Hassan AbaOud, KACST, Riyadh, Kingdom of Saudi Arabia Yaseen ...

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AT SOLARVILLAGE NEAR RIYADHI KINGDOM OF SAUDI ARABIA. Hassan ... and reliable production of hydrogen from solar energy in the technical scale.

INSTALLATION AND STARTUP RESULTS OF THE HYSOLAR 350 kW SOLAR HYDROGEN PRODUCTION PLANT AT SOLARVILLAGE NEAR RIYADHI KINGDOM OF SAUDI ARABIA

Hassan AbaOud, KACST, Riyadh, Kingdom of Saudi Arabia Yaseen AISaedi, KACST, Riyadh, Kingdom of Saudi Arabia Andreas Brinner, DLR, Stuttgart, Federal Republic of Germany

Abstract

The objective of this paper is to present the main results of the Saudi Arabian-German joint ettort between 1991 and 1993 on the design, installation, start up and test of a 350 kW solar hydrogen production demonstration plant which is a main task of the joint program HYSOLAR (HYdrogen from SOLAR energy). The introduction gives a short overview about the milestones of design, installation and start up. After a description of the plant installation some results of solar and grid-connected plant operation will be presented which have been gained during the test phase of the plant between September and Decernber 1993 just after start up. At last an outlook on the experimental operation phase and the next hardware improvements will be given. 1.

INTRODUCTION

The 350 kW solar hydrogen production plant has been erected to demonstrate the safe and reliable production of hydrogen from solar energy in the technical scale. The activity on this program task started in January 1987 with detailed proposals for the plant specification. In March 1988 a Belgium company "Hydrogen Systems" (HS) has been contracted to design, assemble and start up the electrolysis plant together with the already existing 350 kW Photovoltaic field (PV-field) which stems from the Saudi Arabian-American joint program SOLERAS. Until the end of December 1990 the electrolysis system -installed in three 20 feet standard skids- has been installed in its operation rooms in the PVPS-building (PhotoVoltaic Power System) at the Solar Village. Due to the unsuccessful startup of the plant with the original electrolysis cell block (0.5m 2 of electrode area, 144 cells) and various shortcomings in the safety systems which have been found during a detailed examination of the hardware and documentation it was decided in October 1990 to contract the German safety authority TÜV to compile a risk analysis of the plants' safety technique and to order directly a new improved cell block (0.25m 2 of electrode area, 120 cells) from METKON in Switzerland. In May 1991 the HYS 350 team with Saudi and German program members started independently with the redesign of the plant by hands of the first intermediate TÜV examination results and took over the full plant responsibility from HS in August 1991. The redesign of the plant and the TÜVs' risk analysis were completed until December 1991. Also the first contracts for the assembly of new safety subsystems have been submitted at that time. In February 1992 a new main subcontractor "Südrohrbau" (SRB) has been selected to examine the plant on site in detail in order to compile detailed hardware improvement proposals. The plant improvements started in Mayl June 1992 with the dismantling of the . original skids and building civil works. In August the rebuilding of the system hardware and the

operation program code irnprovement have been started in parallel to the civil works. The plant installation lasted until the end of August 1993 interrupted regularly by startups of subsystems wh ich have been completed. Although the TÜV was involved continuously du ring design and erection it was invited officially to perform its inspections of the mechanical and electrical plant equipment before startup fully according to the German safety regulations. As an immediate result of the successful inspection an official provisional operation permission has been given on site followed later on by a final report with detailed recommendations on the safety and proposals for the inspection of components in regular time intervals. The plant has been started up on the 29th of August 1993 mainly to test the operation ability and the safety equipment. Between August 31 st and September 11 th, 1993 the regular startup procedure including solar and grid-connected operation time intervals has been performed. Since the start up could be performed successfully the plant has been operated between September and December, 1993 during a first test phase with solar operation periods and specific experiments to examine the plant performance in detail. At the end of December the plant has been taken over officially into its experimental operation phase after an intensive training "on the job" of the operation staff.

2.

