IJERD – International Journal of Environmental and Rural Development (2020) 11-2

Research article
erd

Efficiency Evaluation of Solar Pumping System for Wadi
Agriculture in Djibouti
MAKOTO SHINOZAKI
Graduate School of Agriculture, Tokyo University of Agriculture,
VSN, Inc., Minato-ku, Tokyo, Japan
Email: wt2bp24955@gmail.com

SAWAHIKO SHIMADA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: shima123@nodai.ac.jp

AYAKO SEKIYAMA
Faculty of Regional Environment Science, Tokyo University of Agriculture, JapanKIYOSHI TAJIMA
Faculty of Regional Environment Science, Tokyo University of Agriculture, JapanHASSAN ALI BARKADInstitute of Industrial Technology, University of Djibouti, Djibouti
Received 11 Septem 2020

Accepted 30 November 2020(*Corresponding Author)

Abstract Crop cultivation in Djibouti is mainly done by irrigation agriculture obtaining
groundwater from wadi aquifer. The decreasing in the efficiency of solar power generation
system due to panel-on-dust is reported to be the issue in terms of energy loss in pumping up
water. In this paper, the effect of dust deposition for solar pumping system was evaluated at
wadi agriculture farm in Dikhil, Djibouti. The amount of panel-on-dust was measured to be
1.88 and 2.1 g/m2 in cooler season (dry deposition) and in hot season (wet deposition),
respectively. Clearance of the panel-on-dust resulted a decline in the output power ofphotovoltaic panel due to the rise in panel surface temperature in January (cooler season),whilst the output power increased in September (hot season) when the panel surface
temperature was relatively higher. The conversion efficiency of the photovoltaic power
generation was calculated to be about 5 - 6% lower in September than in January. The wholeconversion efficiency of solar pumping system was estimated to be about 2%. Since the ideal
conversion efficiency was calculated as 6.76%, the gap from observed value of about 4.5%
can be implied by suppressing water leakages from the system in pumping process.
Keywords Djibouti, panel-on-dust, photovoltaic panel, wadi agriculture

INTRODUCTION
The Republic of Djibouti, Northeastern Africa, locates under high temperature and low-rainfall
climate environment. Most of the land surface is dominated by barren land (67-89%; Shimada et al.,2006) and the rainwater easily run off from the ground surface through wadi, ephemeral riverbed.
Due to this harsh natural environment, agricultural activity is very difficult. In Djibouti, groundwateris pumped up to be used since enough amount of water cannot be collected from rainwater for
agriculture. In the arid land under low-latitude regions such as Djibouti, abundant solar radiation isavailable, hence solar power generation has a potential for the pumping system. However, initialexpense for installation of solar power system costs relatively higher than that of engine system. For
this reason, engine systems are the most adopted cases for wadi agriculture, although the runningcost exceeds in the long run for the engine pumps and causes pressure on management. TheGovernment of Djibouti pronounces the use of renewable energy as a great important issue for theⒸ ISERD98

IJERD – International Journal of Environmental and Rural Development (2020) 11-2

management of sustainable water resources to enhance the agricultural productivity. Therefore, it isimportant to establish an optimal method for operating solar power generation system in terms ofcost and efficiency. Previous studies analyzed the cost of a pumping system using photovoltaic panel
in wadi agricultural farm in Djibouti, a method for estimating an appropriate scale of pumping system(Tajima et al., 2012; 2014). However, in arid areas such as Djibouti, dust tends to accumulate on
photovoltaic panels, and the dust accumulation normally reduces its output power (Sulaiman et al.,2011; Ghazi et al., 2014; Maghami et al., 2016; Daher et al., 2018). When introducing a PV system
for agriculture, in arid environment like Djibouti, it is necessary to consider the effects of dust
accumulation on photovoltaic panel. However, only a few studies analyzed on this effect andevaluated quantitively on photovoltaic pump in arid area like Djibouti (e.g., Tajima et al., 2012; 2014;
Aden et al., 2009). In the current paper, we investigated one whole pumping system of wadi
agricultural farm, where photovoltaic power generation is introduced as groundwater pumping
system, in Dhikhil, Djibouti, in order to evaluate the efficiency of the system including the effect ofdust deposition on photovoltaic panel.
METHODOLOGY
The target farmland located in Dikhil city (11.08863° , 42.40089°E) (Fig. 2). The configuration ofthe solar pumping system used in the farm was as follows. LORE TZ: PS1800, SOLARWORLD:
SW80 poly R A: 80 W x 18 sheets. The solar array installation inclination angle was 11°, theazimuth angle was 130° (i.e., southeast), and the area of the array was about 12 m2.

