Techno-economic and environmental evaluation of the performance of a solar water pumping system in arid and desert climates

Abstract

This study introduces a refined techno-economic, demand-oriented methodology to assessment and optimization of solar water pumping systems in line with the needs of sustainable agriculture in arid, water-limited regions. For Baghdad, Iraq, winter wheat, we balanced technical performance versus economic viability. System performance for three fixed-tilt angle strategies was analyzed using PVsyst software: summer-tuned (17°), winter-tuned (47°), and annual-tuned (28°). The analysis revealed the most efficient to be the summer-optimized tilt angle of 17°. This approach not only boasts the highest high-performance ratio but also yields the highest average volume of pumped water (298.8 m³/day) precisely when it is most critical: during the plant’s crucial growth stage. Moreover, the 17° tilt angle has the highest overall system and pump performance coupled with the lowest percentage of missing water. The approach is also the most cost-effective, with the lowest water cost at 0.4 $/m³. These findings unequivocally prove that a peak-demand-optimized, demand-based design is technically superior and less expensive than conventional annually optimized solutions. This research offers an adaptable and reliable framework for the formulation and implementation of effective solar water pumping systems; hence, it greatly enhances food and water security in desert areas.

Introduction

Background

Fossil fuels like oil, gas, and coal are rapidly depleting, contributing to air pollution and releasing CO₂, accelerating the depletion of fossil fuel reserves, and causing significant environmental damage^1,2. Fossil fuels pose health risks and warn of climate change, prompting growing political acceptance of renewable energy transition, particularly in developed nations^3,4. Transitioning to cleaner, greener renewable energy sources is crucial for achieving low-GHG output⁵.

In the agricultural sector, a significant energy consumer, one of the most promising applications of this transition is the use of renewable energy for water pumping, which can make farming more economical and sustainable⁶. Solar energy, as an abundant and renewable resource, plays a pivotal role in the global transition toward sustainable energy systems due to its vast availability⁷, minimal environmental impact, and increasing cost-effectiveness driven by technological advancements⁸. PV panels convert solar radiation into electrical energy and are used in reverse osmosis facilities, spacecraft, satellites, water pumping devices, and utility-scale energy generation^9,10. The water pumping system is a useful and effective method of supplying water in remote areas without access to the national electricity distribution system¹¹.

Literature review

Research on techno-economic modeling of Solar Water Pumping Systems (SWPS) has evolved in a straightforward manner. Early research primarily concentrated on establishing technical feasibility and stipulating generic frameworks for economic analysis. To this effect, the Life Cycle Cost (LCC) approach became the benchmark on which to compare solar systems with diesel systems¹². Numerous case studies worldwide have used this method since then to confirm the long-term economic and environmental benefits of SWPS¹³. Such analyses were often complemented by sensitivity analyses for key physical parameters, such as pumping head and solar irradiance, to outline how site-specific variables dictate system design and cost¹⁴.

The second generation of studies moved from simple analysis to optimization in a systematic way, seeking the best techno-economic design. To this end, computer aids like HOMER and metaheuristic algorithms were employed to optimize hybrid (solar-diesel) systems, determining the most economical design to meet a specified irrigation load¹⁵. These techniques were further advanced with the application of multi-objective optimization. Studies such as that by Muhsen et al. (2016)¹⁶ used evolutionary algorithms to simultaneously optimize competing objectives like cost (LCC) and reliability (Loss of Load Probability, LLP), yielding a Pareto front of optimal solutions. This technological advancement was pushed further by addressing more significant technical challenges; e.g., Herraiz et al. (2022)¹⁷ addressed the dynamic stability of large battery-less systems by developing a systematic tuning process for frequency controllers and proposing new metrics like the number of sudden stops.

In recent years, the scope of research has expanded beyond purely agricultural applications into innovative domains such as public drinking water supply¹⁸, policy and business models for national promotion¹⁹, and the integration of alternative renewables like wind energy²⁰. Furthermore, new technologies like floating photovoltaic (FPV) have gained attention due to benefits such as increased efficiency and reduced water evaporation²¹. Moreover, optimization models have also been made more comprehensive by including optimal siting and optimal sizing²².

Current Iraqi studies present a cautious attempt at addressing pressing energy and water requirements through realistic alternatives. Al-Hamzawi and Al Sailawi (2025)²³ designed a solar-powered multi-generation system for Basra through the integration of parabolic trough solar thermal technology with Multi-Effect Distillation (MED). The upgraded system achieved a desalination rate equivalent to 104.7 kg/s and an efficiency improvement of 20%, confirming that solar thermal is the secret to maximum desalination at high irradiance levels. Suwaed et al. (2023)²⁴ examined solar water heating in Kirkuk, where the solar fraction was 86% for evacuated tube collectors on open-loop and closed-loop systems as an economic and green source compared to electric heaters.

For off-grid applications, Qasim et al. (2025)²⁵ found the most cost-effective hybrid arrangement for Baghdad with the lowest levelized cost of energy ($0.0521/kWh) and an unprecedented reduction in CO₂ emissions. Al Essa (2022)²⁶ also proposed the utilization of a photovoltaic-wind-battery system for domestic uses, having the ability to produce 226 kWh/month and save electricity expenses and CO₂ emissions, with a payback time of three years.

All these studies emphasize collectively Iraq’s resolve to incorporate and optimize multiple renewable energy technologies in achieving energy self-sufficiency and environmental sustainability.

Research gap

Despite significant advancements in the economic and technical simulation of SWPS, a fundamental conceptual and empirical limitation persists in the literature: the explicit correspondence of system design with strongly seasonal and critical water demands of strategic crops in arid agricultural areas. Although many studies are methodologically advanced, they often exhibit one or more of the following limitations:

Optimization models, even those employing newer techniques, typically prioritize energy-related factors such as LLP¹⁶ or system efficiency. In agricultural applications, however, the most relevant Key Performance Indicator (KPI) is a secure supply of water, specifically minimizing “Missing Water” during the crop growth season. There is obviously a shortage of research studies classified as routinely redefining optimization objectives to specifically maximize agricultural water security, even if it comes at the cost of composite annual energy measures.

