Hybrid Solar Sizing Cuts Rural Cold Storage Energy Costs in Nigeria
Researchers have designed and computationally evaluated an off-grid hybrid solar photovoltaic and diesel generation system engineered to deliver continuous electrical power to agricultural refrigeration facilities in rural Nigeria. Using Itunta Village in the Ikwuano Local Government Area of Abia State as an empirical case study, the investigation combined deterministic thermal load calculations with an 8760-hour stochastic performance simulation in MATLAB R2024a to solve severe power reliability deficits that threaten agricultural preservation across Sub-Saharan Africa. The study established an analytical baseline architecture pairing a 17.0-kilowatt-peak solar photovoltaic array with a 159.0-kilowatt-hour deep-cycle battery bank and a 15-kilovolt-ampere diesel backup generator to satisfy a daily refrigeration demand of 78.2 kilowatt-hours. Simulation findings confirmed that the integrated baseline layout achieves a 95 percent renewable energy fraction, supplying 27,115 kilowatt-hours annually from solar generation while keeping the overall Loss of Load Probability below 0.5 percent, thereby demonstrating an effective engineering framework for preserving critical temperature-sensitive produce in isolated tropical communities.
The operational load profile was developed for a commercial-scale walk-in cold room designed to store perishable agricultural commodities according to thermal standards from ASHRAE. To reflect genuine post-harvest cooling requirements in the southeastern Nigerian climate, the researchers modeled the thermal pull-down demand for a two-thousand-kilogram batch of harvested tomatoes requiring temperature reduction from 25 degrees Celsius to 4 degrees Celsius. Thermophysical heat gain modeling incorporated four discrete load mechanisms: structural heat transmission through walls, roof, and flooring amounting to 1092 watts under an ambient-to-internal temperature differential of 28 Kelvin; infiltration heat gains through scheduled door openings calculated at 68.6 watts; internal sensible heat from lighting and service equipment totaling 200 watts; and product cooling power removing 163,800 kilojoules over a twenty-four-hour cycle, which added an average thermal extraction load of 1896 watts. Combining these individual thermal inputs established a continuous refrigeration power requirement of 3256.6 watts, translating into a constant daily electrical energy consumption of 78.2 kilowatt-hours and a steady peak load of 3.257 kilowatts.
To satisfy this uninterrupted 78.2 kilowatt-hour daily load, the team designed the primary solar generation subsystem using meteorological data from the Photovoltaic Geographical Information System covering historical records from 2005 through 2025. Local solar radiation in Itunta averages between 5.1 and 5.8 kilowatt-hours per square meter per day, providing a design peak sunshine parameter of 5.15 hours per day. Sizing calculations accounted for a battery round-trip efficiency of 90 percent alongside an overall derating factor of 0.85 to capture operational losses caused by dust soiling, module mismatch, and ambient thermal elevation. These mathematical parameters established an analytical baseline photovoltaic capacity of 17.0 kilowatt-peak, projected to generate a theoretical average yield of 74.4 kilowatt-hours per day. Crucially, the engineering design rejected standard low-voltage configurations in favor of a 48-volt direct-current bus architecture, which lowered maximum circuit current to 354.2 amperes, curbed internal ohmic losses, reduced required copper conductor cross-sectional dimensions, and substantially minimized thermal dissipation across critical terminal connections.
The electrical balance-of-system architecture integrated dedicated power electronics and reserve electrochemical storage configured to manage dynamic compressor startup demands without experiencing service interruptions. The analytical storage baseline incorporated fifty-two deep-cycle lead-acid battery units, each rated at 250 ampere-hours and 12 volts, organized into thirteen parallel strings of four series-connected batteries to match the 48-volt system voltage. Array current was regulated by four parallel 100-ampere Maximum Power Point Tracking charge controllers that provide operational redundancy and safeguard charging pathways. While baseline running power suggested that a 5-kilovolt-ampere power inverter could theoretically manage continuous cooling, refrigeration compressors exhibit intense inrush starting currents that routinely exceed steady operational ratings. Consequently, the researchers specified a 10-kilovolt-ampere inverter to prevent transient motor trip events and provide headroom for system expansion. A 15-kilovolt-ampere soundproof diesel generator operating with a dedicated 100-ampere motorized automatic transfer switch and an external 500-liter storage tank completed the backup subsystem, designed to run at its optimum 75 to 80 percent load window.
Because static sizing tools frequently overlook rapid temporal fluctuations in weather and equipment behavior, the investigators executed a high-resolution 8760-hour stochastic simulation covering a full operational year. Real-world refrigeration demands fluctuate as ambient weather alters heat transfer and routine door usage introduces humid air into the cold chamber. The simulation captured these dynamics by applying a Gaussian noise factor with zero mean and ten percent standard deviation to the baseline load time series, reflecting ten percent operational variances. Solar harvesting calculations incorporated hourly Global Horizontal Irradiance data alongside a thermal derating model based on Itunta’s 26.1 degrees Celsius mean ambient temperature, an estimated nominal operating cell temperature of 45 degrees Celsius, and a negative 0.4 percent per degree Celsius power loss coefficient. The simulation tracked distinct seasonal shifts, showing theoretical photovoltaic output climbing to an annual high of 2841.5 kilowatt-hours during clear conditions in January before plunging to an annual nadir of 1702.5 kilowatt-hours in July under dense monsoon cloud cover.
