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A PV pumping system
Applied Energy 65 (2000) 145±151
www.elsevier.com/locate/apenergy
A PV pumping system A. Al-Karaghouli*, A.M. Al-Sabounchi Energy and Environmental Research Center, Jadiriyah, PO Box 13026 Baghdad, Iraq
Abstract A PV system is designed and used in order to reclaim the soil of a farm located 35 km NE of Baghdad using brackish water from a well and discharging it to a nearby drainage stream. The system is designed according to the climate of Baghdad city and the hydrogeological data of the area. An evaluation of the both PV and drainage systems was made for a complete year of operation. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction The project was performed at the Energy and Environmental Research Center, Agriculture Experimental Station located 35 km NE of Baghdad, at 33 330 N Latitude, 44 140 E Longtitude and 34 m above sea-level. The locality has been formed by deposits from the rivers Tigris and Diala. These deposits were transported to the area with the ¯ow of irrigation and ¯ood water that made the soil of a silty nature. The high content of salt in the Diala river, which is used to irrigate the area led to salination of the soil. Also the continuous irrigation of the soil has increased the saltiness problem. A study of soil reclaimation for the project area has been undertaken using a vertical drainage technique of underground water through draining water from a pumping well and sending it to a drainage stream using an appropriate water pump. The project soil is a loam containing 52% silt, 29% clay, 19% sand and 0. 7±1.1% oganic matter, with underground water at about 100 cm depth. 2. Project requirements According to the emphasis placed by the FAO [1], the critical level of underground water that corresponds to the project requirements should not be less than * Corresponding author. 0306-2619/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S0306-2619(99)00080-X
146
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
120 cm depth. Therefore, it was important to draw down the underground water level of the project by not less than 20 cm at its farthest end. To achieve that, a well of 29 m depth and 20 cm diameter was dug in the middle of the project area:four other observation wells of 10 cm diameter each were also dug at distances of 50 and 100 m from the main well. By applying the Jacob Eq. [2], using the hydrogeological data of the project, bearing in mind that the farthest end of the project zone from the pumping well is 100 m, the results are shown in Table 1. Since the farthest end from the pumping well is 100 m, then the suitable choice of drainage is 10 l/s which will ensure an appropriate draw down even at the farthest ends of the project. A decision to use an electric water-pump energised by a PV system was taken. 3. PV pumping station design The main goal of this study is to achieve a suitable and optimum design of a PV pumping station for vertical drainge in order to decrease the underground water level and eventually reclaim the soil. The main parts of the system are shown in Fig. 1.
Table 1 Descent levels of underground water for dierent pumping discharge rates at 50 and 100 m distances Qa Rb Hc a b c
5 50 0.25
5 100 0.18
10 50 0.5
10 100 0.36
Q Ð Pumping discharge in l/s. R Ð Distance from pumping well, in metres. H Ð Steady state maximum draw down, in metres.
Fig. 1. The system's operation principle.
15 50 0.75
15 100 0.54
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
147
3.1. Water-pump design The demanded hydrologic power, Ph in watts, of the pump [3] is ph pgQh
1
where: p g Q h
- water density=1000 kg/m3; - gravitational acceleration=9.81m/s2; - water ¯ow rate, in m3/s; - water pumping head, in m.
To ®nd the hydrologic power required by the pump, Eq. (l) is used with h=16 m and Q=O.01m3/s: it gives Ph=1569.6. Assuming an overall eciency of the pump and electric motor to be 40%, yields a demanded input electric power, Pe of 3924 W. Practically a motor and pump unit of power exceeding the theoretical value is used and also to face any decay in the volume of drainage. Hence Pe is multiplied by a safety factor equal to 1.25 to give a new value of Pe equal to 4905 W. A suitable Grundfos submersible pump type SP72-2N is used: it is a multi-stage centrifugal pump directly coupled to a 3 phase-380 V submersible 2-pole asynchronous, squirrelcage motor of 5 kW rating. 3.2. PV systems design An operation period of at least 10 h daily is required. Therefore, the corresponding daily demand of electric energy should be not less than 49.05 kWh. To get a PV system of ecient design, the tilt factor consideration is taken into account, where the value of tilt factor (Tf) is expressed according to the Lin and Jordan formula [4], as: Tf
RbHTb l cosB HTd l cos B HT HT 2 2
2
where: Rb HTb and HTd B
Ð direct beam elevation factor Ð monthly daily average total horizontal beam and diuse radiations; Ð inclination, in degrees; Ð ground re¯ectivity.