SYSTEM DESCRIPTION

The HYSOLAR 350 kW plant is installed at the KACST Solar Village about 50 km north-west of Riyadh (Altitude 650 m, Lat. 24.54:47 N., Long. 46.24:21 E.) and is representative of a typical Saudi Arabian location. The system consists of two main parts, the PV-field and the electrolysis system. The PV-field has 160 concentrating, two axis tracking module arrays with an effective photo voltaic cell area of 3805 m 2 . On each array are 64 modules of 4 Fresnellenses (concentration factor: 33) over 4 monocrystalline PV-cells (diameter: 2.25 inch) fixed connected and mounted on a common air-cooled heat sink. Actually each two and a half trackers are connected in se ries and form a branch giving a maximum power point voltage (MPP) of 280 - 285 V. All branches are connected in parallel. The branches are grouped into 8 parallel subfields separately connectable to the electrolysis plant. After 13 years of operation the PV-field MPP output power has decreased remarkably. Therefore it has been repaired and improved stepwise in parallel to the installation of the electrolysis facility between May 1992 and September 1993. Due to a lack of spare parts which are not available any more, the PV-subfield 8 could not be repaired and has therefore been isolated electrically from the other subfields for a later rebuilding with new PV-technology. The remaining 7 subfields give at 1000 W/m 2 and 25°C a maximum MPP output peak power of 289 kW at a current of 700 A. The availability of the PV-field comes to 87.5 %. At the north-west corner of the PV-field the PVPS-building is located which houses both the original electricall control equipment of the PV-field and the newly erected electrolysis plant. Due to the safety requirements of an electrolysis system its operation rooms and extern al equipment had to be designed and erected completely newly within the existing basic structure of the building. For the interconnection of the original electrical PV-subsystems to the new electrolysis plant several new subsystems had to be installed. Figure 1 gives an overview about the "As Built" installation of the electrolysis system and its extern al equipment showing a cut-out of the PVPS-building with the electrolysis operation areas, Utilities Room, Process Room and Gas Handling Room and the original rooms wherein new subsystems have been installed. In the figure the original equipment is shown with dashed lines. Starting from left to right in the figure a new electrolysis Control Panel (HS CP) has been installed in the Control Room besides the original PV control board (C&D Panel).

In the Electrical Room the two new power distribution switch cabinets (HPD DC) for PVfield connection and (HPD AC) for the supply with 480 V AC from the grid and 110 V AC from the uninterruptable power supply (UPS) are located. The Utilities Room is the new electrolysis control room housing the safety systems, product Gas Analysis System (GAS), operation Room Air Supervision System (RASS), HardWired Safety System (HWSS) and Air Conditioning Control Panel (AC CP). Within the utilities skid frame (US) the plant support systems for power supply of the electrolysis block via gridconnected rectifier or from the PV-field, water treatment system, power distribution panel, motor and valve control centre and the operation control computer (PLC) are installed. Outside this room on the east side another steel frame with the chiller and blower cooling systems and in front an underground electrolyte collection vessel are located. The Process Room houses a skid frame (PS) with the electrolysis block, electrolyte loop, gas separators, hydrogen and oxygen gas piping and its auxiliary subsystems. In the Gas Handling Room the intermediate hydrogen storage vessel and the hydrogen compressor are installed. On the north side of this room a roofed outdoor area with two exchangeable Hydrogen Bottle racks (HB1, HB2) and the Nitrogen Bottling System (NBS) for electrolyser purging has been erected. Process, Gas Handling Room and the roofed outdoor area have been designed and equipped completely explosion-proof to fulfil the German safety regulations. In a distance of 3 meters around the operation rooms and the bottling station an area with access restriction has been formed with steel posts.

