Certification for Solar Panel Reuse: A Systematic Review of Cross-Sector Practices and Gaps

Abstract

This systematic literature review examines the development of a conceptual certification framework for solar panel reuse, positioned within the broader context of the circular economy. It emphasizes sustainable production and consumption in response to the climate crisis and resource depletion. This review was conducted using Scopus and Google Scholar, following a structured search strategy. A final set of 63 sources, including peer-reviewed journal articles, conference papers, and gray literature recommended by domain experts, were selected to analyze existing certification frameworks across various sectors, focusing on their relevance to solar panel reuse. Key aspects of product reuse such as safety, quality, and technical standards are explored, highlighting the unique challenges associated with the long lifespans and environmental exposure of solar panels. Through this analysis, this study reveals the core elements vital for an effective certification framework. While structured certification frameworks are essential for sustainability, empirical evidence on their effectiveness in the solar panel reuse remains scarce, and regulatory inconsistencies add complexity. Using established practices in electronics, batteries, and other high-liability sectors as an anchor, the proposed framework, emerging from this systematic review, aims to extend solar panels’ lifecycle, contributing to environmental sustainability and socio-economic equity. The findings provide valuable insights for policymakers, industry stakeholders, and researchers by addressing key certification gaps and identifying future research directions in solar panel reuse standardization.

1. Introduction

In the modern era, the surge in economic growth has been paralleled by an increase in production and consumption, especially in developed nations [1]. This growth often leads to overconsumption, stretching beyond basic necessities, thereby contributing to significant resource depletion and the generation of unsustainable waste [2]. To address these critical issues, the concept of a circular economy has gained prominence as a viable solution [3]. The circular economy represents a significant departure from the traditional linear economic model. It emphasizes a transformative approach to managing products throughout their lifecycle, aiming to prolong product life and minimize waste. This approach is seen as key to a sustainable future, with secondary markets playing a vital role in this regard [4]. The circular economy framework advocates for environmentally friendly practices, prioritizing reuse and recycling over traditional disposal methods like incineration and landfill [5,6].

Circular economy concepts have become central in political and corporate discourse, driven by growing concerns about resource scarcity and the environmental impact of resource wastage [7,8]. It encourages sustainable production and consumption, fostering economic growth, socio-economic equality, and environmental protection [9].

Transitioning from the linear to a circular model that emphasizes the “4Rs” (Reduce, Reuse, Recycle, and Recover) across the product lifecycle is crucial. According to Russell (2018), the Basel Convention (2016), and the International Resource Panel (IRP, 2018), there are four critical operations for extending product life: direct reuse, repair, refurbishment, and remanufacturing [10]. These processes are instrumental in achieving the intended end-of-life (EOL) criteria for products, thereby aiding resource conservation and environmental sustainability. The term “re-use” has been variably defined in the literature, but the EU Waste Framework Directive (2008/98/EC) categorizes it as operations wherein products or components not classified as waste are used again for their original purpose. This includes product repair, refurbishment, and remanufacturing, all of which are often environmentally preferable to material recycling and new product manufacturing due to resource savings, reduced global warming potential, and the safer handling of toxic materials [11]. A key aspect of sustainable waste management and resource conservation is the categorization of reuse strategies. The Center of Remanufacturing and Reuse (CRR) proposes a comprehensive classification encompassing nine EOL strategies: remanufacturing, reconditioning/refurbishing, reuse, repurposing, repair, recycling, composting, incineration, and landfill [12]. This categorization offers an understanding of diverse reuse strategies across different stages of the product lifecycle. The critical role of repair, reuse, and remanufacture in sustainable waste management and resource conservation is widely recognized [13,14]. While classifications of reuse options may vary, the focus here is on refurbishment, repair, and remanufacturing as key components of reuse.

The waste hierarchy triangle outlines several waste management options, ranging from disposal to reuse (See Figure 1). Moving upwards on the triangle indicates an environmentally friendly option. While both reuse and recycling have a smaller negative environmental impact than incineration and landfill, in terms of environmental benefits, reuse is widely seen as a better alternative than recycling [5,6]. Recycling, although beneficial, emits more emissions due to the energy necessary to break down and process the materials [15]. Reusing solar panels can help to further cut emissions by prolonging their lifespan and lowering the need for new manufacturing.

The International Renewable Energy Agency (IRENA) projected a cumulative PV waste of 1.7 to 8 million tonnes by 2050, raising urgent concerns for sustainable end-of-life management of solar technologies. Despite this growing issue, reuse remains significantly underrepresented in both the academic literature and practice, with the majority of end-of-life (EOL) studies focusing on recycling pathways. Implementing product reuse certification frameworks is increasingly important, promoting standardized and responsible reuse practices [16]. These frameworks guide businesses and consumers, ensuring informed decisions regarding second-hand products. Within this broader context, it is insightful to compare the reuse practices in the solar panel sector with those in other established sectors such as electronics, batteries, and mobile phones. These sectors have integrated reuse, refurbishment, and remanufacturing as part of their circular approach, offering valuable insights into the extension of product lifespans and the conservation of resources. However, the application of these practices to solar panels presents unique challenges and opportunities. Solar panels, with their longer operational lifespans and specific environmental exposure, demand a more tailored approach to effective reuse (i.e., ensuring technical performance, enabling market adoption, meeting regulatory expectations, and advancing environmental sustainability) [16]. This gap raises critical questions: Despite the potential for significant waste reduction and lifespan extension through reusing photovoltaic modules [17], why are standardized reuse practices not yet prevalent in the solar panel sector? What barriers exist, and how can they be overcome? To address this research gap, we conduct a systematic review to answer the following research question.

