Economic and Environmental Analysis of Photovoltaic-Thermal Systems Integrated with Shea Butter as a Phase Change Material in Nigeria

Nigeria’s dependence on fossil fuels for energy poses environmental challenges, notably in the form of greenhouse gas (GHG) emissions. Additionally, rural regions experience electricity shortages due to excessive reliance on the national grid. By 2023, the share of the Nigerian population with access to electricity was 61.2% (World Bank Group, 2023) [1]. The adoption of renewable energy sources, such as solar power, has the potential to decentralise Nigeria’s electricity supply, mitigate GHG emissions, and enhance electricity access in underserved rural communities [2,3,4]. Consequently, an economic and environmental evaluation of the photovoltaic-thermal system integrated with a phase change material (PV-T/PCM) utilising shea butter as the PCM will provide valuable insights into the feasibility of deploying this technology in remote Nigerian communities.

The United States Department of Energy targets an unsubsidised levelised cost of energy (LCOE) of USD 0.02 per kilowatt-hour for residential solar photovoltaic (PV) projects by 2030 [5]. The cost of electrical and thermal energy within a specific region influences the economic viability of the PV-T/PCM system [6]. Regions with high solar radiation are more conducive to implementing PV-T/PCM systems; however, local energy tariffs exert a greater influence on system feasibility than abundant solar radiation [3]. Subsidies also constitute a key factor affecting the viability of this technology; heavily subsidised butane gas boilers or energy prices can diminish the economic appeal of PV-T/PCM systems. This issue represents one of the primary obstacles to the widespread adoption of this technology [7].

Sub-Saharan Africa is renowned for its high, sustained solar radiation levels, which can raise the temperatures of photovoltaic (PV) cells. According to the World Sunshine Map, Africa receives more annual hours of sunshine than any other continent. Extended exposure to sunlight on the PV panels increases the surface temperature of the PV cells. This temperature increase reduces the panels’ electrical efficiency: a 10 °C rise results in approximately a 5% reduction in PV system performance [8]. Previous studies have examined the energetic, economic, and environmental performance of PV-T and PV-T/PCM systems under different climatic and operating conditions. In general, the integration of thermal recovery and PCM-based temperature regulation can increase total energy utilisation, reduce PV-cell temperatures, and improve carbon-mitigation performance relative to standalone PV systems. Nevertheless, reported economic outcomes vary substantially with system design, climate, energy prices, discount rates, and the method used to value the recovered thermal energy.

For example, Odeh and Aden [9] estimated a payback period of approximately 6–7 years for a residential PV-T hot-water system in Sydney and found that the combined system performed more favourably than separately installed PV and solar hot-water systems. Maatallah et al. [10] reported an approximately six-year payback period for a water-based PV-T/PCM system, together with an 11.26% reduction in payback time and an approximately 27% improvement in lifecycle conversion efficiency relative to a conventional PV system. Comparable payback periods were reported for the PV-T/PCM configurations investigated by Babu et al. [11] and Zheng and Zhou [12], with the latter study reporting CO₂ mitigation of 104.1 kg/m².

Other investigations have demonstrated that the economic benefit of PCM integration is not uniform. Soliman [13] found that PCM cooling reduced the energy cost of a bifacial PV system under different project lifetimes and interest rates. Emam et al. [14] reported a payback period of 1.58 years and higher annual carbon-emission reductions for a water-based PV-T/PCM system than for a conventional PV system. Hossain et al. [15] similarly concluded that a two-sided serpentine-flow PV-T/PCM configuration was economically more attractive than a standalone PV system. In contrast, Asefi et al. [16] found that although a porous-PCM/PV-T system generated the highest annual power output and had a lower LCOE, its additional output did not fully compensate for its higher investment cost; the reported discounted payback period was 16 years, compared with 5 years for the reference PV system.

The principal characteristics and findings of these systems are compared in Table 1. The comparison demonstrates that the literature is dominated by conventional or unspecified PCMs and by studies conducted outside Sub-Saharan Africa. Moreover, most environmental evaluations quantify avoided operational CO₂ emissions but do not examine the cradle-to-gate impacts associated with producing the PCM itself.

Despite the high and sustained solar resource available across Sub-Saharan Africa, comparatively few studies have assessed the economic performance of PV-T/PCM systems under the region’s climatic, tariff, and financing conditions. Adun et al. [17] investigated a residential PV-T application in Sub-Saharan Africa and reported an LCOE range of US$0.252–0.384/kWh. However, that study did not evaluate PCM integration or compare locally available bio-based storage materials with fossil-derived PCMs. More broadly, the available literature provides limited evidence on the application of bio-based PCMs in PV-T systems and does not establish whether a locally available material such as shea butter can offer simultaneous economic and environmental advantages over paraffin wax.

