Photo redox flow batteries as a promising pathway to sustainable energy storage: Case studies of Morocco and Poland

Economics, Management and Sustainability journal home page: https://jems.sciview.net Boutouil, M., Boulika, H., Chiki, Z., El Amrani El Idrissi, N., Bilan, Y., Idrissi Kandri, N., & Hazm, J. E. (2025). Photo‑redox flow batteries as a promising pathway to sustainable energy storage: Case studies of Morocco and Poland. Economics, Management and Sustainability, 10(2), 6-25. doi:10.14254/jems.2025.10-2.1. ISSN 2520-6303 Corresponding author: Mohammed Boutouil E-mail: [email protected] This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.0 license. ‹ 6 › Scientific Platform Photo‑redox flow batteries as a promising pathway to sustainable energy storage: Case studies of Morocco and Poland Mohammed Boutouil *,** , Hamza Boulika * , Zineb Chiki * , Najiba El Amrani El Idrissi * , Yuriy Bilan *** , Noureddine Idrissi Kandri * , Jamal Eddine Hazm ** * Signals, Systems and Components Laboratory (LSSC), Faculty of Sciences and Techniques, Sidi Mohamed Ben Abdellah University, Fez, Morocco [email protected] ** Processes, Materials and Environment Laboratory (LPME), Faculty of Sciences and Technology, Sidi Mohamed Ben Abdellah University, Fez, Morocco *** Centre of Sociological Research (CSR), Szczecin, Poland Abstract: Purpose. The paper examines how photoredox flow batteries can support a sustainable energy transition in Morocco and Poland by simultaneously harvesting and storing solar energy, thereby reducing dependence on fossil fuels and mitigating the intermittency of renewables. Methodology. The study combines a review of national energy policies and renewable energy targets with a comparative techno-economic assessment of photo-redox flow battery deployment scenarios in both countries, focusing on system performance, grid integration, and long-term sustainability indicators. Results. The findings show that photo-redox flow batteries can significantly increase the share of solar energy in national power mixes, improve grid stability, and lower lifecycle emissions compared to conventional storage and fossil-based generation, with particularly strong gains under high-renewables scenarios for Morocco and coal-replacement pathways for Poland. Theoretical contribution. The paper extends the emerging literature on next-generation energy storage by conceptualizing photo-redox flow batteries as a dual harvest–store technology and by linking their deployment to macro-level energy security, decarbonization, and resilience outcomes in middle-income and coal-dependent economies. Practical implications. The results provide policymakers and energy planners with evidenceArticle history: Received: April 23, 2025 1st Revision: August 29, 2025 Accepted: November 16, 2025 JEL classification: Q41 Q43 C22 C32 O55 DOI: 10.14254/jems.2025.102.1 ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 7 › based guidance on integrating photo-redox flow batteries into national energy strategies, including indicative design parameters, investment priorities, and regulatory measures to accelerate clean energy deployment while managing economic and geopolitical risks. Keywords: Photo-Redox Flow Batteries (PRFBs), Morocco, Poland, renewable energy, energy storage, solar energy, sustainable energy storage Sustainable Development Goals (SDGs): SDG 7: Affordable and Clean Energy; SDG 9: Industry, Innovation and Infrastructure; SDG 13: Climate Action 1. Introduction The gradual expansion of global energy demand, driven by population growth, industrialization, transport electrification and the development of digital infrastructures is putting considerable pressure on nations to find more sustainable ways to produce and recover energy (Rezk et al., 2023; Zemlickienė et al., 2024; El Boutalbi et al., 2024; Amraouet al., 2024; Redouani et al., 2024; Talbi et al., 2025; Sebbaghi et al., 2025; Piccinetti et al., 2025; Taib et al., 2025; Rezk et al., 2025; Smaliukienė & Katina, 2025; Chiki et al., 2025; Vestertė et al., 2025). Global energy demand rose by around 2.2% in 2024, while electricity consumption jumped by around 4.3% over the same period, notably due to increased use in industry, cooling, and digital services. Traditionally, dependence on fossil fuels cannot meet this growing demand indefinitely without exacerbating climate change, pollution, and resource depletion. Countries are therefore turning