of test data have been gathered on unsteady system operation. In addition, extensive data on the steady and unsteady operational characteristics of the different modules in the system have been gathered. Typical performance data for a test conducted on 2 November 1993are shown in Figs 3-6. Two electrolysers
n
3:oo
Time
of Day(PM)
EXPERIMENTAL
100 2:30
Fig. 4. Voltage beforeand after load matchingdevice.
2
Pd
2
3Y1O-O0 >
I
0.05
X"
were used in this test. The third was being repaired. Water at a constant temperature of 26.1”C and a flow rate of 9.5 1min-’ was piped to the hydrogen storage tank being charged. The initial tank pressure was 206.9 kPa. Charging was initiated at approximately 5 min into the test. Figure 3 shows the time history of current before and after the load matching device (LCB). The time variation of insolation is also shown in this and subsequent figures. The voltage characteristics before and after the LCB (at the electrolysers) are shown in Fig. 4. These data show that despite the unsteady nature of the insolation, the voltage at the electrolysers (voltage after LCB) does not fluctuate significantly. The voltage drop across the LCB is accounted for by the increase in current to the electrolysers, as indicated in Fig. 3. Figure 5 demonstrates that hydrogen production is insolation (or current) sensitive; that is, as insolation changes the hydrogen production changes accordingly. During this test, 26.5 1 of hydrogen was produced by the electrolysers and stored in the hydride tank. The pressure characteristics of the two electrolysers and the tank being charged are shown in Fig. 6. The increase in tank pressure during the test was due to an increase of the H/M ratio in the tank. Figure 6 further shows that the electrolysers and charging tank pressuresdo not exhibit the sameunsteady behavior as the insolation. SUMMARY
w
of Day(PM)
The status of this project is as follows: l
l
Fig. 5. Hydrogenflow rate to storagetank.
The photovoltaic array has been designed,constructed and tested, and is performing satisfactorily. The electrolyser module has been designed, constructed and tested, and is performing satisfactorily.
A PHOTOVOLTAIC
ENERGY CONVERSION SYSTE,M
The hydride tank module has been designed,construeted and tested and is performing satisfactorily. A computer model for sizing components of such a photovoltaic energy conversion system has been written, debugged and is running satisfactorily. Initial tests of the entire current system, producing and storing hydrogen. have been successfully conducted.
l
l
l
The remaining work on this project will consist of shakedown testing of the current system,procuring a fuel cell and inverter, and combining all parts into a reliably functioning and automatically controlled photovoltaic energy conversion system. rl[,knowludyements--The performance data shown in Figs 336 were obtained by Gus Block, Ricardo Drilon, Anthony T. Lomma, Steven Monaghan and Mahendra Nandkishore as part of their senior project. The work described in this paper was supported over the years by laboratory development funds of The Cooper Union for the Advancement of Science and Art.
24.’
9. H. Barthels and P. Ritzenhoff, Determination of the solar
radiation supply for the design and operation of an autonomous solar-electric photovoltaic plant. Forschungszentrum Jillich GmbH D-52425 Jillich, Germany. ISES Soiw World Congress, Budapest (1993). W. Grasse and F. Oster, HYSOLAR: solar hydrogen 10. Energy; results and achievements 1985-1989. Deutsche Forschungsanstalt fur Luft und Raumfahrt (DLR), Univcrsity of Stuttgart, Pfaffenwaldring, Germany (1990). P. S. Kauranen ef al., Hydrogen energy storage for photo‘I’ voltaic systems.Helsinki University of Technology, Department of Technical Physics, Espoo, Finland (1990). 12, L. M. Manninen, P. D. Lund and A. Virkkula, PHOTO A computer simulation program for photovoltaic and hybrid energy systems(Document and user’s guide). Report TKKF-F-A, Helsinki University of Technology, Department of Technical Physics, Espoo, Finland (1990). 13. J. Vanhanen, Simulation of solar hydrogen energy systems. Report TKK-F-C133, Helsinki University of Technology. Department of Technical Physics, Espoo, Finland (1991). 14. J. Vanhanen, H2 -- DESIGN TOOL 1.0for solar-hydrogen energy systems. Report TKK-F-A701. Helsinki Universitv of Technology, Department of Technical Physics, t’spoc:. Finland (1992). 15. G. P. Dinga, Hydrogen: the ultimate fuel and energy carrier. Int J. Hydrogen Energy (1989).
