Syam and Arafa Sustainable Energy Research (2023) 10:22 Sustainable Energy Research

https://doi.org/10.1186/s40807-023-00094-9

REVIEW Open Access

Selection process of photovoltaic standalone

pumping systems
Fathy A. Syam1* and Osama M. Arafa1

Abstract
The application of a standalone photovoltaic (PV) system for water pumping has increased nowadays in remote areas
of developing countries due to proven economic feasibility compared to other traditional alternatives. Pump–motor
set manufacturers always give the pump characteristic at the motor’s nominal speed. The traditional selection process
of pumps depends simply on selecting a pump with the highest peak efficiency that can satisfy the desired duty
point with its peak efficiency occurring at that duty point. However, this simple selection process could lead to select-
ing a pump that is not the best selection from among a given set of candidate pumps for the targeted service.
In this paper, this fact is revealed by comparing two pumps each having the same peak efficiency and each of them
can operate at the desired duty point with one critical difference between the two pumps. One of the two pumps
has its peak efficiency occurring at the right of the duty point and the other has its peak efficiency occurring
at the left of the desired duty point. The methodology of this research is based on calculating the daily efficiency
of each pump by calculating the hydraulic power produced with the electrical power of the solar system. The effi-
ciency calculation has been calculated over two working days, one with low radiation (3 kW/m2/day) and the other
with high radiation (7.3 kW/m2/day). The search for the all-day efficiency for low radiation levels revealed
that the pump with left-shifted peak efficiency gives 42.5% while for high radiation level gives 40.3%. In two cases
the pump with left-shifted peak efficiency constitutes the best choice.

Highlights

• We propose a new method to select the best PV pumping system.

• The proposed method uses a simplified method to compare between two completely identical PV pumping sys-
tems except for the use of two different centrifugal pumps.
• This method aims at selecting the proper centrifugal pump according to maximum all-day efficiency.
• The proposed method was tested under the different solar radiation levels.

Keywords Solar Energy, PV system, Pump System, Centrifugal Pump, Duty Point, Induction Motor, Pump Efficiency

Introduction
Water pumping in many countries relies mainly on con-
ventional electricity or diesel-generated electricity. It has
become necessary to depend on a solar water pumping
*Correspondence:
Fathy A. Syam system to reduce the use of diesel fuel or coal-based elec-
fathy@eri.sci.eg tricity. The use of diesel water pumping systems leads to
1
Researcher at Power Electronics & Energy Conversion Department, noise and air pollution in addition to the exorbitant cost
Electronics Research Institute, Cairo, Egypt
of fuel. The photovoltaic industry has seen significant

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Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 2 of 13