Accordingly, this study numerically models a 3.0 kWp residential PV-T/PCM system in TRNSYS under Nigerian climatic conditions and compares shea butter with paraffin wax as the thermal-storage material. The novelty of the work lies in integrating: (i) a locally available bio-based PCM into a PV-T configuration; (ii) a Nigerian economic assessment incorporating local capital costs, electricity tariffs, financing conditions, and sensitivity scenarios; and (iii) a cradle-to-gate environmental comparison covering global warming, acidification, and eutrophication potentials. The results are intended to clarify the technical, economic, and environmental feasibility of adopting shea-butter-based PV-T systems in Nigeria and other Sub-Saharan African settings.

Unlike earlier PV-T/PCM studies, this work evaluates a locally available bio-based PCM under Nigerian climatic and financial conditions and directly compares its system-level economics and cradle-to-gate environmental impacts with those of conventional paraffin wax.

An economic analysis has been conducted regarding the installation of a PV-T/PCM system designed to supply electricity and hot water to households in sub-Saharan Africa. Oyedepo et al. (2019) [18] indicated that the electricity demand for a typical Nigerian household in a rural area is 0.986 kWh/day, whereas an urban household’s demand is 3.77 kWh/day. Elinwa et al. (2021) [19] reported electrical energy consumption for hot water use in Nigeria across a studio, a three-bedroom, and a four-bedroom residence as 2.01 kWh/day and 57.6 L/day, 2.77 kWh/day and 79.2 L/day, and 3.52 kWh/day and 100.8 L/day, respectively. Furthermore, the lighting (LED lamp) power consumption was recorded as 133.33 W, 183.33 W, and 233.33 W for the studio, three-bedroom, and four-bedroom residences, respectively. The unit power consumption of electrical equipment was established at 240 W, 330 W, and 420 W for the studio, three-bedroom, and four-bedroom residences, respectively.

Economic analysis is imperative for evaluating the feasibility, cost-effectiveness, and financial viability of implementing a PV-T/PCM system. When deploying such a system within a rural community in sub-Saharan Africa to provide electricity and hot water to households, it is crucial to undertake a thorough economic assessment. This process encompasses several essential stages, including:

A nominal PV capacity of 3.0 kWp was selected as a representative residential design case consisting of ten 300 Wp modules. The capacity was not derived from a cost-minimising or load-matching optimisation; therefore, it is a fixed capacity evaluated in the TRNSYS model. The system was assessed against an urban household electrical demand of 3.77 kWh/day and a three-bedroom hot-water demand of 2.77 kWh/day. The additional PV capacity provides energy for battery charging, system losses, variations in solar availability, flexible loads, and possible future load growth.

The system produces 12.65 kWh/day of electricity and 34.33 kWh/day of thermal energy. After satisfying the adopted daily demands of 3.77 kWh of electricity and 2.77 kWh of hot-water energy, the nominal surpluses are 8.88 kWh/day of electricity and 31.56 kWh/day of thermal energy. These values represent energy balances at the modelled system boundary and do not necessarily represent saleable energy.

The electrical surplus may be used to charge a battery, supply flexible daytime loads, support neighbouring or community loads, or, where technically and legally permitted, be exported through a grid-compliant inverter and bidirectional meter. If no load, storage, or approved export connection is available, the inverter must curtail PV generation.

Nigeria’s 2026 net-billing framework permits eligible customers to export surplus renewable electricity to a distribution network in exchange for bill credits. However, the present 3 kWp household installation is below the regulation’s 50 kWp minimum eligibility threshold. Grid-export revenue is therefore excluded from the individual-household base case and is considered only as a conditional scenario involving aggregation or a larger community installation [20,21]. Figure 1 depicts a schematic of the PV-T/PCM system integrated with a household.

All component prices were initially estimated in Nigerian Naira (₦) and subsequently converted to US Dollars ($) to conform with international standards. The applicable exchange rate was 1 US$ = ₦1500.999, as reported by the Central Bank of Nigeria (CBN) as of 12 September 2025 [22].

The cost of a solar PV system varies depending on factors such as the manufacturer, capacity, components, and installation procedures. Quotes for PV panels and accessories were obtained from Vexiums Innovations Technology Ltd. (Abuja, Nigeria), a local distributor in Nigeria, in the year 2025. Furthermore, prices for thermal system components were collected from various online marketplaces in Nigeria, including Jumia, Jiji, Frankem, and Me3energy [23,24].

Therefore, the total CapEx for the PV-T/PCM system is US$8194.96.

Annual maintenance, encompassing panel cleaning, routine inspections, and minor repairs, accounts for approximately 2% of Capital Expenditures, according to the assumed data.

Therefore, the yearly maintenance (OpEx) costs 2% of US$8194.96, amounting to US$163.89 annually.

The system produced an average of 12.65 kWh per day, totaling 4617.24 kWh annually.