1.
2.
3.
4.
6.
REFERENCES G. Schoener and G. A. Strickland, An integrated test bed for advanced hydrogen technology: photovoltaic array/electrolyzer system. Interdepartmental Report BNL 51577, Brookhaven National Laboratory, Upton, New York (1982). Leigh, Metz and Michalek, Photovoltaic electrolyzer system transient simulation results. Interdepartmental Report BNL-40081, Brookhaven National Laboratory Upton, New York (1983). T. N. Veziroglu, and R. E. Billings, (editors), Project Hydrogen ‘91: Conference Proceedings. American Academy of Science, Independence MO (1992). P. A. Lehman, and C. E. Chamberlin, Operating experience with a photovoltaic-hydrogen-fuel cell energy system. HYDROGEN 92. 9th World Hydrogen Energy Co@ Paris, France (22-25 June 1992). C. J. Winter, and J. Nitsch (editors), Hydrogen as an Energy Carrier: Technologies. Systems, Economy. Springer, Berlin (1988). A. Szyszka, Demonstration plant, Neunburg Vorm Wald, Germany, to investigate and test solar-hydrogen technology. Int. J. Hydrogen Energy 17,485-498 (1992).
H. Barthels and W. A. Brocke, Simulation and design of the energy management system for the Jiilich solar hydrogen plant. Forschungszentrum Jiilich GmbH D-52425 Jiilich, Germany. ISES Solar World Congress, Budapest (1993). H. Barthels et al., Realized design of an autonomous solar electric energy supply. Forschungszentrum Jiilich 52425 Jiilich, Germany. ISES Solar World Congress, Budapest (1993).
16. H. Betancourt, Final Design ofthe energy autonomous earth sheltered house. Senior Project Report. The Cooper l.rnion (1983). 17. P. R. Comrie, A design for the roof mounting of a 1.8 kW wind electric generator. Masters Thesis. The Cooper Union (1982). 18. K. Philogene, The design of a hydride sotrage system for a small wind energy conversion system. Masters Thesis, The Cooper Union (1982). 19. A. R. Rizzo, A computer model of the steady state performance of a small wind energy conversion system with hydrogen storage. Masters Thesis, The Cooper Union t 1983). 20. K. Lewis, Investigation of a Jacobs wind turbine generator with a simulated SPE electrolyzer load, Masters Thesis, The Cooper Union (1984). 21. E. C. Mathisen, Design and modelling of a hydride tank and test loop. Masters Thesis, The Cooper Umon (1985). 22 M. P. Witzing, A computer model of a photovoltaic energy conversion system with hydrogen energy storage. Mastery Thesis, The Cooper Union (1988). 23. P. J. DeBarnardo, Design of a hydrogen energy storage system for a photovoltaic array powered electrolyzer. Masters Thesis, The Cooper Union (1991). 24 Kaplan, Leung. Lakeram, Modroukas, Rojas and Stone, ‘The continued development of a photovoltaic energy conversion system with hydrogen energy storage’. Senior Project Report, The Cooper Union (1992). 25 E. L. Huston and G. D. Sandrock, Engineering properties of metal hydrides. .I. Lcw-Common Metals 74. 435443 (1980).
Pergamon
DEVELOPMENT
Copyright
OF A PHOTOVOLTAIC ENERGY CONVERSION WITH HYDROGEN ENERGY STORAGE
SYSTEM
J. W. HOLLENBERG, E. N. CHEN, K. LAKERAM and D. MODROUKAS The
Cooper
(Received
Union,
New
York,
for publication
NY
10003. U.S.A.
29 March
1994)
Abstract-This paper describes an ongoing project to develop an integrated solar-hydrogen energy production, storage and utilization system consisting of a photovoltaic array, SPE electrolysers, metal alloy hydride tanks, an SPE fuel cell and an automatic control system.The hydrogen production and storage portions of the system,described herein, have been completed, successfullytested and typical performance data presented for a test run which occupied 2 h on the afternoon of 2 November 1993,producing and storing 26.5 1 of hydrogen, for isolation ranging between 200 and 800 Wm - ‘. A computer simulation, useful for sizing studies on systems of this type, was developed and a typical output from it is shown, The program code may be obtained from the referencesat the end of the paper
NOMENCLATURE El E2 AHa H/M LCB MR seem
ing system for an energy autonomous home design, it started out as a wind energy-based hydrogen energy system,where the wind turbine was subsequently replaced by a photovoltaic array for safety and rehability reasons [ 16-203. Design, testing and debugging work on individual components of the system during the 19% led to the construction of an integrated PECS system, whose hydrogen generation and storage modules were operated for the first time in April 1992 [21-241.