advances in both improving efficiency and reducing costs submersible pump performances. The selection of a
in the past two decades. The initial total cost, opera- suitable PV pumping system may be based on the daily
tion and maintenance costs, and replacement of a diesel required volume of water and the overall system effi-
pump are 2 to 4 times higher than that of a PV pump. ciency and cost.
(Xie et al., 2021) compared the cost-effectiveness of solar (Abdelmalek et al., 2011) carried out an experimental
PV and diesel energy for groundwater pumping for irri- study to investigate the performance of a simple, directly
gation. The observed cost-effectiveness of solar-pow- coupled photovoltaic-powered water pumping system.
ered groundwater irrigation relative to diesel-powered The system comprises a PV array, a Direct Current (DC)
groundwater irrigation varies across scenarios. Overall, motor, and a centrifugal pump. The experiment was con-
the results of the study show that solar PV is a promising ducted over a period of 4 months and the system perfor-
energy solution to support groundwater-fed irrigation mance was monitored under different climatic conditions
development. In many cases, solar energy can serve as a and varying solar radiation with two static head configu-
substitute for diesel to power groundwater pumping for rations. It has been observed that the system is more suit-
irrigation more economically and non-polluting to the able for low delivery flow rate applications. The efficiency
environment. of the system can increased by carefully selecting the size
(Chandel et al., 2015) found that the application of of the PV array, its orientation, and the motor–pump
standalone direct-coupled electromechanical PV systems system.
for water pumping has gained wide popularity in remote (Ghoneim, 2006) presented the performance optimiza-
areas of developing countries recently. Providing water tion of a photovoltaic-powered water pumping system
for agricultural and domestic use using photovoltaic in the Kuwait climate. The direct-coupled photovoltaic
water pumping technology is a sustainable and environ- water pumping system studied consists of the PV array,
mentally friendly solution. Solar water pumping system centrifugal pump, DC motor, a storage tank that serves
is known to be more reliable and more effective for irri- a similar purpose to battery storage, and a maximum
gation applications especially in remote areas compared power point tracker to improve the energy consumption
to other alternative systems. (Kolhe et al., 2004) analyzed rate of the system. A computer simulation program is
the performance analysis of the directly PV-powered per- developed to determine the performance of the proposed
manent magnet motor coupled with a centrifugal pump system in the Kuwait climate. The simulation program
at different solar intensities and corresponding cell tem- consists of a model for the PV array with a maximum
peratures. It has been observed that the system operates power point tracker and models for both the DC motor
most of the daytime because of its torque sufficiency and the centrifugal pump. The size of the PV array, PV
even at low solar intensities. array orientation, and the pump–motor–hydraulic sys-
(Allouhi et al., 2019) investigated the optimal configu- tem characteristics are varied to achieve the optimum
ration of a photovoltaic system supplying a submersible performance for the proposed system.
pump to meet the domestic water of five isolated houses (Chandrasekaran et al., 2012) achieved the simula-
located in a remote area. It has been ruled that the config- tion of a PV array-based DC motor pumping system and
uration with a maximum power point tracking (MPPT) permanent magnet motor pumping system. The com-
converter is the most convenient method to supply water parison of the two systems has been done and proved a
needed by the five dwellings considered in the case study. simple but efficient photovoltaic water pumping system
The variations in the performance ratio indicate that the among them. Motors and centrifugal pumps operate at
MPPT configuration is higher than that of the direct variable speeds in a photovoltaic pumping system. How-
coupling system in general. Moreover, the missed water ever, the characteristics of motors and pumps are usually
ratio for the MPPT configuration was found less than the only given for a single voltage and speed. To analyze the
direct coupling one. operation of a pumping system, where solar radiation
(Renu et al., 2017) analyzed the effect of radiation and causes variation in the photovoltaic power, the input/out-
temperature changes on the amount of water produced put relationship of the motor pump assembly and motor
by photovoltaic water pumps. A methodology is pro- characteristics must be determined. The results obtained
posed to optimize the performance of PV pumps based from the simulation of the system are satisfactory. It is
on water head and pump duty point using the most com- found that a permanent magnet motor pumping system
mon site conditions. The selection of optimum array is better.
sizing for a pump has been done based on the occur- (Abdourraziq and Bachtiri, 2017) carried out a com-
rence of desirable input power and subsystem efficiency. parative study on two similar PV pumping systems, one
(Boutelhig et al., 2011) investigated two different PV of them is driven by a permanent magnet DC motor,
pumping system configurations based on two different and the other is driven by an AC motor. The studied AC
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 3 of 13