to renewable energies such as solar, wind, and hydro power, which offer more environmentally friendly solutions to meet growing demand. Nevertheless, the intermittent nature of these renewable sources poses a significant challenge, without efficient energy recovery and storage systems to compensate for imbalances between supply and demand, much of the clean energy produced could remain unused or destabilize the power grid (Bethany, 2025). In this context, photo-redox flow batteries (PRFBs) appear to be a promising technology for large-scale energy storage. Unlike conventional batteries, PRFBs integrate light capture directly into the redox flow system, enabling them to both capture solar energy and store it in liquid electrolytes. This dual functionality reduces the need for separate photovoltaic panels and recharging infrastructure, while improving energy conversion efficiency and sustainability (Chen et al., 2018). In addition, PRFBs easily adapt to grid requirements without compromising performance, enabling the direct conversion of solar energy into stored electrical energy. These devices offer a compelling solution to address the intermittency of renewable energy sources and support the transition to cleaner energy systems. Morocco, with its abundant solar potential, and Poland, facing the challenge of an energy transition in line with European decarbonization targets, could find PRFB solutions tailored to their national energy strategies. By examining the fundamental principles, recent advances, and potential applications of this emerging technology, this article highlights how PRFBs can help make global energy systems more resilient and sustainable. 2. Morocco 2.1. Morocco’s historical energy composition Morocco’s energy sector has historically been heavily dependant on imported fossil fuels, particularly coal, oil, and natural gas, due to the scarcity of domestic hydrocarbon resources. Imports cover more than 90% of the country’s energy needs, making Morocco one of the most energy-importdependent countries in the MENA region. According to the national energy balance in Figure 1, oil accounts for approximately 51%, coal for 38% and renewable energies for just 8.8% of total primary energy supply (Benbba et al., 2024). This composition underscores Morocco’s longstanding reliance on fossil fuels for electricity generation, particularly coal-fired power plants. This heavy dependence has made Morocco vulnerable to global price volatility and substantial import costs, which negatively affect the national trade balance (Benbba et al., 2024). Beyond financial constraints, the energy portfolio, dominated by fossil fuels, is responsible for significant ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 8 › greenhouse gas emissions, with the electricity sector accounting for approximately 45% of total CO2 output (Benbba et al., 2024). Moreover, the rapid expansion of industrial and residential electricity demand, which is expected to increase by around 5% annually since 2004, has exacerbated these issues (Sakhraoui et al., 2024). Figure 1: Breakdown of primary energy demand in 2022 (a), Overall energy consumption in Morocco during 2022 (b) Source: Bennouna, 2023 The geopolitical risks associated with fossil-fuel imports were clearly illustrated by the closure of the Maghreb-Europe gas pipeline in 2021, which interrupted natural gas deliveries and forced Morocco to turn to more expensive liquefied natural gas imports (Benbba et al., 2024). As a result, the current energy mix raises pressing concerns regarding energy security, economic fragility, and environmental sustainability. These limitations have prompted Morocco to reassess its energy strategy and accelerate the transition to renewable sources (El Hafdaoui et al., 2025a; Laaroussi & Bouayad, 2020). 