According to the Minister of Power, Adebayo Adelabu (2025), Nigeria’s electricity prices are ₦209 per kilowatt-hour (US$0.139/kWh) for Band A households and businesses. Meanwhile, private generation costs are ₦915 per kilowatt-hour (US$0.61) for diesel engines and ₦750 per kilowatt-hour (US$0.5) for petrol engines [26].

Hence, the yearly savings amount to US$643.33 from grid power and US$2816.52 from diesel generation.

If a household needs 2.77 kWh of thermal energy daily for hot water and the system generates 34.33 kWh each day, the yearly total reaches 12,531.84 kWh. As a result, the annual savings on grid hot water amount to US$1741.9. In comparison, using a diesel engine yields annual savings of US$7644.42.

The unit price for hot water in Nigeria was not specified; instead, the electricity price served as a proxy.

Therefore, the total annual energy savings for the grid amount to US$2385.23.

The surplus of electrical energy remaining after satisfying the daily load demand was quantified at 8.88 kWh per day, totaling 3241.2 kWh annually. Revenues derived from the sale of this excess energy to the grid are estimated to amount to US$451.61 per annum.

The total annual benefit includes electricity savings and revenue from the sale of excess electricity, excluding thermal energy sales. Consequently, the overall annual benefit attributable to the electrical sector amounts to US$2836.84.

The financial analysis was performed assuming a 20-year project duration and a 27.5% discount rate as of March 2025 in Nigeria.

The annual benefit is calculated as gross income minus annual operating expenses, amounting to US$2677.

The net present value (NPV) is calculated by utilising the present value of an annuity formula as shown in Equation (1) [27].

where $$p$$ is the value of each payment; r represents the interest rate per period expressed as a decimal; and n indicates the number of periods.

In our calculation, we substitute the present value and a 20-year lifetime into Equation (1) to arrive at $$PV=$$ 3.61.

Therefore, the present value (PV) of net annual benefits = 3.61 × US$2677 = US$9663.97 over 20 years. However, the net present value (NPV) is determined by subtracting the total annual costs from the present value of net annual benefits; that is, NPV = PV − (CapEx + OpEx) = US$9663.97 − (US$8194.96 + US$163.89) = US$1305.

The Internal Rate of Return (IRR) is presented in Equation (2); however, in this study, it was calculated using an Excel spreadsheet.

Therefore, the internal rate of return (IRR) amounts to 32%.

The levelised cost of energy (LCOE) represents the average electricity cost per unit over a power plant’s or energy project’s entire operational lifespan. It encompasses all costs, including initial investment, operations, maintenance, fuel, and decommissioning, while considering the time value of money to facilitate a standardised comparison of different energy technologies. The LCOE calculations are provided in Equations (3) to (5) [28].

For this type of project, it is recommended to utilise annualised CapEx, computed using the Capital Recovery Factor (CRF) from Equation (4) [29].

Substituting r = 27.5%, and n = 20-years in Equation (4)

The $$\mathrm{C}\mathrm{R}\mathrm{F}$$ value is 0.278

Therefore, the annualised capital expenditure = US$8194.96 × 0.278 = US$2278.

The total annual expenditure = annualised Capital Expenditure (CapEx) + Operating Expenses (OpEx) = US$2442.

Therefore, a revised LCOE formula for hybrid systems is provided in Equation (5) [29].

According to Equation (5), the Levelized Cost of Energy (LCOE) for the PV-T/PCM system is established at US$0.131 per kilowatt-hour.

The LCOE was calculated separately and did not treat hot-water savings as financial credit; the reported electrical LCOE used only discounted lifecycle costs and discounted electrical output as presented in Equation (5)

This financial metric evaluates an investment’s profitability by comparing the net profit or loss to the initial investment cost. The formulas for calculating return on investment (ROI) are presented in Equations (6) to (9) [30].

Net profit is determined by deducting total expenses, including the initial capital outlay, from total revenue. Investment cost pertains to the initial amount invested.

For total return over time:

If the project is financed with debt, interest expenses will reduce net profit.

Therefore,

In the context of solar energy projects, the most pragmatic approach to calculating interest expenses is to use the simple interest method, adjusted for the proportion of debt financing. The formula is as follows:

Interest Expense = Initial Investment × Loan Portion Ratio × Annual Interest.

The total nominal net returns amount to US$53,540, calculated as US$2677 multiplied by 20 years.

Net profit is calculated as US$53,540 minus US$8358, resulting in US$45,181.

Therefore, $$\mathrm{R}\mathrm{O}\mathrm{I}=5.405$$ × 100%

Therefore, the investment yields an annualised return of 9.73%.

This financial metric assesses the duration necessary to recuperate an initial investment in a project or asset through the cash flow, savings, or profits generated; it is essential for investment decision-making [6]. The payback period is calculated using the formulas provided in Equation (10) and Equation (11) [31].

The straightforward payback period (ignoring the time value of money) is provided by Equation (10).

Equation (11) defines the dynamic payback period, accounting for interest rates via discounting.

Equation (12) is used to determine the discounted factor.