system consists of a PV array, a DC–DC boost converter, water heads, the BEP concept does not offer the best effi-
an inverter, a motor–pump set, and a storage tank. In ciency design.
addition, a maximum power point tracking algorithm is Many studies have been done to evaluate the perfor-
used to improve the energy consumption rate of the PV mance of the pumping system. (Odeh, 2013) investigated
system. The comparison was carried out to define the photovoltaic pumping systems for three years of field
characteristics and the performance of each system. Each data analysis. (Belkacem, 2013) designed the pumping
subsystem is modeled to simulate the whole system. The system based on two important elements: the PV array
results obtained from the simulation of the system are and the storage tank. (Babkir, 2018) developed a com-
satisfactory and will make it possible to provide a very parative assessment model for three types of solar water
high speed of rotation in an AC motor compared to a pumps based on the concept of levelized energy cost.
Permanent Magnet (PM) motor, which is an important (Koor et al., 2016; Roberto Valer et al., 2016) studied the
source of power for driving a pump. operation of the pumping system to obtain the best effi-
(Gasque et al., 2020, 2021) analyzed a method for dis- ciency with variable rotation speed.
tributing the power generated in a photovoltaic pump- It is interesting to know that a similar situation exists
ing system equipped with two equal pumps, working in in electrical transformer design. Power and distribution
parallel. The system equipped with two pumps was inves- transformers are differentiated on the basis of service
tigated. Experimental tests at five different working fre- type. Power transformers are supposed to operate at or
quencies, and at six pumping heads were carried out. The near full load most of the time and therefore, their peak
results for the different pumping heads show differences efficiency should be targeted by design as close as possi-
between higher and lower heads. (Gutierrez et al., 2021) ble to a high-loading condition. While distribution trans-
evaluated the efficiency of a photovoltaic water pumping formers always operate at partial load and here stems
system. Hydraulic performance needs to be determined the concept of all-day efficiency. Designers are therefore,
under the solar irradiance available. Performance ratio requested to shift the peak efficiency occurrence to the
(PR) was used to determine the hydraulic performance left on the load axis to optimize the all-day efficiency. A
of a photovoltaic pumping system, operated by a variable similar concept is apparently applicable to PV pumping
frequency inverter coupled to a conventional alternating systems which operates at variable load most of the time.
current surface pump. (Almeida et al., 2018) evaluated This paper presents a comparison between two identi-
a new method for selecting a pump for large-power PV cal PV pumping systems, each of which supplies the same
irrigation systems working at a variable frequency. This load at the same operating point (H, Q). The two pumps
can have a significant impact since the traditional way mainly have different H–Q curves, while having the same
of selecting the pump is based on maximizing the effi- peak efficiency. This peak efficiency occurs at different
ciency of the pump at a single duty point (normally at the values of flow rate for each pump. The research aims
nominal operating frequency), which is not useful for PV at selecting the proper centrifugal pump according to
irrigation systems working at variable frequencies. The maximum all-day efficiency with different levels of solar
proposed method starts by considering the pumps with radiation. This research provides great benefits to users
H–Q curves with a high slope and the duty point in the in the field of agriculture and irrigation in remote places.
right-hand third of the curve to ensure a wide range of Selecting the best pump saves the cost of daily operation.
operating frequencies. Then, the efficiency within the The study is organized as follows: Section “Photovoltaic
whole range of frequencies. Also, (Yadav et al., 2019) pumping system configuration (PVPS)” describes the PV
investigated of the energy efficiency of PV pumping sys- system configuration covering the PV array, the motor,
tems based on solar radiation, temperature, and opera- the centrifugal pumps, and the load hydraulic character-
tional heads. The study identifies the shortcomings in the istics. Section “Methodology” describes the methodology
conventional design method based on the Best Efficiency of the system operation under given site conditions. Sec-
Point (BEP) concept. According to this concept, a centrif- tion “Selecting the proper pump” discusses the selection
ugal pump has an optimum efficiency duty point, known process of the proper pump. Section “Results and dis-
as the Best Efficient Point (BEP), usually specified by the cussions” introduces the results and discussion. Section
manufacturer. (Wanderley et al., 2021) confirmed that “Conclusion” includes the conclusion of this study.
the assumption of the companionship of best hydrau-
lic efficiency to the selection of a pump with the highest Photovoltaic pumping system configuration (PVPS)
efficiency at the desired nominal duty point is valid only The configuration of the modeled PVPS is shown in Fig. 1.
to fixed frequency and voltage type pumps. However, in The system, which represents the most common configu-
the case of PV pumping systems, due to variations in the ration found in direct coupled PV pumping applications,
solar intensity, ambient temperature, and operational is composed of a PV generator, a power control system
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 4 of 13