Then, the necessary area, A, in m2 of PV modules is determined as: A
E SF TfGpv R B in
3
148
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
where: E SF G pv R B in
Ð monthly daily average demand of electric energy, in Wh; Ð safety factor=1.25; Ð monthly daily average insolation on a horizontal surface, in Wh/m2; Ð solar module's eciency; Ð regulator eciency; Ð battery eciency; Ð inverter eciency.
The corresponding peak power PPv, is calculated as: PPv ScApv
4
where, Sc is the solar constant equal to 1000 W/m2. Substituting Eq. (3) into Eq. (4) yields: A
1000 E 1:25 Tf G R B in
5
where R is taken =0.95, ZB=0.7 and in=0.9, while the data for the insolation of Baghdad city are substituted for G. To get the optimum choice of the PV system design, multi systems are considered for dierent inclinations from 0 to 60 . For each inclination,the monthly values of tilt factors are calculated according to Eq. 2. Then Eq. 5 is applied to calculate the PV peak-power demands for each month. The result for the worst month is considered to be the feasible solution of that inclination. Finally, the inclination of the minimum worst month demand of PV peak-power is considered as the ®nal optimum choice of the design. Fig. 2 and Table 2 show the results of this procedure. It is clear that the 50 inclination is the optimum solution, corresponding to the minimum PV peak-power demand. 4. PV system con®guration 4.1. PV array A PV array consisting of 23 041 ft 3 ft solar modules each of speci®cation 14.5 V, 759 mA and 11 W, are arranged to give an output power of 25 344 W at a voltage of 522 V and a current of 48 A. Tho array includes 8 parallel sub arrays, each consisting of 18 series panels, where each panel contains 2 series of 8 parallel modules. Each 4 panels are assembled on a single support unit as indicated in Fig. 3. As a result, the whole arrangement of the PV array consist of 36 units distributed on 36 supports, arranged in 4 rows of 9 units per row. Fig. 4 shows a simple line diagram of the whole PV system.
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
149
Fig. 2. PV peak-power demand of the system for various inclinations shown during the year.
Table 2 PV peak power demand (in watts) of the worst months in a year at dierent inclinations B
0
10
20
30
40
50
60
Mon.
Dec.
Jan.
Jan.
Jan.
Jan.
Jan.
May.
Ppv
39960
33167
29642
27369
25996
25337
27529
Fig. 3. Single-unit circuit diagram.
150
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
Fig. 4. Simple circuit diagram of the whole PV array.
Because the units are arranged in multi rows, a reasonable distance of about 8m between each successive row avoids shadowing between rows during winter days; the height of each support is 4 m. 4.2. Charge regulator The most important function of the regulator is to protect the battery against over charge and deep discharge. If the battery voltage exceeds the allowed limit, a regulator isolates the 7 subarrays and 1 subarray remains connected to provide the batteries with a maintenance current. 4.3. Storage battery system A storage battery system capacity in ampere-hour, Ah, is designed to provide sucient supply to the system for 3 successive days without insolation by applying the following equation: Ah 3 E=DDL 504Vin
6
where DDL is the deep discharge level of the battery and assumed to be 0.6. Applying Eq. (6) gives the battery capacity as 540.6 Ah. To match the demand a storage svstem of 252 batteries connected in series, each rated at 2 V, 600 Ah is chosen. 4.4. Inverter A modi®ed inverter (Danfoss type), 380/415 V is choosen to provide 3380 V, 50 Hz a.c. from 504 V d.c. storage battery: it has output regulation with respect to voltage and frequency.