Initial investment consists of Capital Expenditures (CapEx) and Operating Expenses (OpEx).

The annual net cash inflow, calculated as total cash received (revenue minus operating costs), yielded a discounted payback period of 8 years.

Table 3 summarises the financial metrics for the hybrid system compared with those of the conventional PV system.

According to Table 3, the hybrid system demonstrates a moderate positive Net Present Value (NPV) and Internal Rate of Return (IRR), with a payback period of eight years. This suggests that the project is financially profitable and feasible. However, it also has a high Levelized Cost of Electricity (LCOE), indicating higher energy costs than those of a photovoltaic (PV) system. The conventional PV system presents the lowest NPV and IRR, a four-year payback period, and a moderate LCOE. The PV system’s comparatively lower financial metrics relative to the hybrid PV-T/PCM system are primarily due to the hybrid system’s higher Capital Expenditure (CapEx). However, if the per-unit price of thermal energy in Nigeria is factored into the analysis, along with high hot water demand, the payback time of the PV-T/PCM system will be shorter than that of the PV panel.

Compared with the existing literature, Maatallah et al. [10] reported a payback period of approximately 6 years for the PV-T/PCM system, which aligns more closely with the findings of the present study. However, the payback period for the PV-T/PCM system documented in the literature was shorter than that for the PV system. Additionally, Adun et al. [17] indicated a Levelized Cost of Electricity (LCOE) range of $0.252/kWh to $0.384/kWh for the hybrid PV-T system, with an average value of $0.306/kWh. Conversely, the typical payback period for a photovoltaic system in Nigeria, used by residential households or small businesses, ranges from 3 to 5 years [32].

A sensitivity analysis was conducted to evaluate the impact of variations in the price of a 3-kW photovoltaic panel system, discount rates, and energy prices. The analysis covered 20 years in Nigeria, from 2005 to 2025.

From 2005 to 2025, the cost of solar systems worldwide declined substantially, driven by lower global prices. Nonetheless, regional factors such as import duties, the devaluation of the Naira, and increased demand contributed to pricing fluctuations. The integration of global photovoltaic (PV) price reductions with Nigeria’s foreign exchange rates and import duties was conducted using data from Our World in Data—Solar Photovoltaic Module Prices (1975–2024) [33,34,35,36].

Three price scenarios have been established for the sensitivity analysis based on the current price: a low-price scenario (−30%), a base-price scenario (0%), and a high-price scenario (+20%), all of which are subject to foreign exchange shocks. This range captures potential technological cost reductions, as well as possible increases resulting from exchange-rate depreciation and supply chain disruptions. The primary findings of this photovoltaic (PV) system price sensitivity analysis are summarised in Table 4 and Figure 2.

Figure 2 presents an analysis of financial performance under various scenarios: low-case (–30%), base-case (0%), and high-case (+20%). As demonstrated, both Net Present Value (NPV) and Internal Rate of Return (IRR) decline, reflecting diminished profitability. The Levelized Cost of Energy (LCOE) shows a marginal increase, indicating elevated energy production costs in the high-CAPEX scenario. Furthermore, the Payback Period is modest but remains within a reasonable range across all scenarios.

The instability in Nigeria’s discount rates from 2005 to 2025 is monitored using the Monetary Policy Rate (MPR) [37]. According to the literature, the low, baseline, and high case scenarios are defined as 11.5%, 16.3%, and 27.5%, respectively.

Table 5 summarises the results of the sensitivity analysis on variations in the discount rate and is presented in Figure 3.

Figure 3 illustrates the variations in Net Present Value (NPV), Internal Rate of Return (IRR), Levelized Cost of Energy (LCOE), and Payback Time across three discount rate scenarios: 11.5%, 16.3%, and 27.5%. The figure emphasises the pronounced sensitivity of NPV, LCOE, and Payback Time to fluctuations in the discount rate, with profitability diminishing, energy costs escalating, and other cost metrics increasing as the discount rate rises. The IRR remains invariant across all scenarios, indicating a stable internal rate of return, whereas the Payback Time ranges from 4 to 8 years, reflecting a slower recovery of investment at elevated discount rates.

Electricity prices in Nigeria have increased substantially from 2005 to 2025, primarily due to cost-reflective tariffs, reductions in government energy subsidies, and currency devaluation. Tariffs have risen from ₦16 per kilowatt-hour in 2015 to as much as ₦225 per kilowatt-hour for band A customers in 2024/2025 [38,39,40]. The percentage fluctuation bands used for the sensitivity analysis were derived from the scholarly literature and represent low, base, and high scenarios of −10%, 0%, and +50%, respectively.

Table 6 summarises electricity price fluctuations in Nigeria from 2005 to 2025 as presented in Figure 4.