Research Question (RQ)—What are the key elements required for an effective certification framework for solar panel reuse?

Most of the current research and systematic literature studies on end-of-life (EOL) solar panels have focused on recycling and its environmental consequences. While these findings are helpful, there is already a large body of research on recycling pathways [18,19,20]. Solar panel reuse has received very limited attention despite the fact that it offers major environmental and financial benefits. This review focuses primarily on reuse, with the goal of filling the research gap identified above and adding new insights to the circular economy discourse around the reuse of photovoltaic modules.

This systematic literature review significantly contributes to the field of sustainable energy practices by developing a comprehensive understanding of the need for and structure of a certification framework for solar panel reuse. This study’s exploration into the key aspects of product reuse—including safety, quality, and technical standards—provides valuable insights into creating a robust certification framework. SLR is an essential method as it provides a comprehensive and unbiased overview of the current state of research, helping to identify gaps, understand the diversity of methodologies and findings, and inform future work in the field of solar panel reuse and certification [21]. This paper’s findings pave the way for the development of standardized reuse practices in the solar panel sector.

This systematic literature review aims to explore the benefits and challenges of product reuse certification, drawing on insights from existing frameworks across relevant sectors. The objective is to inform the development of a certification framework for the reuse of solar panels. This review will identify key components and criteria in existing certification frameworks, assess challenges and best practices in product reuse certification, and propose a tailored framework for solar panels.

2. Methodology

Systematic literature reviews (SLRs) are essential to synthesizing and evaluating existing research, especially in fields as dynamic and rapidly evolving as solar panel reuse and certification [22]. An SLR provides a comprehensive, unbiased overview of the current state of knowledge, ensuring that conclusions are drawn from a broad and representative sample of the relevant literature [23]. This approach is particularly crucial in the context of solar panels, where technological advancements, environmental considerations, and regulatory frameworks are constantly changing. The SLR is crucial for this study as it provides a comprehensive understanding of the emerging field of solar panel reuse certification. By systematically analyzing diverse research, the SLR helps to identify gaps in current research, understand the diversity of methodologies and findings in the field, and offer a consolidated foundation for future research, policy-making, and practical applications [24,25]. This rigorous methodology not only enhances the reliability and credibility [26] of our findings but also paves the way for evidence-based advancements in the reuse and certification of solar panels.

We conducted a systematic literature review to enable a reliable assessment of key components and criteria for product reuse. This approach ensures that the assessment is grounded in a wide array of the scientific literature, offering a robust and holistic view that is essential for developing effective and sustainable reuse strategies in line with the latest technological and regulatory developments. Following the methodology outlined by Petticrew and Roberts (2008) [26], our review was structured into six detailed steps to ensure a comprehensive analysis. Initially, we identified specific keywords and search terms relevant to solar panel reuse and certification frameworks. This was followed by the development of targeted search strings, using these keywords for an extensive literature search. Next, we listed articles that met our predefined inclusion and exclusion criteria. We conducted keyword searches in databases like Scopus and Google Scholar covering publications in fields pertinent to reuse certification and the circular economy. The rationale for selecting these databases was to encompass a comprehensive range of the relevant literature. The fourth step involved a thorough quality assessment of these articles, ensuring their relevance and credibility.

To ensure the quality and reliability of the sources included in this systematic review, a rigorous quality assessment process was applied. We selected peer-reviewed articles and conference papers. All journal articles were in reputed Scimago Q1/ranked A* or A in the Australian Business Dean Council (ABDC) list. All conference papers were peer reviewed. In addition to these peer-reviewed articles, a limited number of gray literature sources from credible sources (such as government reports) were included based on their relevance and credibility. We used domain experts to assess the quality of these sources. We excluded unpublished academic theses, working papers, and other non-peer-reviewed materials such as tutorials and posters from the review. Each article included in the final dataset met at least one of these criteria, thereby ensuring a robust baseline for methodological and conceptual credibility.

Subsequently, we analyzed the evidence within these articles, particularly focusing on key aspects of product reuse and the necessary certifications. The final step of our review process was to synthesize this information into coherent themes that aligned with our research objectives. Throughout this process, a three-person expert panel, consisting of one industry expert specializing in the circular economy and solar panel technology, and two from the business sustainability field, provided valuable insights at every stage, thus enhancing the depth and applicability of our review. The literature was scrutinized in a systematic way, following the Preferred Reporting Items for Systematic Reviews and meta-Analyses (PRISMA) guidelines [27]. The following section provides the details that guided the selection of our research material.