2.1

Plant Subsystems

The plant consists of 16 subsystems with various interconnections in-between them as presented in figure 2. Thereby the PV-field with its original subsystems is summarised in the single subsystem SOLAR POWER SUPPL Y. The HARD-WIRED SAFETY SYSTEM (HWSS) is the main safety system and supervises certain safety limits which shall not be exceeded during operation. Any alarm of this system always leads automatically to an emergency shutdown with immediate stop of operation, depressurisation and nitrogen purging of the plant so that the system comes into a fail-safe mode. Besides tl1ese alarms the HWSS indicates also several warnings to give the operator a possibility to react before any emergency shutdown. The ROOM AIR SUPERVISION SYSTEM (RASS) supervises continuously the hydrogen in air content (H 2 in air) of the Process and Gas Handling Room directly below the room ceiling, the H2 in air content inside the GAS switch cabinet and the oxygen in air content (0 2 in air) directly above the electrolysis block. The H2 & O2 GAS ANAL YSIS SYSTEM (GAS) is the primary certified safety measure for the electrolysis process supervision. It measures continuously the gas purities (H 2in0 2• 02inH2) of the product gases witl1 independent gas loops for hydrogen and oxygen. The system gets its gases through trace-heated tubes -to avoid condensation of the saturated gases- from two gas probes in the gas separators located directly above the outlet pipes of the electrolysis block. The OPERA nON COMPUTER (PLC) is a standard process computer based on the Siemens S5 series and has been equipped especially with certified potential-separation cards for all measurement sensors, valves and motors to separate the explosion-proof areas from the Utilities Room. The PLC controls the complete facility operation including the connection of PV-subfields. For safety reasons it is not possible to change the program code during operation. All subsystems have its own subprogram code which can be operated completely automatically or in the manual mode if an operator command does not collide with any basic safety requirement. Current, temperature and pressure of the hydrogen production can be pre-

set and changed at any time during operation. Hydrogen production and storage are completely separated so that any disturbance of the storage subsystems does not interrupt the continuous experimental operation. The electrolysis block can be supplied with power either from the SOLAR POWER SUPPL Yor -for experimental purposes- from a grid-connected RECTIFIER. The PV-field is still controlled by its original operation system for PV-module tracking. But the connection of certain subfields to the electrolysis block is under full control of the PLC. The number of connected PV-subfields depends on the current setpoint. Only a direct connection of PVsubfields with the electrolysis block is actually possible so that the electrolyser fixes the common operating point. The electrolysis block is the most important component of the ELECTROL YTE LOOP. It has 120 single cells in series with an electrode area of 0.25 m2 • Besides the block the loop includes also an electrolyte pump with over pressure loop around it, an electrolyte cooler, two gas separators and the treated water supply. The operation limits of the electrolysis block with its plastic cell frames have fixed the layout of all other plant subsystems. Compared to other electrolysers of this size a main step forward could be reached because neither the change speed nor the absolute minimum level of the electric input power restrict the operation ability so that the electrolyser can directly operate from the PV-field without any electric buffer. Nevertheless the electrolyser is actually equipped only with pure Nickel-electrodes on the anodic side and sulphate-activated electrodes on the cathodic side which increase the specific energy consumption compared to electrolysers with advanced activated electrodes. When the product gases leave its gas separators saturated with water vapour they have to pass through the HYDROGEN & OXYGEN GAS TREATMENTwith separate gas cooler and condenser each. The gases are always hold at a temperature around 1OCC to decrease the water losses remarkably. The condensed water is directly given back into the electrolyte loop separatelyon the hydrogen and oxygen side. At its outlet the oxygen is depressurised to ambient pressure and led directly to air on the roof of the Process Room. Depending on the selection of the operator the hydrogen is led either into the hydrogen storage vessel or the gas is led to air after depressurisation through an outlet pipe with detonation protector on the roof of the Gas Handling Room. The H2 STORAGE VESSEL has a geometrical volume of 4.78 Nm 3 and is designed and certified for a maximum pressure of 800 kPa. The minimum deload pressure has been fixed to 150 kPa for safety reasons. The vessel operates as a bypass buffer so that it is possible to feed the hydrogen compressor with continuously produced hydrogen from the electrolyser whilst the vessel is depressurised by the compressor in parallel. The HYDROGEN COMPRESSOR is a usual two-stage membrane piston compressor with two high-pressure outlets. Its inlet pressure can vary between 100 and 800 kPa. The maximum outlet pressure has been fixed to a limit of 15 MPa. The electric/ pneumatic equipment of the compressor is fully integrated into the common facility operating system. Two standard H2 BOTTLE RACKS each with 12 50 liter standard gas bottles can be filled with hydrogen from the compressor one after the other. Always all 12 bottles of a rack will be filled in parallel. The exchange of a full bottle rack is possible at any time. The NITROGEN SUPPL Y subsystem is the main process safety system to purge electrolyser block, gas separators, coolers, demistors, hydrogen vessel, compressor and H; 02 piping from pure gases or gas mixtures after any emergency shut down or before start up after a longer regular shut down. The system operates without any external power source and can therefore automatically purge the electrolysis facility in tl1e case of any possible event. The nitrogen consumption for a regular purging procedure comes to 2.3 Nm 3 . All valves inside the explosion-proof areas are operated with PRESSURISED AIR. Therefore a subsystem with air compressor and main air vessel in the US and buffer tanks in . both operation rooms has been installed. It is possible to operate the facility 15 minutes only from the air buffers. If no pressurised air is available no hydrogen production is possible.