The conventional design approach in SWPS design is selecting a single optimal constant tilt angle to achieve maximum annual power output. The common practice ignores natural seasonality and non-homogeneity of farm water demand, particularly for strategic crops such as winter wheat. Power output in fallow seasons or seasons of minimum irrigation demand has a smaller contribution to agricultural water security and causes large power waste and increased unit water costs. Detailed investigations have strongly validated the techno-economic benefits of demand-responsive tilt angle optimization to align power generation with periods of maximum crop water demand.

While individual studies compare independent measurements (e.g., performance ratio, system efficiency, water provided, unit cost of water), a notable lack of comparative studies exists across multiple criteria that specifically address the impact of various demand-matched design strategies (e.g., summer-optimized, winter-optimized, or year-round-optimized tilt angles). Such research is crucial for evaluating their simultaneous impact on energy efficiency, agricultural water delivery reliability (lost water), and overall economic viability for the farmer. There must be an appropriate evaluation to determine the true effectiveness and benefits of demand-driven SWPS environments.

This is rather than usual energy maximization. It aims at optimal system design in which solar energy output is properly matched with the seasonal water demand pattern of a given strategic crop in a region, basically by the strategic selection of the tilt angle of the PV array. The aim here is to maximize economic return and water security for agriculture by having the water come at the most opportune time, when both plants and human beings will gain most from it, rather than simply maximizing annual energy production.

Objectives and novelty

Despite significant advancement in the techno-economic analysis of SWPS, the literature reveals a well-documented gap in directly matching system planning to the highly seasonal and critical water demand patterns of strategic crops in arid agricultural areas. While many studies propose new methodological strategies, they often share one or more of the following limitations: prioritizing energy-based metrics over agricultural water security, applying customary constant tilt angles that do not account for seasonally varying demands, or failing to provide comprehensive multi-criterion comparisons of demand-matched design possibilities.

This research aims to mitigate these limitations by developing and validating a demand-driven optimization model for an SWPS in a real-world agricultural setting in Baghdad, Iraq. Of primary interest is evaluating how different fixed-tilt angle methods (winter-optimized, summer-optimized, and annually optimized) influence both the technical performance and economic viability of an SWPS when particularly designed to meet the water requirements of winter wheat.

The novelty of this study lies in its multi-criterion analysis, extending beyond conventional energy efficiency indicators (e.g., performance ratio) to include prominent agricultural values like missing water and the unit cost of pumped water. By directly linking the system’s output with the specific crop cycle, this research provides an applicable and transferable method for designing SWPS that are not only technically efficient but also agriculturally productive and cost-effective for farmers in desert conditions. This research contributes a feasible model to achieve effective solar water pumping systems, thereby enhancing food and water security in desert environments.

Methodology

The sizing procedure involves accurately estimating water demands in the targeted zone, followed by evaluating the design phase based on factors like pump power, field size, solar PV capacity, operating conditions, and repository dimensions. The system’s efficacy is then assessed through extensive simulations based on the outputs of the design phase. Lastly, estimates and discussions of pertinent economic indexes are provided. A synopsis of the performance and economic indexes, mathematical model equations, and a brief explanation of the sizing procedure are shown below.

Modelling

The SWPS that has been designed is to provide a reliable source of water for domestic use in an off-grid area. The system design shown in Fig. 1 consists of a PV array converting solar energy to direct current (DC) electricity, an MPPT-enabled alternating current (AC) inverter to control power transfer and convert DC to AC, a submersible centrifugal water pump, and a water tank. The following sections describe the modeling and sizing procedure for each of these large components.

Fig. 1

Schematic diagram of the SWPS.

Sizing procedure

A thorough approach is provided to ensure that the suggested SWPS used for residential purposes is designed adequately.

Power from hydraulic pumping

The hydraulic head (H) and the system’s design flow rate (Q) determine the hydraulic power. Here’s one way to phrase it:

$$\:{\text{P}}_{\text{h}\:}=\text{p} \cdot \text{g} \cdot \text{H} \cdot \text{Q}$$

(1)

where g is the gravitational acceleration (m/s) and ρ is the water density (kg/m³). The following are the hydraulic head and design flow rate:

$$\:\text{Q}=\sum\:_{i=1}^{5}\frac{W \cdot {N}_{i}}{{n}_{s}}$$

(2)

The number of sunshine hours each day is denoted by n_s, and W.N_i is the amount of water that one residence in the research area demands each day.

Three key terms make up the hydraulic head²⁷:

$$\:H={H}_{s}+{H}_{f}+{H}_{dd}$$

(3)

where the gap between the water elevation and the discharge level is represented by the static head, H_s. H_f represents the friction losses in the hydraulic circuit, and H_dd is the drawdown water level. The sum of the static head and drawdown water level in this connection is 40 m. Friction losses in pipes are caused by the fluid’s viscosity (ΔH₁) or matching elements (ΔH₂), which consist of elbows, valves, and junctions. Consequently,

$$\:{H}_{f\:}=\varDelta\:{H}_{1}+\varDelta\:{H}_{2}$$

(4)

Operating point

A number of actions can be taken in order to graphically calculate the pump operating point. The hydraulic head is first calculated theoretically for a range of volumetric flows in order to depict the hydraulic circuit’s characteristic curve. The second step is to plot the pump characteristic curve, which is often provided by the pump manufacturer as Eq. (5). Finally, the junction points that match the operational condition under examination are found.

$$\:f\left(Q,{U}_{p},H,{I}_{p}\right)=0$$

(5)

where the voltage and current provided to the pump are denoted by the symbols U_p and I_p, respectively.

PV sizing

The DC electricity required to run the pump and a DC motor is generated by PV modules. The necessary electrical rated capacity (C_R) can be expressed as follows:

$$\:{\text{C}}_{{\text{R}}} = \frac{{P_{h} }}{{\upeta _{{sys}} }} = \frac{{P_{h} }}{{\upeta _{m} \cdot \upeta _{p} }}$$

(6)

where η_p, η_m, and η_sys stand for pump, motor, and pumping system efficiency, respectively. At STC, the PV power ought to be marginally greater than the nominal pump power. It should be noted that, in contrast to the direct coupling design, solar PV capacity may be decreased when an MPPT AC converter is utilized.