Fig. 1 Configuration of a direct-coupled PVPS

(Inverter and maximum power point tracking unit), an Substituting for D1/D2 from Eq. (1) into Eq. (2)
induction motor, and a centrifugal pump (Rahrah et al., 3
2015). N2

Q1 H1 2
= 22 (3)
Q2 N1 H2
Methodology
Centrifugal pump characteristics For the same discharge flow rate (Q1 = Q2), the values of
Both the H–Q curve and the efficiency versus flow rate H2 in terms of speed ratio and H1 can be determined by
curve (ηP-Q) characterize the performance of centrifu- rearranging Eq. (3) as follows:
gal pumps. The manufacturer’s data sheet provides these 4
curves at rated pump speed. However, in PVPS, the cen-

N2 3
H 2 = H1 (4)
trifugal pump operates at different speeds as the available N1
solar resource varies. Such variable speed operation obeys
the affinity laws that express the mathematical relation- Therefore, the H–Q curve for the specified pump at
ships between the several variables involved in pump per- 2500 rpm (or any other arbitrary speed) can be deter-
formance. These variables include the pump’s mechanical mined given that the curve is known at 2900 rpm (rated
input power (Pm), the flow rate (Q), the water head (H), pump speed) as shown in Fig. 3.
and the pump’s rotating speed (N) (Alonso et al., 2003).
Figure 2 is adapted from a motor pump manufacturer
company datasheet (SAER ELECTROPOMPE Software, Characteristics curve of the hydraulic system
2019). It shows the H–Q and ηP–Q curves for the SAER In a hydraulic system, the total head (h) against which the
ELECTROPOMPE Curvas-IR32-125A at rated speed. The pump must operate is given by the sum of the static head,
best efficiency is given at H = 18.7 m, Q = 16.4 ­m3/hr. At the drawdown of the water level, and the friction losses.
these conditions, the maximum efficiency is close to 56%. Figure 4 illustrates the different water heads in a typical
Consider a pump rotating at speed N1, at an operating pumping application. The static head is 20.5 m and the
point (H1, Q1). A new operating point for the pump (H2, friction factor (k) is about 5%. Equation (4) represents the
Q2) can be reached by changing the pump speed to a new system’s H–Q curve, as given by several works in the lit-
value N2 given that (Bansal, 2010): erature (Ahonen et al., 2012).

Q1 N1 D13 H = h + kQ2 (5)

= (1)
Q2 N2 D23 The required duty point for this system at H = 21.5 m
and Q = 12.8 ­m3/hr.
H1 N 2 D2
= 12 12 (2)
H2 N2 D2
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 5 of 13

Fig. 2 Head and efficiency curve with flow rate ­(m3/hr.)

Solar array A = Solar array area.

Pm = Motor rated output power.
∅ = Maximum solar radiation.
The size of the solar array used is determined by the rated ηpv = Efficiency of solar cell.
power and efficiency of the motor. The pump used is ηm = Efficiency of Electrical motor.
powered by a motor that has 1.5 kW rated power and its ηc = Efficiency of Power Control Unit.
efficiency at the rated power equals 0.82. The size of the The total number of modules can be calculated by
solar array is determined according to the radiation val- dividing the total area by the area of one m1odule.
ues so that the maximum power produced by the array is The solar module used is OPS-100M and its specifica-
approximately equal to the rated motor input power. The tions are shown in Appendix.
motor does not operate at a load greater than its rated
load. The solar array area can be calculated from the fol- Induction motor
lowing equation: A three-phase induction motor is used to drive the pump.
The motor efficiency is important factor to calculate the
Pm input power of the pump and the output power from the
A=
∅ηpv ηm ηc
(6) solar array. The actual value of power during operation is
variable due to radiation change. So, the motor is oper-
where, ating at partial load for some hours and motor speed is
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 6 of 13

