"ICAL 1 / DT X"

沙漠研究 22-1, 337 -340 (2012 )－Refereed Paper－

Journal of Arid Land Studies

Application Example of a Small Solar Pumping Systemin the Djiboutian Wadi Agriculture
Kiyoshi TAJIMA*1), Shinji SUZUKI1), Takashi SHINOHARA2),
Atsushi SANADA3) and Fumio WATANABE1)
Abstract: The Republic of Djibouti is located in northeastern Africa and in a low altitude, therefore the temperature is one of thehighest region in the world. The average annual rainfall is approximately 130 mm, and the rain is heavy with a wide range of yearlyvariation. Therefore the productivity of agriculture is extremely low. The scarcity of rainfall means that agricultural productivity isextremely low, and is typically restricted to areas along wadis, and the most common water sources are wells. In addition, mostsurface soils contain very little organic matter and are volcanic in origin. We have examined the potential application of greening
technology, such as "Waterharvesting", "Stone mulch" and "Double suck" in Djibouti from 1990. The purpose of these methods is toincrease the infiltration of surface water and to maximize the efficiency with water can be used. In 2007, we installed a small solar
pumping system in a farm ofwadi-type agriculture to investigate the possibility of the new integrated farming. The study site was a
1.5 ha vegetable farm in the city of Dikhil. We attempted to integrate traditional farming methods with the use of a small solar
pumping system, other water-saving technologies such as "Stone mulch", and "Bokashi" composting technology in the field in March
2011. The 480 W solar pumping system that was initially installed at the site was subsequently upgraded by an additional 200 W.
The maximum flow was approximately 95 L/min, and the amount of water pumped was 39 m3/day (at 27 MJ/m2) and the quantity ofwater used each day was 60 m3/day.
Key Words: Bokashi, Djibouti, Solar pumping system, Stone mulch, Waterhavesting
pumping groundwater. This study presents the findings offield work that we conducted until March 2011.

1. Introduction
The Republic of Djibouti is located in northeastern Africa
and in a low altitude, therefore the temperature is one of thehighest region in the world. The average annual rainfall isapproximately 130 mm, and the rain is heavy with a wide
range of yearly variation. The scarcity of rainfall means that
agricultural productivity is extremely low, and is typically
restricted to areas along wadis, and the most common water
sources are wells. Techniques such as "Solar energy use
distillation devices", "Water harvesting", "Double suck" and"Stone mulching" have been used in Djibouti since 1990.
These modern techniques promote the infiltration of water into
the ground, and utilize small amounts of water effectively inDjibouti (Ismael et al., 2003, Takahashi et al., 2010; Tajima et al.,2006). In 2007, we combined the traditional wadi-type
agriculture methods with more modern methods that used
domestic animal waste for Bokashi composting. We also
examined the potential for integrating farms to increase
productivity among the vegetable growers in the suburbs ofDikhil.
Among the modern technologies that wereintroduced was a small solar-powered pumping system for

2. Objectives
In this study, we integrated the use of a small solar
pumping system into the traditional wadi-type agriculture
system employed in the Republic of Djibouti. We also
investigated the operating conditions of the system.

3. Description of Study Site
The farm where the solar pumping system was installed
was one of the farms owned by Mr. Djama Guedi who was a
resident in Dikhil. The farm was Arouo farm of area 1.5 halocated on 42°33'E, 11°8'N, 673m above sea level, in Arouo
wadi. The main crops were melon, onion, eggplant, tomato,
forage crops (sugarcane, crotalaria, alfalfa). And a domestic
animal was goat. Figure 1 shows the whole view of theArouo farm, and Figure 2 shows a ground plan. The
characteristic of the farm of Mr. Djama Guedi installed in thewadi was demarcated by a 2 m-height stone wall except someportion around the farm, and there was a hollow (flood control* Corresponding Author: tajima@nodai.ac.jp
1-1-1, Sakuragaoka, Setagaya-ku, Tokyo, 156-8502, Japan
1) Faculty of Regional Environment Science, Tokyo University of Agriculture Tokyo University of Agriculture2) Junior College of Tokyo University of Agriculture3) Faculty of International Agricultural Development, Tokyo University of AgricultureFig. 1. Whole view of the Arouo farm.