2.1. Search String Development

The development of the search string was a critical component of our systematic literature review, designed to comprehensively capture the phenomena under investigation—product reuse and certification frameworks for solar panels. We conducted a series of pilot searches to refine the keywords, using a trial-and-error approach. This process involved eliminating terms that did not contribute additional relevant papers to our search results. After numerous iterations, we established the following search string, divided into three parts, which we used to search within the keywords, title, abstract, and full text of the publications:

Part I (“solar panel” OR “photovoltaic” OR “PV panel” OR “solar module” OR “solar cell”) focused on identifying the literature related to solar energy technologies and advancements, through the search string AND Part II (“reuse” OR “recycling” OR “refurbish” OR “remanufacture” OR “second life” OR “circular economy” OR “sustainability”) addresses the concept of reuse, including various associated terms that encapsulate activities and principles related to product reuse, as well as broader concepts like circular economy and sustainability.

AND Part III (“certification” OR “standardisation” OR “quality assurance” OR “safety standard” OR “environmental impact” OR “performance assessment”) was centered around certification and standardization, where we incorporate terms related to the process of certifying reused products. This includes quality assurance, safety standards, and performance assessments, recognizing that certification often entails a comprehensive evaluation of various product aspects.

The combination of these three parts ensures a thorough and targeted search, capturing the complex interplay between reuse and certification. This comprehensive approach, refined through our pilot searches, allows us to include a wide range of relevant studies, ensuring the robustness, quality, and depth of our literature review.

2.2. Inclusion and Exclusion Criteria

The process of selecting primary studies was anchored on well-defined inclusion and exclusion criteria (see

Table 1. Inclusion and exclusion criteria.

Criteria Type	Criteria Description
Inclusion
Focus	Peer-reviewed studies related to reuse, recycling, refurbishment, or certification of second-hand electronic products.
Content	Studies offering valuable information, artifacts, or techniques essential for certification.
Publication Type	To ensure rigor, peer-reviewed articles and conference papers were selected. In addition to peer-reviewed articles, a limited number of gray literature sources from credible sources (such as government reports) were included based on their relevance and credibility.
Language	Publications in English.
Time Frame	No restriction on publication date to ensure comprehensive coverage.
Exclusion
Relevance	Studies not directly related to the reuse and certification of second-hand electronic products.
Publication Type	Working papers, PhD theses, non-peer-reviewed materials like books, tutorials, and poster publications.

). For inclusion, we focused on peer-reviewed studies that directly related to the reuse and certification of second-hand electronic products, especially those offering valuable information, artifacts, or techniques considered essential for certification. We concentrated our efforts on publications written in English to maintain consistency and clarity in our review. The literature search was conducted without a specified time period. This approach was taken to ensure a comprehensive collection of studies, capturing the entire spectrum of research on this topic, regardless of the publication date. In addition to these peer-reviewed articles, a limited number of gray literature sources were included based on their relevance and credibility, as recommended by domain experts. The earliest relevant studies began appearing in 1997, with a noticeable increase in publications peaking around 2021 (see Figure 2). The search concluded in March 2025.

On the exclusion front, we filtered out publications that did not align with our research objectives. This included working papers, and PhD theses, along with non-peer-reviewed books, tutorials, and poster publications.

2.3. Study Selection Strategy

In our pursuit to comprehensively review the literature on product reuse and certification frameworks, we developed a meticulous and rigorous study selection strategy. This involved conducting searches to encompass a broad spectrum of peer-reviewed studies. Our primary focus was on research that delves into the reuse, recycling, refurbishment, or certification of second-hand electronic products. This review systematically includes both empirical and theoretical papers to provide a comprehensive understanding of the subject. This dual approach ensures a holistic view, encompassing both practical experiences and theoretical advancements, thereby enriching the depth and breadth of our analysis.

We targeted peer-reviewed journals and conference proceedings for their credibility and relevance. After identifying relevant studies, we extracted data focusing on certification criteria, benefits, challenges, and best practices in product reuse. This data was then systematically analyzed to identify common themes and divergences in the existing literature. The search in Scopus and Google Scholar led to the identification of 212 entries. To supplement this dataset, 10 additional records were included through cross-referencing [28], and 7 gray literature sources were added based on expert recommendations. A total of 193 articles remained after excluding duplicates. To ensure a wide information base, scientific articles published in peer-reviewed journals, industry reports, conference papers, and gray literature were included for the screening step. This selection was based on the high standards of peer review and credibility, ensuring reliance on high-quality scientific research. Thus, 50 articles were excluded and the remaining 143 articles were screened by reading the title and the abstract. Articles not fitting the objective of this research were excluded. The eligibility criteria were defined as follows: only studies addressing components under the reuse umbrella concept and subsequent certification and standardization process were included. A final set of 63 papers have been considered for this analysis (Refer to Appendix A). Figure 3 elaborates the systematic review PRISMA flow diagram. (See details in Supplementary Materials).

3. Findings

Our systematic review analyzed 63 articles that met the inclusion and exclusion criteria, each contributing to a comprehensive understanding of solar panel reuse and certification. The key themes that emerged from this extensive analysis included the principles and practices of reuse certification in sectors such as electronics and automotive, approaches to safety and quality assurance, and the challenges of adapting these frameworks to solar panels. This comparative analysis highlights the nuances of implementing a robust certification system in the solar panel sector, informed by models from other industries.