Water storage

The entire daily demand for water and the necessary autonomy (Au in days) largely dictates the amount of storage, assuming no output. Thus, it can be expressed as follows:

$$\:{V}_{ws}=\sum\:_{i=1}^{5}Au\cdot\:{WN}_{i}$$

(7)

Performance analyzing

Reference yield

The Reference Yield (Y_R) is the daily amount of peak sun hours (PSH) and is a critical parameter to determine the solar resource potential of any location. It is calculated using Eq. 8²⁸:

$$\:{Y}_{R}=\frac{{I}_{inc}}{{G}_{ref}}$$

(8)

where I_inc is the global daily irradiation on the inclined plane of the PV modules (in kWh/m²/day), and G_ref is the reference irradiation, a constant value of 1 kW/m² (under Standard Test Conditions). The unit acquired for Y_R is hours/day, which is the equivalent number of hours on which the sun would have to be radiating with peak intensity (1 kW/m²) to produce the same energy as the energy received during a full day.

Energy efficiency at the pump

The monthly effective power accessible via the pump can be expressed as follows (kWh/kW_p/day):

$$\:\text{A}EP=\frac{{E}_{arr}-{E}_{op}-({EL}_{s}+{EL}_{c}+{EL}_{u})}{{C}_{R}}$$

(9)

where E_arr is the month’s nominal electricity (kWh/day). The SWPS system also has three main losses: unused energy losses from a full tank (EL_u), threshold and mismatch losses (EL_s), and collection losses in the photovoltaic array (EL_c). Additionally, the design process indicates that C_R is the installation rated power output (kW_p) and E_op is the pump overloading electricity (kWh/day). The losses involved must be taken into account if an MPPT DC converter is integrated.

Ratio of performance

The effective power at the pump divided by the reference incident energy (Y_R) is the PR:

$$\:PR=\frac{AEP}{{Y}_{R}}$$

(10)

Missed water

The ratio of unsupplied water to total water demand is called Missed Water (MS). This is a key parameter measuring the reliability and ability of the system in supplying all irrigation demands of the crop. A high MS value represents the number of times when the SWPS cannot provide the amount of water demanded, hence resulting in water stress in the crop as well as a reduction in yield. Hence, the reduction of MS is a primary goal in system design. It may be calculated using the following:

$$\:MS = \frac{{\int_{0}^{{8760}} {Q_{t} dt} }}{{365 \times \:{\text{Total}}\:{\text{Daily}}\:{\text{Water}}\:{\text{Demand}}\:{\text{for}}\:16\:{\text{ha}}}}$$

(11)

Where: $\:{\int\:}_{0}^{8760}{Q}_{t}dt$ is the volume of unsupplied water over the span of a year (8760 h), Total Daily Water Demand for 16 ha is the water demand of the entire 16-hectare property, which equals 500.8 m³/day.

Economic modelling

This study uses the life-cycle expense technique to evaluate the economics of environmentally friendly projects compared to conventional systems, accounting for capital, replacement, operation, maintenance, and installation costs. The salvage costs are not taken into consideration in this analysis. Thus, it is possible to write the following equations²⁹:

$$\:{\text{LCC}} = {\text{C}}_{{{\text{capital}}}} + {\text{C}}_{{{\text{installation}}}} + {\text{C}}_{{replacement}} + {\text{C}}_{{maintenance}}$$

(12)

The capital expenses, which include the acquisition of all equipment, are represented by C_capital and are equivalent to²⁹:

$$\:{\text{C}}_{{capital}} = C_{{{\text{PVarray}}}} + C_{{{\text{PVstructure}}}} + C_{{{\text{MP}}}}$$

(13)

C_replacement is calculated using the following formula and includes the cost of replacing equipment when its useful life is coming to an end²⁹:

$$\:{\text{C}}_{{{\text{replacement}}}} = \sum {{\text{C}}_{0} \cdot PW} = \sum {{\text{C}}_{0} \cdot \left( {\frac{{1 + i}}{{1 + d}}} \right)^{n} }$$

(14)

The present worth factor, or PW, is influenced by the discount rate (d), inflation rate (i), and annual cost of equipment replacement (n). The initial cost of every piece of equipment is denoted by C₀.

The cost of maintenance, which is determined as follows, includes things like dusting modules, cabling, and inspecting battery terminals, as well as things like installing fencing to improve system security over the project’s duration²⁹.

$$\:{\text{C}}_{{{\text{maintenance}}}} = {\text{C}}_{0} \cdot \left( {\frac{{1 + i}}{{1 + d}}} \right) \cdot \left( {\frac{{1 - x^{n} }}{{1 - x}}} \right) = {\text{C}}_{0} \cdot {\text{CPW}} \cdot \left( {\frac{{1 + i}}{{1 + d}}} \right)$$

(15)

where n is the project duration, which is 20 years, and CPW is the cumulative present worth factor.

C_installation, or installation cost, remittance, shipping, and cabling expense are invariably estimates as a percentage of the capital cost. On the basis of representative industry values for such soft costs, in this study, installation cost is taken to be 10% of the total cost of capital²⁹.

$$\:{\text{C}}_{{installation}} = {\text{C}}_{{{\text{capital}}}} \cdot 0 \cdot 1$$

(16)

One of the most important economical comparative approaches to companies is the payback period, which is ascertained by dividing the initial investment cost by the average earnings per year, as demonstrated in Eq. 17³⁰:

$$\:{\text{Payback}}\:{\text{period}} = \frac{{capital\:cost}}{{revenues}}$$

(17)

Simulation

Geographic characteristics and site location

The photovoltaic water pumping SWPS with target capacity is to be installed at a remote area in Baghdad, the capital of Iraq. The site-specific latitude and longitude coordinates are employed as 33.3152° N and 44.3661° E, respectively. It is a hot desert climate and therefore an excellent candidate for solar power generation with high seasonally averaged rates of energy production. The radiation and clearness index for each month at this location are provided in Fig. 2.

Fig. 2

Monthly radiation and clearness index in Baghdad, Iraq.

Statistical weather data

The tilt and azimuth angle of the solar panel are what generate most of their power, with Iraq lying in the northern hemisphere latitude, so they need to be angled towards the south to obtain maximum radiation³¹.

Accurate meteorological data are the foundation for a simulation of SWPS performance. For this work, monthly average long-term meteorological data for the location at Baghdad (33.3152° N, 44.3661° E) were accessed through the integrated Meteonorm 7.1 database in the PVSYST 7.1 software³². Meteonorm is a globally recognized meteorological database that provides high-quality and verified solar radiation and weather data derived from a merged network of surface stations and satellites.