Fig. 3. The relationship between hydraulic head and quantity ofwater under the power input condition (P1Watts).

Fig. 4. Whole view of solar pumping system.

Fig. 2. Ground plan of the Arouo farm.

channel) which water flows to at the time of a flood in thecenter of the farm.
The farm where the solar pumping system was installed
was subdivided into sections, each of which measured
approximately 1,200-1,300 m2 and was demarcated by a 1m-high stone wall. Each division is supplied with irrigationwater though a steel pipe with an outer diameter of 76.3 mm(21/2"). Each division is accomplished by furrow or basin
irrigation.
There were approximately 20 breeding goats on the farm.
Sugar cane leaves used to feed the goats and litter of the shed,
and was collected with feces and urine to produce the compost.
To promote fermentation of the compost, some water wasadded. The surface of the compost was then covered withsugarcane leaves to limit the loss of water. In addition, thegoats were used for milk and meat.

4. Summary of the Solar Pumping System
The solar pumping system installed in the field in March,2008 was consisted with 480 W solar module (BP solar
BP380J × 6) and a CU200 controller and SQF5A-6 submarine
type pump (Grundfos SQflex series). After installation of thesystem, additional 200 W solar module (Photowatt PWX500 ×4) was installed by the farmer. A concrete water tank (10×5×1.5 m) with a capacity of 75 m3 was installed at the highest
point on the farm. The hydraulic head (pump lift) wasapproximately 15 m. Figure 3 shows the relationshipbetween hydraulic head and quantity of water under power
input condition (P1 Watts). Based on this Figure 3, the flow
with the 480 W PV module would be approximately 4.5 m3/h
if it were pumping water from a hydraulic head of 15 m.
After the addition of the 200 W module, potential flows could
be increased to approximately 6.8 m3/h. Figure 4 shows thesolar pumping system that was installed.

5. Measurements and Considerations
5.1. Result of measurement
We visited the site in March, 2011 which wasapproximately three years after the system had been installed.
A data logger was installed to measure temperature, relative
humidity (RH), quantity of sunlight, PV module temperature,
PV module voltage and water tank water level of the watertank every five minutes from March 2 to 4 2011. According
to the farmer, daily water use was approximately 50 m3/day.
Details of the crops that were cultivated are shown in Figure 2.
Figure 5 shows schematic of the PV module. About themodules of additional 50W, it was guessed using a middle
terminal by the measurement result of the output voltage of thisterminal that it was connected in parallel.

Table 1. Output Voltage of Modules.
ModuleBP80
PWX500PWX500(broken)
Arrey

Output[V]16.6
8.43～7123Notes
1/2 parallel output
1/2 parallel output

Fig. 5. Wiring of PV array.
100Fig. 7. The damaged PV module by Stone.

Mudule Temp.

700.8

60
50

0.6

40
0.4

30
20

20.2

100
12:00

18:00

0:00

6:00

12:00

18:00

0:00

6:00

012:00

TimeFig. 6. Measurement results of temperature relative humidity andglobal solar irradiance.

RH was low during the daytime (about 20%), which istypical of the dry season, but it was relatively high by nighttime. It is a characteristic of Djibouti located in the shore.
The maximum temperature of the PV module was 54.8°C, andthe minimum was 14.4°C. The maximum temperature of PV
module was approximately atmospheric temperature +15°C.
The global solar irradiance was 1.06kW/m2 and the global
solar radiation was 27 MJ/m2 ･day. In addition, the PV
module array was set up 0° to the south and the tilt angle was10° to horizontal level.
5.2. System operation
One of the 80 W PV modules that were initially installed
was damaged by a stone that had been thrown at the equipment.
Innumerable crack on all of the hard glass of PV modulesurface was observed. And as for the damage, we wereapprehensive about infection in the cell of the damage point.
Table 1 shows measurements of the output voltage of each PV
module under operating conditions. The output voltage of thedamaged PV module was approximately half for 16.6 V of asound module and repeating 7 V and 3 V in a period forapproximately per a second. The output power of array was450 W (voltage 123 V, current 3.66 A), under condition of1.2
Water Level
Global Solar Irra.

