Visualizing the Landscape and Evolution of Solar Energy-Integrated Desalination Systems via Scientometric Analysis

Abstract

Rising population levels exert significant pressure on available freshwater resources. Scientists and researchers from various countries are diligently seeking a long-lasting solution using solar-powered desalination. This research paper investigates the current advancements in solar desalination research by utilizing the method of “scientometrics”. Scientometrics employs traditional methodologies, including bibliometrics, which entails quantifying the number of research papers published, and citation analysis, which involves examining the frequency with which other researchers cite these papers. By integrating these two approaches, scientometrics provides invaluable information about the most influential countries, institutions, and individual researchers in the field. Utilizing the software program VOSviewer, a comprehensive analysis was conducted on 1855 research papers published between 2010 and 2024. These papers were selected based on a predetermined set of ten key search terms. The results of the analysis indicate that China is the leading country in this field, as it boasts the highest number of published papers and the most citations received overall. Notably, Egyptian research institutions have been identified as the most influential in this area. Moreover, a single author has notably amassed 3419 citations for their 54 published works on solar desalination. This analysis unveiled past and contemporary advancements in the field and identified current trends through keyword analysis. It also offers recommendations based on bibliometric findings, including suggestions for addressing the challenges faced by solar-derived systems and addressing research area saturation.

1. Introduction

Water scarcity is a critical problem that has been attributed to various factors, including mismanagement, according to some researchers. Studies by Mekonnen (2016) [1] and Molden (2020) [2] highlighted the environmental and human factors contributing to this worldwide issue. Mekonnen (2016) highlighted that it is imperative that public awareness be raised to address this pressing concern. Moreover, Farooq et al. (2009) [3] emphasized the severe consequences of droughts on agriculture. The unfortunate truth is that the absence of significant freshwater discoveries or extensive seawater desalination could lead to a devastating global crisis.

In light of the expanding water scarcity, coastal nations resort to desalination to augment their freshwater resources. As far back as 1979, researchers acknowledged the potential of employing renewable sources to energize desalination facilities. Despite technological limitations of the era, Balligand et al. (1979) [4] proposed a theoretical method that integrated reverse osmosis desalination with a solar-powered desalting greenhouse.

Over the past decade, research on solar desalination has grown in scope. Investigations have centered on refining conventional techniques, such as multi-stage flash (MSF) desalination, by integrating solar collectors with MSF systems. The viability of this approach has been demonstrated through economic models (Zheng and Hatzell, 2020) [5] and comparable simulations on novel solar heater prototypes (Abutayeh et al., 2013) [6]. On the contrary, the utilization of photovoltaic (PV) cells for the direct conversion of sunlight into power for desalination plants has been extensively explored. According to recent studies, small-scale desalination (SSD) plants powered by PV cells are more efficient than large-scale desalination (LSD) plants, particularly in resource-constrained regions. Kariman et al. (2023) [7] has concluded that multi-effect distillation (MED) is a superior alternative for SSD applications. Additionally, further investigation is needed to explore the potential of hybrid systems that combine existing PV and thermal technologies with portable linear Fresnel concentrators ( García-Rodríguez, 2022) [8].

Furthermore, recent attention has been given to nanoparticle methodologies. In work conducted by Kuzmenkov et al. (2021) [9], a transparent photothermal receiver for seawater photothermal boiling was investigated using nanoparticle technology. This method presents promising innovations that are further discussed in this article. Minimizing the environmental impact is of paramount importance. Zero liquid discharge (ZLD) systems have received considerable attention, particularly in regions with limited options for brine disposal. These systems rely on temperature swing solvent extraction and have demonstrated a significant improvement in efficiency, surpassing traditional methods that utilize energy-intensive multi-stage vapor compression (MSVC)-based brine crystallizers by nearly 63% (Pinnu and Bigham, 2021) [10].

Hybridization and co-processing have also been widely implemented (Velázquez-Limón et al., 2020) [11], employing an open cycle absorption system that integrates Li-Br/H2O absorption with a single-stage flash process. This hybrid system uses waste heat to enhance efficiency. Furthermore, Kim et al. (2018) [12] introduced a solar-powered desalination system that is integrated with a wastewater treatment plant, simultaneously producing hydrogen. This tri-process system utilizes an electro-catalytic setup with photoanodes and platinum foils to generate electricity from sunlight, which powers the wastewater treatment process. Preliminary tests have yielded encouraging results, with simulated light activating the photoanodes.

Further research highlights the importance of optimizing existing desalination systems. Specifically, studies investigate ways to enhance thermal efficiency of hybrid reverse osmosis and multi-stage flash systems by Marcovecchio et al. (2005) [13]. They focused on efficiency by decreasing the energy needed to operate these systems, making them more appealing for regions with limited resources and suitable for industrial applications.

Moreover, Israel’s adoption of concentrated solar power for desalination demonstrates their transition to renewable energy as explained by Meindertsma et al. (2010) [14], while the successful implementation of an integrated vacuum distillation system in Wuhan, China for desalinating brackish water exemplifies the potential of such systems (Wang et al., 2017) [15].