On a horizontal surface, the mean daily universal irradiation in Baghdad varies from 2.62 kWh/m² in December to 7.56 kWh/m² in June. Additionally, other meteorological data, including average temperature, mean total rainfall, and mean number of rainy days, were obtained by using World Weather³³. Figure 3 shows monthly average temperature fluctuations, with the highest temperature being 25.5 °C in July and the lowest being 3.8 °C in January. Natural reservoirs also receive significant precipitation in winter, fall, and early spring, which is used for irrigation, ensuring the required water supply in spring and summer³³.

Fig. 3

(a) Average monthly temperatures and (b) mean total rainfall and mean number of rain days in Baghdad, Iraq.

The average annual relative humidity in Baghdad is 42.3%, with monthly averages ranging from 21% in June to 71% in January. Figure 4 shows the average relative humidity for each month of the year³⁴. The average relative humidity is approximately 75.25% throughout the year. One distinctive characteristic of this area is its high relative humidity, which is crucial for wheat growth.

Fig. 4

Monthly average of relative humidity in Baghdad, Iraq.

Determining the ideal angle for tipping solar panels

The selection of the optimum tilt angle for solar panels is a significant parameter to ensure maximum input of solar energy and consequently the volume of pumped water. While a rule of thumb suggests a fixed tilt angle equal to that of the site latitude (approximately 33° for Baghdad), the approach does not always result in maximum efficiency during the most critical irrigation seasons. Therefore, in this current study, analytical modeling and simulation were used to properly obtain the optimum angles.

Our method involved calculation of the daily effective global irradiation on a tilted surface for a large number of tilt angles (from 0° to 90°), using typical irradiation models and climatic data available for the Baghdad region. The tilt angle yielding the highest cumulative irradiation in a specific period was then selected as the best angle for that period. Three best angles were determined using this analysis as follows:

• Winter Optimal Angle (47°): This angle was also optimized for the highest reception of energy during winter (December, January, and February). During this time, the sun is quite low in the sky, and with a greater tilt angle (above the latitude), it is guaranteed that the rays of the sun strike the panel surface more perpendicularly. The optimal angle of 47°, which approximates (latitude + 14°), was established to provide the most efficient performance at this time.

• Summer Optimal Angle (17°): This is the optimized angle to generate the maximum energy in the maximum growing and irrigation season (April to July). The sun is high during summer, and a lesser slope (more horizontal) tilt angle performs better. An optimal tilt angle of 17°, approximately equal to (Latitude − 16°), was determined to be best for reaping the most energy during this critical phase.

• Annual Optimum Angle (28°): This was an optimal angle determined as a convenient, fixed value to be utilized for the entire year. To determine this angle, annual total irradiation was simulated for various angles. The tilt of 28° was selected since it gave the highest annual total energy production (with 5.54 kWh/m² as the daily average effective global irradiation and 2020 kWh/m² as the annual total irradiation). This takes into account a compromise between optimal winter and optimal summer performance and is an economic option because there is no seasonal adjustment required.

Although single-axis tracking systems (SATS) deliver sensational performance gains, typically summing up to an 8% to 25% increase in energy yield based on site, our design opted for a fixed-tilt setup³⁵. The rationale was primarily in line with the objective of minimizing initial capital expense and operation complexity, the prime factors in system scalability as well as economic viability of the suggested system in the target region. The additional energy required to produce an SATS structure is nominal compared to the considerable amount of energy used to produce PV panels.

The crop’s water demand

During the growth season, the wheat crop demands a lot of water. The amount of water used during the irrigation time must also be known to compute the precise water flow rate demanded to establish the ideal motor-pump size. In the center and northern rainfed regions of Iraq, the principal crops are grains, namely wheat and barley. Winter wheat requires 180–250 days to grow, whereas spring wheat takes 100–130 days. U_p to 90 days of dormancy during the colder months are part of the winter wheat growth period. Rainfall, groundwater, or spring irrigation can all supply the crop’s water demands. The net irrigation water requirement of the wheat crop for the area of Baghdad is an important input in planning the SWPS. Based on agricultural statistics and climatic studies for this specific area, the total net irrigation demand during the entire growth cycle of winter wheat has been estimated as 1142 mm³⁶. The amount includes crop evapotranspiration (ETc) less effective precipitation during the growing season. Table 1 gives the actual difference between the average monthly water requirement of wheat during the irrigation season in the Baghdad region for peak scheduling of irrigation and system design. Average monthly water use for wheat during the irrigation season is shown in Fig. 5. Table 1 gives the actual difference between the average monthly water requirement of wheat during the irrigation season in the Baghdad region for peak scheduling of irrigation and system design. The monthly average water consumption of wheat during the irrigation period is presented in Fig. 5. As clearly observed, irrigation water demand is much larger in the summer months due to enhanced evapotranspiration and much less precipitation, as clearly delineated in Fig. 3b, which shows minimal rain during the same times. Winter’s lower water demand and higher effective rainfall reduce the need for supplemental irrigation.

Table 1 Crop water requirement for wheat³⁶.

Fig. 5

Monthly crop water demand for wheat in Baghdad, Iraq.

Finding the optimal pumped flow rate

As established in the previous section, the net water demand for irrigation of wheat throughout the entire growing season is 1,142 mm. In order to determine the amount of water demanded per hectare, this depth is thereafter multiplied by a hectare’s area (1 ha = 10,000 m²). Thus, the total amount of water demanded per hectare is therefore calculated as:

$$\:Volume\:per\:hectare\:\:=\:\text{1,142}\:mm\:\times\:\left(\frac{1\:m}{1000\:mm}\right)\:\times\:\:\text{10,000}{\:m}^{2}=\text{11,420}\:{\:m}^{3}$$

(18)

The daily amount of water demanded is 31.3 m³/day when this quantity is divided by the quantity of growth days. Because the pumping system is solar-powered, the amount of sunshine each day has a significant impact on how long it operates. It is projected that Baghdad experiences five hours of sunshine per day on average during the irrigation period (5.02 kWh/m²/day). The necessary flow rate, which is 100 m³/h, can be calculated by dividing the demanded water volume by the mean number of sunshine hours per day for 16 ha. Additionally, there are 15 overcast or rainy days in a month, with no more than four consecutive cloudy days. The primary goal of the design process is to create a centralized solar water pumping device for domestic water supply to farm homes. A schematic of the SWPS and its many components is shown in Fig. 6. Additionally, Tables 2 and 3 provide information on the hydraulic installation, including well characteristics and hydraulic circuit specifications.