The facility has its own integrated WATER TREATMENTfacility to produce the water for the electrolysis facility with a minimum conductivity of 0.05 uSo The system gets its raw water from aSO m3 butter tank and pressure pump system at the east side of the PVPS building. The system consists of a decalcifierl carbon filter combination followed by areverse osmosis module and an ion exchanger unit at the end before the treated water butter from where the water can be fed into the electrolyte loop at the electrolyte pump inlet. The water production and feed operates fully automatically depending on the water level in the buHer tank and the liquid levels in the gas separators. For electrolyte cooling aseparate cooling BLOWER LOOPwith counter-f1ow electrolytel water heat exchanger at the pump outlet in the process skid and pump, waterl air cooler outside the building has been installed. The air flow through the air cooler can be forced with three blower fans. The blower loop is designed to hold a temperature ditterence of 9 K between heat exchanger inlet and outlet to guarantee always a sufficient electrolyte cooling. The CHILLER! COOLER LOOP has three independent water cooling loops with pumps for the water treatment system, commonly for the gas coolers and for the hydrogen compressor. The chiller loop reacts independently to the cooling demand of the three subsystems.

3.

RESULTS

The first startup sequences with energy from the rectifier had shown that the electrolyser operated uncritically in all operation ranges even at very fast changes of the electric input energy due to mains power failures. Therefore the HYS 350 team decided to test the plant during a longer period of solar operation from the beginning on and to use the rectifier only for specific experiments.

II

Solar Operation

From September 4th until October 1st, 1993 16 solar operation days with all restrictions from outside such as grid power failures, c10ud coverage and subsystem startup tests have been carried out. Between October 2nd and October 21 st, 1993 a second solar operation test period with 10 operation days has been performed. The electrolyser has been operated only from the PV-field during these days. During the night no potential or temperature preservation has been performed with energy from the grid. The plant has been shut down whenever the PV-fieldl electrolyser current fell below 200 A so that the PV-field has been shut down automatically due to shading of the trackers by themselves. Up to the 21 st of October 1993 the electrolyser has been operated for about 164 hours together with the PV-field. During this time period about 23.6 MWhrs of electric energy from the PV-field have been used for the hydrogen production. Thereby about 1.9 MWhrs of electric energy have been taken from the grid for all miscellaneous purposes of the electrolysis plant. Figure 3 presents a typical solar operation day from sunrise at 7:24 am to sunset at 4:25 pm. The electrolysis block current (I EM) and -with smaller fluctuations- the voltage (U EM) too follow the changes of the solar insolation due to the direct connection to the PV-field. The electrolyser starts with a temperature (T EM) of 45°C due to the high shut down temperature of the last solar operation day. The high increase of the temperature in the first 90 minutes results mainly from the high thermal capacity and low thermal conductivity of the block material wherein the electrolyte temperature remains du ring night always about 10 - 15 K higher than in the external metallic piping and gas separators. Since the content of the loop circulates only twice an hour it needs a long time to reach a complete mixing of the electrolyte. Thereby the temperature decreases again to a lower level and heats up afterwards only by the thermal losses of the process itself. At the end of the day near to shut down the control switches off . the electrolyte cooling due to the fast decreasing current to heat up the block again in order to