According to El-Sebaey et al. (2023) [16], the performance of cylindrical sector solar stills (CSSS) surpassed that of double-slope solar stills (DSSS) in terms of productivity, thermal efficiency, and cost per liter of clean water. Specifically, the CSSS design produced up to 16% more water daily, achieved a thermal efficiency of around 15% higher, and had a potential cost per liter of clean water as low as USD0.0119/L. Recently, El-Sebaey et al. (2024) [17] discovered that the stepped basin tubular solar still (SBTSS) design yielded up to 42% more desalinated water per day with higher efficiency than traditional models. Sathyamurthy et al. (2024) [18] proposed another method that involved enhancing a single slope solar still (SSSS) by incorporating recycled soda cans coated with car exhaust nanoparticles for heat storage, resulting in a significant increase in the SSSS’s desalination performance by over 100%.

Dai et al. (2022) [19] conducted a biblio-literature survey on graphene-based membranes for water desalination between 2011 and 2022, with a focus on solar desalination. Previous research primarily concentrated on membrane development, with limited exploration of the integration of these membranes with solar desalination systems. The recent advancements in solar desalination research have yielded valuable insights, but a clear direction for future studies is lacking. Given the growing need for sustainable solutions, it is particularly concerning. The recent COP28 conference emphasized the critical need for reducing carbon emissions and transitioning away from fossil fuels (Tiwari, 2024) [20]. Solar desalination offers promising technology in this context, but a strategic roadmap is necessary to suggest improvements.

Several key issues require attention in the field of desalination: optimizing existing technologies to enhance efficiency and reduce energy consumption, developing cost-effective and scalable solar desalination systems adaptable to diverse geographic and resource settings, tackling the environmental repercussions, especially concerning brine disposal, and integrating solar desalination with other renewable energy sources and water management strategies.

Therefore, this study extended beyond mere publication counts. It delved into scientometrics, analyzing citation linkages to unveil the global contributions of researchers and institutions, which assists in identifying key figures and potential collaborations that can drive advancements in solar desalination. Moreover, it examined the research landscape of solar desalination methodologies to quantitatively analyze current trends and forecast future directions. Additionally, the scientometric approach was employed not only to highlight the prominent affiliations in desalination research, but also to reveal their broader impact across various scientific disciplines.

2. Methodology

This paper primarily utilized the Web of Science Core Collection as its primary data source. The Web of Science Core Collection offers a wide array of academic articles from various disciplines, including but not limited to engineering and medical sciences. One of the notable features of the Web of Science is its sophisticated filtering system that enables the precise identification of relevant publications based on publication date, type, and author affiliation (Wang and Waltman, 2016) [21].

2.1. Data Collection

The search was conducted in February 2024 with preliminary research conducted during December 2023. Using search syntaxes like quotation marks to indicate the presence of keywords: “desalination”, “solar”, and “solar energy” with conditional keywords such as “hdh”, “thermal”, and “membrane”. The period filter was set to only display fields published in the recent years from 2010 to 2024. In total, the relevant fields amounted to 1855, with most of the fields being articles at 1496 (~80.7%) of the total count.

2.2. Bibliometrics and Citation Analysis, History, and Previous Art

As previously mentioned, bibliometrics serve the purpose of evaluating the impact and influence of scholarly articles, particularly those that have been cited numerous times by various publications, indicating their significance (Cooper, 2015) [22]. Bibliometrics and citation analysis can be performed concurrently to demonstrate the relevance of scholarly articles by identifying connections between authors and their affiliations.

During the latter part of the 19th century, bibliometrics began to be recognized. The modern advancements in bibliometrics can be traced back to the post-World War II era, when the field underwent a “periodical crisis” that led to the increased use of computational analysis. The term bibliometrics as it is known today was first introduced by Eugene Garfield, and later on, Derek John de Solla Price established the field through his research on citation networks (B. Ian Hutchins, 2018) [23].

As mentioned previously, a study conducted by Dai et al. (2022) encompassed an extensive review of advancements in graphene membrane technology. Other scientometric analyses conducted in various fields outside of desalination have also achieved similar success. For instance, a bibliometric study by Fahad et al. (2023) [24] examined the medical applications of plasmonics and employed techniques such as bibliometric coupling and citation networks to investigate the use of magneto-plasmonic sensors in early cancer diagnosis. The study concluded that the majority of research in the field of plasmonic medical applications was led by China, the US, and South Korea. Furthermore, a thorough bibliometric analysis carried out by Faust et al. (2018) [25] on physiological analysis demonstrated an increase in publications during 2017, particularly in the fields of electromyogram (EMG), electroencephalogram (EEG), electrocardiogram (ECG), and electrooculogram (EOG).

A significant bibliometric analysis of IoT Systems was carried out by Ben-daya et al. (2019) [26]. Their literature survey investigated the role of IoT in SCM (supply chain management). The researchers found that the majority of the reviews were confined to analytical models and empirical research, with a strong emphasis on delivery and F&M (food and management) supply chains. Conversely, bibliometrics was also applied through an investigative analysis that examined the various categorized keywords for smart city systems by Martin de Jong (2015) [27]. Utilizing data obtained from Scopus for publications between 1996 and 2013, it was deduced that the most frequently co-occurring keyword and theme was “sustainable city” following twelve-category analysis.

