Use of a Solar Pumping System to Improve the Fogarra Flow Rate in South-West of Algeria

Water forms the most important element for the creation and sustainability of the desert oasis. For centuries, the oasis inhabitants of Saoura in South-West of Algeria have used techniques for acquiring groundwater to meet the domestic needs of the people of the ksars and to irrigate the gardens. The oasis inhabitants through these processes have mastered the management of water; they were able to manage critical situations of long droughts while protecting their environments. These ancestral techniques such as foggaras (foggara : traditional horizontal well) have proven their effectiveness in the past. This is why foggaras have been used in more than 50 countries around the world, even in Latin America. However, with the contribution of modern water collection procedures (boreholes and motor pumps), this ancestral technique deteriorates from year to year and their future is threatened. During 2007 and 2008, rehabilitation projects were launched by the departments concerned and even some oasis residents carried out the maintenance of several foggaras sources and seguias (seguia : traditional open-air canal). In this article, we present an experimental study of characteristics of a prototype of a solar pumping system in view to improve the flow rate of foggaras. The characterization of the pump passes through characterization tests to plot the characteristic curves TMH-Q. These curves allow us to determine the operating conditions that ensure better performance. The test results indicate that the flow rate contributed by the solar pumping system exceeds 3 times the permanent flow rate of foggaras.


INTRODUCTION
The Saoura (south-west of Algeria) has a large number of fogarras for the irrigation of palm groves.The catchment system by the foggaras of the Saoura has experienced in recent years a growth in agricultural activity parallel to the needs for irrigation water.Resorting to the use of modern techniques for capturing and exploiting deep water to meet the growing demand for water, the exodus of farmers to large development areas, the lowering of groundwater levels, the lack of skilled labor and maintenance denounces the sustainability of the traditional foggara collection system and therefore the entire oasis system in general (Boualem et al., 2014).In addition to the diffusion of salinity through the natural drain, the overexploitation of water from the terraces of the Saoura valley and the anarchic proliferation of wells in search of fresh water, intended for the irrigation of the palm grove (Merzougui et al., 2022).It also confirms it (Benmoussa et al., 2020), by the construction of large equipment like Djorf Torba dam on wadi Guir disturbed the ecosystem of the region since it drains more than 80% of the total fow of the wadi Saoura and 20% of the fow comes from the wadi Zouzfana.This new situation has led to an appreciable decrease in shallow fows in Oued Saoura and consequently a reduction of the water table and a deterioration of its quality accelerated by excessive pumping and population growth translated into increased consumption of water.Our objective in this work and to try to exploit the system of the pumps used the solar energy to revive the foggaras in a rational way not to exhaust the layers.

Foggaras operation
The static level of the water table is located above the portion (DE) in (Figure 1), water enters the gallery and moves at atmospheric pressure under the effect of the hydraulic gradient to the portion (C-D), stabilization is done in this part of the point of intersection of the water table and the slope of the gallery, at this point water will flow by gravity towards the part (B-C).Over time, the level of the water table drops, the intersection point moves upstream zone (C-D) to zone (D-E), the hydraulic load decreases and the flow rate from the foggaras falls.The drying up of the foggaras is reached when the flow in point B is zero.This means that the flow from the section (CF) is equal to the flow lost by seepage and evaporation in part (BC), these losses are estimated between 10 and 20% and almost 50% of the flow rate of the foggaras.When the point of intersection of the water table and the gallery reaches point E, the foggaras die (Rezzoug et al., 2017).

Alternative technique
In Saharan areas, pumps powered via solar energy can provide an extra low flow of foggaras (ÇORA, 2020).This contribution is an important element that can bridge the gap and preserve furthermore the foggaras.Especially since these regions are characterized by intensities and quite sufficient sunshine durations to meet energy needs (Kishta, 2002).The characterization of common pumps is carried out by looking for their operating points on the characteristic curves knowing that the power of the pump is constant.The particularity of a photovoltaic solar pump is the power instability due to the variation of daily sunshine.However, the characterization of a solar pump is done by looking for an operating range and not a single point of operation.This range allows determining the best conditions of operation which ensures a better performance (Tiwari et al., 2022).The purpose of this study is to characterize a solar pump by tracing the characteristic curves through experimental tests conducted on a photovoltaic pumping system installed in UDES (development of solar equipment unit) in Adrar.