3.1. Key Components and Criteria for Product Reuse

In the context of sustainability and environmental responsibility, product reuse emerges as an efficient strategy, encapsulating the ethos of “cradle to cradle”. This approach involves making informed decisions about whether to reuse, refurbish, remanufacture, or dispose of products based on their age and condition [29,30]. The burgeoning importance of the second-hand and used product market has led to a significant increase in academic research, especially focusing on end-of-life (EOL) policies. However, despite the extensive literature on EOL policies, there is a noticeable dearth of studies on standardized certification policies for second-hand items. To address concerns about the reliability and safety of products at the end of their first life cycle, manufacturers and dealers are increasingly offering warranties as a form of assurance. This practice underscores the growing importance of warranty in the used product market as a tool for signaling quality and reliability [31,32,33].

The cornerstone of product reuse lies in establishing stringent conditions for safety acceptance and approval. These conditions are broadly categorized into three key areas: (1) quality management, (2) safety management, and (3) functional and technical safety [34]. Ensuring compliance with these conditions is crucial for the successful reuse of products. In the specific context of refurbished products, the adoption of robust certification frameworks is essential for guaranteeing their safety, performance, and sustainability [35]. Prominent among these frameworks are those provided by UL Solutions, BSI, and Intertek. These organizations offer comprehensive guidelines and standards that play a pivotal role in building consumer trust and supporting the circular economy. UL Solutions, for instance, adheres to the 2020 National Electrical Code [36]. Their process involves the removal of original listing marks from refurbished equipment and replacing them with a rebuilt equipment listing mark from an approved Nationally Recognized Testing Laboratory. This rigorous certification process ensures that refurbished products meet the same standards as new products, encompassing extensive testing and inspection to validate the refurbishing process, materials used, and manufacturing suitability.

Similarly, the British Standards Institution (BSI) offers the Kitemark for remanufactured and reconditioned products. This certification scheme, based on the BS 8887 series of standards and the principles of ISO 9001 [37], verifies the processes of remanufacturers and reconditioners, ensuring adherence to best practices within the circular economy. The Kitemark is instrumental in reducing carbon emissions, optimizing material usage, and enhancing global market sustainability.

Intertek’s ETL Refurbishment Program, aligning with the U.S. National Electric Code, NFPA 70—2020, mandates that reconditioned or refurbished products which previously received ETL certification must undergo reassessment and recertification. This is to ensure adherence to all applicable safety standards, thus allowing these products to bear the ETL Listed Mark for refurbished products. The program emphasizes quick market access for refurbished products while ensuring compliance with global regulatory standards.

These certification frameworks highlight the critical importance of safety, reliability, and environmental sustainability in the refurbishment sector. Adherence to these rigorous standards enables manufacturers and refurbishers to not only build consumer trust but also significantly contribute to the sustainability goals of the circular economy [38,39]. Complementing these industry-specific standards are various regulations issued for each safety-critical domain, which are essential in the development, implementation, validation, and maintenance of safety-critical systems. These include standards such as AS/NZS 5377, IEC 61508 [40], ISO 26262 [41], and EN 50126 [42] which cover a range of industries from automotive to medical equipment and ensure safety and reliability across industries [43,44]. Understanding the similarities and differences among these standards is vital for informed decisions regarding reuse. However, the pursuit of a “common language” for safety across these diverse domains remains a distant goal. Insights from sectors like electronics, automotive, and battery reuse offer valuable templates for solar panel repurposing. In particular, recent EU policy initiatives targeting extended producer responsibility and digital product passports for electronics and EV batteries [45,46] illustrate the feasibility of embedding traceability and quality assurance in circular supply chains. These strategies can be adapted to the solar domain, where fragmented data on panel performance, ownership, and degradation remains a barrier to reuse. Introducing standardized data protocols and lifecycle transparency, as implemented in battery safety standards such as UL 1974 and IEC 62933-5-3 [47], can help align stakeholder confidence with market readiness for second-life PV modules. Currently, it is crucial to have a clear understanding of the similarities and differences among these standards to inform decisions regarding reuse [48]. A comprehensive analysis of these standards is necessary to address their differences and similarities.

3.2. Certification for Refurbished Electronics

The certification landscape for refurbished electronics, especially smartphones, shows a lack of clear, universally accepted standards. While some guidelines offer direction, they do not establish comprehensive standards for refurbishment [49]. While guidelines such as UL 110 [50] and the Electronic Product Environmental Assessment Tool (EPEAT) offer some direction for making products more suitable for refurbishment, they fall short of establishing comprehensive standards for the refurbishment [51]. The R2 electronics recycling standard, a voluntary scheme, attempts to bridge some of these gaps. It encompasses responsible recycling and reuse of electronics, mandating R2-certified companies to employ effective test methods, uphold quality assurance, and maintain product return plans, ensuring that the electronics are fit for resale [52]. Despite its influence, the R2 standard focuses more on the broader spectrum of electronic waste management rather than the detailed intricacies of refurbishing specific product categories.