Fig. 6

Layout of the SWPS.

Table 2 Well characteristics for SWPS.

The m/m³/h unit of measurement for Specific drawdown in Table 2 determines the drawdown in meters per cubic meter per hour of water pumped. It quantifies how much the level of water in the well drops (in meters) for every cubic meter of water pumped per hour. The specific drawdown is a characteristic of the ground and the borehole. It is defined by

$$\:Drawdown=\:\frac{Lower\:Dynamic\:Level\:-\:Static\:Level}{Max\:Flow\:Rate}$$

(19)

Table 3 Hydraulic circuit for SWPS.

Required pump power

Tables 4 and 5 provide the details of the storage tank and the pump characteristics. The calculated results from previously introduced mathematical formulas were used to determine the size of the proposed units. To ensure the required flow, the system comprises four pumps, each with a 10-kW power output, connected in tandem. The necessary water tank volume of 300 m³, which permits autonomy for four days in a row, was determined by the required pump power.

Notice that the system design utilizes a 300 m³ water buffer as the energy storage in place of battery storage. This was the outcome after a rigorous techno-economic analysis aimed at large-scale irrigated agriculture in arid climates. While battery storage has the potential of moderating threshold losses and enhancing short-term reliability, the high daily water requirement necessitates an equally sized and costly battery bank, which would increase life-cycle costs and the unit cost of pumped water significantly. Besides, water storage presents a simpler, more robust, and lower-maintenance solution for immediately resolving the final irrigation water demand, without additional energy conversion losses inherent with electrical battery storage. This is cost-effective and based on simplicity of operations for the targeted agricultural use.

Table 4 Pump characteristic for SWPS.

Table 5 Information about the SWPS storage vessel.

Sizing PV modules

20% of the investment cost is approximated to be accounted for by engineering, planning, and installation³⁷. Maintenance and operating expenses for pump systems that are powered by solar energy are normally minimal and are estimated to be around 5% of the investment cost. Additionally, it was approximated that the pump and AC converter would need to be replaced once during the project lifetime, which is typically 20 years in the photovoltaic pumping system case. Iraq inflation was 2.7% in 2024³⁸, while the Iraqi interest rate stood at 5.50%³⁹.

The economic evaluation relies on reliable cost data for the system elements. For the sake of this study, unit costs for all the principal equipment, i.e., PV array, inverter, and pump, were taken from the comprehensive technical and economic analysis done by A. Allouhi et al. 2019⁴⁰. The reason for doing so is that it offers estimates of renewable energy prices in the developing world, therefore offering relevant data for the Iraqi scenario. Table 6 is offered with the explicit costs.

Table 6 Component costs of solar pump system⁴⁰.

Results and discussion

Technical results

Several simulations were run for various tilt degrees in order to determine the ideal inclination angle for the solar modules (see Fig. 7). The location’s latitude is approximately correlated with the tilt angle. Significant changes in annual energy generation are observed within + 14°, -5°, and − 17° of the ideal tilt angle. A typical mono-Si module’s maximum annual energy output is achieved at a tilt angle of 17° (during the summer) at the research site. As seen in Fig. 7, the maximum average PR value of 0.403 was achieved by the 17° (summer) tilt. Even if this value may be small with regard to grid-connected systems, it is normal for off-grid SWPS in hot climates. The principal technological reasons for such a PR level are: (1) Thermal Losses: high ambient temperatures in Baghdad reduce the conversion efficiency of PV modules; (2) Pumping Threshold: the pump would only function once solar irradiation crosses a certain minimum limit, causing losses during dawn and dusk hours; and (3) Unused Energy: the produced energy is limited by the system when the storage tank fills up, reducing the overall performance ratio significantly. The slope at 17° reduces the latter effect by more evenly balancing water consumption and power production.

Fig. 7

Effect of tilt angle on average PR.

The loss chart derived from PVsyst (Fig. 8) below is a better indication of the performance of the system and reasons behind the obtained PR of approximately 0.403. The diagram presents an overall, quantitative representation of energy losses at various steps of the SWPS, from the original global horizontal irradiation of 1790 kWh/m² to the final water supplied, explaining losses encountered at different stages of energy conversion.

This detailed analysis proves that while the summer-optimized tilt of 17° effectively aligns the generation of energy with the maximum water demand by plants, significant losses of energy are still registered. These are highest in ‘unused energy (tank full)’ at 40.72% and ‘converter loss due to voltage threshold’ at 14.81%. This identifies the need for design being demand-oriented and conservative management of storage in realizing the in-use performance of SWPS. Furthermore, loss in PV due to temperature (9.08%) and PV conversion efficiency (19.94%) points to inherent limits of solar technology, suggesting room for improvement through superior module cooling or use of more efficient PV technologies. As the system is already meeting only 59.8% of the user’s water demand, advanced design adjustments or operation techniques are required to handle greater overall system efficiency and system capacity to supply water.

Fig. 8

Energy flow and loss analysis of a SWPS.

Figure 9 indicates the monthly effective global solar irradiation for three fixed tilt angles. The results reflect a well-documented seasonal performance trade-off. Summer-optimized 17° tilt peaks around 207 kWh/m² in July, perfectly suited to optimize energy harvesting from the elevated sun of summer. The reverse, the winter-optimized 47° tilt, beats the rest by far from October to February when the sun is low. The annually optimized 28° angle is an in-between performance evenly balanced throughout the year.

Fig. 9

Effect of tilt angle on monthly average effective global solar irradiations.

Figure 10 illustrates the seasonal trend of pump operating energy, which follows the agricultural irrigation schedule. The demand for energy is highest between March and June, and the summer-efficient 17° tilt attains a highest monthly value of approximately 4,900 kWh in May. Remarkably, operating energy is minimized to zero over all the tilt angles from August to October, representing the fallow period when there is no irrigation. Per year, the highest total operating energy (28,333 kWh) is provided by the 17° tilt angle, then 28° (27,912 kWh) and 47° (26,652 kWh) tilts. The calculation confirms that seasonal performance varies, but pump energy consumption is ultimately defined by crop water demand.