Figure 4 shows that a low electricity price results in a negative Net Present Value (NPV), whereas an elevated electricity price yields a positive NPV for a feasible project. As electricity prices increase, the payback period decreases. Furthermore, the Internal Rate of Return (IRR) escalates with higher prices, while the Levelized Cost of Energy (LCOE) remains unchanged.

Table 7 presents the computed financial metrics for these phase-change materials.

The economic comparison between shea butter and paraffin wax phase change materials (PCMs) for PV-T system applications, as detailed in Table 7, emphasises differences in NPV and LCOE. Paraffin wax produces more thermal energy, resulting in higher annual benefits and a larger NPV. However, shea butter has a lower LCOE because it generates more electricity than paraffin wax. The shea butter system outperforms the paraffin wax system in electrical power output, suggesting that shea butter cools the PV panel more effectively during peak sunlight hours.

Conventional PV modules are generally designed for an operational lifetime of approximately 25–30 years, although gradual output degradation is expected. Dust, partial shading, humidity, corrosion, ultraviolet exposure, thermal cycling, encapsulant discolouration, delamination, and interconnection fatigue can reduce long-term performance. Published reviews identify dust accumulation, shading, and humidity as important factors in outdoor degradation [41,42].

Integrating a thermal absorber and PCM may reduce PV cell operating temperature and thermal stress, thereby improving instantaneous electrical efficiency and potentially reducing temperature-related degradation. However, the hybrid configuration introduces additional components and failure modes. These include leakage from the PCM enclosure or hydraulic circuit, corrosion between dissimilar materials, PCM phase segregation, chemical degradation after repeated thermal cycling, volume-change stresses during melting and solidification, thermal-contact deterioration between the PV backsheet and absorber, pump and sensor failure, blockage of fluid channels, insulation deterioration, and controller malfunction.

Effective mitigation strategies encompass chemically compatible, sealed PCM encapsulation, expansion volume, corrosion-resistant absorber materials, pressure- and temperature-relief devices, leak detection, replaceable pumps and sensors, accessible hydraulic connections, thermal bypass control, over-temperature protection, periodic water-quality assessments, and routine inspections. Additionally, lifecycle costs should account for battery and inverter replacements, as their service lives might be shorter than those of the PV modules.

The PV-T/PCM system incorporating shea butter achieved an LCOE of US$0.131/kWh, compared with US$0.146/kWh for the paraffin-wax system. This difference was primarily attributable to the higher annual electrical output of the shea-butter configuration. Shea butter’s lower latent heat capacity caused the circulation pump to operate during periods of peak solar irradiance, improving PV-cell cooling and electrical generation. In contrast, paraffin wax continued charging during these periods due to its higher latent heat capacity, resulting in greater thermal output but lower electrical generation. These findings demonstrate a trade-off between the electrical advantage of shea butter and the thermal-storage advantage of paraffin wax.

The LCOE of the shea-butter system was also lower than the Nigerian grid-electricity price of US$0.139/kWh and substantially lower than the diesel-generation cost of US$0.61/kWh. The system achieved a positive NPV, an IRR of 32%, an annualised ROI of 9.73%, and a discounted payback period of 8 years. However, its payback period remained longer than the 4 years estimated for the standalone PV system, mainly because of the higher capital cost of the thermal subsystem and Nigeria’s high discount rate.

The sensitivity analysis showed that PV-system cost, discount rate, and electricity tariff significantly affected economic performance. The discount rate had the greatest influence on NPV, LCOE, and discounted payback time. Higher discount rates reduced NPV, increased LCOE, and extended the payback period, whereas higher electricity tariffs improved NPV and shortened the payback period. Consequently, lower-cost financing, targeted subsidies, local manufacture of thermal components, and effective utilisation of surplus electrical and thermal energy could improve the system’s economic viability.

Overall, shea butter offers a promising, locally available, bio-based alternative to paraffin wax for PV-T applications in Nigeria. Nevertheless, further optimisation of system capacity, thermal subsystem cost, energy storage, and surplus energy utilisation is required before large-scale deployment. Revenue from surplus electricity or useful thermal energy should be included only where technically feasible, supported by actual demand, and permitted under the applicable regulatory framework.

Shea butter is extracted from the kernels of Vitellaria paradoxa, a tree that grows naturally across the West African “shea belt”, which extends through more than 20 countries. Approximately 800,000 tonnes of shea kernels are collected annually in West Africa, supporting the food and cosmetics industries and providing income for millions of rural households [43]. Nigeria accounts for an estimated 35–40% of global shea-nut production, making the country an important producer and a potentially significant source of shea butter for bio-based thermal-energy-storage applications [44,45].

Shea butter is commonly produced using traditional processes that include crushing, roasting, milling, kneading or churning, boiling, and separation. These processes are labour- and energy-intensive, with reported human-energy inputs ranging from 2000 to 6100 kJ per kilogram of shea butter [46,47]. Mechanical extraction provides an alternative approach in which oil is recovered by pressing the processed kernels. Most shea kernels are obtained from naturally occurring parkland trees rather than cultivated plantations, reducing the need for dedicated agricultural land but creating challenges related to resource management, seasonal availability, and supply-chain variability.