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
151
Table 3 Evalued data for the system's operation for 1 year Mon
Tf
Ga
EGb
E
WVc
D1d
D2d
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
1.57 1.38 1.1 0.9 0.8 0.71 0.73 0.85 1.04 1.34 1.54 1.69
4479 5307 5152 4847 4720 4924 5256 5542 5848 5928 4934 4661
57 068 67 618 64 768 57 969 57 318 57 719 58 932 62 890 65 569 67 272 60 351 57 803
49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050
418 496 475 425 420 423 432 461 481 493 442 424
1.58 1.68 1.65 1.59 1.58 1.58 1.59 1.64 1.66 1.68 1.61 1.59
1.41 1.49 1.47 1.42 1.41 1.42 1.43 1.46 1.48 1.49 1.44 1.42
G Ð monthly daily average insolation at 50 inclination, in Wh/m2. EG Ð monthly daily average of generated energy that suppplies the load Wh. c Wv Ð monthly daily average draining water volume in m3. d D1,D2±depths of steady-state levels of underground water at 50 and 100 m distances from the pumping well, in m. a
b
5. PV pumping station evaluation As was discussed before, the station is designed to discharge water at a ¯ow rate of 10 l/s for a daily operation of 10 h. This means that a volume of drainge of about 360 m3 daily must be pumped and drained to the nearby stream. An evaluation of the station operation was made for a period of 1 year: the resulting data are as indicated in Table (3). Table 3 shows that during the system operation, the new minimum level of underground water is in January: that corresponds to our design in which January is regarded as the worst month of the year. Also the new levels for all months during the year exceed the critical permissible depth of underground water (1.2 m) signi®cally keeping the soil healthy even during periods not included in the hours of daily operation. References [1] [2] [3] [4]
Irrigation Ð drainage and salinity. FAO, 1973. Todd D. Ground-water hydrology. New York: Wiley and Sons, 1980. Holand FA, Chapman FS. Pumping of liquids. New York: Reinhold Publishing Corporation, 1966. Lunde PJ. Solar thermal engineering. NewYork: Wiley and Sons, 1980.
www.elsevier.com/locate/apenergy
A PV pumping system A. Al-Karaghouli*, A.M. Al-Sabounchi Energy and Environmental Research Center, Jadiriyah, PO Box 13026 Baghdad, Iraq
Abstract A PV system is designed and used in order to reclaim the soil of a farm located 35 km NE of Baghdad using brackish water from a well and discharging it to a nearby drainage stream. The system is designed according to the climate of Baghdad city and the hydrogeological data of the area. An evaluation of the both PV and drainage systems was made for a complete year of operation. # 1999 Published by Elsevier Science Ltd. All rights reserved.
1. Introduction The project was performed at the Energy and Environmental Research Center, Agriculture Experimental Station located 35 km NE of Baghdad, at 33 330 N Latitude, 44 140 E Longtitude and 34 m above sea-level. The locality has been formed by deposits from the rivers Tigris and Diala. These deposits were transported to the area with the ¯ow of irrigation and ¯ood water that made the soil of a silty nature. The high content of salt in the Diala river, which is used to irrigate the area led to salination of the soil. Also the continuous irrigation of the soil has increased the saltiness problem. A study of soil reclaimation for the project area has been undertaken using a vertical drainage technique of underground water through draining water from a pumping well and sending it to a drainage stream using an appropriate water pump. The project soil is a loam containing 52% silt, 29% clay, 19% sand and 0. 7±1.1% oganic matter, with underground water at about 100 cm depth. 2. Project requirements According to the emphasis placed by the FAO [1], the critical level of underground water that corresponds to the project requirements should not be less than * Corresponding author. 0306-2619/00/$ - see front matter # 1999 Published by Elsevier Science Ltd. All rights reserved. PII: S0306-2619(99)00080-X
146
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
120 cm depth. Therefore, it was important to draw down the underground water level of the project by not less than 20 cm at its farthest end. To achieve that, a well of 29 m depth and 20 cm diameter was dug in the middle of the project area:four other observation wells of 10 cm diameter each were also dug at distances of 50 and 100 m from the main well. By applying the Jacob Eq. [2], using the hydrogeological data of the project, bearing in mind that the farthest end of the project zone from the pumping well is 100 m, the results are shown in Table 1. Since the farthest end from the pumping well is 100 m, then the suitable choice of drainage is 10 l/s which will ensure an appropriate draw down even at the farthest ends of the project. A decision to use an electric water-pump energised by a PV system was taken. 3. PV pumping station design The main goal of this study is to achieve a suitable and optimum design of a PV pumping station for vertical drainge in order to decrease the underground water level and eventually reclaim the soil. The main parts of the system are shown in Fig. 1.