Experimental
Description of the testing bench The testing bench is shown in (Figure 2).A system of 8 solar panels supplies the submerged solar pump SP5-A7 (1) which has variable parameters: flow rate Q; total manometric head H and efficiency η.It is driven by a motor (2) asynchronous with variable speed and rated power of 550 W (0.75 Hp).The pump (1) draws water from the well (3) to a total depth of 15.52 m and a diameter of 1.35 meters with a static level of 8.30 m.The pump is placed at a depth of 12.6 m and draws water to drive back through a galvanized steel pipe equipped with a water meter (4).The Direct reading of pressure is done utilizing the manometer (5).And to measure the instantaneous flow rate, a digital flow meter is used (6).A valve ( 7) is mounted at the end of the pipe to control the delivery pressures and the flow regulation.The water is forced through the pipe to a reservoir (8) which will return it to the well to close the circuit.The irradiance data, current and electrical voltage are saved in data acquisition.

Purposes of testing
The intended purpose of planned tests is to characterize the solar pump SP5-A7.In other words, look for the best operating conditions that allow optimal performance according to the weather of the site (sunshine duration and intensity) and the geometric data of the well (flow rate, TMH) (Kishta, 2002).To do so, the behavior pump must be drawn based on the abovementioned parameters, afterwards, look for the pump operating points.

Experimental procedure
Given the ongoing changes in parameters such as sunshine and the speed of the pump, it is difficult to trace the characteristics of such pumps.So we try to keep some parameters constant to see the change in others.However, two types of tests are conducted on two pumping systems of the same size working in the same conditions.The tests consist to show the variation of the flow rate depending on the intensity for a degree of closure of the valve (at constant TMH).The test was repeated several times while varying the valve closure per day.The procedure is therefore to maintain the closure of the valve in a fixed position during the test and measure the flow rate depending on the irradiation every 30 minutes throughout the day.The same test was repeated for several levels of closure of the valve.The measurements allow reading for each position of the valve and every 30 minutes, differential pressure, and flow rate.

Introduction
Characterization methods of ordinary pumps required the establishment of a relationship between certain operating parameters such as TMH, power, or performance depending on the flow rate Q since it is possible to study these parameters separately by varying the others as we please.However, the characterization of solar pumps is difficult because it is impossible to study these parameters separately.The parameters used in the characterization of solar pumps are the solar intensity Ec, the total manometric head TMH, the flow rate Q, and the electric power P of the motor (Roy et al., 2015).

Parameters involved in the characterization
Since the operation of the solar pump is associated with its place of installation, the insulation, and the daily load, i.e. the flow rate Q and the pushing back height, it is useful to show the variation of these parameters during a typical day.Thus, it is possible subsequently to study the behavior of the solar pump as a function of these parameters.

Solar intensity Ec [W/m²]
The solar intensity represents the energy emitted by the sun collected on a collecting area of 1m 2 .It depends on the altitude of the place, the day of the year, and the time of the day as well as the orientation of the collector area (Narale et al., 2013).Indeed, the graph below (Figure 3) shows the variation in solar intensity on the day of the test.It has the shape of a bell.Low values are around sunrise and sunset.The maximums are located in the middle of the day for a couple of hours depending on the length of the day.The curves also show an axis of symmetry located in the middle of the day.It's midday which is the true solar time.

Pumping flow rate:
The graph below shows the variation of the pumping flow rate in m 3 /h along the day of tests for a fixed delivery head (aspiration height).It is evident that like the solar intensity, the flow rate varies in a shape of a bell.It reaches its maximum around midday true solar time.While low flow rates are located at the limits of the day.This is explained by the fact that the solar intensity acts directly on the pump speed.Far from the middle of the day when the intensity is low, the speed of the pump is small (Figure 4); the instantaneous flow rate presents its minimum.We can say that the instantaneous pumping flow rate varies in the same direction as that of the solar intensity.Moreover, the daily water production may be estimated by calculating the area of the surface below the flow rate curve.Indeed, knowing that the permanent flow of foggaras is 2,3 l/s, the solar pumping system installed supports an important rate of flow (Figure 5).It can reach up to 3 times the rate of permanent foggaras to more than 9 l/s.