30

N=2900 rpm
25
N=2500 rpm

20
Head (m)

15

10

0
0 5 10 15 20 25
Flow Rate (m3/hr)
Fig. 3 The H–Q curve at different speeds for the IR32-125A pump

40 determine the actual rotation speed of the coupling shaft

35 (motor to pump) that corresponds to the radiation value.
The motor torque changes with the load change by a
30
small amount due to the approximately flat load line and,
25 therefore, the motor torque value in the operating region
Head (m)

Duty Point
20 can be considered constant.
15
PPV ∗ ηm
10
ω= (7)
T
5
where,
0 PPV = Output of PV array.
0 5 10 15 20 25
Flow rate (m3/hr) T = Rated motor torque.
Fig. 4 Hydraulic System Load Pump
Pump operation under solar radiation
The motor is powered by electricity produced by the
solar cells. This power is variable due to the change in
variable. The electrical motor used is SAER MT2 and its insolation values. Therefore, the motor does not oper-
specifications are shown in Appendix 2 ate at its rated power through the whole daytime. The
pump will operate at the operating point that results
from the intersection of pump characteristic curve
For any given radiation, the output power of the PV with the system load curve and achieve the same flow
arrays represents the input power of the inverter feed- rate and head. When the power is less than the rated
ing the electric motor. Since modern inverters have a value, the operating point will be achieved at a rota-
high efficiency that is above 98%, if the inverter efficiency tional speed lower than the rated speed. Figure 5 shows
is approximated to unity, then Eq. (7) can be used to a set of H–Q curves of the pump under variable speed
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 7 of 13

30

28

26

24

22

20

18
Head (m)

16

14

12

10
N=2900 rpm N=2800 rpm N=2700 rpm N=2600 rpm
8
N=2500 rpm N=2400 rpm N=2300 rpm N=2200 rpm
6

4
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Flow rate ( m3/hr)
Fig. 5 A Set of H–Q curves of pump 1 at different speeds

operation and their intersection with the system curve. input power to the electric motor. The output power
The upper curve is for the rated speed 2900 rpm and of the motor which drives the pump depends on the
the lower curves are for a set of speeds that is reduced motor efficiency. The motor efficiency changes with
with decrementing step of 100 rpm. The operating the load ratio and a typical motor efficiency curve as a
point is determined by finding the head of the pump as function of the percentage of full load is given (Betka &
a function of flow rate and solving this function with Moussi, 2004). However, the change in motor efficiency
Eq. (5). Therefore, H–Q pump curves at different rota- is so small that it can be discarded. Therefore, the
tion speeds need to be found. One solution to this motor efficiency is considered constant in this work.
problem is achieved by a curve fitting program. The To determine the operating point at which the pump
H–Q equation at rated speed for the specified pump is curve intersects the load curve, the H–Q equation of
given by Eq. (8) (similar equations are determined for pump Eq. 8 is solved with the H–Q equation of system
other speeds). load (Eq. 9).

H = −0.0305Q2 + 0.0909Q + 25.23 (8) H = 20.5 + 0.0061Q2 (9)

Figure 5 shows that below a certain speed threshold, After determining the operating point, the hydraulic
the pump H–Q characteristics will not intersect with power can be calculated by Eq. (10).
the load hydraulic line and hence there will be no oper-
ation at these speeds. This is why a minimum speed
Ph = ρgHQ (10)
limit is set for the inverter since below such speed no
useful output is produced and the pump and motor are
just heated without sufficient coolant circulation. We can calculate the hourly hydraulic power according to
If N1 is the rated speed and N2 is the actual rotating the radiation value and calculate the approximate overall
speed of the pump. The value of N2 depends on the day efficiency of the pump system by Eq. (11).
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 8 of 13

36
N=2900 rpm
34
N=2800 rpm
32 N=2700 rpm
N=2600 rpm
30
N=2500 rpm
28 N=2400 rpm
N=2300 rpm
26
N=2200 rpm
24 N=2100 rpm
N=2000 rpm
Head (m)