All these bibliometric applications exhibit the usefulness of conducting such analyses. By identifying trends and research gaps, as well as suggesting improvements and making informed predictions, bibliometrics proves to be a valuable tool. Additionally, this study aimed to promote scientometrics as a highly beneficial utility, contributing and shedding light on the advancements made in photo-integrated desalination systems overall, including the entire solar-derived methodologies.

The methodology utilized in this scientometric analysis aligned with the bibliometric approaches previously discussed, and consequently, no substantial alterations were implemented. It is worth mentioning that the visualization software utilized in this study differed from those used in previous analyses; various visualization tools are available in the field of scientometrics, such as CiteSpace or other alternatives. VOSviewer software employed in this study remains unique.

3. Visualization Algorithm and Discussion

To visualize the bibliometric and citation strengths of the scholarly articles, VOSviewer version 1.6.20 was used to show the keyword and bibliometric clusters.

VOSviewer is a specialized software designed to display citation and bibliometric networks using exported data from a major publication database such as Web of Science. The software filters and sifts through the data according to the user-specified prerequisite requirements, such as minimum citation metrics or minimum document count. It is able to accommodate the user’s restrictions and limitations.

A small breakdown of the process is as follows:

• Data input: VosViewer can accept data from different sources primarily through:

  ○

  APIs—OpenAlex, Europe PMC, Semantic Scholar, Wikidata etc.

  ○

  Bibliographic database files from websites such as Web of Science, Scopus, Lens, PubMed etc.

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  Reference manager files like RefWorks, EndNote, RIS etc.

• Citation network formation: This network forms the backbone of the bibliometric visualizations. Citation networks are created depending on the user requirement such as: authors, publication titles, keywords, countries, affiliations etc. They are identified as “nodes” or “labels” which are then interconnected with a series of lines which represents the citations between each respective node (author names, titles, keywords, countries etc.). Co-citation is also represented by the thickness of said lines (thicker lines between two nodes indicate frequent citation by other publications citing both “nodes” together).
• Bibliographic coupling: VOSviewer utilizes bibliographic coupling to arrange nodes in clusters. Based on the user’s input requirements, such as the focus on authors, countries, publication titles, or keywords, the nodes are grouped together if they share a similar or identical set of references. For instance, if two publications cite the same source, they will be bibliographically coupled, resulting in the closer proximity of their nodes in the visualization. The distance between two nodes indicates the number of shared references they possess, with a node being farther away indicating fewer shared references, and nodes closer together indicating numerous shared references.
• Thematic clustering and visualization: Combining both the citation network and bibliographic coupling, the software assigns a color scheme of differing colors to differentiate one theme from another, this color scheme can be manually overridden should the user wish to assign their own personal color schemes. Displaying the combined citation network and the bibliographic coupling as one scientometric map. The automated sizing of these nodes is conducted by the software based on their centrality or significance within the network.

The underlying algorithm of VOSviewer cannot be altered, but its working algorithm can be modified by simply adjusting the input data from the database source using different keywords. Researchers who wish to discover more about a particular author or institution can apply these keywords in Web of Science and pinpoint their area of interest, such as flash systems or photovoltaic, within the field of solar desalination. Unless their research interests extend beyond solar energy, the primary search keywords can be simply replaced with an alternative term, such as “solar desalination”, in the source database.

Given that keywords serve as the variables utilized to obtain datasets, researchers can identify themes of their interest, such as nanoparticles or plasmonic research in desalination systems. The data obtained from Web of Science is adaptable and can be customized to meet the researcher’s requirements by employing keywords or specific topics within the main area of desalination. As a result, when the keywords are modified, they consequently modify the variables.

On applying the “export” function in Web of Science in the “tab delimited file” format, all 1855 results were extracted on 10 February 2024.

3.1. Findings

Following the examination of the VOSviewer visualizations, it can be deduced that China held the highest position in terms of the number of contributions and document count, as depicted in

Table 1. The top 10 countries which have the highest influence this past decade (citation limit was set to 1970). (Data obtained from Web of Science 2024).

Rank	Country	Collective Citations	Number of Records
1	China	23,621	625
2	USA	10,903	185
3	Egypt	7906	219
4	India	6665	286
5	Saudi Arabia	5510	176
6	Iran	4633	158
7	Spain	3306	78
8	Australia	2770	71
9	United Arab Emirates	2308	38
10	England	1976	57

.

Table 1 indicates the leading countries in solar desalination research were China, the United States, and Egypt, whose prominence is demonstrated by their impressive citation metrics: 23,621, 10,903, and 7906, respectively. Notably, the United Arab Emirates, despite its lower publication count of 38, boasts a high citation metric, possibly attributable to the positive influence of their “Water Security Strategy 2036” (Alzaabi and Mezher, 2021) [28]. This comprehensive plan seeks to shift desalination methods towards sustainable sources while guaranteeing potable water quality and availability under normal and emergency circumstances.

