沙漠研究 23-4, 179 -183 (2014 )－APCSEET2013 Refereed Papers－

Journal of Arid Land Studies

Effectiveness of Solar Pumping Systemin the Wadi Agriculture in Northern East Africa
Kiyoshi TAJIMA*1), Atsushi SANADA2), Ryuichi TACHIBANA1) and Fumio WATANABE1)
Abstract: Authors installed a small solar pumping system in a farm which ran Wadi agriculture in the northeastern African Republicof Djibouti 2008 and carried out experiments to confirm its effectiveness. The average annual precipitation in this area and the
maximum amounts of solar radiation, are 130 mm year-1 and 25 MJ m-2 day-1 each (Ismael et al., 2003). The farm area is 1.5 ha andthe cultivated crops are melon, onion, pepper, tomato, eggplant etc. as food and pastures as livestock’s feed. The livestock are mainly
goats and serve as dairy and meat and its excrement is use as compost. The quantity of solar radiation, PV-module output and waterlevel of the water tank were measured in March 2011 and August 2012 to estimate the quantity of water required as well as theappropriate scale of the system. As a result, it was found out that, a system of about 1 kW is reasonable for either season having awater tank of 75 m3 lifted 15 m head from well (Tajima et al., 2012). And last time one of the PV-module had been damaged bystone, so a new PV-module was installed in 2012.
Key Words: Agro-pastral, Djibouti, Solar pumping system, Wadi agriculture
80 W×5 + NET SM55 : 95 W×1 + PHOTOWAT TPWX500 :50 W×4, Total 695 W, Water Tank with 5×10×1.5 m＝75 m3).
In addition, the PV module array was set up 0° to the south and1. Introduction
Authors installed a small solar pumping system in a farm
which ran Wadi agriculture in the northeastern African
Republic of Djibouti 2008. The farm is one of a practical
farmer having three farms in the Dikhil city suburbs, andmelon and onion are cultivated mainly there with grass orcover crops to breed the domestic animal for the making ofcompost. And the farm is located to midstream of Arouo
Wadi, 42°33'E, 11°7'N, and 679 m above sea level.
In March, 2011 when three years passed after installing, we
carried out an investigation into operation state of the solar
pumping system. Because the system was operating although
one of the PV-module included damage by the stone-throwing,
we estimated the loss by the damage. As the result, as for the
average quantity of discharge of pumping was 39 m3 day-1, andthe estimated loss by damage was 9.24% (Tajima et al., 2012).
In August, 2013, we changed the damaged PV-module andinvestigated the operation situation of the system in thecomplete state. And we compared and considered about
different in irrigation water quantity between March, 2011 andAugust, 2012. In addition, the PV-module that we changed
assumed it a single crystal silicon type one of the same size,
because it was hard to obtain a same type PV-module in Japan.
Figure 1 shows a ground plan of the farm and Figure 2 shows
the whole view of solar pumping system (Tajima et al., 2012)(GRUNDFOS:CU-200, SQF5A-6 with BP-SOLAR BP380J :Fig. 1. Ground plan of the farm (Aug.2012).

PV Array
Well

Field
Tank
Water

Fig. 2. Whole view of solar pumping system (Tajima et al., 2012).
（Received, October 3rd, 2013; Accepted, January 17th, 2014）* Corresponding Author: tajima@nodai.ac.jp
1-1-1, Sakuragaoka, Setagaya-ku, Tokyo, 156-8502, Japan
1) Department of Agriculture Engineering, Tokyo University of Agriculture2) Faculty of International Agricultural Development, Tokyo University of Agriculturethe tilt angle was 10° to horizontal level, and total array area
was 5.82 m2.

2. Objective
Identifying the appropriate scale of the system byinvestigating the operation situation of the solar pumping
system for well which installed temporarily in Wadi agricultureof Republic of Djibouti. And we aimed to establish theinvestigation technique by using these data and to grasp thewater income and expenditure when seasons are different.