22
Load curve
20

18

16

14

12

10

6
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Flow Rate (m3/hr)
Fig. 6 A set of H–Q curves of pump 2 at different speeds

ρg ni=1 Hi Qi

H = −0.405Q2 + 5.91Q + 12 (11)
ηo = n (11)
i=1 PPV i
It is obvious that the gradient of the second pump
where, (change of H with respect to change of Q is steeper for
ρ = Water density. the second pump than for the first pump). The efficiency
g = Acceleration of gravity. curves for the two pumps are shown in Fig. 8. From
As mentioned earlier, this work compares two pumps Fig. 8, it is shown that the two pumps can be operated
each of them having the same peak efficiency and each of and provide the system with the required water. As the
them can operate at the desired duty point with one criti- pump will operate at power levels lower than the rated
cal difference between the two pumps. One of the two power during a number of operating hours due to the
pumps has its peak efficiency occurring at the right of the change in radiation, the operating efficiency will change
duty point and the other has its peak efficiency occurring during the operating period. Therefore, the total effi-
at the left of the desired duty point. Figure 5 shows the ciency of each pumping system will vary due to different
H–Q curves for pump 1 under different speeds with the operation points due to changing the rotational speed of
system curve and Fig. 6 for pump 2. the pump and working on different H–Q curves.
The two pumps have the same maximum efficiency but
Selecting the proper pump the maximum efficiency point occurs at different flow
In this work, we assume two pumps have the same maxi- rates and different heads. For pump 1, the maximum
mum efficiency and the system balance is identical (PV efficiency point occurs at Q = 18.7 ­m3/hr and H = 16.4 m
array size, same power conditioning unit, and same elec- while for pump 2, the maximum efficiency point occurs
tric motor). The two pumps are selected such that the at Q = 10.4 ­m3/hr and H = 23 m. As mentioned earlier,
duty point (H = 21.5, Q = 12.8) for the system load can this work aims at determining the proper one of these
be supplied by the two pumps as shown in Fig. 7. At this two pumps based on the all-day efficiency.
duty point the head in Eq. 6 for pump 1 is equal to the As detailed earlier, the H–Q curve can be redrawn at
head of pump 2 which has another equation. The H–Q different operating speeds according to the power val-
equation for pump 2 at rated speed is given by Eq. 11. ues produced from the solar cells at each hour where
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 9 of 13

35
Pump 1

30 Pump 2

Load curve
25
Head (m)

20

15

10

5
0 5 10 15 20 25
Flow rate (m3/hr)
Fig. 7 The H–Q curves of the two pumps

0.6

Pump 1
0.5

Pump 2
0.4
Efficiency

0.3

0.2

0.1

0
0 5 10 15 20 25
Flow rate m3/hr
Fig. 8 The efficiency curves of the two pumps

the motor equation (Eq. No.7) is used to determine the To determine the operating point at which each pump
rotational speed at each power level. Thus the operating curve intersects with the load curve at a specific rota-
curves of the pump at different rotational speeds can be tional speed, the H–Q equation of each pump at the rated
obtained using the Eqs. (3, 4). speed should be adapted to the specific speed using Eq. 3.
The Eq. 6 can be rewritten at the new rotational speed
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 10 of 13