The environmental performance of shea butter depends strongly on the production method, energy source, processing efficiency, and transportation distance. Reported greenhouse-gas emissions range from 3.14 to 3.31 kg CO₂e/kg of shea butter for rural processors and from 2.29 to 2.54 kg CO₂e/kg for urban processors [48]. Transportation also contributes to the environmental burden through fuel consumption and associated emissions of CO₂, CH₄, N₂O, SO₂, and NO_x during the movement of kernels and processed butter between collection points, production facilities, and markets [49]. The global warming potential (GWP) of these gases, as documented by the Intergovernmental Panel on Climate Change, is as follows: CO₂ = 1, CO = 1.9, CH₄ = 27.75, and N₂O = 298 kg CO₂-equivalent per kilogram of fossil fuel combusted [50]. These emissions contribute to climate change, acidification, eutrophication, and local air pollution.

Higher emission values have been reported for traditional production systems that rely extensively on fuelwood. The production of 1 kg of cosmetic-grade shea butter is estimated to generate approximately 10.374 kg CO₂e, with wood combustion during post-harvest processing and crude-butter extraction accounting for approximately 75% of the total emissions [49]. Differences between published estimates reflect variations in system boundaries, production technologies, fuel types, allocation procedures, and the treatment of biogenic carbon. Consequently, emission values obtained from different studies should not be compared without considering their methodological assumptions.

Fuelwood consumption is one of the principal environmental hotspots in traditional shea-butter production. Approximately 1.7–2.0 kg of fuelwood may be required to produce 1 kg of shea butter, while the total energy requirement for unrefined shea-butter production has been estimated at 103–172 MJ/kg, predominantly supplied by firewood [48,51]. Improved cookstoves can substantially reduce fuel consumption and associated global-warming impacts. Previous research reported reductions of up to 78%, from 18 to 4.1 kg CO₂e/kg and from 11 to 2.4 kg CO₂e/kg relative to conventional stove configurations [47]. More efficient stoves and mechanical extraction methods have also been estimated to reduce emissions by approximately 28% and 20%, respectively [51]. These findings indicate that the environmental performance of shea butter can be considerably improved through process modernisation and cleaner energy sources.

Material-flow analysis provides a structured basis for quantifying the resources consumed and wastes generated during shea-butter production. Using 1 kg of shea butter as the functional unit, Jasaw et al. [52] examined inputs such as shea kernels, water, fuelwood, electricity, and labour, as well as outputs including shea butter, shea cake, wastewater, and other residues. Such an inventory is necessary to identify environmental hotspots and to compare shea butter consistently with conventional fossil-derived PCMs, including paraffin wax.

In the present study, the environmental assessment follows the life cycle assessment framework established by the ISO 14040 and ISO 14044 standards. The assessment comprises four interconnected phases: goal and scope definition, life cycle inventory analysis, life cycle impact assessment, and interpretation of results. A cradle-to-gate system boundary is applied to quantify the environmental impacts associated with shea-kernel collection, transportation, processing, and production of shea butter before its integration into the PV-T system. This approach enables the global-warming, acidification, and eutrophication impacts of shea butter to be compared with those of paraffin wax on a consistent functional-unit basis.

Although the PV-T/PCM system was modelled for Nigerian climatic and household conditions, the original shea-butter environmental inventory was not developed specifically for Nigeria. Process data and an electricity emission factor of 0.55 kg CO₂e/kWh were obtained from a Burkina Faso shea-processing study and used as a West African proxy because a complete and methodologically compatible Nigerian inventory was unavailable at the time of the assessment. The reported shea-butter GWP should therefore not be interpreted as a definitive Nigerian production footprint. Differences in electricity generation, process heat, transport distance, processing technology, water consumption, and waste management may affect the applicability of the Burkina Faso inventory to Nigeria.

To examine geographical sensitivity, the electricity-related contribution was recalculated using a Nigeria-specific grid emission factor. However, changing the electricity factor alone does not convert the Burkina Faso process inventory into a fully Nigerian inventory. The grid-adjusted result remains a proxy unless the entire inventory data is also replaced with Nigerian data.

Figure 5 presents the system boundary for producing 1 kg of shea butter from cradle to gate, and Figure 6 presents the life cycle of shea butter.

The primary inputs for shea butter production include shea kernels, water, energy, and time. The outputs include shea butter, wastewater (effluent), and shea cake. According to data from [53], processing 86.3 kg of shea kernels requires 305.2 L of water, 49.7 kg of fuelwood, and 15.11 h. This process yields 29.7 kg of shea butter, 46.86 kg of shea cake, and 202.3 L of wastewater, respectively.