2.2. Morocco’s strategy for energy transition and the central role of solar energy Faced with growing energy needs and its dependence on fossil fuel imports, Morocco adopted a comprehensive national energy strategy in 2009 aimed at reshaping its electricity sector to ensure its sustainability. This strategy is based on four pillars: energy security through diversified supply, affordable access, environmental protection through renewable energy, and regional cooperation. This plan established key institutions, such as MASEN (2010), ONEE, and AMEE, to manage renewable energy initiatives and regulations (Benbba et al., 2024). The targets include an installed renewable energy capacity of 42% by 2020, 52% by 2030, and 70% by 2040, in line with the Paris Agreement goals (Amegroud, 2015.) Solar energy is driving this change, exploiting Morocco’s primary resources: an average GHI of 5.8 kWh m-2. day-1 and DNI of 1800–3000 kWh m-2. Year-1 in areas like Ouarzazate and Errachidi (Benbba et al., 2024). The Noor program (Figure 2) illustrates this with the Ouarzazate complex between 2016 and 2018, providing 580 MW of energy from Concentrated Solar Power (CSP) and solar Photovoltaic (PV), thereby reducing CO2 emissions by 760,000 tons per year. Expansion projects include Noor Midelt (800 MW hybrid) and decentralized PV initiatives such as Noor Atlas. Supporting measures encompass PROMOSOL and SHEMSI for solar water heating, as well as more than 10.000 PV irrigation pumps to reduce fuel consumption in rural areas (El Hafdaoui et al., 2025b). The Green Hydrogen Strategy targets 8 GW of new renewable energy by 2030, using solar electrolysis to produce clean fuels. Challenges remain, including concentrated solar power (CSP) costs, limited local PV production, grid inflexibility, storage needs, regulatory barriers, and financing gaps (Amegroud, n.d.). Solutions include supporting local industry, advancing storage technologies such as photo-redox flow batteries, and improving connections to the European grid. In 2023, renewables exceeded 41% of capacity, proving that emerging markets can drive transformation through policy, institutions, and vision. ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 9 › Figure 2: Geographic distribution of major solar power projects in Morocco, including the NOOR and ONEE initiatives Source: Masen, 2020 3. Poland 3.1. Historical energy mix of Poland The Polish energy sector has long been dominated by coal and lignite, highlighting its heavy dependence on local fossil fuels. Under Soviet rule, particularly from the 1970s to the 1990s, the country built a highly carbon-intensive energy infrastructure, resulting in extensive environmental damage and inefficient consumption patterns. This period was characterized by high energy intensity, minimal hydrocarbon utilization, and a pricing mechanism that encouraged wastefulness by decoupling energy costs from economic logic. Coal has played a pivotal role in safeguarding Poland’s energy security and, despite its declining dominance, remains a key component of the energy mix. Over the years, repeated attempts to restructure the coal mining sector have fallen short of expectations (Kotelska, 2025) primarily due to the entrenched perception of coal’s vital importance to national security, as well as the influential power of mining unions, whose views have historically been and continue to be taken into account by every Polish government. Coal-fired power plants were the core of the electricity grid, a configuration that persisted into the 2000s with scant modernization. Despite joining the EU in 2004, coal remained the dominant fuel, comprising 42.6% of electricity production in 2020 (Figure 3) and positioning Poland among the most coal-reliant nations in Europe. Faced with growing economic, environmental, political, and legal pressures, especially from the European Union, Poland began a concrete shift away from coal around 2019, as the sustainability of its carbon-intensive energy model came under intense scrutiny. Economically, rising extraction costs, depleting reserves, and the rising viability of imported fuels and renewables have eroded coal’s dominance in electricity generation. Environmentally, growing concerns about air pollution, CO2 emissions estimated to be 316.41 (Kt.) in 2020 (Mrozowska et al., 2021), and health impacts have accelerated the fight against the use of fossil fuels. Politically and legally, European Union instruments such as the Emissions Trading System and the European Green Deal have imposed penalties for exceeding emissions. In 2018, with coal still accounting for 73.6% of electricity production, its lack of economic viability became apparent, prompting reforms in favor of renewable energies (Zupančič et al., 2018). ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 10 › Figure 3: Poland’s electricity generation breakdown (%) in 2022 Source: Czepło & Borowski, 2024 3.2. Poland’s strategy for energy transition and the central role of solar energy Poland’s energy transition strategy, as detailed in the Polish Energy Policy until 2040 (PEP2040), prioritizes a phased exit from coal dependence in favor of diversified, low-carbon alternatives, positioning solar energy as a cornerstone of this shift. This plan targets slashing coal’s share of electricity from over 70% to less than 11% by 2040, in line with EU climate mandates and national sustainable development goals. Solar PV has gained prominence for its scalability, speed of installation, and lower costs, making it suitable for decentralized and prosumer models. Initiatives such as the (My Electricity) (Mój Prąd) program and net metering have accelerated its adoption, particularly in households, propelling Poland to become one of the fastest-growing solar sectors in Central Europe. Although solar resources are modest compared to those in southern Europe, they are sufficient for large-scale deployment, especially in rural areas and former mining regions undergoing ecological revitalization. By emphasizing decentralized solar energy alongside grid upgrades and EU funding, the strategy highlights its contributions to energy autonomy, technological progress, and regional economic renewal, thereby consolidating solar energy’s role as a catalyst for a resilient, diversified, and sustainable energy landscape (Dębicka et al., 2024). 4. Basics of redox flow batteries (RFBs) 4.1. Components and working principle Over the past few decades, electrochemical energy storage (EES) devices have emerged as key technologies for large-scale integration of renewable energy into the power grid (Luo et al., 2015). Redox flow batteries (RFBs) are electrochemical energy storage devices that store energy in liquid electrolytes containing redox-active species. Unlike conventional solid-state batteries, in which energy is confined to the electrodes, RFBs separate power and energy (Z. Huang, Xiao, et al., 2025). This system is built around three key components (Figure 4.a): the cell, the electrolytic system, and the battery management system. These components work in synergy to ensure efficient energy storage and release. The cell is the central component of RFBs, where the electrochemical reactions that enable the mutual conversion between electrical and chemical energy occur. Charging and discharging cycles are achieved by electron transfer in the external circuit and by ion migration in the electrolyte. Typically, a battery comprises several individual cells connected in series or parallel. The structural components of a single cell include the ion exchange membrane, which separates positive and negative electrolytes while facilitating ion conduction, as well as electrodes, electrode frames, seals, bipolar plates, current collectors, insulating plates, connecting plates, and nuts (Figure 4.b). Among these elements, electrodes often use porous carbon-based materials that provide the reaction interface and catalyze the redox reactions of the active substances (Jiang et al., 2023; Y. Liu et al., 2025; Loghavi & Zarei-Jelyani, 2023). ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 11 › Figure 4: Schematic representation of a redox flow battery, operating principle with electrolyte circulation and redox reactions (a), 3D view of the cell components (b) The proton exchange membrane (PEM) is another key component of the RFB. It regulates the transport of ions between the two half-cells while ensuring the chemical separation of the electrolytes (Figure 5). Its primary function is to allow H+ protons to pass between the two electrolyte compartments, maintaining charge balance during redox reactions at the electrodes. At the same time, it prevents the passage of active redox species between the anolyte and catholyte solutions, which would lead to contamination, capacity loss, and self-discharge (Leba Akman et al., 2025). The electrolytic system mainly comprises electrolyte storage tanks, pumps, and piping. It is one of the most essential components of a deep-cycle battery (RFB), as its energy storage capacity and electrochemical performance are directly linked to it. In a conventional RFB, two electrolytes, commonly referred to as catholyte and anolyte, are stored in separate tanks and circulate through the electrochemical cell during operation. These solutions contain redox-active species that undergo reversible oxidation and reduction reactions at the electrodes, enabling conversion between electrical and chemical energy (Leba Akman et al., 2025). Consider the example