In Europe, the landscape is different, with a focus on consumer protection laws like Directive 1999/44/EC mandating a minimum one-year warranty for refurbished smartphones [53]. However, these laws do not specify the processes for refurbishment, leaving a gap in standardization. The UK’s standards for the reuse of waste electrical and electronic equipment (WEEE) provide a more detailed approach, covering safety, testing, disassembly, repair, replacement, cleaning, and quality assurance [54]. Yet, these standards primarily address items within the waste stream and do not extend to the broader market of refurbished electronics. The refurbishment processes for used smartphones are notably diverse, reflecting the standards and capabilities of the refurbishing organizations. Original Equipment Manufacturers (OEMs) often claim to conduct a ‘rigorous’ refurbishment process using specialized equipment and replacement parts designed specifically for their devices [55,56]. The typical refurbishment process usually starts with the physical cleaning of the device, data reset, and basic functional tests [57].

The safety and reliability of battery systems, particularly in the context of their second-life applications, such as in electric vehicles (EVs) and stationary storage systems, are paramount. Designing these systems, even with new cells, is a complex engineering challenge [58]. Therefore, manufacturers are highly motivated to design battery systems that are both safe and reliable, incorporating rigorous safety tests as a standard part of the development process. A key aspect of this process is managing the risks associated with an unregulated second-life battery market. To ensure the success of second-life applications, regulations and testing standards need to be developed and continually updated. For example, UL 1974 is a standard that covers the evaluation of used battery safety and performance. It refers to the same standards used for systems built with new battery cells and components for the certification of the second-life battery system itself. The tests recommended under UL 1974 include the following: Measurement of Open Circuit Voltage (OCV); Insulation Test for High Input Voltage; Capacity Test; and Measurement of Internal Resistance [59]. Another relevant standard is IEC 62933-5-3. However, it remains unclear how these testing standards could be adapted to cover battery systems built from used battery components, particularly considering the varying quality of used batteries and their impact on testing representability.

This varied landscape of refurbishment processes and standards creates a significant challenge for consumers trying to gauge the quality and reliability of refurbished products. Without clear guidelines from regulatory bodies, resolving safety and reliability issues becomes a complex endeavor. The lack of standardization and transparency in these processes not only affects consumer trust but also impacts the sustainability goals of the circular economy. It highlights the need for more specific guidelines and frameworks in the industry that can ensure consistency in the quality and reliability of refurbished products.

The optimal utilization of used batteries for second-life applications relies on precise diagnostics and the integration of Battery Management Systems (BMSs) [60]. The process begins with a thorough physical examination to assess the battery’s integrity and identify any significant damage, with severely damaged batteries being recycled or disposed of [61]. This is followed by the estimation and validation of the State of Health (SOH), using key performance indicators like capacity and power capabilities [62,63,64]. Batteries failing these assessments are either repurposed for less demanding applications or disposed of [62]. Advanced methods such as Coulomb Counting and Electrochemical Impedance Spectroscopy, supplemented by simulation tools, help in accurately gauging the battery’s performance [65]. After initial selection and transport, batteries with an SOH above 80% are typically reused as spare parts in electric vehicles, while those with an SOH between 80% and 64% find applications in less demanding roles like renewable energy firming or power supply systems [62]. Batteries below this range are dismantled for further use [62]. This comprehensive approach not only ensures the safe and efficient reuse of batteries but also supports their integration into a circular economy, offering both environmental and economic benefits [66].

3.3. Proposing a Reuse Framework for Solar Panels

Based on the systematic literature review, we propose a conceptual reuse framework for solar panels. The proposed conceptual reuse and certification framework for solar panels draws inspiration from the methodologies used for batteries, and involves several key steps, each critical to ensuring their viability and safety for second-life applications. We elaborate the specific stages below and depict the framework in Figure 4. Such a reuse and certification process should preferably be legislated as part of a product stewardship scheme for solar panels to provide stakeholders a strong context for such a legislated reuse and certification process [67].

As the first step, a thorough physical examination of used solar panels is essential. This step is akin to the battery repurposing process and involves checking for any physical damages like cracks, delamination, or degradation [68]. This inspection is crucial to assess the integrity of the panels and to identify potential safety hazards. Panels exhibiting significant damage are typically not suitable for repurposing and are instead directed towards recycling or safe disposal in compliance with local environmental regulations.

In the second step, following the physical assessment, the State of Health (SOH) of the solar panels is analyzed. This is a critical step where various performance metrics, such as efficiency, maximum power output, and the condition of the photovoltaic cells, are evaluated [69]. The SOH provides a clear picture of the panel’s current performance level compared to its original state [70,71]. Panels that fail to meet the required performance criteria are either recycled or considered for applications where lower performance is acceptable.

The third step involves electrical and performance testing. This is integral to the certification process [72]. These tests, including measures of open-circuit voltage, short-circuit current, and maximum power point, provide detailed insights into the panel’s operational capabilities. Advanced techniques, like Electroluminescence (EL) imaging, play a pivotal role in detecting internal defects, such as micro-cracks, that are not visible externally [73]. In parallel, simulation tools and predictive analysis are employed to forecast the future performance of the solar panels. These simulations, leveraging both physics-based and data-driven models, enable a reliable prediction of panel longevity and efficiency in various potential applications. This predictive approach is vital in deciding the suitability of panels for different second-life applications.