The process of grinding or milling the shea kernel into paste, extracting the fat, and clarifying the oil requires electricity, water, and heat. Traditionally, shea butter production predominantly relies on fuelwood, requiring approximately 8–10 kWh of heat per kilogram when using improved cookstoves or roasters [45]. An illustration of the shea butter production process is provided in Figure 7.

Preliminary inventory data for producing 1 kg of shea butter in Ouagadougou (ASY), Burkina Faso, were obtained from [46], and the final inventory data for producing 1 kg were subsequently formulated and detailed in Table 8.

The electrical grid in Burkina Faso exhibits an Emission Factor of approximately 0.55 kg CO₂e per kWh of electricity consumed [54,55]. Consequently, the Global Warming Potential (GWP) is computed utilising the data presented in Table 8 as outlined below.

Therefore, electricity contributes approximately 0.15 kg CO₂e per kilogram of shea butter.

LPG emission factor is 0.063 kg CO₂ per megajoule [56,57].

Therefore, 0.95 kWh of LPG = 3.42 MJ

The LPG impacted 3.42 MJ × 0.063 kg CO₂/MJ = 0.216 kg CO₂/kg of shea butter

The LPG emissions impact is ≈0.22 kg CO₂/kg of shea butter.

The firewood emission factor ranges from 0.093 to 0.095 kg CO₂ per megajoule (MJ) for direct biogenic CO₂ emissions [56,58].

The input energy from firewood is 6.82 kWh, corresponding to 24.55 MJ.

The emission factor for non-CO₂ combustion by-products, such as CH₄ and N₂O, is 0.010 kg CO₂e per megajoule [59].

Therefore, the direct biogenic CO₂ emissions from firewood are calculated as 24.55 × 0.093 = 2.28 kg of CO₂.

The emissions of methane (CH₄) and nitrous oxide (N₂O) total 24.55 multiplied by 0.010, yielding 0.245 kg of CO₂-equivalent non-CO₂ emissions.

Consequently, the total GWP (excluding biogenic CO₂) is determined by summing the impact of electricity and thermal sources: 0.15 + 0.22 + 0.245 = 0.615 kg CO₂e per kilogram of shea butter.

This GWP (0.615 kg CO₂e/kg of shea butter) from this study closely corresponds to the GWP (0.613 kg CO₂e/kg of shea butter) documented in Kaiama, scenario 1, by (Ewemoje & Oluwaniyi, 2016) [49].

The potential for eutrophication and acidification from 1 kg of shea butter was assessed as follows:

The input value for electricity is 0.27 kWh.

The conversion factor for water eutrophication is 0.0002 kg PO₄e per litre [60].

Electricity eutrophication = 0.0002 kg PO₄e/kWh [60].

Therefore, the total eutrophication is calculated as 0.27 × 0.0002 + 13.22 × 0.0002 = 0.0027 kg PO₄e.

The electricity acidification is 0.0025 kg SO₂e/kWh, and the firewood acidification is 0.00015 kg SO₂e/MJ [60].

Therefore, the total acidification = 0.27 × 0.0025 + 24.55 × 0.00015 = 0.0043 kg SO₂e

This study finds that the eutrophication potential associated with producing 1 kg of shea butter is 0.0027 kg of PO₄e, and the acidification potential is 0.0043 kg of SO₂e.

Bio-based phase change materials (PCMs), such as shea butter, generally produce lower greenhouse gas emissions than fossil-fuel-based PCMs and offer superior renewable qualities. However, paraffin provides higher latent heat, increased durability, and reduced variability [49]. From a life cycle assessment (LCA) perspective, shea butter minimises fossil CO₂ emissions, whereas paraffin wax depends on fossil sources with a higher cradle-to-gate global warming potential (GWP). Table 9 offers a comprehensive comparison of the environmental impacts of shea butter and paraffin wax.

Table 9 demonstrates that paraffin wax has a higher fossil GWP; however, eutrophication is lower than that of shea butter due to the absence of agricultural or wastewater inputs. Figure 8 and Figure 9 depict the environmental impacts of shea butter and a comparison between shea butter and paraffin, as presented in Table 9.

Shea butter demonstrated a substantially lower cradle-to-gate global warming potential of 0.615 kg CO₂e/kg, compared with 3.75 kg CO₂e/kg for paraffin wax [61]. This represents an approximately 84% reduction in GHG emissions, indicating a clear climate-related advantage for shea butter as a renewable, bio-based PCM. The difference is primarily associated with the fossil origin and energy-intensive production of paraffin wax. However, the comparison depends on consistent functional units, system boundaries, allocation procedures, and treatment of biogenic carbon.

The environmental advantage of shea butter was not consistent across all impact categories. Its acidification potential of 0.0043 kg SO₂e/kg exceeded the 0.002–0.003 kg SO₂e/kg reported for paraffin wax, while its eutrophication potential of 0.0027 kg PO₄e/kg was considerably higher than the paraffin-wax range of 0.0003–0.0005 kg PO₄e/kg. The higher acidification impact of shea butter was mainly associated with fuelwood combustion and electricity use during processing, whereas its eutrophication impact was linked primarily to water consumption and wastewater discharge. These findings indicate that replacing paraffin wax with shea butter shifts part of the environmental burden from global warming to more localised impacts on air quality and aquatic ecosystems.