The World Bank Group is a partnership of five institutions with 189 member countries that contribute to global data and statistics. According to the World Bank data from 2018, there were over 18,246 desalination plants operating globally (Bank, 2019) [29].

According to Table 1 and data from the International Water Association (Alegre et al., 2016) [30], there is a disparity between the distribution of desalination plants and electricity consumption for water production. Despite having a lower number of desalination plants compared to other regions, the United States leads in electricity consumption for water treatment, accounting for approximately 40% of the global total. China and the Middle East come in second and third, respectively, with electricity consumption for water treatment amounting to 15% and 9% of the global total, respectively.

It is noteworthy that China devotes a substantial portion, amounting to approximately 66.56% of its desalinated water for industrial purposes. This dedication to innovation is demonstrated through the country’s investment in research and development projects. One such endeavor is the Five-Year Program, which has been approved under the auspices of the N.K.P.D. (National Key Basic Research Program and National High-tech R&D Program), and is valued at 339.9 million CNY (Lin et al., 2021) [31]. Similarly, the Ministry of New and Renewable Energy in India launched several initiatives between 2015 and 2016 to promote advancements in solar desalination technology (India, 2015) [32]. One of these initiatives was the “Research, Design, and Development of Solar Photovoltaic Technology (SPV) and Solar Thermal Technology (ST)” program. This program aimed to promote research and development through national solar science fellowships (Chandrashekara and Yadav, 2017) [33].

Figure 1a illustrates the collaboration strength between various countries, including China, the USA, Singapore, South Korea, and others represented by the line thickness that shows the frequency with which authors from these countries have co-authored publications. Figure 1b further enhances this depiction by presenting a timeline color scheme that showcases the time period during which these collaborations occurred. Figure 1a,b indicate that China has made the most contributions and has the highest citation metric in the past decade, as demonstrated by its scale representation. Additionally, other countries such as the United States, Egypt, and India have also engaged in collaborations as shown in Figure 1a with China and other countries such as South Korea, Saudi Arabia, and Canada.

The analysis presented in

Table 2. An unbiased table depicting the respective affiliates influence and their published document count. (Data obtained from Web of Science 2024).

Rank	Affiliation	Citation Count	Number of Records
1	Tanta University	5808	116
2	Kafrelsheikh University	3355	68
3	Nanjing University	2877	15
4	Chinese Academy of Sciences	2625	53
5	Huazhong University of Science Technology	2380	33
6	MIT	2002	16
7	Islamic Azad University	1751	53
8	Plataforma Solar Almeria	1720	40
9	Georgia Institute of Technology	1608	6
10	King Fahad University of Petroleum & Minerals	1494	23

pertains to the time frame of 2010 to 2024. The data utilized for this analysis was obtained from the Web of Science Core Collection through the application of the keywords “desalination solar” with the search condition stipulating that “solar desalination” must be present in the selected papers. This refined dataset was subsequently employed to create Table 2. According to Table 2, Tanta University and Kafrelsheikh University, both located in Egypt, have demonstrated the highest citation impact among the considered universities. Specifically, Tanta University has achieved a citation impact of 5508, while Kafrelsheikh University has attained a citation impact of 3355. Nevertheless, the mere fact of having a low publication volume does not necessarily lead to a low citation impact. To illustrate this point, Nanjing University has released a limited quantity of papers, totaling 16, but their cumulative citation count is remarkably high at 2877, placing it in third position.

Figure 2 depicts the top 10 affiliations in their respective countries that have made significant contributions to the field of solar desalination, with a minimum of 1490 total citations. It is worth mentioning that Tanta University and Kafrelsheikh University are particularly prominent, with the highest publication counts among the affiliations, at 116 and 68 papers, respectively.

In order to generate the network visualization depicted in Figure 3a,b, specific search criteria were applied to the data. These criteria included the implementation of the “full counting” methodology, which accounts for all citations, as well as a minimum document strength of one and a minimum citation threshold of 1490. This threshold was established to eliminate papers with fewer citations, ensuring that only well-cited sources were included in the analysis. Figure 3a depicts international linkages between various research institutions worldwide. This includes the top 12 prominent institutions such as MIT, Nanjing University, and the Georgia Institute of Technology. Affiliations within closer proximity have published more papers together, suggesting a stronger collaborative network. For instance, the right-most cluster in Figure 3a highlights authors from Huazhong University, Kafrelsheikh University, and Tanta University who frequently co-author papers.

Figure 3b focuses on a specific timeframe (2016–2020) and uses a different color scheme to show collaborations between eight universities that have collaborated in 2019~2020 (represented by yellow). However, the color representation in Figure 3b does not directly correspond to operation in isolation, but rather to show how each affiliate embraces a collaborative approach to research. As illustrated in the line connections between each label, the thickness correlates to the frequency of co-authorship between authors of said affiliates (thicker line equates to more co-authorships).