of vanadium RFB, whose tanks store V3+/V2+ and V5+/V4+ solutions, a common choice for commercial purposes for years (Ulaganathan et al., 2016; Voropay et al., 2024). This popularity stems from the fact that the transfer of redox-active species between half-cells does not permanently reduce cell capacity, as vanadium ions can return to their initial oxidation state during recharging. Figure 5: Role and impact of the proton-exchange membrane in redox flow batteries Source: (Machado et al., 2021) During charging, electrical energy is applied to the cell, causing vanadium ions to be oxidized from a lower to a higher oxidation state. On the positive side, V4+ (VO2+) is oxidized to V⁵⁺ (VO2⁺), while on the negative side, V3+ is reduced to V2+. This process is facilitated by ion exchange across the membrane, which selectively allows H⁺ ions to pass, thereby maintaining charge neutrality throughout the system. Conversely, during discharge, the chemical reactions are reversed: VO2+ is ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 12 › reduced back to VO2+, and V2+ is oxidized to V3+, releasing the stored energy as electrical energy (Cheng et al., 2025; Guarnieri et al., 2025a; Marahatta, 2025; Zou & Jung, 2025). The following equations (1,2,3,4,5, and 6) describe the reactions taking place at the electrodes (Bandpey et al., 2025; Guang et al., 2025, 2025) : • Charge direction Anode Cathode • Discharge direction Anode Cathode 4.2. RFBs vs Lithium-ion, Sodium-ion and Solid-State Batteries 4.2.1. Chemistry and charge storage mechanisms As shown in Figure 6, RFBs store energy in liquid solutions containing redox-active chemicals. These liquids are pumped through electrochemical cells when the battery is in use, allowing the amount of stored energy and the power delivered to be controlled independently. On the other hand, traditional Lithium-ion (Li-ion) and Sodium-ion (Na-ion) batteries work quite differently. They are closed systems in which ions move in and out of solid electrode materials, such as lithium cobalt oxide (LiCoO2) or sodium iron phosphate (NaFePO4) (Abraham, 2020; Wenhua et al., n.d.). In these batteries, energy capacity and power output are closely linked as both depend on the properties of the solid electrodes. Solid-state batteries (SSBs) take a different approach by replacing the liquid electrolyte with a solid ionic conductor (Lou et al., 2021). This design can support higher voltages and improve safety, but it also introduces challenges, such as interface resistance and more complex manufacturing processes. Thus, while RFBs rely on redox reactions in fluid electrolytes, Li-ion and SSBs depend on the ion intercalation into solid lattices, leading to fundamentally different performance characteristics. ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 13 › Figure 6: Comparative schematic illustrating the chemistry and design of various battery types, including redox flow, sodium-ion, lithium-ion, and all-solid-state batteries including, RFBs (a), Na-ion (b), solid-state battery (c) and Li-ion (d) Source: Dang et al., 2024; Naseer et al., 2025 4.2.2. Energy storage technologies Energy efficiency is a key metric for evaluating an energy storage system, indicating how much of the stored energy can be used without waste. Alongside this, the system’s rated power and capacity are two essential specifications: rated power indicates the maximum power output during discharge, while capacity tells you the total amount of energy it can hold, and both directly influence how the system fits into real-world applications. For a fixed rated power, the discharge duration, essentially how long the system can keep delivering that power, reveals the scale of its energy capacity. The duration and rated power of various ESTs are shown in Table 1. Beyond specification factors like safety, the availability of the resources needed for construction, and environmental footprint, economic feasibility also plays a significant role in shaping the future of ESTs. Table 1 provides a sideby-side comparison of different electrochemical EST across all these aspects, providing a clear and complete view of their unique characteristics and overall potential for growth and adoption. Table 1: Comparative summary of key performance parameters and characteristics of different Energy storages Battery type RFB Li-ion Na-ion Solid-state Resource abundance Medium Low High Low Environmental impact High