Electrolyser no. 1 Electrolyser no. 2 Change in enthalpy (kJ gmol- ‘) Hydrogen to metal atoms ratio Linear Current Booster Electrical resistance Flow rate INTRODUCTION
Recent work on photovoltaic energy conversion systems with hydrogen energy storage has been carried out at Brookhaven National Laboratories [l, 23, Humboldt State University [3, 41, in Germany and Saudi Arabia (Solar Wasserstoff Bayern, kFA and HYSOLAR) [S-lo], in Finland [l l-141, as well as other countries [is]. These efforts have included computer simulations, design work, construction and testing of pilot systemsof varying sizes of up to several hundred kilowatt output. However, none of these solar hydrogen energy projects have the particular configuration described in this paper, combining unsteady solar energy conversion, passive load conditioning between the photovoltaic array and SPE electrolysers, and a metal hydride storage tank system operating at sufficiently low pressures to eliminate the need for a compressor.Such an approach involves many advantages and it is the purpose of this paper to describe the design and initial testing of our photovoltaic energy conversion system (PECS) constructed along these lines. At The Cooper Union, the PECS has been an ongoing project for more than a decade,developed over the years by senior mechanical engineering students and masters degreecandidates. Initially conceived as a power generat-
DESCRIPTION OF SYSTEM Figure 1shows a schematicdiagram of our Photovoltaic Energy Conversion System(PECS). As it currently exists, the PECS is composed of three main modules (outlined in Fig. 1): a photovoltaic module, an etectrofyser (generation) module and a hydrogen storagemodule. The fourth and final module of the PECS is the hydrogen utihzation module, which will consist of a solid polymer electrolyte (SPE) hydrogen-air fuel ceil, and is currently in its design and implementation phase, as is the automatic control system for the entire PECS. All modtrIes of the PECS were developed with the additional capabihty of independent operation for testing and debu Sunlight incident upon a photovoltaic array is the power input to the PECS. The array’s power, totaling 150 W maximum, is derived from two Solartwst Ekctric ASIand two Arco M-73 panels. The direct current output from the array is then conditioned through a passive load matching device (Bobber LCB-28) which couples the photovoltaic array to the SPE e#ectrolysers. The load matching device converts excess voltage to current, resulting in a greater production of hydrogen from the electrolyser array.
239
J. W. HOLLENBERG et al.
240
PHOTOVOLTAICMODULE r------ -----------------------~ I c& q,o q,o c& 1I PHOTOVOLTAIC
I1 /
I I
HYDROGENSTORAGE MODULE
~--------------------------~~~-----------~~~~~
VACUUM
PUMP
__._
CULLI
WATER
DEIONIZER WATER FROM -A&&& NYC t WATER TANK
MAIN LINE
GAS MANIFOLD
~~
HOT WATER
1
PURIFICATION
SUBSYSTEM t ELECTROLYZERS (3)
i WATER TO DRAIN
ELECTROLYZER MODULE LEGEND SYMBOL RI cd
DESCRIPTION DIAPHRAGM CHECK
VALVE
THROTTLING z
PRESSURE
&
RELIEF
B
FLOWMETER
SYMBOL
VALVE VALVE REGULATOR
VALVE
f T @ 8
DESCRIPTION PRESSURE
TRANSDUCER
PRESSURE
GAUGE
HYDROGEN UTILIZATION MODULE
(PROPOSED)
VOLTMETER AMMETER TYPE
T THERMOCOUPLE
P
Fig. 1. Schematiclayout of the PECSat The CooperUnion.