System behavior across seasonal extremes was quantified using the Solar Performance Ratio, defined as the proportion of actual cooling energy demand met by available solar photovoltaic production. In the dry months from November to March, high solar irradiance supported superior system efficiency, with January yielding a performance ratio of 85.3 percent and producing surplus energy that maintained battery reserves at elevated states of charge. Conversely, during the heavy rainy season extending from June through September, elevated atmospheric humidity and thick cloud cover severely restricted solar harvesting while cooling loads remained steady. In July, monthly photovoltaic generation fell 721.7 kilowatt-hours below demand, pushing the monthly performance ratio to a peak of 142.4 percent and indicating that refrigeration requirements exceeded available solar electricity by nearly fifty percent. Rather than dramatically oversizing the array to satisfy rare weather deficits, the simulation used the 15-kilovolt-ampere generator as a targeted bridge, generating 1428 kilowatt-hours annually to cover the critical five percent energy deficit.
Long-term technical viability hinged upon understanding electrochemical degradation in hot tropical environments, where sustained thermal stress accelerates battery aging. The researchers applied an Arrhenius-based kinetic degradation model to track the battery bank’s State of Health across a simulated ten-year operational span. To preserve battery chemistry, the dispatch control logic imposed strict operating limits, enforcing an eighty percent maximum depth of discharge and maintaining a minimum twenty percent reserve state of charge throughout the entire 8760-hour cycle. When solar generation proved insufficient and battery reserves declined to the twenty percent lower boundary, the priority control system immediately triggered the diesel generator to supply the cooling load and recharge the cells. Under these controlled dispatch constraints and Itunta’s local average ambient temperature of 26.1 degrees Celsius, the battery bank exhibited a steady exponential decay rate, reaching its eighty percent end-of-life capacity threshold after approximately 9.2 years, indicating that only one complete battery bank replacement would be necessary across a twenty-year facility lifespan.
Beyond the analytical baseline, the investigators performed a dual-target multi-objective optimization using a comprehensive grid search algorithm across varying equipment capacities. The computational evaluation analyzed photovoltaic array sizes spanning 10 to 50 kilowatt-peaks alongside battery storage capacities ranging from 20 to 160 kilowatt-hours to minimize the levelized cost of energy while reducing the Loss of Load Probability. This algorithmic search mapped a distinct Pareto-optimal sweet spot at 30 kilowatt-peaks of solar photovoltaic capacity and 60 kilowatt-hours of battery storage. Comparing this global optimum against the 17-kilowatt-peak and 159-kilowatt-hour baseline demonstrated that oversizing photovoltaic generation while substantially downsizing electrochemical storage yields superior techno-economic efficiency. In tropical regions with daytime cooling loads, an expanded 30-kilowatt-peak array meets continuous compressor power directly during daylight hours even under diffuse radiation, allowing a more compact 60-kilowatt-hour battery bank to handle brief fluctuations and nocturnal cooling while curbing total capital expenditure and battery replacement liabilities.
The economic analysis assessed lifecycle expenses by comparing the hybrid solar PV-diesel system against a commercial diesel-only baseline designed for identical cold storage service. To ensure practical relevance within the contemporary Nigerian economic environment, component pricing was derived from verified local commercial suppliers and Jumia Nigeria at a conversion rate of 1500 naira per United States dollar. The initial capital expenditure for the baseline hybrid installation was determined to be 31,891 dollars, whereas the diesel-only baseline required an initial capital outlay of 5,500 dollars, reflecting 8.25 million naira for an industrial-grade 15-kilovolt-ampere generator with automatic switching and protective housing. However, recurring operational and maintenance costs reversed this upfront advantage: the hybrid system incurred annual operating expenses of only 4,000 dollars, whereas the conventional diesel alternative demanded 13,167 dollars per year due to continuous fuel consumption, routine servicing, and local fuel market volatility following subsidy removals.
Lifecycle economic metrics confirmed substantial financial advantages for the hybrid architecture, yielding a levelized cost of electricity between 0.18 and 0.23 dollars per kilowatt-hour, compared to 0.85 to 1.15 dollars per kilowatt-hour for the diesel configuration. This eighty percent reduction in generation costs enabled the baseline hybrid system to attain a simple payback period of 3.47 years, recovering its initial investment within the first third of its projected operational lifecycle. Throughout 8760 simulation hours, dynamic loss of load modeling demonstrated that the hybrid dispatch protocol successfully restricted unmet cooling load to less than 0.5 percent of annual demand. By replacing nearly ninety percent of traditional diesel fuel consumption with renewable photovoltaic generation, the hybrid configuration shields rural agricultural infrastructure from volatile fossil fuel pricing while preserving temperature-sensitive produce. The researchers concluded that this validated modeling framework provides a reliable, scalable engineering blueprint for expanding sustainable cold chain and off-grid electrification systems across underserved developing regions.
Subject of Research: Hybrid solar-diesel refrigeration system design for off-grid cold chains
Article Title: Multi-objective optimization and stochastic reliability modeling of a hybrid SPV-diesel system for sustainable cold chain applications in Itunta, Nigeria
Article References: Eze, I. J., Uwakwe, A. J., & Eze, E. E. (2026). Multi-objective optimization and stochastic reliability modeling of a hybrid SPV-diesel system for sustainable cold chain applications in Itunta, Nigeria. Discover Energy, 6(1), Article 57. https://doi.org/10.1007/s43937-026-00160-5
Image Credits: AI Generated
DOI: 10.1007/s43937-026-00160-5
Keywords: solar photovoltaics, diesel generators, cold chain, agricultural refrigeration, rural electrification, stochastic modeling, battery degradation, energy optimization, Multi-objective, optimization, stochastic, reliability
News Source: Denise Maddox. (November 12, 2026). Hybrid Solar Sizing Cuts Rural Cold Storage Energy Costs in Nigeria. Scienmag.
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