Medium High Low Safety High Medium High High Lifetime (cycles) 12000 to 18000 1000 to 5000 2000 to 4000 5000 to 10000 Power rating (MW) 1 to 200 0 to 100 0 to 50 0.3 to 1.2 Energy density (Wh/kg) 10 to 35 75 to 200 50 to 150 250 to 400 Duration (hours) 0 to 4 0 to 4 0 to 4 1 to 5 Source: Famprikis et al., 2019; Li et al., 2018; Mahlia et al., 2014; Rad et al., 2020; Schöne et al., 2022; Wali et al., 2024; Zhang et al., 2018; Zhao et al., 2020 ISSN 2520-6303 Economics, Management and Sustainability, 10(2), 2025 ‹ 14 › 4.3. Limitations of RFBs 4.3.1. Low energy density A key drawback of Redox Flow Batteries is their relatively low energy density, which is comparable to that of Li-ion batteries or even solid-state batteries. This issue stems mainly from the limited solubility of redox-active materials in the electrolyte and the modest cell voltage (1.26 V) in standard configurations such as VRFBs (Q. Huang et al., 2025). Researchers are working on improvements, such as incorporating mixed-acid electrolytes, non-aqueous solvents, or organic redox pairs, that could increase energy density. However, these approaches often entail trade-offs, such as higher viscosity, reduced chemical stability, and heightened safety risks (Yu & Manthiram, 2022). 4.3.2. Ion crossover and electrolyte imbalance One ongoing challenge for RFBs is the crossover of ions through the selective membrane, leading to electrolyte imbalance, gradual capacity loss, and reduced efficiency over extended use. In VRFBs, for instance, V2+ and V5+ ions may migrate across the membrane, mixing into the wrong compartments and upsetting the redox balance (Kyeongmin et al., 2019). Even with advancements in materials like Nafion and hydrocarbon-based membranes, it’s tough to strike the perfect balance among high ionic conductivity, long-term chemical stability, and adequate selectivity for vanadium ions. This ion crossover not only erodes the battery’s capacity but also triggers pH changes and unwanted electrolyte precipitation, requiring regular rebalancing and maintenance. While innovative solutions such as specialized membrane coatings and optimized flow designs are emerging, they tend to add layers of complexity and raise overall costs (W.-F. Liu et al., 2023). 4.3.3. Kinetic limits and efficiency losses RFBs frequently face slow redox reaction kinetics on electrode surfaces, resulting in lower voltage efficiency, typically 70 to 85% compared to Li-ion batteries, which exceed 90%. The reaction speeds for vanadium-based couples, especially the V3+/V2+ pair, are hindered by electron transfer barriers and limitations in mass transport (Pan et al., 2026). Additionally, during charging, hydrogen evolution reactions (HER) can occur at the negative electrode, depleting active materials and worsening overall performance (Guarnieri et al., 2025b). Applying catalytic enhancements to graphite felt electrodes, such as the incorporation of dopants like cobalt or nickel, has improved kinetics. These modifications often introduce greater complexity and higher costs. As a result, refining electrode architecture, surface properties, and flow field configurations continues to be a critical focus for research aimed at minimizing these kinetic drawbacks. 4.3.4. Electrolyte instability and thermal sensitivity Another key constraint in RFBs is the chemical instability of the electrolyte, especially the vanadium species in sulfuric acid environments. With prolonged operation or temperature variations, V5+ tends to form precipitates like V2O5, which lowers the concentration of usable vanadium and diminishes the overall capacity of the system (Zou & Jung, 2025). To mitigate this degradation, the electrolyte must be kept within a tight temperature range of 10 to 40°C, which increases the energy demands for cooling or heating systems. Moreover, undesirable side reactions, such as oxygen evolution and electrolyte breakdown at high charge levels, further restrict the battery’s usable range. Emerging solutions like mixed-acid blends and stabilizing additives have enhanced solubility, yet they often lead to higher viscosity and increased corrosion risks (Naseer et al., 2025). 4.3.5. System integration and operational complexity RFBs require careful oversight of fluid dynamics, temperature control and electrolyte equilibrium resulting in more intricate system management than solid-state alternatives. 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