Fig. 1 Location of the study site in Djibouti

Fig. 2 Overview of the target farmland in Dikhil

Overview of solar pumping system is shown in Fig. 3, and agricultural system is shown in Fig.
4. During daytime, the farmers use solar pumping system to store groundwater into reservoir tank(about 100 m3 storage). After around sunset, they switch to engine pumping system to pump up thegroundwater from the well. The farmers use all the water needed for the farm management, such asirrigation, livestock, and others.

Fig. 3 Overview of solar pumping system inthe target farmland

Fig. 4 Agriculture-livestock material cycling
scheme in the target farmland

Survey was conducted in 2 seasons, i.e., cooler season (December 29, 2018 - January 14, 2019),and hot season (September 1, 2019 - September 30, 2019). Table 1 shows the items and periods ofthe data measurements, and Fig. 5 shows the overview of the measuring equipment in the farmland.
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Solar pumping system consists of photovoltaic system and pump, which converts the electric power
into the potential energy of water. However, the system has some loss of efficiency in the process ofenergy conversion (Fig. 6). The output electric power of the solar pumping system was measured by
the multiplication of current and voltage. The values were compared before and after cleaning thepanel-on-dust. The output efficiency was evaluated by comparing the changes in the output of thephotovoltaic system with the output of the pumping system. The output efficiencies regarding panelon-dust and panel surface temperature were also evaluated.
Table 1 Items and periods of data measurements

Fig. 5 Overview of the measuring equipmentin the target farmland

Fig. 6 The flow and loss of energy in thefarm solar pumping system

RESULTS AND DISCUSSION
Cleaning of panel-on-dust was conducted on January 6, September 13 and 24, for the cooler and thehot season experiments, respectively. Fig. 7 shows the schedule and measured dry weights on
cleaning of panel-on-dust. The panel-on-dust seems to occur more in September than in January.
Dust accumulation for cooler season was observed to be dry deposition and weighed 1.88 g/m2 indry mass, while weighed more than 2.1 g/m2 in dry mass and seemed as wet deposition due to rainfall
events for hot season.
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Fig. 7 Results of panel-on-dust measurement
Fig. 8 shows comparison of the output electric power of the photovoltaic system before and after
clearance of panel-on-dust in January and September. As a result, the effectiveness of panel cleaningon output power was negative in January (75%), while positive in September (140%). This result
indicates that clearing of the dust on the solar panel can cause decrement of photovoltaic efficiencyin cooler season (January). This efficiency loss can be explained by the reason that effect of risen
temperature of the photovoltaic panel surpassed the increase in input solar irradiance from theclearance of panel-on-dust.

Fig. 8 Output power with solar irradiance (horizontal and on panel) before andafter cleaning panel-on-dust (Left: cooler season, Right: hot season)

Fig. 9 Surface temperature of photovoltaic panel, air temperature and power loss
before and after cleaning panel-on-dust (Left: cooler season, Right: hot season)
Fig. 9 shows panel surface temperature in January and September, and the output power loss
due to the panel surface temperature. The maximum panel surface temperatures in January andSeptember were 60.8℃ and 71.9℃, respectively. The theoretical daily power loss due to high panel
temperature calculated from the photovoltaic panel specification (-0.48% ℃-1) was 11-13%, and 1316%, in January and September, respectively. From the above results, the power loss from the highpanel temperature is more remarkable in the hot season (September) than in cooler season (January).
Clearance of panel-on-dust in the hot season can gain the efficiency of the output power, although
theoretical energy loss from high panel temperature is relatively higher.
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Table 2 shows calculated pumped water amount in January and September. Fig. 10 shows input
and output energy of whole solar pumping system. Input energy is the solar radiation intensity
received by the panel. The input energy was observed to be greater in January than in September.
Ideal efficiency was estimated as 6.76% (Fig. 6), however, the efficiency of whole pumping system
was calculated to be between 2.1 - 2.4% (Fig. 10). The reason for this gap in efficiency might cause
mainly in the water loss, such as leakage from the water pipe.
Table 2 Output capacity of water pumping system before and after cleaning panel-on-dust

Fig.10 Input and Output energy of daily integrated energy before and after
cleaning panel-on-dust (Left: cooler season, Right: hot season)
CONCLUSION
The panel-on-dust effects on photovoltaic efficiency for wadi agriculture solar pumping system in
Djibouti was examined. The efficiency decline by the clearance of panel-on-dust in cooler season
was discovered in this paper for the first time. This energy output loss was implied by the effect ofrisen temperature of the photovoltaic panel from the clearance of panel-on-dust. However, theclearance of panel-on-dust in the hot season can gain the efficiency of the output power.
The whole conversion efficiency of solar pumping system of wadi agriculture in Djibouti wasalso evaluated in this study. It was estimated to be slightly above 2%, although the ideal conversion
efficiency was calculated as 6.76%, which gap can be caused by the water loss in the pumpingprocess.
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