Three multi-cell SPE (perfluorinated sulfonic acid) electrolysers wired in parallel make up the generation module. The electrolysers are Aadco units, each rated at a maximum voltage of 6.8 V and a maximum current of 14 A, and each has a maximum hydrogen production rate of 225 seem.The hydrogen flow rate from the array is directly dependent on the current and hence an increase in hydrogen production is a result of the current-boosting capability of the power conditioning device. Deionized water (resistance greater than 1 MQ) is supplied to the electrolysers whose output is oxygen gas, which is safely vented, and hydrogen gas, which can be stored in the hydride tanks for future use. The electrolytically generated hydrogen is first dried of its water vapor content, then purified by a Matheson PFH2 Purifilter to less than 10 ppm impurities. Once purified, the hydrogen gas can be sent to the hydrogen storage module at pressures in the range of O-100 psig, produced by the electrolysers. The hydrogen storage module is composed of two Ergenics ST-45 hydride tanks, each with a maximum storage capacity of 1274 standard liters of hydrogen gas.
Each tank contains 10.5 kg of a mischmetal-nickelaluminum hydriding alloy whose chemical composition is given by Mn0,9,Ni4,5A10.5, commercially known as HYSTOR-208. The hydriding alloy is stored in six stainless steel tubes, surrounded by a water jacket that facilitates heat exchange during absorption and desorption of hydrogen gas in and out of the metal hydride. These tanks are oversized in comparison to the electrolysers, so the heat of reaction during hydriding from the electrolyser output results in a negligible cooling water temperature rise using normal water flow rates. Hydrogen gas reacts with the metal alloy granules in the tank at a specific temperature and pressureaccording to the Van? Hoff equation, liberating heat in the process (for HYSTOR-208, this is - 6.7 kcal mol - ’ H,) [25]. Heat, in the form of hot water, can be supplied to the metal alloy via the heat exchanger to discharge the hydrogen gasfor utilization as required by the load. These hydriding and dehydriding reactions occur at convenient temperatures and at pressures deliberately matched to the specifications of the electrolysers, eliminating the need for a compressor.
241
A PHOTOVOLTAlCENERGYCONVERSlONSYSTEM
PECS
Time
II
Ptatio [Hrs 1 [degFl
: 112.000 : 70.470
Torap
PHOTOVOLTAICS Config : 1 x
: 829.000 : 14.059
In801
Volts
4 [ SXPI
7.145
Ampa voc
:
ISC
17.899 7.712
[W/M21 Woltl
[Amps1 [Volt] [Amps]
HYDRIDE TANK # of Tanks: Ii2 Stored in
1: 99.9 2: 3: 4:
5:
1.8
2 Tanks
#
Max
.DAT .DAT . CHG
Charging HS/Metal: Prees Stored
Discharg: Ha/Metal: Press Stored Moles Mass
2
1
[ [Psia
[% I [G-Mel] [Grams]
Flowi
1.787 7.926 15.978 2.000
[Gpm
Temp:
77.029
[deg
Moles
[%I [%I
8: 9:
[%I [%I [%I
Mass H20 H20
: .095 14.846
[%I
[%I 10:
Datafile:aolar3 Loadbile:loadZ Savefile:whatZ FUEL CELLS Load : 50.000 H2 Flow : .OOl Voltage : 16.715
7:
[%I
1
[Watts] [Watts]
ELECTROLYZERS # Cells : 8 I 1 Ii2 Prod : .036 [GMolMl Eng Eff : 84.289 [% Volt Eff: 69.935 1% ; V/Cell : 1.757 [Volts] 1 1
[%I [%I
6:
[%
: 99.996 : 100.452 : 100.456
Act
: :
:
1
1 Fl
Current
H20
:
2.991
[Watts]
IQXolMl [Volts] [Amps i i
I
1 : : :
Flow:
Ii20 Temp :
.799 75.367 99.906 66.464 134.019 2.000 127.183
1
[ [Psia 1%
I I
[G-Mall
[Grams]
[Gpm [deg
1 Fl
Fig. 2. Output screenof PECScomputermodel “PECS-II”.
At the present time, the PECS is operated manually, with an automatic control system under development. Several safety interlocks have already been installed, including a hydrogen gas leak detection system, which can automatically shut down the entire PECS in the event of a major gas leak. COMPUTER
SIMULATION
A computer model, PECS-II, was developed by DeBernard0 [23]. It is a quasi-steady model of a PECS configuration operating for extended periods of time, which simulates performance characteristics and aids in sizing components. The main purpose of the model is to size the components of a PECS configuration to satisfy a power load. Given an input of load and insolation data on an hourly basis, the program can be used to determine the optimum number and size of PV arrays, electrolysers and hydride storage tanks, and model their performance as hourly output data. The program reads in the following user-specifiedinput quantities: l
l l l
These are displayed on an output screen generated by the program, as shown in Fig. 2.