Overall, shea butter offers a significant climate benefit over paraffin wax, but it cannot be considered environmentally superior across all impact categories. Its environmental performance could be improved through efficient cookstoves, cleaner electricity, mechanical extraction, wastewater treatment, sustainable fuelwood management, and shorter transport distances. Furthermore, a system-level comparison based on the quantity of PCM required to provide an equivalent thermal storage service would yield a more complete assessment, particularly because shea butter and paraffin wax have different latent heat capacities, operating temperatures, and service lives.

The results demonstrate that shea butter is a promising, locally available, bio-based PCM for PV-T applications in Nigeria. Compared with paraffin wax, the shea-butter system achieved a lower LCOE of US$0.131/kWh and a substantially lower cradle-to-gate GWP of 0.615 kg CO₂e/kg, while maintaining a positive NPV of US$1305, an IRR of 32%, and an annualised ROI of 9.73%. However, its eight-year discounted payback period, high thermal-subsystem cost, and greater acidification and eutrophication impacts indicate important economic and environmental trade-offs. Large-scale deployment will therefore require lower-cost financing, system-capacity optimisation, productive use of surplus energy, cleaner processing methods, and sustainable management of the shea supply chain. Subject to these improvements, shea-butter-based PV-T systems could support decentralised energy provision, reduce dependence on fossil-derived PCMs, and create additional economic opportunities for shea-producing communities in Nigeria and other parts of Sub-Saharan Africa.

First, the PV-T/PCM system was evaluated using a TRNSYS numerical model rather than a full-scale experimental installation. Although the model provides a consistent basis for comparing shea butter and paraffin wax, field validation is required to confirm the predicted electrical and thermal performance under actual operating conditions in Nigeria.

Second, the selected 3 kWp capacity represents a fixed residential design case and was not obtained through formal load-matching or cost optimisation. The system generated more electrical and thermal energy than the adopted household demands. Therefore, economic performance depends on the availability of battery storage, flexible household loads, community energy sharing, thermal storage, or an approved grid-export arrangement. Unused or curtailed surplus energy would reduce the economic benefits.

Third, the economic analysis depends on assumptions concerning component prices, electricity tariffs, discount rates, maintenance costs, system lifetime, and the value of useful thermal energy. These variables may change due to inflation, exchange-rate fluctuations, financing conditions, and energy policy reforms. In addition, the estimated thermal-subsystem cost was based on market quotations and requires validation through detailed engineering design and local supplier quotations. Potential replacement costs for batteries, inverters, pumps, sensors, and controllers may also affect lifecycle profitability.

Fourth, grid-export revenue should be interpreted as a conditional scenario rather than a guaranteed income stream. The feasibility of injecting surplus electricity into the Nigerian distribution network depends on system capacity, regulatory eligibility, technical approval, bidirectional metering, grid-compliant protection, and an agreement with the relevant distribution company. Accordingly, economic results that include export revenue may not apply directly to an individual 3 kWp residential installation.

Fifth, the environmental assessment used a cradle-to-gate boundary and therefore excluded impacts associated with PCM integration, transportation to the installation site, operation, maintenance, replacement, leakage, end-of-life treatment, and disposal or recycling. The comparison was also based on 1 kg of PCM rather than an equivalent thermal-storage service. Because shea butter and paraffin wax have different latent heat capacities, operating temperatures, quantities required, and expected service lives, future assessments should compare the materials per unit of useful thermal energy stored over the complete system lifetime.

Finally, the long-term thermal stability, compatibility, and durability of shea butter were not experimentally evaluated. Repeated melting and solidification may affect its thermophysical properties, while leakage, oxidation, phase separation, corrosion, biological degradation, and interaction with containment materials could influence system reliability. Future work should therefore include experimental thermal-cycling tests, field validation, capacity optimisation, full lifecycle assessment, and uncertainty analysis before large-scale deployment is recommended.

During the preparation of this manuscript, the author(s) used Grammarly and Microsoft 365 Copilot for language formatting. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the published article.”

Conceptualisation, K.R.A.; Methodology, K.R.A.; Software, P.K.; Validation, K.R.A.; Formal Analysis, K.R.A.; Investigation, K.R.A.; Resources, K.R.A.; Data Curation, K.R.A.; Writing—Original Draft Preparation, K.R.A.; Writing—Review & Editing, K.R.A., P.K. and K.P.; Visualisation, K.R.A.; Supervision, P.K. and K.P.

Not applicable.

Not applicable.

The raw data supporting the conclusions of this article will be made available by the authors on demand

The author(s) declared that financial support was not received for this work and/or its publication.

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.