Fig. 10

Effect of tilt angle on monthly average pump operating energy.

Figure 11 shows the available energy at the pump (kWh) for the three fixed-tilt angle scenarios by month. Results show that there is an unmistakable seasonal energy delivery trade-off. The 47° winter-optimized tilt has the greatest available energy in winter (e.g., December, January), and the 17° summer-optimized tilt fares best in the hottest summer months (e.g., May). The annually optimized 28° angle offers an even performance that closely tracks the performance of the top-performing seasonal angle, thereby ensuring maximum year-round energy availability for pumping.

Fig. 11

Impact of tilt angle on average monthly energy availability at the pump.

Figure 12 plots the average monthly reference incident energy on a tilted surface for three fixed-angle configurations: winter-optimized (47°), summer-optimized (17°), and annually optimized (28°). The results graphically indicate a performance trade-off. The steeper 47° tilt captures the most energy during the winter months (December-February) when the sun is low in the sky, well exceeding the other angles. Conversely, the 17° shallower slope is superior in summer (May-August) when it has the ability to capture the highest energy available from the sun that is at its maximum during summer. The 28° all-season optimum angle has a proportional but never optimal performance year-round. The discussion emphasizes the absolute need for selecting the tilt angle by the seasonal energy demand.

Fig. 12

Tilt angle’s impact on the region under study’s monthly average reference incident energy.

Table 7 indicates that the year-round 28° tilt experiences maximum system losses. This can be technically explained by the fact that its power generation curve does not coincide with the pump operation limits. The 28° orientation produces a moderate but consistent level of power on an annual basis. This has the effect of generating longer spans where the power generated lies just below the level needed for operating the pump or just above the pump’s operating limit, leading to higher threshold and overloading losses than the seasonally specific 17° and 47° orientations.

Table 7 Average losses per year for the solar water pump system.

Figure 13 illustrates the modeled monthly pumped water quantity (m³/day) for the photovoltaic irrigation system under three fixed-tilt angle scenarios: a winter-optimized tilt angle (47°), a summer-optimized tilt angle (17°), and an annual-optimized tilt angle (28°). The result indicates a well-defined seasonal performance trend based on the interaction between solar irradiance and the corresponding irrigation needs of the selected crop rotation.

The 17° summer-optimized tilt angle is receiving the maximum total average daily water volume pumped, which is approximately 298.8 m³/day. This is greater than the annually optimized tilt of 28° and winter-optimized tilt of 47°, with averages of 294.7 m³/day. The enhanced performance of the 17° tilt is also most pronounced during May and June, the maximum solar months, when it harvests maximum energy from the high-altitude sun, resulting in the maximum water output of approximately 640 m³/day.

One of the most important observations from the data is the complete cessation of pumping activity for the period of August, September, and October, where the amount of water pumped per day is zero for all tilt angles. It is not equipment failure or lack of solar energy but a deliberate outcome of the pre-specified irrigation schedule based on crop water demand. Throughout this period, the land is lying idle, following the harvesting of the summer crop (e.g., tomatoes, in early August) and before sowing the ensuing winter crop (e.g., wheat, in November). Because no crop is being cultivated on the field, irrigation is not necessary, and thus the pumping system is made available to be in the off state in an attempt to conserve both water and system life. Such a scheduled downtime is a critical component of a more efficient and sustainable irrigation management program, where energy and water resources are utilized only, when necessary, by agriculture.

Fig. 13

Impact of tilt angle on average monthly water pump volume.

Figure 14 plots daily pumped volume of water versus daily global effective solar irradiation, revealing the prominent system performance characteristics over one year. There are a clear positive trend wherein increased irradiation pumps more water, with the system firmly in pumping at low irradiation levels of 1.5 kWh/m²/day.

Distribution of data is non-uniform with distinct operating clusters. A tight cluster in zero pumped volume for fallow months (August-October) with no irrigation need exists. A horizontal cluster at 110–120 m³/day also exists, which states that pumping is not limited by solar input but by hydraulic capacity or by pre-programmed irrigation entitlements. This case shows the complex, non-linear interdependence between solar availability, system efficiency, and dynamic agricultural water demand that in turn govern water delivery.

Fig. 14

Daily effective global sun irradiation over the summer compared to daily pumped water.

Figure 15 shows the system efficiency, pump efficiency, and missing water for the three considered tilts. Results show that 28° and 17° fixed plane tilts are associated with the maximum system and pump efficiency, respectively. Moreover, the fixed plane tilt of 17° shows the minimum percentage of missing water. This finding is rather significant, as it determines that the summer-optimum orientation is the most dependable for meeting the water demand of the wheat crop at its peak growth stage. A fraction of lost water is proportionate to a stronger irrigation network, reduced danger of loss in crop yield, and ultimately greater economic security to the farmer.

Fig. 15

Effect of tilt angle on system efficiency, pump efficiency, and missing water.

Economic results

The cost of investment and operating expenses are shown in Tables 8 and 9, respectively. The cost of capital is $106,290.50, whereas the operating expenses in one year are $8,310.91.

Table 8 SWPS cost of investment.

Table 9 Operating costs of SWPS.

The lowest payback period for each direction is compared in an attempt to evaluate the economic viability of SWPS. The cost of water supply for this area is estimated as 0.131 dollars per cubic meter, the average cost of water supply in the country. Hence, Table 10 gives the results that were derived. Pumped water cost analysis shows clear economic disparities between the directions. The summer-optimal tilt of 17° was the most economical at 0.40/m³. The annual tilt of 28°, in relation to this, cost virtually nothing at $0.41/m³, and the winter-optimal tilt of 47° was the least economical with the maximum cost of $0.43/m³. Based on such calculations as payback period, net present value, and return on investment, the economic analysis report of PVSYST software shows that fixed plane tilt 47° is totally uneconomical. Compared to fixed plane tilt 28°, fixed plane tilt 17° is economically viable.

Table 10 Return on investment of SWPS.