Studies have proposed structured frameworks for determining the reusability of decommissioned PV panels, incorporating various testing methodologies [74]. Many studies suggest different methods to test reusability, including visual inspection, insulation resistance tests, IV curve analysis, and EL imaging (see

Table 2. Criteria for determining the reusability of PV panels.

Reference	Number of Panels Tested	Panel Age (Years)	Tests Conducted	Reusability Percentage
Marinna et al., 2025 [74]	76	22	Visual inspection, Insulation testing, IV tests, EL imaging	68%
Rabanal-Arabac, 2023 [75]	1000	-	Visual inspection, IV tests, EL, IR imaging	30–34%
Stromberg, 2021 [76]	221	2–20	Visual inspection, IV tests, Thermal imaging	64%
Skoczek et al., 2009 [77]	204	19–23	Visual inspection, IV tests, Thermal imaging	65%

).

The fourth step involved in repurposing solar panels is the certification and standardization process. Just as with batteries, repurposed solar panels must meet certain industry standards to ensure they are safe and reliable for use [78]. By establishing structured acceptance and rejection criteria, this framework reduces inconsistencies in panel assessment and provides a scalable solution for the secondary PV market. This certification process builds consumer trust and is crucial for the broader acceptance and integration of repurposed solar panels into the market.

The potential applications for this framework for the reuse of solar panels are diverse. High SOH panels can be effectively utilized in environments like residential rooftops, off-grid setups, or as components of hybrid renewable systems. Panels with moderate SOH might find their place in community solar projects or for educational purposes, where maximum efficiency is not the primary concern. Recent research on second-life solar panel classification aligns with this framework [71,79,80]. Under this classification framework, modules in Second Life Class A (78% + efficiency) were said to be suitable for high-performance applications, while those in Class B (below 78%) were assigned to less demanding uses. Additionally, this classification system minimizes mismatched power losses in series configurations, thereby maximizing the overall efficiency of repurposed PV systems.

Advancements in traceability can assist in making this framework more reliable. The automotive sector offers transferable lessons for traceability and reuse certification. Systems like the International Dismantling Information System (IDIS) and the International Material Data System (IMDS), developed in response to the EU EoL Vehicle Directive, enable detailed tracking of component materials and support informed decisions during dismantling [81]. Using these as an anchor, a similar digital passport system could be conceptualized for solar panels, enabling access to lifecycle data, performance records, and environmental history. This traceability mechanism would significantly support thr certification, resale, and safe repurposing of decommissioned modules, as also explored in recent proposals for digital product passports in the electronics and battery sectors.

The economic and environmental aspects of the repurposing process are paramount. It is important to weigh the costs associated with the collection, transportation, testing, and certification of these panels against the benefits. Additionally, the environmental impact of repurposing should be assessed against the production of new panels to ensure a net positive environmental benefit.

At the same time, several operational barriers must be addressed to make such a certification framework feasible. These include the high cost of diagnostic testing, the lack of infrastructure for testing and certification and uncertainty around consumer acceptance of graded second-hand panels. Moreover, integrating reuse certification with existing recycling programs may present coordination challenges. Recognizing and addressing these practical hurdles is critical to translating the proposed framework into a workable solution.

By embracing a structured approach to solar panel repurposing, similar to that used for batteries, the renewable energy sector can significantly extend the lifecycle of these resources, contributing to a more sustainable, efficient, and circular economy.

To consolidate insights across reuse sectors,

Table 3. Comparative matrix of certification elements across reuse sectors.

Certification Element	Electronics (Smartphones)	Batteries	Automotive (EoL Vehicles/Parts)	Solar Panels (Proposed)
Physical Inspection	Visual, cosmetic, and damage inspection (e.g., EN 50614:2020) [82]	External/internal inspection for damage, corrosion, leakage (UL 1974)	Mechanical and structural checks during dismantling (ARA guidelines)	Cracks, delamination, and discoloration checks
State of Health (SoH)	Limited device-level testing; ~80% battery health threshold common	Capacity, internal resistance, performance metrics (≥70–80% threshold in UL 1974)	Functional testing of major components (e.g., engines, pressure, emissions)	Power output retention; typically, ≥70–90% of original efficiency
Performance Testing	Electrical safety, functionality and system integrity testing (EN 50614, PAT+)	Load, insulation resistance and dielectric withstand testing (UL 1974)	Functional safety and system-level performance verification (ARA, PAS 777) [83]	Flash test (IV curve), electroluminescence imaging, insulation checks (per IEC 61215/61730) [84]
Traceability Systems	Unique identifiers, refurbishment logs, and serial tracking (EN 50614 compliance)	Full lifecycle records; upcoming EU Digital Battery Passport	VIN-based tracking and dismantler records (e.g., IDIS/IMDS in EU)	QR-code/blockchain based history logs proposed (e.g., EU Digital Product Passport pilot)
Warranty and Consumer Assurance	Typically 90-day to 1-year warranty; 90-day minimum recommended (EN 50614)	Limited warranty (~1–5 years); based on risk assessments	30–90 day parts warranty; longer for critical components (ARA Gold Seal)	Proposed class-based assurance
Classification Framework	Functional and cosmetic grading (e.g., “full function” vs. “key functions” per R2)	Class A/B based on capacity and degradation metrics (UL 1974)	Typically tagged as remanufactured or refurbished (ARA Damage Codes)	Proposed: Gold, Silver, Bronze based on SOH
Certification Standards	EN 50614:2020, R2 Standard, ANSI/NRTL certifications	ANSI/CAN UL 1974, EU Battery Regulation (2023/1542)	ARA Gold Seal certification	No unified standard