Total manometric head (TMH) a) Plotting the conduct characteristic:
To find the pump operating point for each delivery head, it is necessary to draw first the characteristic curve of the discharge conduct.The latter consists of several linear sections with the same diameter thus inducing linear head losses and some singularities such as elbows and measuring devices.To simplify the problem, it is considered an equivalent linear pipe that generates the same head loss (Yaichi et al., 2016).

b) Characteristics Curves TMH = f (Q)
To show the behavior of the solar pump with respect to the delivery head, several tests have been made at different times of the day and in different closures of the valve.Often this feature is drawn at a constant speed.However, it is difficult to maintain To overcome this difficulty, it is necessary to conduct the tests in a fairly as short time as possible to consider the solar intensity constant and thereafter the constant speed.To vary the delivery head, we play on the head loss generated by the gradual closing of the flow control valve (Figure 6).Indeed, the curves in (Figure 7) show the profiles of TMH based on flow rate at different moments of the day.It is remarkable that in general, the TMH decreases as the speed increases.In other words, for a given geometric height, the TMH decreases with the flow rate because it affects the losses of linear and singular pressure.The shape of the TMH-Q curves proves parabolic, that which is confirmed by the theory (Falcon, 2015;Shinde & Wandre, 2015) In addition, when the solar intensity rises, the TMH-Q curves maintain the same pace but change their amplitudes.This is because when the solar intensity is huge, the speed of rotation increases, and subsequently the TMH-Q changes its amplitude.
The intersection of the characteristic curve of the conduct (Rh.Q²) pressure line with the TMH-Q curves determines the operating points.From the curves in Figure 6, it is evident that, for the same delivery head, the operating point changes its position during the day.It presents a translation during the morning to tend towards an almost stable operating point during the half day.Thus, we can have, for the same working conditions several operating points of the pump.
The instability of the operating point can be explained by the fact that, during periods that are far from midday, the solar intensity remains low compared to the rated power of the pump.However, the pump runs at a speed quite inferior to its nominal rotation speed.The closer we are to midday when the solar intensity is comparable to the nominal power, the more the operating point gets stabilized.We can say that at each sunshine value, the pump changes the speed.If for the same service conditions of the pumping system the discharge head changes, the characteristic of the pump changes.Indeed, the curves in (Figure 7) shows the effect of TMH (15m, 25m, 35m, 45m, and 55m) on the daily production (throughput) for different solar intensity.It is visible that the more the discharge head increases, the more the daily production of water decreases.Also, for the same solar intensity (constant speed), the flow rate changes when the height changes.If for the same solar intensity the height doubles, the flow rate decreases by more than half.Hg+Rh.Q²

CONCLUSION
In the present work, the point is the study of the operating characteristics of a solar pump for improving the flow rate of fogarras in arid areas.
The characterization is performed by passing first through a check of the sizing of PV plants supplying the pump then the characteristic curves were plotted through tests at different discharge heights and service conditions.To vary the height of the pumping, we took advantage of the gradual closure of the valve to create a local head loss.The test results indicate that the power required to pump supply depends on the pump head design parameters, flow rate, and especially the solar intensity.
The flow rate varies constantly depending on the given time of the day, month, and season.In general, it follows the same trend as that of solar intensity.The More the solar intensity increases, the more the instantaneous flow rate is important.It is possible to find distinct operating points of the pump.Except that, this stabilizes at around noon TST.In addition, for any delivery height, the max flow rate is located between 11h and 16h, i.e. in the middle of the day near noon TST.The pumping system tested in this study can provide considerable support to the foggaras flow rate that can reach 7 m 3 /h.

Figure 2 .
Figure 2. Testing bench with a solar pump.

Figure 3 .
Figure 3.The solar intensity in March 2016.

Figure 4 .
Figure 4. Flow rate evolution in a day.

Figure 5 .
Figure 5. Solar intensity effect on flow rate.
speed, because of the variation in solar radiation.

Figure 6 .
Figure 6.TMH-Q Characteristics at different moments of the day.

Figure 7 .
Figure 7. TMH influence on the flow rate according to the solar intensity.