24
t
Q 1nmoIation Q Current
before
LGB
900
The number and arrangement (series or parallel) of PV panels in the array, and the temperatures and insolation dependent characteristic (I-V) curve information. Hourly temperature and insolation data. The number of hydride tanks. The power load, to determine the hydrogen output flow rate and therefore define the discharging parameters of the hydride tanks.
The program then calculates, for each hourly time step, the following quantities: l
calculated optimum operating point. The amount and flow rate of hydrogen produced from the electrolysers. The pressure, H/M and amount of hydrogen stored for each hydride tank, and the water temperature for charging or discharging each tank. The voltage, current and H, gas flow rate required to drive a fuel cell to power the specified hourly load.
The voltage, current and power generated by the PV array, both at the maximum power point and a
Time
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Fig. 3. Current before and after load matching device
J. W. HOLLENBERG et al.
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Fig. 6. Electrolyserand storagetank pressures.
RESULTS
The first unsteady operation of the PECS was conducted on 9 April 1992. Following this date, more than 24 h of test data have been gathered on unsteady system operation. In addition, extensive data on the steady and unsteady operational characteristics of the different modules in the system have been gathered. Typical performance data for a test conducted on 2 November 1993are shown in Figs 3-6. Two electrolysers
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were used in this test. The third was being repaired. Water at a constant temperature of 26.1”C and a flow rate of 9.5 1min-’ was piped to the hydrogen storage tank being charged. The initial tank pressure was 206.9 kPa. Charging was initiated at approximately 5 min into the test. Figure 3 shows the time history of current before and after the load matching device (LCB). The time variation of insolation is also shown in this and subsequent figures. The voltage characteristics before and after the LCB (at the electrolysers) are shown in Fig. 4. These data show that despite the unsteady nature of the insolation, the voltage at the electrolysers (voltage after LCB) does not fluctuate significantly. The voltage drop across the LCB is accounted for by the increase in current to the electrolysers, as indicated in Fig. 3. Figure 5 demonstrates that hydrogen production is insolation (or current) sensitive; that is, as insolation changes the hydrogen production changes accordingly. During this test, 26.5 1 of hydrogen was produced by the electrolysers and stored in the hydride tank. The pressure characteristics of the two electrolysers and the tank being charged are shown in Fig. 6. The increase in tank pressure during the test was due to an increase of the H/M ratio in the tank. Figure 6 further shows that the electrolysers and charging tank pressuresdo not exhibit the sameunsteady behavior as the insolation. SUMMARY
w
of Day(PM)
The status of this project is as follows: l
l
Fig. 5. Hydrogenflow rate to storagetank.
The photovoltaic array has been designed,constructed and tested, and is performing satisfactorily. The electrolyser module has been designed, constructed and tested, and is performing satisfactorily.
A PHOTOVOLTAIC
ENERGY CONVERSION SYSTE,M
The hydride tank module has been designed,construeted and tested and is performing satisfactorily. A computer model for sizing components of such a photovoltaic energy conversion system has been written, debugged and is running satisfactorily. Initial tests of the entire current system, producing and storing hydrogen. have been successfully conducted.
l
l
l
The remaining work on this project will consist of shakedown testing of the current system,procuring a fuel cell and inverter, and combining all parts into a reliably functioning and automatically controlled photovoltaic energy conversion system. rl[,knowludyements--The performance data shown in Figs 336 were obtained by Gus Block, Ricardo Drilon, Anthony T. Lomma, Steven Monaghan and Mahendra Nandkishore as part of their senior project. The work described in this paper was supported over the years by laboratory development funds of The Cooper Union for the Advancement of Science and Art.
24.’