Table 1 Descent levels of underground water for dierent pumping discharge rates at 50 and 100 m distances Qa Rb Hc a b c
5 50 0.25
5 100 0.18
10 50 0.5
10 100 0.36
Q Ð Pumping discharge in l/s. R Ð Distance from pumping well, in metres. H Ð Steady state maximum draw down, in metres.
Fig. 1. The system's operation principle.
15 50 0.75
15 100 0.54
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
147
3.1. Water-pump design The demanded hydrologic power, Ph in watts, of the pump [3] is ph pgQh
1
where: p g Q h
- water density=1000 kg/m3; - gravitational acceleration=9.81m/s2; - water ¯ow rate, in m3/s; - water pumping head, in m.
To ®nd the hydrologic power required by the pump, Eq. (l) is used with h=16 m and Q=O.01m3/s: it gives Ph=1569.6. Assuming an overall eciency of the pump and electric motor to be 40%, yields a demanded input electric power, Pe of 3924 W. Practically a motor and pump unit of power exceeding the theoretical value is used and also to face any decay in the volume of drainage. Hence Pe is multiplied by a safety factor equal to 1.25 to give a new value of Pe equal to 4905 W. A suitable Grundfos submersible pump type SP72-2N is used: it is a multi-stage centrifugal pump directly coupled to a 3 phase-380 V submersible 2-pole asynchronous, squirrelcage motor of 5 kW rating. 3.2. PV systems design An operation period of at least 10 h daily is required. Therefore, the corresponding daily demand of electric energy should be not less than 49.05 kWh. To get a PV system of ecient design, the tilt factor consideration is taken into account, where the value of tilt factor (Tf) is expressed according to the Lin and Jordan formula [4], as: Tf
RbHTb l cosB HTd l cos B HT HT 2 2
2
where: Rb HTb and HTd B
Ð direct beam elevation factor Ð monthly daily average total horizontal beam and diuse radiations; Ð inclination, in degrees; Ð ground re¯ectivity.
Then, the necessary area, A, in m2 of PV modules is determined as: A
E SF TfGpv R B in
3
148
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
where: E SF G pv R B in
Ð monthly daily average demand of electric energy, in Wh; Ð safety factor=1.25; Ð monthly daily average insolation on a horizontal surface, in Wh/m2; Ð solar module's eciency; Ð regulator eciency; Ð battery eciency; Ð inverter eciency.
The corresponding peak power PPv, is calculated as: PPv ScApv
4
where, Sc is the solar constant equal to 1000 W/m2. Substituting Eq. (3) into Eq. (4) yields: A
1000 E 1:25 Tf G R B in
5
where R is taken =0.95, ZB=0.7 and in=0.9, while the data for the insolation of Baghdad city are substituted for G. To get the optimum choice of the PV system design, multi systems are considered for dierent inclinations from 0 to 60 . For each inclination,the monthly values of tilt factors are calculated according to Eq. 2. Then Eq. 5 is applied to calculate the PV peak-power demands for each month. The result for the worst month is considered to be the feasible solution of that inclination. Finally, the inclination of the minimum worst month demand of PV peak-power is considered as the ®nal optimum choice of the design. Fig. 2 and Table 2 show the results of this procedure. It is clear that the 50 inclination is the optimum solution, corresponding to the minimum PV peak-power demand. 4. PV system con®guration 4.1. PV array A PV array consisting of 23 041 ft 3 ft solar modules each of speci®cation 14.5 V, 759 mA and 11 W, are arranged to give an output power of 25 344 W at a voltage of 522 V and a current of 48 A. Tho array includes 8 parallel sub arrays, each consisting of 18 series panels, where each panel contains 2 series of 8 parallel modules. Each 4 panels are assembled on a single support unit as indicated in Fig. 3. As a result, the whole arrangement of the PV array consist of 36 units distributed on 36 supports, arranged in 4 rows of 9 units per row. Fig. 4 shows a simple line diagram of the whole PV system.