start the electralyser at the next morning with the highest possible temperature. The gas pressure (P H2) of the electrolyser depends at startup on the pre-set value and on the pressure losses due to temperature decrease over night. The PLC controls the gas pressures equallyon both sides within a control band of +/- 5 kPa. The electrolyte circuit pressure is always 50 kPa higher than the gas pressures due to the constant fluid pressure losses. Any gas pressure between 150 and 800 kPa in steps of 1 kPa can be selected by the operator. The praduct gas impurities (H 2in0 2, 02inH2) start with relatively high values because the electrolyser remains closed during the night without nitrogen purging. Normally within 15 minutes the gas impurities reach its minimum starting values. During the day the gas impurities fluctuate mainly due to input energy and small pressure changes. Additionally the gas impurities rise a little bit caused by the block temperature increase. The fast increase of impurities near shut down caused by a fast decrease of input energy and an increase of temperature have been expected. But the absolute height of the curve shape vary from day to day unexpected. For the explanation of the constant rise and daily variation several possibilities have to be examined in detail during the experimental operation. Nevertheless the impurities stay always far away from any critical values during solar operation and all experiments with the rectifier. Until now no specific change of the gas impurities could be observed.

U

Specific tests

Between September 4th and October 25th, 1993 various specific experiments have been performed on 10 days with grid-connected operation to gain first electrolysis characteristics under contralied boundary conditions such as fixed temperature and pressure. Also several solar operation days have been used for specific experiments such as efficiency measu rements.

3.2.1

First I-V-Characteristics

The two characteristics in figure 4 have been gained during grid-connected operation over a time period of four hours each and cover the daily temperature range during solar operation at 800 kPa. Compared to advanced small electrolysers the electrochemical performance is bad because no advanced activated electrodes could be installed. At the moment the comparable specific energy consumption at 200 mAlcm 2 and 800 kPa moves between 4.75 (U ce ll=1.95V) and 5.15 kWh/Nm 3 (U ce ll=2.11V) in the temperature range from 50 to 80°C. During a solar operation day the specific energy consumption varies only between 4.83 kWh/Nm 3 (U ce ll=1.98V) in the morning as the lowest value and 5.09 kWh/Nm 3 (U ce ll=2.09V) at noon as the highest value.

3.2.2

Product Gas Impurities

The product gas impurities have been measured together with I-V-characteristics during grid-connected operation. In the case of HYS 350 current density, temperature, water vapour content, operating pressure level and the small pressure fluctuations from the pressure control influence the impurities. Until the end of October two measurements of the characteristics have been performed. Figure 5 presents the results of one measurement set as an example for the electrolysis operation at 50°C and 800 kPa. The second measurement has been performed at 80°C and 800 kPa. In principle the curve shapes of both measurements are similar although the absolute height of the values is higher at 80°C. At tile time being the gas impurities can only be measured fram a current density of 120 mA/cm 2. The H2in0 2-content moves during constant operation in the range between 0.83 Vol% at 120 mA/cm 2 and 0.69 . Vol% at 320 mA/cm 2 whilst the 02inH2-content stays between 0.65 Vol% and 0.09 Vol% in the

same current density range. No significant rise of the gas purities could be observed so far but the daily values vary about +/- 0.3 Vol% during a longer time period of operation. ~