Figure 3b reveals a shift in recent research contributions (2020 onwards) towards affiliations in the Middle East and China. This trend likely reflects growing concerns about water scarcity and the increasing demand for clean drinking water in these regions.

A prime example of an international collaboration is a 2020 review paper featuring researchers from the Advanced Membrane Technology Research Centre (Malaysia), Centre for Water Advanced Technologies and Environmental Research (CWATER, UK), and NYUAD Water Research Centre (UAE). This collaboration explored previously employed strategies for mitigating fouling in forward osmosis and membrane distillation. (Lee et al., 2020) [34].

Figure 4 indicates a substantial uptick in the number of published papers commencing in 2019, attaining its pinnacle in 2022. This rise might be attributable to a buildup of research findings being disseminated. It is possible that prioritization has diverged from the global COVID-19 pandemic, enabling papers that were earlier postponed to be sanctioned and classified. On the other hand, lockdowns might have afforded researchers the opportunity to devote greater lengths of time to data examination and manuscript completion (Karimi-Maleh H, 2022) [35].

Figure 5 is a comprehensive examination of highly cited authors within the field of solar desalination research. The analysis employs citation metrics to assess their level of influence. Among the most prominent figures are Lin Zhou, Abd Elnaby Kabeel, and Liangbing Hu. It is worth noting that the most impactful authors, such as Lin Zhou and Abd Elnaby Kabeel, have predominantly published highly cited papers since 2018. The cluster map depicts that their citations and document counts, which correspond to the number of published papers, are attributable exclusively to research on solar desalination techniques during the specified timeframe.

The line connections simply indicate how frequently these authors have collaborated with thicker lines indicating higher frequency, the size of the author labels indicate their citation metrics, so an author such as Abd Elnaby Kabeel will have a correspondingly larger label size. Finally the brackets indicate the time period with which these collaborations occurred.

Table 3. Showing the top 10 authors with the most collective citations of papers on solar derived desalination.

Author Name	Citations	Publications
Abd Elnaby Kabeel	3419	54
Lin Zhou	2826	10
Zhu Jia	2763	5
Swellam Sharshir	1876	38
Yudi Kuang	1483	5
Chaoji Chen	1461	6
Liangbing Hu	1455	7
John H. Lienhard	1237	6
Yu Guihua	1146	5
Shuaiming He	1129	5

highlights the top ten authors with the greatest number of citations for their contributions to solar desalination research. A.E. Kabeel emerges as the most prominent author. His highly acclaimed publication delved into the incorporation of advanced technologies, such as multi-layer perception and wavelet transform-based neural networks, to enhance the performance of existing solar desalination systems, particularly concentrated on solar stills (Elsheikh et al., 2019) [36]. Additionally, Lin Zhou is a notable author, having co-authored the most cited paper with over 1554 citations, which focused on the application of a plasmonic-based aluminum solar evaporator for improved desalination efficiency (Zhou et al., 2016) [37].

3.2. Implications

Table 3 includes authors who have a minimum citation count of 960 in the Web of Science database. This ensured that the designation of “top author” was relevant and accurate. It is important to note that citation metrics can vary across different databases. For example, articles may have higher citation counts in Google Scholar compared to Web of Science or Scopus (Meho and Yang, 2007) [38]. This may be due to factors such as duplicates or Google Scholar’s broader indexing practices (De Winter et al., 2014) [39]. Additionally, some articles may be misidentified by Google’s automated indexing algorithms (Martín-Martín et al., 2018) [40].

Beyond co-authorship analysis, keyword analysis is crucial for understanding research trends in the past decade. It can reveal areas of intense focus and potential research gaps that deserve future exploration.

Figure 6a unveils the existence of three notable clusters in the keyword network map. The first cluster, represented by the red colored labels which revolve around the key terms “solar” and “energy”, clearly emphasizes the central theme of solar desalination. Notably, the terms “water desalination” and “seawater desalination” are interchangeably present within this cluster. The second cluster represented by the green label grouping draws attention to the keywords associated with “solar stills”, with a focus on enhancing their performance and productivity.

Finally, the third cluster represented by the blue labelling explores novel modifications to existing desalination methodologies, focusing on enhancing steam and water generation efficiencies in systems. Each color in Figure 6a represents the interconnectedness of keywords within a cluster (i.e., how frequently these keywords co-occur in the 1855 analyzed publications) from the red, green, and blue coloring scheme.

Figure 6b displays a keyword timeline cluster map that aligns with the observed increase in publications between 2018 and 2022. This is consistent with the high frequency of certain keywords during this period. It is noteworthy that more recent publications (post-2021) demonstrate an increasing interest in integrating nanoparticles into membrane-based systems and humidification-dehumidification systems. This is evidenced by the significant rise in mentions around 2019.

Table 4. Top 10 most used keywords in recent years (2014 to 2022) from the keyword occurrence search.