3. Methodology
WellFig. 3. Global horizontal irradiance, temperature, relative humidity
and water tank level.

Field

We measured the output voltage and output current of theTank
PV system, sunlightstrength, a change of the water level of thewater tank and the well everyWater
five minutes. And we
demanded a correlation of sunlight strength and quantity ofpumping of the solar pumping system and, from provided data,
estimated the operation situation of the irrigation system. But
there was the intake, the discharge that we could not predict
because an engine pump was used together for pumping, andthe intake to a water tank and the discharge by the use were
performed appropriately in any time. Thus, we found intake
by the solar pumping from sunlight strength, and it wasnecessary to calculate irrigation quantity of water used forfarming and the quantity of the intake by the engine pumping.
The measure which used a pyrheliometer (EIKO:
ML-020VM), ammeter (SANWA: CL-22AD), a voltage
measurement and data logger (SI-ELECTRONICS: TH3a),water level sensor (HOBO: U20 Water Level Logger 4 m),
temperature-humidity meter (T&D: TR72U, TR71Ui). We
carried out the measurement in 4.5 days until 12:00 of August
30 since August 25, 2012 and the interval of each measurement
was five minutes.

4. Results
4.1. Global
horizontal
irradiance,
temperature,
PV-module temperature, and relative humidity
Figure 3 shows the 3-days results of a measurement until
25-27 days in August. Although it was a fine day as for theweather and was relatively stable, a change of the sunlight by
the passage of the cloud was accepted. As for the global
irradiance of 26th that was fine weather, up to 1.00 kW m-2, thequantity of global horizontal irradiance were 26.0 MJ m-2 day-1.
As for the highest temperature, the module temperaturequite reached approximately 40°C, the minimum temperature
with temperature +20°C with 62.6°C at approximately 25°C.
It became lowest and, about the relative humidity, cut 10% at

Fig. 4. Relationship between Global Horizontal Irradiance andDischarge of Pump.

about 2:00 p.m. when I showed the highest temperature. It
was approximately 60% at about 6:00 of the daybreak to haveshown the highest humidity. It was with the value that
August that was the end of the wet season than March that was
the end of the dry season was low about the humidity.
4.2. Global solar radiation and water level of the water tank
Figure 3 also shows the measurement results of the global
solar irradiance and the water level of the water tank.
Sunlight was stable and performed identification(approximately three hours of August 25 7:04 a.m.-12:59 p.m.)of time considered that there were not the intake from anengine pump and not use of the water in this result. Thus wedemanded global solar irradiance relations of the pumping
quantity of the solar pump. Figure 4 shows the result. In
addition, the number of the data was 72.
As a result of having recurred with a second curve, thecoefficient of correlation was 0.9673, and the significant
difference by the statistical significant test was meaningful with
1% of levels of significance.
4.3. Output of the PV-module array
Figure 5 shows the result of measurement of the output
voltage and current of the PV-module array. The output
current became shape that was approximately similar to achange of the solar irradiance. In addition, the output power
wave pattern became approximately similar to solar irradiancebecause the output voltage was flat. And the output voltage

Fig. 5. Output of PV-module array.

Fig. 7. Intake and discharge of the tank (1).

Fig. 8. Intake and discharge of the tank (2).
Fig. 6. Evaluated discharge of solar pump.

was approximately 130 V, the output current was up to 4.5 A,
the output power was up to 530 W each.
Using the equation of regression that we found in section
4.2, we estimated the discharge of pumping from the global
solar irradiance data during all measurement period. Figure
6 shows the result of the estimation. Because relations of the
global solar irradiance and the discharge of pumping wasprovided with a quadratic function curve, the pumping
discharge was provided as a semicircular curve of the convex
on the top. During the 4 days (August 25 6:00 a.m.-August
29 6:00 a.m.), the maximum pumping discharge was 109 L
min.-1 and the maximum pumping quantity per day was
34.1-37.8 m3, the total pumping quantity was 144 m3 and theaverage pumping quantity was 36.1 m3 day-1.
4.4. Intake and discharge of the water tank
We found the intake to the water tank and the discharge
from the water tank by multiplying the horizontal cross sectionof the water tank by the result that differentiated the water levelchange wave pattern of the water tank. Figure 7 shows theresult. In addition, because the differential calculus wave
pattern was unstable and vibrational, the data was smoothedwith the moving average method with 6 data (5 minutes × 6 =30 minutes). In Figure 7, the + side shows intake to watertank and the - side shows the discharge from the water tankwhich is mean the water use. Both of intake and discharge
wave patterns were spike shape, and these wave patterns wereclearly different from the intake rate wave pattern with thesolar pump.