To attain a strong economic viewpoint for the SWPS, a comparative analysis was performed with an average diesel-engine water pumping system, a typical off-grid method in remote rural locations of Iraq. An equal hydraulic power (40 kW) diesel system is sized to provide the same pumping rate as the proposed SWPS. The economic analysis for the diesel system considers the following assumptions:

The initial cost of a diesel pump system, including the engine and installation, is approximately $15,000. Operating at an average specific fuel consumption of 0.28 L/kWh (ranging from 0.25 to 0.30 L/kWh) and meeting an average daily energy demand of 77.6 kWh (derived from a 17° tilt case, equating to approximately 28,333 kWh/year), the system consumes about 21.73 L of diesel per day. With the cost of diesel fuel at $0.57 per liter in Iraq⁴¹, fuel is a significant operating expense. Maintenance each year is estimated at 10% of the capital cost, or $1,500 per year, to cover the increased wear and tear of diesel engines compared to photovoltaic water pumping systems. The diesel engine will have a 10-year life and therefore require replacement or overhaul once during a 20-year project life. The replacement expenses are estimated at 80% of the initial investment, based on a more developed market. Environmentally, diesel pumps used in agriculture have life cycle CO₂ equivalent emissions of 700 g CO₂eq/kWh. This is much higher than that of off-grid solar power plants, whose emissions have been estimated at 40 g CO₂eq/kWh.

A critical economic distinction emerges when evaluating the cost per cubic meter of water pumped: the SWPS is significantly more economical at $0.40/m³, compared to the diesel system’s estimated $0.61/m³. This higher unit cost for diesel is attributed to volatile fuel prices and consistent maintenance demands.

Environmentally, the SWPS exhibits profound advantages. At an annual operating energy for the pumps of 28,333 kWh/year, the SWPS achieves an approximately 17.5 times cut in CO₂ emissions compared to a diesel equivalent. This immense decrease in greenhouse gas emissions highlights the indispensable contribution of solar water pumping towards curbing climate change and promoting sustainable agriculture, particularly in arid climates. Conclusively, with higher upfront cost, the SWPS offers improved economic payoff in the long run (lower cost of water) and excellent environmental gains (much lower CO₂ emissions). These features render SWPS a more sustainable and desirable alternative to diesel-based options, aligning with increasing environmental awareness and the imperative for water resource sustainability on a long-term scale (Table 11).

Table 11 Comparative economic and environmental analysis: SWPS vs. diesel pumping system.

Results of sensitivity analysis

The results of our sensitivity analysis for the summer-optimized 17° tilt angle (which yielded the most favorable economic outcomes) are summarized in Fig. 16.

Decreasing the discount rate (e.g., to 4.5% or 3.5%) quite considerably increases the NPV and decreases the payback period, favoring the project. A higher discount rate (e.g., 6.5% or 7.5%) decreases the NPV, and the project is not viable (negative NPV) at a discount rate of 6.5% and above and increases the payback period. This shows how important the cost of capital is in determining project viability.

An increase in the inflation rate (to 3.7% or 4.7%) brings a higher NPV and lower payback period. It happens because our revenue (returns on selling water) is going to stay consistent with inflation, while some of the expenses (such as initial capital) are static, and operating costs get inflated, but overall profitability improves when discounted. On the other hand, the decline of the inflation rate (e.g., to 1.7% or 0.7%) is negative for the NPV, making the project uneconomical at lower inflation rates and increasing the payback period.

Sensitivity analysis confirms that while the summer-optimized 17° tilt angle has good economic rationale in the base case, its profitability remains sensitive to changes in the discount and the inflation rates. The project remains economically feasible in a range of these parameters, particularly when the discount rate is lowered or the inflation rate is raised above the base case. The results indicate the significance of accurate forecasting of these economic variables at project planning and decision-making for dry region solar water pumping schemes.

Fig. 16

Sensitivity analysis of NPV and Payback Period (PBP) to variations in discount rate (a) and inflation rate (b) for the solar water pumping system at a 17-degree tilt angle.

To enhance our economic conclusions further, a sensitivity analysis was performed on the life spans and replacement costs of the pump and inverter, predominant systems in determining the long-term viability of the system. Based on industry practices and past research⁴⁰, the base case considered 10 years of life span for the pump and inverter, with one replacement within the 20-year project life. Replacement costs were set at 100% of its original cost (C₀).

For sensitivity analysis, two situations were considered: a pessimistic situation with shorter lifetimes (7 years for inverter and pump) and higher replacement cost (110% of C₀) and an optimistic situation with longer lifetimes (13 years for inverter and pump) and lower replacement cost (90% of C₀). The summer-optimal tilt angle of 17° was chosen for investigation due to its economic merit. The result of this sensitivity analysis is included in Table 12.

Table 12 Sensitivity analysis of economic indicators to pump and inverter lifespan and replacement costs (17° Tilt angle).

Table 12 values also suggest that component life and replacement cost play a critical role in determining the economic feasibility of the SWPS. The lowest possible estimate of shorter lives with large replacement costs leads to a longer payback period and an unfavorable NPV, indicating possible non-viability on economic grounds under these assumptions. The best scenario provides a much greater payback period and over twice the NPV, with the added benefits of longer component life as well as low-cost replacements. In this paper, the necessity of good-quality components, good maintenance practice, and conservative cost estimation in rendering such systems economically viable in the long term is emphasized.

Comparison of results with already existing work

The findings of this paper are supported and supplemented by the rest of the research abstracts included in this work, all of which tackle the same issues about renewable energy for irrigation purposes.

All others also fully agree with the fundamental conclusion of the original paper. Carroquino et al. (2015)¹⁵ find that the optimal tilt angle of a PV array will not only be set by the seasonal demand but also by the diurnal pumping schedule. Sarkar et al. (2017)¹⁹ note that, if not consumed or stored properly, the “excess electricity fraction” is over 80%, which is the wastage of energy problem blamed in the main paper on the 47° tilt.

There are some articles that give solutions to the energy surplus problem. Nikzad et al. (2019)¹³ give a very cost-effective remedy: selling excess power to the grid, which was capable of covering nearly 60% of the system life cycle cost.

While the fundamental assumption of the base study is an isolated PV system, other research suggests hybrid systems are typically the best option. Sarkar et al. (2017)¹⁹ suggest a PV-generator-battery hybrid for high loads, and Maleki et al. (2025)²² and Carroquino et al. (2015)¹⁵ conclude that PV-diesel or PV-diesel-battery hybrid systems possess the best cost-reliability trade-off.