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
149
Fig. 2. PV peak-power demand of the system for various inclinations shown during the year.
Table 2 PV peak power demand (in watts) of the worst months in a year at dierent inclinations B
0
10
20
30
40
50
60
Mon.
Dec.
Jan.
Jan.
Jan.
Jan.
Jan.
May.
Ppv
39960
33167
29642
27369
25996
25337
27529
Fig. 3. Single-unit circuit diagram.
150
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
Fig. 4. Simple circuit diagram of the whole PV array.
Because the units are arranged in multi rows, a reasonable distance of about 8m between each successive row avoids shadowing between rows during winter days; the height of each support is 4 m. 4.2. Charge regulator The most important function of the regulator is to protect the battery against over charge and deep discharge. If the battery voltage exceeds the allowed limit, a regulator isolates the 7 subarrays and 1 subarray remains connected to provide the batteries with a maintenance current. 4.3. Storage battery system A storage battery system capacity in ampere-hour, Ah, is designed to provide sucient supply to the system for 3 successive days without insolation by applying the following equation: Ah 3 E=DDL 504Vin
6
where DDL is the deep discharge level of the battery and assumed to be 0.6. Applying Eq. (6) gives the battery capacity as 540.6 Ah. To match the demand a storage svstem of 252 batteries connected in series, each rated at 2 V, 600 Ah is chosen. 4.4. Inverter A modi®ed inverter (Danfoss type), 380/415 V is choosen to provide 3380 V, 50 Hz a.c. from 504 V d.c. storage battery: it has output regulation with respect to voltage and frequency.
A. Al-Karaghouli, A.M. Al-Sabounchi / Applied Energy 65 (2000) 145±151
151
Table 3 Evalued data for the system's operation for 1 year Mon
Tf
Ga
EGb
E
WVc
D1d
D2d
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
1.57 1.38 1.1 0.9 0.8 0.71 0.73 0.85 1.04 1.34 1.54 1.69
4479 5307 5152 4847 4720 4924 5256 5542 5848 5928 4934 4661
57 068 67 618 64 768 57 969 57 318 57 719 58 932 62 890 65 569 67 272 60 351 57 803
49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050 49 050
418 496 475 425 420 423 432 461 481 493 442 424
1.58 1.68 1.65 1.59 1.58 1.58 1.59 1.64 1.66 1.68 1.61 1.59
1.41 1.49 1.47 1.42 1.41 1.42 1.43 1.46 1.48 1.49 1.44 1.42
G Ð monthly daily average insolation at 50 inclination, in Wh/m2. EG Ð monthly daily average of generated energy that suppplies the load Wh. c Wv Ð monthly daily average draining water volume in m3. d D1,D2±depths of steady-state levels of underground water at 50 and 100 m distances from the pumping well, in m. a
b
5. PV pumping station evaluation As was discussed before, the station is designed to discharge water at a ¯ow rate of 10 l/s for a daily operation of 10 h. This means that a volume of drainge of about 360 m3 daily must be pumped and drained to the nearby stream. An evaluation of the station operation was made for a period of 1 year: the resulting data are as indicated in Table (3). Table 3 shows that during the system operation, the new minimum level of underground water is in January: that corresponds to our design in which January is regarded as the worst month of the year. Also the new levels for all months during the year exceed the critical permissible depth of underground water (1.2 m) signi®cally keeping the soil healthy even during periods not included in the hours of daily operation. References [1] [2] [3] [4]
Irrigation Ð drainage and salinity. FAO, 1973. Todd D. Ground-water hydrology. New York: Wiley and Sons, 1980. Holand FA, Chapman FS. Pumping of liquids. New York: Reinhold Publishing Corporation, 1966. Lunde PJ. Solar thermal engineering. NewYork: Wiley and Sons, 1980.