4.5. Estimate of the intake with the engine pumping andthe discharge of the water usage
We estimated the water consumption and quantity of thewater pumping with the engine pump, by deducting thedischarge of the solar pump which calculated in section 4.2(Fig. 6) from the discharge that we calculated from the waterlevel of the water tank (Fig. 7). We show the result that wasmatched with the water level of the tank in Figure 8. In this,the + side of the figure showed the intake to a tank and the side showed the discharge from a tank. In addition, theseparation of the part that driving and the irrigation of thepump were carried out at the same time was difficult, but as aresult of having demanded the quantity of water every each
event by integral calculus, showed it in addition.
During the 4 days (August 25 6:00a.m.-August 29
6:00a.m.), the total quantity of pumping with the engine pumpwas 30.6 m3, the use quantity of water was 167 m3, and the day
average was 7.66 m3 day-1, 41.7 m3 day-1 each.

5. Considerations
5.1. Output power of the PV-module array
We changed one of the modules that glass part was
damaged by stone-throwing three years ago and measured theoutput. We estimated that there was 9.24% of loss incomparison with the data just after the setting by the previous
announcement in 2008. But we were not able to confirm thetruth by the following reasons.
There was a difference to the ① solar irradiance and ②
module temperature, because of the season when we measured.
① It was 62.9°C in March, 2012 whereas August, 2011 wasup to 54.8°C in the daytime, and ② it was 25.0 MJ m-2 day-1
August, in 2012 whereas March, in 2011 was 27 MJ m-2 day-1
with the maximum. Generally, the output power would be
dropped by the temperature of the PV-module in crystal silicon
type with 0.41% °C-1 (Itagaki et al., 2013). Therefore in 2012,
0.41 × (62.9 - 54.8) = 3.32 % might be lower than data of 2011.
In addition, because the output under 25°C in the standard of
the performance notation of the module, it was expected 19-38
points of output dropped. When we watched a measurement
result of 2012, the measured maximum output 547 W was
equivalent to 82.6% of notation output 695 W, thus it wasconsidered that the main reason of the output drop would be
the temperature rise. Furthermore, the PV-module which wechanged in 2012 was a mono-crystal silicon type. A researchis pointing out that there is possibility of the degradation of
performance in the mixture use of such a heterologous
PV-module, although it is higher-performance than apoly-crystal silicon type before the exchange is accomplished(Nishikawa, 2008).
5.2. About quantity of pumping of the solar pump
The quantity of pumping of August, 2012 was 36.1 m3-1
day whereas the pumping quantity as of March, 2011 was
39.0 m3 day-1. It is thought that the latter was 25.0 MJ m-2
day-1 other than a difference of the temperature of the module
whereas quantity of former sunlight was 27.0 MJ m-2 day-1.
However, it is necessary to convert it into the direct solar
radiation on the inclined surface ID to obtain the array input
because these values are the direct global solar radiation HD.
Therefore we try to get the ratio T of these radiations by thefollowing equations.
The first measurement was carried out at 4th March 2011,
therefore n = 63, δ = -7.12°, ωs = ωt = 91.5° were determined.
And in the second measurement at 26th August 2012, n = 238,
δ = 10.69°, ωs = ωt = 87.8° could be determined.
𝐼

𝑇= 𝐷 =
𝐻𝐷𝜔𝑡 sin(𝜑−𝜃) sin 𝛿+cos(𝜑−𝜃) cos 𝛿 sin 𝜔𝑡(1)

𝜔𝑠 sin 𝜑 sin 𝛿+cos 𝜑 cos 𝛿 sin 𝜔𝑠(2)𝜔𝑠 ＝ cos −1(tan 𝜑 tan 𝛿)𝐻0 =24
2𝜋(𝑛 − 2)
× 𝐼𝑆𝑆 × �1 + 0.033 cos �
��
𝜋
365

× (cos 𝜑 cos 𝛿 sin 𝜔𝑠 +𝜔𝑠 sin 𝜑 sin 𝛿)

KT = H / H0
K = 0.9166 + 0.0866KT - 2.8445KT2 + 1.8582KT3
Hd = H × K
HD = H - Hd
ID = T × HD
Id = (1 + cosθ) × K × H / 2
Ir = (1 - cosθ) × ρ/100 × H / 2
It = ID + Id + Ir

(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)