Keyword	Occurrences
solar desalination	924
desalination	501
energy	425
performance	411
water	244
system	242
still	231
solar still	203
solar energy	195
seawater desalination	182

lists the top ten most frequently utilized keywords in recent years, as demonstrated by the keyword occurrence search. A thorough examination of the keywords in both Figure 6a and Table 4 indicates a pronounced emphasis on sustainable energy sources for desalination. This aligns with the prominent authors’ research focus, as depicted in Figure 6a. Moreover, keywords such as “performance” and “system” in these papers suggest a trend towards optimizing existing desalination methods.

Table 5. The word occurrences for solar methodologies from 2010 to 2024.

Solar Methodologies	Occurrences
still	231
solar still	203
nanoparticles	145
membrane	125
humidification-dehumidification	114
photovoltaic	19

demonstrates a detailed analysis of word occurrences associated with specific desalination methodologies.

Table 5 presents a compilation of keywords associated with solar desalination methodologies. Among these keywords, “still” was the most prevalent, underscoring its enduring significance in research studies. This observation concurred with the salient position of solar stills illustrated in the keyword timeline depicted in Figure 6b.

Another significant trend was the increasing use of the term “nanoparticle systems”, particularly after 2018. This suggested a growing interest in this emerging technology for desalination. In contrast, the relatively low occurrence of the keyword “photovoltaic” suggests that photovoltaic (PV) systems may require further development to effectively compete with other desalination methods.

3.3. Citation Analysis

Citation analysis is a valuable tool for evaluating the impact of research within a specific field by assessing the frequency with which a publication is cited in other scholarly works (Garfield, 1972) [41]. Although citation analysis has its limitations, it remains a powerful tool for determining research significance. Despite potential biases that may arise due to factors such as citation bias or self-citation (Easterbrook et al., 1991) [42].

The data in

Table 6. Categorization of the top 15 most cited publications.

Rank	Title	Citation	Broad Theme	Category
1	3D self-assembly of aluminum nanoparticles for plasmon-enhanced solar desalination (Zhou et al., 2016) [37]	1554	Plasmonic enhanced absorber	Modified Material Based Evaporator
2	Graphene oxide-based efficient and scalable solar desalination under one-sun with a confined 2D water path (Li et al., 2016) [43]	907	Foldable Graphene Oxide Film absorber
3	A hydrogel-based antifouling solar evaporator for highly efficient water desalination (Zhou et al., 2018) [44]	614	Hybrid hydrogel (with capillary channels), antifouling properties
4	Scaling and fouling in membrane distillation for desalination applications: A review (Warsinger et al., 2015) [45]	580	Discusses crystalline fouling, causes, prevention, and future research	Review
5	A High-Performance Self-Regenerating Solar Evaporator for Continuous Water Desalination (Kuang et al., 2019) [46]	579	Self-regenerating natural wood substrate evaporator	Modified Material-Based Evaporator
6	Nature-inspired salt resistant bimodal porous solar evaporator for efficient and stable water desalination (He et al., 2019) [47]	436	Balsa wood-based evaporator, bimodal and porous interconnected channels
7	Solar assisted sea water desalination: A review (Li et al., 2013) [48]	362	Discusses solar desalination research, suggests modifications	Review
8	Solar-driven simultaneous steam production and electricity generation from salinity (Yang et al., 2017) [49]	352	PV-Blue energy system, using carbon nanotube filter paper with commercial Nafion membrane	Hybrid System
9	A hydrophobic surface enabled salt-blocking 2D Ti3C2 MXene membrane for efficient and stable solar (Zhao et al., 2018) [50]	337	Usage of a hydrophobic Mxene membrane, covered with a Ti3C2 nanosheet	Modified Material-Based Evaporator
10	Synergistic Energy Nanoconfinement and Water Activation in Hydrogels for Efficient Solar Water Desalination (Guo et al., 2019) [51]	315	Light-absorbing sponge-like hydrogel evaporator
11	Renewable and sustainable approaches for desalination (Gude et al., 2010) [52]	313	Discusses detailed financial assessment on desalination systems	Review
12	Solar powered desalination—Technology, energy, and future outlook (Ahmed et al., 2019) [53]	311	Discusses RO hybrid systems, new advances in solar desalination
13	Nanofluids effects on the evaporation rate in a solar still equipped with a heat exchanger (Mahian et al., 2017) [54]	311	Effects of heat exchanger on solar still performance indices	Modified Solar Collector
14	Analysis and optimization of the low-temperature solar organic Rankine cycle (ORC) (Delgado-Torres and García-Rodríguez, 2010) [55]	302	Expands upon theoretical research by a solar ORC through Solar Collectors
15	Graphene oxide-based evaporator with one-dimensional water transport enabling high-efficiency solar desalination (Li et al., 2017) [56]	298	porous carbon black/graphene oxide (CB/GO) composite layer-based evaporator	Modified Material-based Evaporator

indicates that the most frequently cited work (ranked first) on the subject of solar desalination using membrane technology is a research article authored by Zhou et al. (2016). This paper investigated the viability of a self-assembled three-dimensional structure composed of aluminum nanoparticles on a porous plasmonic absorber. It also compared this method to conventional solar still systems, which are characterized by high initial costs and relatively low efficiency. Plasmonic membranes, which exhibit exceptional efficiency, have gained considerable interest in recent years. This can be attributed, in part, to the potential of noble-metal-based plasmonics in medical and other applications that use plasmonic properties. Nevertheless, aluminum-based plasmonic membranes present a promising alternative for desalination due to their unique capacity to focus incoming light into specific subwavelengths.