summarizes certification practices for reused products in sectors such as electronics, batteries, and automotive. This comparative matrix highlights cross-industry approaches to testing, classification, traceability, and assurance, providing a transferable foundation for shaping solar panel reuse certification frameworks.

4. Discussion

The lack of comprehensive legislation and guidelines governing solar panel reuse and recycling in many regions complicates efforts to establish structured certification frameworks. While various legislative frameworks and guidelines exist for solar panel waste management, they differ significantly across regions, with some countries leading in structured regulations and others still in the early developmental stages. The European Union (EU) has taken significant steps with the Waste Electrical and Electronic Equipment (WEEE) Directive, which mandates recycling and sets standards for the responsible disposal of solar panels [85,86]. The EU’s framework ensures the collection and processing of end-of-life (EoL) solar panels, which has encouraged the growth of specialized recycling and reuse programs [87]. This directive serves as a model for other regions looking to establish structured guidelines for solar panel lifecycle management. The absence of clear Extended Producer Responsibility (EPR) policies in some countries limits incentives for manufacturers to invest in sustainable recycling and reuse strategies. Australia lacks a nationwide solar panel recycling directive, with states like Victoria leading localized initiatives to prevent solar panel waste from entering landfills [48]. These regulatory gaps highlight the critical need for policy studies that examine how frameworks can be optimized to support both the adoption of reuse standards and incentivize innovation in this sector [88].

By highlighting these limitations and gaps, our review contributes to the field by not only synthesizing the existing body of knowledge but also by pointing out under-explored areas that could significantly advance understanding and practices in solar panel reuse certification. It lays the groundwork for future research endeavors that are more aligned with the evolving technological, economic, and policy landscapes, thereby pushing the boundaries of current knowledge and contributing to more sustainable and effective reuse practices in the solar energy sector.

4.1. Challenges and Best Practices Associated with Product Reuse Certification

The certification of refurbished electronic products, particularly batteries and mobile phones, is a complex process that involves various challenges. Consumer acceptance of refurbished products is influenced by their perceived quality, safety, and environmental impact, with concerns over the quality and safety of these products presenting significant hurdles in reintroducing refurbished devices into the market [89,90]. A stable regulatory framework is crucial for supporting product reuse efforts and clear policies are necessary to ensure widespread adoption and proper end-of-life management [91]. Additionally, the competition between product recovery methods, such as remanufacturing and refurbishing, raises strategic and operational considerations for original equipment manufacturers (OEMs), including pricing strategies and incentive alignment [92]. The refurbishment process itself presents challenges related to contamination, detailed investigations, and innovative risk management models [92]. Some studies suggest that existing PV panels do not currently reflect circular design considerations, and further investigation into PV panel design can make them more durable and repairable [93]. Furthermore, the reuse of Battery Management Systems (BMSs) in second-life applications faces challenges of limited transparency in BMS software and algorithms, as well as the lack of open standards in BMS integration [58].

International policy developments such as the European Commission’s proposed “battery passport”, which aims to create an electronic record for individual batteries to track their characteristics and history, provide an interesting model for solar panel certification [94]. Corporate partnerships and collaborations are highlighted as potential solutions to integration challenges [94]. Moreover, the willingness of consumers to pay for eco-certified refurbished products and the development of green marketing strategies are essential in promoting acceptance [95]. Balancing the allocation of consumer returns between warranty claims and the remarketing of refurbished products is a complex challenge for OEMs [96]. The challenges and best practices associated with the certification of refurbished electronic products require a comprehensive approach that encompasses consumer preferences, quality and safety assurance, environmental considerations, innovative marketing strategies, and collaborative efforts in technology integration [97].

4.2. Implications

As the global emphasis on renewable energy intensifies, the solar panel industry faces a crucial challenge in managing the lifecycle of these products. Certification of used solar panels is not just about extending their operational life but also about ensuring they meet stringent safety and performance standards akin to new panels. This study’s exploration of certifying used solar panels yields several critical implications, each interlinked and vital for advancing sustainable energy solutions.

First, this study has implications for environmental sustainability. It underscores the importance of extending the operational life of solar panels through a certification process. This process not only promises a reduction in waste and a decrease in the environmental impact associated with the manufacturing and disposal of new panels but also aligns with the larger goals of a circular economy [21,98].

Second, this study offers implications for market development and consumer trust. By ensuring that used solar panels meet stringent safety and performance standards akin to new panels, certification can instill confidence in consumers [99]. This confidence is crucial for the development of a secondary market for these products, enhancing their broader acceptance and integration into various applications, from residential installations to community projects.