using the cure fitting program to obtain the H–Q equa- shown from the results that the pump with a higher slope
tion at new speed. Then we get the operating point by is higher in all-day efficiency as well.
equalization the head equation of the pump by the head
equation of the load system. Operating at constant head
In most applications, the pump is installed in a station-
Results and discussions ary system to raise the required amount of water. For
Operating at duty point the comparison to be complete, the performance of each
The performance of the pump should be evaluated pump at a constant head should be studied. The perfor-
throughout the year. However, to simplify the analysis, mance of each pump was studied at a head above the
the performance was evaluated during a day of low radia- operating point (22 m) and another below the operating
tion equal to 3 kW/m2/day and another day of high radia- point (15 m).
tion equal to 7.3 kW/m2/day. Figure 7 shows that pump 1
does not operate with the system load if the speed is less
than 2500 rpm. Figure 8 shows that pump 2 is operating Operating at head 22 m
at a wide range of speeds compared with pump 1. There- Figures 5, 6 show that pump 1 can operate with a 22 m
fore, at the low radiation days, the number of operating head at a speed of more than 2750 rpm while pump 2
hours for pump 2 is more than the number of operating may operate at a speed slightly more than 2250 rpm with
hours for pump 1. the same head. The operation results for two pumps at
The operating efficiency along time slots of one hour low and high radiation days are illustrated in Table 2.
of each pump is shown in Table 1 for a low radiation day Graphically, pump 2 which has a high slope will give a
and another high radiation day. From the results, it is higher flow rate. So, the efficiency and total performance
shown that the operating efficiency of pump 2 is higher of pump 2 is better than pump 1.
than that of pump 1. From the results shown in the table, we find that at low
The efficiency of the two pumps is identical at rated rates of radiation, pump 1 does not operate at low radia-
speed but the efficiency of pump 2 is higher than pump tion and doesn’t give water. For a head equal to 15 m,
1 at all speeds less than the rated speed. From Fig. 5 it is Pump 2 is better than Pump 1.
shown that pump 1 is not operable at a speed less than
2500 rpm. This means that the minimum electrical power Operating at head 15 m
required to operate the pump with the load is 1280 W In the case of installing the pumps to raise the water to
which corresponds to the value of radiation equal to a fixed height lower than the proposed duty point, the
0.713 kW/m2. On the other hand, pump 2 can be oper- performance evaluation is different. Pump 1 has a low
ated at speeds down to 2100 rpm. This means that the slope will give a higher flow rate. This result is shown in
minimum electrical power required to operate the pump Table 3.
with the load is 1080 W which corresponds to the value From the results shown in the table, we find that at low
of radiation equal to 0.6 kW/m2. Therefore, pump 2 is not rates of radiation, pump 1 is better than pump 2, but it
only more efficient but also gives more water. To com- may not give the required amount of water due to the
pare two pumps operating at the same operating point, small number of operating hours.
the H–Q curve for each of them will differ in slope. It is

Table 1 Operating the two pumps at duty point

Operating hour Low radiation day efficiency % High radiation day efficiency %
Operating speed Pump 1 Pump 2 Operating speed Pump 1 Pump 2
(rpm) (rpm)

1 2330 Not operating 42 2550 15 41

2 2530 16 42.3 2820 37 40.8
3 2650 29 43 2900 38 38
4 2350 Not operating 42.5 2900 39.6 39.6
5 2830 37 40.5
6 2600 27 42
Day eff. 22.6 42.5 32.8 40.3
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 11 of 13

Table 2 Operating the two pumps at constant head 22 m

Operating hours Low radiation day flow rate (Q) ­m3/hr High radiation day flow rate (Q) ­m3/hr
Operating speed Pump 1 Pump 2 Operating speed Pump 1 Pump 2
(rpm) (rpm)

1 2330 Not operating 10.3 2550 Not operating 11.3

2 2530 Not operating 11.3 2820 10.4 12.5
3 2650 Not operating 11.9 2900 11.9 12.6
4 2350 Not operating 10.4 2900 11.9 12.6
5 2830 10.4 12.5
6 2600 Not operating 11.8

Table 3 Operating the two pumps at constant head 15 m

Operating hours Low radiation day flow rate (Q) ­m3/hr High radiation day flow rate (Q) ­m3/hr
Operating speed Pump 1 Pump 2 Operating speed Pump 1 Pump 2
(rpm) (rpm)