Plasmonic research has shown that each metal has an inherent subwavelength frequency. Notably, aluminum has a higher ultraviolet range compared to silver or gold. This characteristic translates to promising desalination effects, achieving up to four orders of magnitude improvement. The resulting desalinated water meets the potable water salinity standards set by the World Health Organization and the US Environmental Protection Agency (Zhou et al., 2016) [37]. The key to this approach lies in the 3D arrangement of the aluminum plasmonic structure. This design allows for a low-cost and scalable process, using aluminum as the sole raw material.

The study conducted by Zhou et al. (2016) has gained considerable recognition due to its innovative approach to membrane systems. Consequently, preliminary laboratory tests have validated the efficiency of this approach. Moreover, the design possesses the potential to be expanded for use in larger and more remote areas across the globe. Furthermore, aluminum’s affordability and inherent structure that facilitates automatic membrane flotation without external inputs make it a suitable modification for surface desalination systems.

The second-most cited paper, authored by Li et al. (2016) [43], offers similar findings to those of Zhou et al.‘s (2016) research but employed a graphene-based membrane instead. The authors of this study reported an estimated thermal efficiency of approximately 80% under one-sun condition. However, Zhou et al. (2016) attained considerably higher steam generation efficiencies, reaching 88.4% and 91% under four-sun and six-sun conditions, respectively.

The third most cited paper also investigated a graphene-based solar evaporator, but with a focus on fouling. Zhou et al. (2018) [44] detailed the detrimental effects of crystalline salt accumulation on the graphene membrane performance. Their experiment, conducted under one-sun irradiation without a hydrogen gel for water transport, revealed significant salt-crystal buildup after 96 h. This finding underlined the importance of antifouling strategies for graphene-based solar evaporators. In addition, Zhou et al. (2018) conducted a study to compare the evaporation rates of water samples with different salinity levels (5% to 25%). Their findings revealed that crystalline fouling became a major problem only when the salinity exceeded 20%. It is worth noting that the performance of the evaporator without the antifouling hydrogel remained comparable to the one with the hydrogel up to a salinity level of 20%.

A recent study by Kuang et al. (2019) [46] utilized a rationally designed artificial array on a natural wood substrate to fabricate a solar evaporator, resulting in an impressive energy conversion efficiency of 87.5% under one-sun illumination. This accomplishment built upon prior research by He et al., (2019) [47], who achieved similar results using a similar method. Additionally, 3D printing is a promising technique for solar desalination.

The analysis also considered non-membrane desalination techniques due to the extensive research on graphene-based and other membrane technologies. Starting from rank 13, a study by Mahian et al. (2017) [54] examined the performance of a conventional photothermal still enhanced with nanofluids. The researchers explored various combinations, including two different particle sizes of nanofluids (7 nm and 40 nm), different nanoparticle volume fractions (0.5%, 1%, and 2%), and three mass flow rates. Furthermore, simulations were conducted to mimic long-term use and considered two water depths while incorporating weather conditions.

The experimental configuration comprised two flat-plate solar collectors connected in series, a heat exchanger, and a slanted single solar still. The still was connected to a tank containing the nanofluid. The entire system was tested for a period of 24 days (approximately 3.4 weeks). The results indicated that solar irradiation intensity and ambient temperature were the two most critical environmental factors. As anticipated, higher levels of solar irradiation resulted in increased productivity. Additionally, due to the experimental design, lower ambient temperatures led to increased condensation on the slanted glass section, resulting in greater water collection. The solar still’s orientation was also considered, with a 13° placement relative to the test location’s latitude. The study’s outcomes were intriguing, as it became evident that weather conditions had a more significant impact on evaporation rates than the water based SiO₂ and Cu nanofluids. The impact of the heat exchanger was insignificant for inlet temperatures below 50 °C, while the net positive effect was observed to be at its highest at 70 °C. The study found that using nanofluids with a nanoparticle size of ~7 nm did not significantly improve the performance indices of the solar still. Mahian et al.’s (2017) experiment offers valuable insights. While it demonstrates the potential of nanofluids in solar desalination stills, it also highlights the importance of considering pretest and ambient conditions. The study suggests that simply adding heat exchangers to existing solar desalination systems may not always be beneficial, as these external factors can significantly impact performance.

The analysis of keyword clusters revealed that modified membrane-based methodologies dominate current research in solar desalination. This was evident from the rising popularity of keywords like “nanoparticles” and “salt or hydrogel capillary-abled channels”. These advancements aim to enhance the performance of solar material-based evaporators. There were two main key-points to this research: improving water flow and mitigating fouling. Nanoparticle integration and capillary channels address the first aspect by facilitating water movement through the membranes. Hydrogel channels, on the other hand, combat the issue of salt crystallization buildup, which has been a major challenge for solar evaporators.