Electrolyser Efficiencies

The three electrolyser efficiencies, Faraday-, LHV and overall electrolyser efficiency, have been measured two times during solar operation and four times du ring grid-connected operation as weil. Figure 6 shows the efficiency curve shapes during a solar operation day with sine wave insolation shape. From the principle of measurement it is not possible to measure continuously during a full day. Therefore the presented curve shapes are combined from several pieces of about one hour of measurement each with an interruption of half an hour. The missing pieces have been interpolated. The Faraday-efficiency shows the expected curve shape of a solar-operated electrolyser with increasing/ decreasing efficiency before and after noon due to the increasing/ decreasing current. At the highest input current the Faraday-efficiency comes to about 96 % at a partial load of 61 %. The curve shape of the second measurement day is similar but in this case a maximum efficiency of 98 % has been measured at the same partial load level. The curve shape of the LHV efficiency with its constant rise during the day is different compared to smaller solar-operated electrolysers. The rise in the morning is similar whilst the rise in the afternoon where a slow decrease has been expected results from the high thermal capacity of the block and the automatic switch off of the electrolyte cooling if the input power decreases remarkably during solar operation. 80th, Faraday- and LHV efficiency, determine the total electrolyser efficiency. The absolute maximum value with 59 % is relatively low compared to advanced electrolysers but can be improved simply by the use of advanced electrodes which shift the LHV efficiency to a much higher value. The curve shape of the total efficiency is just only a combination of the two others.

3.2.4 power Consumption 01 the Plant and power Matching One important aspect of a future commercial electrolysis facility will be the internal power consumption because it influences very much the overall plant efficiency. In the case of a plant operated under Saudi Arabian climate conditions the energy amount for cooling purposes is critical. In the HYS 350 plant only the absolute minimum equipment has been installed with respect to the optimisation of the miscellaneous energy amount. The experience up to now has shown as presented in figure 7 that during solar operation days only 7.96 % of the total incoming energy are necessary to cover all miscellaneous energy demands of the electrolysis operation. The main influence on the total efficiency of a directly connected solar-operated electrolysis plant is the optimal operation of the PV-field always at or near its MPPs. During solar operation the HYS 350 electrolyser voltage moves only within a small range fram 226.5 V in the morning as the lowest and 250.4 V at noon as the highest voltage. The variation between different days is with 1.09 V in the morning and 2.72 V at noon very small at about 60 % of the nominal load of the electrolyser. If the PV-field shall give its design current of 1000 A at noon the voltages will move between 256.6 V in the morning and 279.5 V at noon. For optimal power matching the PV-field has to be reconfigured therefore.

4.

OUTLOOK

Within the next two years three different phases of activities, hardware improvements of PV-field and electrolysis, regular solar operation and specific measurement campaigns will

be performed in a very close Saudi Arabian-German co-operation in Germany as weil as in the Kingdom. For the hardware improvements various areas have to be defined so far such as optimisation of the power matching between PV-field and electrolyser, improvement of PVsubfield 8 with new PV technology, definition, contracting and installation of a new data acquisition system, installation of a new UPS, installation of a new pressurised air system and improvement of the AC power supply for the rectifier. The improvements will be performed stepwise. The regular solar operation shall cover the whole next year as aminimum. The experience with the HYS 10 facility has shown that a minimum of 80 days statistically distributed over all seasons of the year are necessary to gain statistical results. The specific measurement campaigns with selected solar-operation days but mainly grid-connected operation will be used to perform all experiments to describe the characteristics of the electrolyser and PV-field and to examine the important link between both in detail.

5.

SUMMARY

After the plant design phase between May 1991 and May 1992 of the Saudi-German joint HYS 350 team the plant hardware works started at the end of May 1992 and lasted until the middle of August 1993. The plant has been inspected and accepted by the German safety authority TÜV giving an official operation permission. At the 29th of August the plant has been started up and has been operated successfully unIil the end of December 1993 during a first test phase with solar and grid-connected operation periods. At the end of December 1993 the plant has been taken over into its experimental operation phase. During the first test phase a complete set of experiments has been performed to examine the experimental possibilities themselves and to gain first results about the startup status of the facility (see chapter 3). The main purpose of the Saudi-German joint cooperation for the HYSOLAR 350 kW demonstration plant between 1991 and 1993 was the design and erection of a safe and reliable plant. This goal could be reached and demonstrated successfully. HYS 350 PV-ELECTROLYSIS SYSTEM Cut out of PVPS-Iouilcling , HYS350 instollo tions

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