1 2330 Not operating 13 2550 16.5 13.5

2 2530 16.5 13.5 2820 19.2 13.8
3 2650 17.6 13.8 2900 20 14.1
4 2350 Not operating 13 2900 20 14.1
5 2830 19.2 13.8
6 2600 17.5 13.7

Selecting the proper pump results in low speed and pump 1 can’t operate under
The method proposed in this work can be used to select 2500 rpm with a head of 22 m.
the pump that best fits the requirements of a given At a head lower than the pre-designated head, the
photovoltaic pumping system. The traditional method pump with a lower inclination curve gives higher effi-
for pump selection is applied to obtain the maximum ciency. Therefore, pump 1 in this case gives high all-day
efficiency with the load requirements. When the pump efficiency compared with pump 2.
system is supplied electrically from solar cells, it’s
found that the rotational speed of the pump is varied Conclusion
because the electrical power is changed with radia- In this paper, a comparative study is presented to choose
tion values. The location of the maximum efficiency the most suitable pump to work with the solar cell sys-
point on the H–Q curve of each pump depends on tem. Two pumps with different characteristics are com-
some impeller design parameters. From the results of pared at the same operating point with the required load
the comparison, it is shown that the efficiency of each system. The characteristic curve of each pump is differ-
pump at each operating hour is different. So, the overall ent in inclination, but they have a common operating
day efficiency is different for the two pumps. In general, point and the same maximum efficiency value. The rota-
pump #2 which has a steeper H–Q curve gives higher tion speed of the pump changes with the change in the
all-day efficiency. In the case of operating at the desired value of the power produced by the solar cell system. The
load (H, Q) point, the efficiency of pump 1 is 22.6% and performance of each pump has been studied at different
pump 2 is 42.5% for low radiation day. At high radia- levels of radiation and different rotational speeds. When
tion days, the overall efficiency and water quantity are choosing the best pump to operate at a specific duty
increased for two pumps. The efficiency of pump 1 is point, the duty point should be located to the right of the
32.8% and pump 2 is 40.3%. If the pumps are operating pump’s maximum efficiency point. If for some reason,
at a constant head higher than the pre-designated head, the load requirements increase in the head for the same
pump 2 is the best compared with pump 1. The results setup, the pump that has a steeper characteristic curve
at a constant head equal to 22 m showed that pump 1 will outperform the one with a lower slope with respect
is not operable at low radiation because the low power to the all-day efficiency. Conversely, if the load head
Syam and Arafa Sustainable Energy Research (2023) 10:22 Page 12 of 13

requirements are decreased for the same setup, the pump Subscripts
h Hydraulic
with a lower slope of the characteristic curve is prefer- m Motor
able. In the future, a software program can be prepared c Control unit
to choose the best pump that gives the highest operating o Overall day
efficiency with changing solar radiation values.
Acknowledgements
The authors thank the Electronics Research Institute.
Appendix 1 Author contributions
The first author (Corresponding author) designed the system, performed the
simulation, analysed the results and writing the article. The second author
Model No OPS-100M suggested the method, presented literature review, analysis of results, and
review writing.
Maximum Power (Pmax) 100 WP
Funding
Voltage at Maximum Power (Vmpp) 19.8 V The research was done in my institute “Electronics Research Institute”.
Current at Maximum Power (Impp) 5.05 A
Availability of data materials
Open Circuit Voltage (Voc) 22.6 V
All data are available in the article, except for solar radiation values, which can
Short Circuit Current (Isc) 5.45 A be obtained from any atlas of the geographical area.
Module Efficiency 20%
Module Dimensions (H/W/D) 1020 × 510 × 30 mm Declarations
Cell Type Monocrystalline
Ethics approval and consent to participate
Not applicable.
Appendix 2 Consent for publication
Not applicable.
Model No SAER
MT2-IE2- Competing interests
80-2P-2 The authors declare that have no competing interests.

Nominal power 1.5 kW

Voltage 400 V Received: 29 March 2023 Accepted: 30 November 2023
Current 3.3 A
Motor efficiency 82%
Number of poles 2
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