3.4. Challenges

Solar desalination, despite its potential, faces several obstacles that impede its large-scale deployment, particularly in developing countries. This study provides an academic perspective on the current state of research in solar desalination, highlighting the trends and continued interest in this field among researchers in recent years.

Table 7. The challenges that solar derived methodologies need to address.

Challenges	Description
high startup costs	When implementing at large industrial scales, the startup costs are very high to maximize the light collected (especially solar stills) (Zheng et al., 2023, Reif and Alhalabi, 2015) [57,58]
low efficiency compared to non-solar	The need for further optimization and the energy loss from solar is high, more research and funding are needed to remediate this (Zheng et al., 2023, Reif and Alhalabi, 2015) [57,58]
massive brine disposal	The increase in desalination plants, brine generation (highly concentrated saline water) increases which is costly and has detrimental environmental effects (Jones et al., 2019) [59]
lack of cost efficiency	The high initial costs drive the payback period to become unfeasible, factoring construction and maintenance costs into account especially when compared to other non-solar derived methodologies (Reif and Alhalabi, 2015) [58]
(with regards to PV) energy storage	Systems that make use of photovoltaic cells run into the issues of inefficient storage of harnessed energy through batteries, diminishing the cost-effectives of such systems (Reif and Alhalabi, 2015) [58]
lower system operation uptime	Concentrated solar stills/Fresnel concentrators require a lot of upkeep as well as higher end materials to drive the efficiency to acceptable rates, usage of lower quality materials results in less operational uptime (Zheng et al., 2023, Reif and Alhalabi, 2015) [57,58]

outlines the major challenges currently hampering the broad adoption of solar desalination technologies.

Table 5 demonstrates that solar desalination technologies, despite their potential, necessitate additional improvement. According to Do Thi et al. (2021) [60], employing life cycle assessment (LCA), PESTLE analysis, and multi-criteria decision analysis (MCDA) can help pinpoint areas for enhancement. These methodologies offer a comprehensive and structured examination of a system’s operations, covering the initial phase (material procurement and construction), operational phase (energy consumption and water production), and recycling phase (if applicable).

3.5. Limitations

Data collection and analysis presented some difficulties. One issue that emerged was the inconsistency in citation counts when comparing data from the Web of Science Core Collection with other scientific databases (Rejeb et al., 2022) [61]. Furthermore, the keyword-based search approach concentrated primarily on scholarly articles and journals. Future scientometric research might gain from incorporating additional publication formats to increase the scope of the study.

One potential disadvantage is the concentration on publications dating from 2010 onwards. This could have resulted in the exclusion of highly influential and frequently cited works from earlier years. The reasoning behind this choice was to investigate trends in a rapidly advancing field like desalination, where more recent publications likely represent the escalating interest in renewable energy solutions. It should be emphasized that the lower citation metrics for pre-2010 publications do not necessarily indicate a lack of research validity, but rather reflect the growing emphasis on renewable technologies in recent times.

In addition, the minimum threshold of three authors per publication may have excluded relevant authors who did not meet these criteria. Lastly, while the study examined a substantial number of publications, it did not investigate the textual analysis of more recent and developing desalination technologies. This presents a potential area for future scientometric research.

4. Conclusions

The purpose of this scientometric analysis was to evaluate existing research on solar desalination and to determine potential areas for future advancement. The following are the primary results of the study:

• Leading countries in solar desalination research were China, USA, Egypt, India, and Saudi Arabia.
• Prominent research institutions according to the analysis performed in this manuscript were Tanta University, Kafrelsheikh University (Egypt), and Nanjing University (China).
• Peak research activity from 2018 to 2022 used “stills” as the most frequent keyword; the keyword occurrence was 904.
• Top cited researchers were A.E. Kabeel and Lin Zhou. Moreover, Lin Zhou had the highest cited paper on solar desalination with 1554 citations.
• The dominant research theme was modifications to material-based evaporators (graphene membranes and hydrogel channels).

Potential avenues for future research could include enhancing the energy retention efficiency of photovoltaic (PV) systems. The current low occurrence of this topic in keyword analysis suggests that there is a need for more advanced PV systems. Additionally, future research could explore the co-processes and hybrid systems that can be used to improve the current technology. While current research primarily focuses on modifying existing technology, exploring new avenues for innovation could lead to the development of novel combinations that overcome current limitations.

This scientometric analysis shed light on research trends and provided insights for future work. Our examination indicates a pronounced emphasis on membrane or surface desalination systems, accompanied by a noteworthy dearth of research on photovoltaic (PV) systems. This presents a promising opportunity for researchers, as there is a lack of highly influential PV studies, thereby offering ample room for original contributions. Researchers can embark on exploring and experimenting with PV systems or related themes without the risk of replicating existing work.

In addition, this scientometric analysis provides a significant source of inspiration. The wide-ranging themes identified, spanning from plasmonics to surface desalination, can induce innovative research ideas and direct future investigations. However, although the study considered a substantial body of publications, it did not explore the textual analysis of more recent and emerging desalination technologies. This offers a promising direction for future scientometric research.