Pumped water cost varies greatly across studies. The 0.40 $/m³ cost in the lead paper, though greater than some optimized systems (e.g., 0.05 $/m³ by Okakwu et al. (2022)¹⁴ or 0.045 $/m³ by Muhsen et al. (2017)²⁷, is considerably less than an estimated $0.61/m³ for a comparable diesel-fueled pumping system in the Baghdad region. This would most probably be a result of system size, location (solar irradiation), economic assumptions (investment costs, inflation), and technology applied.

The topic of this study is the economic and environmental efficiency of the diesel and SWPS. While the initial price of the diesel system is cheaper ($15,000 versus $106,290.50 for SWPS), its ongoing running costs, powered by operation and maintenance, are considerably higher ($6,010.60 for diesel versus $8,310.91 for SWPS, with financing, maintenance, and insurance included).

Application of the demand-driven optimization model to different crop cycles

The study records the techno-economic benefits of an optimized demand-driven solar water pumping system with a paradigmatic example of its applicability to summer irrigation of winter wheat in Baghdad. The key recommendation is a 17° summer-optimized tilt angle for this crop but with universal applicability to diverse agricultural climates and crop cycles. The demand-driven strategy links solar PV energy generation to the seasonal water demand of a crop. It does so in three major steps: first, the accurate calculation of a crop’s water demand over its growth phase, with consideration of stages of growth, evapotranspiration, and effective precipitation. Second, performing a site-specific solar resource assessment, using software like PVsyst to simulate global daily irradiation on tilted surfaces at various tilts and seasonalities.

Third, determining the optimal tilt angle to generate maximum energy during the critical irrigation period of the crop, as compared to taking a fixed optimum annual angle. For autumn-peaking crops, an intermediate tilt angle would be chosen, while winter-demanding crops would necessitate a winter-optimized angle (e.g., 47°).

Finally, an integrated techno-economic analysis evaluates the chosen tilt angle strategy on the basis of both energy-based criteria (PR, system efficiency) and agriculture-based performance criteria like “Missing Water” and “Unit Cost of Pumped Water.” This multi-criterion framework justifies the system’s energy efficiency, agricultural production, and economic acceptability for the farmer. This flexible framework offers a robust design template to design solar water pumping systems in specific agro-climatic conditions with the perspective of maximizing agricultural production and water security.

Policy implications

This study, based on a case study in Iraq, demonstrates the potential of solar water pumping to irrigate agriculture. While the study is unique to high-solar-radiation, semi-arid regions with severe water stress, the methodology and most relevant conclusions have broader relevance. Optimization principles for the tilt angles of solar panels against seasonal irrigation requirements and synchronization of system output with the growth stage of the crop are general in nature and can be applied for any agro-climatic zone interested in the use of solar energy for sustainable water management. This work, therefore, presents a viable framework, which can be adapted for various climatic conditions with poor solar resources.

The large-scale SWPS adoption across Iraq will be driven by the development of focused financial frameworks to enhance their economic appeal to farmers. We see several principal policy controls from our techno-economic assessment to enhance Return on Investment (ROI) and accelerate adoption rates. First, upfront capital subsidies are necessary, as they directly reduce the principal barrier of high capital outlay, lowering payback periods drastically and increasing NPV. Second, farm banks’ soft loans and concessionary financing at reduced interest rates and longer maturities would actually reduce the cost of capital and increase overall profitability by reducing the present worth of future costs. Third, carbon credit mechanisms and green certificates as part of the system would introduce an essential new source of revenue for system owners, enhancing economic viability and serving national environmental goals directly. Lastly, tax credits and duty exemptions for importing PV parts would lower capital expenses even further, making the systems more cost-effective. In order to make these functional, a pilot project for a targeted fund, simplified application processes, and training farmers, particularly in such regions as Baghdad, are recommended to test such policies for scale-out across the country. Such a concerted framework is required for unlocking Iraq’s solar potential to enable sustainable water and food security.

Conclusion

This study strongly proves the techno-economic viability of an SWPS as a secure water supply option for Baghdad, Iraq, a semi-arid city. Through systematic study, it was found that the optimization of tilt angle for seasonal needs, i.e., summer-optimized 17°, significantly improves the performance.

This direction provides the maximum energy during most irrigation periods, with the resulting maximum mean day volume of water pumped (298.8 m³/day), high performance ratio, and minimum percentage of wasted water.

The 17° inclination also had the lowest water cost (0.4 $/m³), and it is much more economical and sustainable than annually optimized (28°) and winter-optimized (47°) inclinations and conventional diesel pumping systems. The demand-oriented design concept, which focused on matching energy production to crop water demand during peak periods, proved to be technically more advanced and economical than an average annually optimum solution. This article highlights the need for site-specific, demand-based design approaches for agricultural SWPS and proposes a platform to enhance food and water security in water-scarce nations with a reduced carbon footprint.

Proposed future work

Future research on Solar Water Pumping Systems (SWPS) will focus on more realism, stability, and evaluation. A key area is more sophisticated system dynamics analysis to model various aquifer parameters, pumping effects, and hydraulic losses at transient flow conditions, leading to better performance predictions.

A thorough techno-economic analysis is also necessary. This entails a thorough comparative analysis of fixed-tilt and tracker systems based on a more premium Levelized Cost of Water (LCOW) calculation, particularly for desalination. Moreover, a techno-economic analysis of hybrid PV-battery-pump systems versus the existing PV-water tank pump system will examine costs, complexity, and efficiency for farm scales to improve autonomy and reduce losses. Integration of a backup system for 100% reliability will also be considered. Long-duration field monitoring at diverse locations, such as Baghdad, is necessary to achieve extended experimental verification for obtaining empirical information to enhance model development and improved prediction tools. Subsequent studies will continue to refine the tilt angle for larger sets of crops with diverse seasonal water demand, beyond single-crop profiles. A full Life Cycle Assessment (LCA) will take into account more than CO₂ release by also covering water footprint, land use, and material depletion. This expanded LCA, combined with a worldwide economic analysis that also incorporates government subsidies and carbon credits, will represent an even more complete picture of economic and environmental incentives. Dynamic economic sensitivity analysis will forecast the impact of future anticipated changes to PV device cost, fuel cost, discount rate, and inflation and greatly increase awareness and value to sustainable agriculture of SWPS applications.