Third, this study highlights the implications for policy and regulatory frameworks. The success of certifying used solar panels heavily depends on the establishment of industry-wide standards and protocols, which are essential for ensuring the safety, quality, and market acceptance of these panels. In particular, regulatory bodies may consider introducing minimum State of Health (SOH) criteria to determine a panel’s eligibility for reuse, ensuring consistency and safety across second-hand products. This calls for a coordinated approach involving policy and regulatory bodies, industry stakeholders, and technical experts to address the unique challenges of assessing the fitness for reuse of these panels, which are subjected to varied environmental stresses over extended lifespans. The integration of digital product passports (DPPs) can further enhance traceability by capturing a panel’s lifecycle data—from manufacturing and usage history to testing outcomes—thereby supporting informed decisions about reuse. Additionally, reuse targets could be included in Extended Producer Responsibility (EPR) schemes to ensure that manufacturers and importers are accountable for taking back used panels and finding safe ways to reuse them. The influence of policy development on sustainable practices in renewable energy sectors, including solar panels, cannot be understated [100].

Recent industry initiatives further illustrate the feasibility of implementing such certification and reuse strategies. For example, the TRUST-PV project, funded under the EU Horizon 2020 program, deployed a data-driven Decision Support System (DSS) across operational PV plants to detect and replace underperforming modules while evaluating the reuse potential of removed panels. This allowed selective revamping while minimizing waste. Likewise, a Belgian case study presented at EU PVSEC 2023 showcased an applied reuse framework integrating electrical safety testing, performance analytics, and digital tracking to repurpose decommissioned PV panels [45]. The approach demonstrated how digital infrastructure, such as module-level traceability could support second-life certification practices. These developments closely align with the reuse framework proposed in this study, reinforcing both its technical and regulatory relevance.

In summary, while certifying used solar panels presents an opportunity to advance sustainable energy solutions, it necessitates a multifaceted approach that considers technical, economic, and regulatory dimensions. Addressing these challenges effectively is essential for paving the way towards a more sustainable and economically viable solar energy ecosystem.

4.3. Limitations

This systematic review, while comprehensive in its approach, does encounter certain limitations that must be acknowledged for a complete understanding of its scope and implications.

Firstly, the review’s exclusive focus on English-language literature may omit valuable insights present in non-English publications, especially from regions with advanced solar panel technologies or unique environmental policies. Secondly, including only the peer-reviewed journal articles, conference proceedings, and the gray literature excludes a variety of other relevant literature types, such as white papers, which may often contain practical applications, policy discussions, and recent innovations not yet captured in academic journals.

Moreover, the primary focus on second-hand electronic products may not fully encompass the unique aspects and challenges specific to solar panel reuse and certification. This is particularly relevant considering the distinct characteristics of solar panels, such as longer lifespans and different environmental exposures. Lastly, this review indicates a need for a more in-depth exploration of how policy frameworks can be optimized to support the adoption of reuse standards and incentivize innovation in the sector.

In addition, the current research landscape in solar panel reuse certification exhibits several notable limitations which open avenues for further investigation. Firstly, there is a pronounced gap in empirical studies that rigorously evaluate the long-term effectiveness and practical challenges of implementing certification frameworks [16,101]. This limitation underscores the need for more robust, real-world assessments that can provide concrete data on the performance, durability, and market acceptance of reused solar panels. Additionally, the literature largely overlooks the nuanced interplay between technological advancements and certification standards [35]. Rapid developments in solar panel technology often outpace the establishment of corresponding standards, creating a lag that can hinder the adoption of reuse practices [48].

These limitations highlight crucial areas for future research and emphasize the importance of interpreting the review’s findings within its defined scope, underscoring the need for a more comprehensive understanding of the field in subsequent studies.

5. Conclusions

The literature review highlights that while recycling has traditionally received more attention, reuse sits higher on the waste hierarchy and deserves greater focus in advancing a circular economy. By examining certification practices in sectors like electronics, batteries, and automotive, this study identifies key elements needed for a reliable solar panel reuse framework—such as physical inspections, performance testing, state of health assessments, and systems for tracking and documentation.

Solar panels present unique challenges due to their long lifespans, environmental exposure, and limited traceability. While practices from other sectors offer valuable foundations, they need to be carefully adapted to suit the specific conditions of solar panel reuse. This makes it essential to develop a tailored framework that combines cross-sector insights with solar-specific testing and certification methods.

However, it is important to acknowledge that this framework is conceptual in nature and based on the existing literature, with no empirical validation yet due to the limited availability of sector-specific studies.

A well-designed certification system can help address these challenges. It can boost trust in second-life solar products, support new market opportunities, and reduce environmental waste. For policymakers, this means introducing standards and regulations that support reuse. For businesses, it offers a chance to recover value from used panels. And for researchers and certifiers, it points to the need for better tools and systems to test and track solar panel performance over time.

The review provides a foundation for developing a certification framework that addresses safety performance and environmental impact assessment. By shifting our attention to reuse we can move more effectively toward environmental sustainability and circular economy goals.