Here,
T: The ratio of ID for HD
ID: Direct normal irradiance [W m-2]
HD: Direct global horizontal irradiance [W m-2]
ωt: Sunset - hour angle for array direction [degrees]ωs: Sunset - hour angle for horizontal surface [degrees]
θ: Array tilt angle [degrees]
δ: Solar declination [degrees]
φ: Latitude [degrees]
H: Global horizontal irradiance [W m-2]
H0: Extraterrestrial horizontal irradiance [W m-2]
Isc: Solar constant = 1.382 [kW m-2] = 4.97 [MJ m-2 hr-1]
n: Day number in the day [No.]
It: Normal irradiance [W m-2]
Id: Diffuse normal irradiance [W m-2]
Ir: Reflected normal irradiance [W m-2]
Hd: Diffuse horizontal irradiance [W m-2]
ρ: Reflectance of the ground = 20%
Here, we got the solar radiation on inclined surface (I t)values, 28.3 MJ m-2 day-1 and 24.5 MJ m-2 day-1 by the upper
expression (1)-(11) (Watanabe et al., 2013, Liew et al., 1960).
Therefore we could calculate the conversion efficiency of thesystem, about 2011, 39.0 × 103 × 9.8 × 15 ÷ 5.82 / (28.3 × 106)
× 100 = 3.48%, and about 2012, 36.1 × 103 × 9.8 × 15 ÷ 5.82 /(24.5 × 106) × 100 = 3.73 %.
In addition, the maximum discharge quantity was high with
108 L min. -1 for 2012 whereas it was 88.0 L min. -1 for 2011.
We think that we cannot identify the cause that this difference
produced when we do not analyze a change of the water levelof the well which we did not measure in 2011 and relations
with the solar irradiance. In addition, the change of theground water level in the well in measurement period 2012,
was 0.8 m at 14.4-15.2 m in lift, therefore we considered that it
would be little influence in this simulation.
5.3. About use quantity of water
The use quantity of water of 2012 was fewer
approximately 30% than 60.2 m3 day-1 of 2011 in 41.7 m3 day-1.
This was not only caused by difference of the solar irradiation,
but by the difference of the planting crops. Anyway, we thinkthat to perform correct analysis, data sampling period was too
short.
In addition, there was little quantity of pumping with theengine pump with 7.66 m3 day-1 for 2012 whereas it was 21.5
m3 day-1 for 2011. It became 695 / 36.1 × (36.1 + 7.66) =842W when we predicted necessary PV-module capacity
based on a result of 2012 and was less than a prediction in2011 saying that 957 W was necessary.

5.4. General consideration
We tried to confirm an output drop by the damage of the
PV-module by comparing the measurement of August, 2012
with the measurement of March, 2011, but a difference of the
PV-module temperature was big and was not able to confirm it.
And if seasons were different, not only climatic condition but
also the crops cultivated were different. Therefore weunderstood that the use quantity of water (irrigation water +domestic animal water to drink + compost fermentation water)
was changed significantly.
Because we established technique in pursuit of the water
use situation by measuring water level and the quantity of thewater tank and the global solar irradiance, we want to connect
it with establishment of the technique to chase not only theevaluation of the solar pumping system but also the water
income and expenditure by a long-term measurement exactly
in future in Wadi agriculture. In addition, about not only the
traditional furrow irrigation but also the saving water effect bysprinkling irrigation or the drip irrigation (Amu-mensah et al.,
2000; Takahashi et al., 2010), we would like to investigate
these technology effects in Wadi agriculture with a local
farmers.

6. Conclusions
We identified the appropriate scale of the system byinvestigating the operation situation of the solar pumping
system in the Djiboutian Wadi agriculture. In addition, weestablished the investigation technique. Furthermore, wegrasped the water income and expenditure when seasons aredifferent. As a result of the executed field measurements forthe purpose of identifying the appropriate scale of the system inMarch, 2011 and August, 2012, we got the following
conclusions.
(1) There was a difference of around 8°C in PV-moduletemperature in two seasons and influenced the array output.
By the driving of August, it was around 78.7% of driving
output of the indication output.
(2) The quantity of pumping was 39.0 m3 day-1 in lift ofapproximately 15 m in 36.1 m3 day-1 (695 W), March, 2011in August, 2012 (680 W one of the PV-module wasdamaged).
(3) The conversion efficiency of the system which I calculated
from quantity of whole sky sunlight and quantity ofpumping was 3.69 % with both years.
(4) The use quantity of water in the integrate Wadi agriculture(using grass production and a goat, product a melon andonions mainly while making soil) of 1.5 ha was 60.2
m3day-1 in 41.7 m3day-1, March, 2011 in August, 2012.

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