9. H. Barthels and P. Ritzenhoff, Determination of the solar
radiation supply for the design and operation of an autonomous solar-electric photovoltaic plant. Forschungszentrum Jillich GmbH D-52425 Jillich, Germany. ISES Soiw World Congress, Budapest (1993). W. Grasse and F. Oster, HYSOLAR: solar hydrogen 10. Energy; results and achievements 1985-1989. Deutsche Forschungsanstalt fur Luft und Raumfahrt (DLR), Univcrsity of Stuttgart, Pfaffenwaldring, Germany (1990). P. S. Kauranen ef al., Hydrogen energy storage for photo‘I’ voltaic systems.Helsinki University of Technology, Department of Technical Physics, Espoo, Finland (1990). 12, L. M. Manninen, P. D. Lund and A. Virkkula, PHOTO A computer simulation program for photovoltaic and hybrid energy systems(Document and user’s guide). Report TKKF-F-A, Helsinki University of Technology, Department of Technical Physics, Espoo, Finland (1990). 13. J. Vanhanen, Simulation of solar hydrogen energy systems. Report TKK-F-C133, Helsinki University of Technology. Department of Technical Physics, Espoo, Finland (1991). 14. J. Vanhanen, H2 -- DESIGN TOOL 1.0for solar-hydrogen energy systems. Report TKK-F-A701. Helsinki Universitv of Technology, Department of Technical Physics, t’spoc:. Finland (1992). 15. G. P. Dinga, Hydrogen: the ultimate fuel and energy carrier. Int J. Hydrogen Energy (1989).
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REFERENCES G. Schoener and G. A. Strickland, An integrated test bed for advanced hydrogen technology: photovoltaic array/electrolyzer system. Interdepartmental Report BNL 51577, Brookhaven National Laboratory, Upton, New York (1982). Leigh, Metz and Michalek, Photovoltaic electrolyzer system transient simulation results. Interdepartmental Report BNL-40081, Brookhaven National Laboratory Upton, New York (1983). T. N. Veziroglu, and R. E. Billings, (editors), Project Hydrogen ‘91: Conference Proceedings. American Academy of Science, Independence MO (1992). P. A. Lehman, and C. E. Chamberlin, Operating experience with a photovoltaic-hydrogen-fuel cell energy system. HYDROGEN 92. 9th World Hydrogen Energy Co@ Paris, France (22-25 June 1992). C. J. Winter, and J. Nitsch (editors), Hydrogen as an Energy Carrier: Technologies. Systems, Economy. Springer, Berlin (1988). A. Szyszka, Demonstration plant, Neunburg Vorm Wald, Germany, to investigate and test solar-hydrogen technology. Int. J. Hydrogen Energy 17,485-498 (1992).
H. Barthels and W. A. Brocke, Simulation and design of the energy management system for the Jiilich solar hydrogen plant. Forschungszentrum Jiilich GmbH D-52425 Jiilich, Germany. ISES Solar World Congress, Budapest (1993). H. Barthels et al., Realized design of an autonomous solar electric energy supply. Forschungszentrum Jiilich 52425 Jiilich, Germany. ISES Solar World Congress, Budapest (1993).
16. H. Betancourt, Final Design ofthe energy autonomous earth sheltered house. Senior Project Report. The Cooper l.rnion (1983). 17. P. R. Comrie, A design for the roof mounting of a 1.8 kW wind electric generator. Masters Thesis. The Cooper Union (1982). 18. K. Philogene, The design of a hydride sotrage system for a small wind energy conversion system. Masters Thesis, The Cooper Union (1982). 19. A. R. Rizzo, A computer model of the steady state performance of a small wind energy conversion system with hydrogen storage. Masters Thesis, The Cooper Union t 1983). 20. K. Lewis, Investigation of a Jacobs wind turbine generator with a simulated SPE electrolyzer load, Masters Thesis, The Cooper Union (1984). 21. E. C. Mathisen, Design and modelling of a hydride tank and test loop. Masters Thesis, The Cooper Umon (1985). 22 M. P. Witzing, A computer model of a photovoltaic energy conversion system with hydrogen energy storage. Mastery Thesis, The Cooper Union (1988). 23. P. J. DeBarnardo, Design of a hydrogen energy storage system for a photovoltaic array powered electrolyzer. Masters Thesis, The Cooper Union (1991). 24 Kaplan, Leung. Lakeram, Modroukas, Rojas and Stone, ‘The continued development of a photovoltaic energy conversion system with hydrogen energy storage’. Senior Project Report, The Cooper Union (1992). 25 E. L. Huston and G. D. Sandrock, Engineering properties of metal hydrides. .I. Lcw-Common Metals 74. 435443 (1980).