1.75

1

1.5
0.8

1.25
10.60.75

0.4

0.5
0.2

0.25
012:00

18:00

0:00

6:00

12:00
Time

18:00

0:00

6:00

Global Solar Irradiance［kW/㎡］

1

Global Solar Irra.

Water Level of Tank［m］

Relative Humidity
80

Global Solar Irradiance[kW/㎡]

Temperture[℃]/Relative Humidity[％]

1.2

Temperature

90

012:00Fig. 8. Measurement result of the water level of tank.

global solar irradiance 856 W/m2. The ratio of output against
the specifications of the module was 72.9% (=350/480) at 350
W against the PV module specification of 480 W by ameasurement at the original setting of May, 2008. We tried toapply this ratio to the 2011 result.
For the specifications of the module of 680 W(=480+200),
we can expect an electricity output of 496 W(=680×72.9%).
Consequently, the loss in power output due to damage by thestone can be calculated as 9.24 %(=(496-450)/496). Figure 7
shows the state of a module damaged. Figure 8 showschanges in the water level of the tank over time. The weather
during the sampling period was clear, and the pump wasoperated under sunny conditions of approximately 530 W/m2(global solar irradiance) or more. Generally, the system wasconsidered to be operated it under favorable conditions during
the daytime.
5.3. Evaluation of the system
We calculated the relationship between the quantity ofsunlight and quantity of water pumped and the quantity ofwater actually used. Figure 9 shows the result of estimationthat was converted to the water level of the tank. The quantityof water pumped was 39 m3/day (0.78 m), and the quantity ofused water were 60.5 m3/day (1.21 m). And from result of
Figure 9, we can calculate output and input of the tank. TheActual & Virtual Water Level［m］

2.5

pumping of 52.5 m3/day (=7.0×7.5) is provided.

Solar Pumped(Estimated)
Water Level（Measured)
Used(Estimated）

26. Conclusion

1.5
1
0.5
0
12:00

18:00

0:00

6:00

12:00
Time

18:00

0:00

6:00

12:00

Fig. 9. Water balance of tank by virtual water level.
150
100

Flow Ratio ［L/min.］50
0-5012:00

18:00

0:00

6:00

12:00

18:00

0:00

6:00

12:00

-100
-150

In arid areas, optimal utilization of water for agriculture isessential. This requires the adoption of integrated farmingmethod that use domestic animals, forage crops and compost,
as these are all have a marked influence on water use andsupply. Integrated farming methods employed near wadis arewell suited for arid land farming particular at the scale (1.5 ha)
examined in this study. In addition it was found that a small
solar pumping system such as that examined in this study(900-1,000 W) was effective for farms of this size in arid
environments.

-200
Used
Solar Pumped

-250
-300

Reference-350
Time

Fig. 10. Input and Output of water tank.

maximum pumping flow rate was 88.0 L/min., the maximum
water using flow rate was 280 L/min. If the damage to themodule was 9.24%, then assuming no electricity energy waslost, the quantity of water pumped would be 43.0 m3/day(=39.0 × 100/(100-9.24)). And 957 W (=680 × 60.5/43.0) is
necessary to serve 60.5 m3/day of the actually use quantity ofwater. This result corroborated those in Figure 3 whichshowed that 900 W would be required to pump lift the water at
a rate of 7.0 m3/h at hydraulic head 15 m. Since, if 27
MJ/m2･day is provided, we can expect the daylight hours of
7.5 hours (=27000/3600) at 1 kW/m2, therefore quantity of

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Ismael Tabareck M., Watanabe F., Tajima K., Takahashi S.,
Sekiyama T. (2003): Distillation of Saline Water by Solar
Radiation Energy. Journal of arid land studies, 13(3):163-172.
Takahashi S., Suzuki S., Takahashi S., Tajima K., Watanabe F.
(2010): Water Usage and Greening Technology in AridRegion. Journal of arid land studies, 20(1): 55-61.
Tajima K., Watanabe F., Shimada S., Takahashi S., Sekiyama
T. (2006): The Efficiency and Improvement of Simple
Distillation Device by Solar Energy. Journal of arid landstudies (Proceedings of DT VIII), 15(4): 87-290.