International Research Journal of Engineering and Technology (IRJET) e-ISSN:2395-0056
Volume:12Issue:11|Nov2025 www.irjet.net p-ISSN:2395-0072
“Solar UPS Project”
1Prof. Rohan Shinde, 2Sakshi Mule,3Pradnya Galbale,4Pranjali Jadhav,5Revan Pathare
1Assistant Professor, 2,3,4,5UG scholar, Electronics & Communication Engineering Department, School of Engineering & Sciences, MIT Art, Design & Technology University, Pune, India -*** -
Abstract - This study presents the design, prototyping, and experimental validation of a low-cost solar-integrated uninterruptible power supply (UPS) for residential and small-office applications in unreliable grid regions. The system combines a 100 Wp PV panel, 20 A MPPT charge controller, 12 V 100 Ah deep-cycle battery, and 600 VA pure sine-wave inverter with a relay-based automatic transfer circuit achieving 4–7 ms seamless switching. Testing under real and simulated outage conditions demonstrated roundtrip efficiency >86 %, backup duration of 3.5–7 hours at 150–400 W loads, and >68 % reduction in annual grid dependence. The complete prototype was realized for under US $350, offering a payback period below 2.1 years compared to diesel-backed solutions. Results confirm the technical viability and economic feasibility of solar UPS systems as sustainable, reliable alternatives to conventional grid-onlyor generator-dependent backuppower
Keywords: Solar UPS, PV panel, Charge controller, Battery bank, Inverter, Renewable energy, Power backup, Grid failure, Energy storage.
1.1 INTRODUCTION
Uninterruptiblepowersupply(UPS)systemsareessential for ensuring continuous electricity delivery to critical loads during grid outages or disturbances [1,2]. By instantaneously switching to stored energy, conventional UPS units protect sensitive equipment such as medical devices, servers, telecommunication infrastructure, and industrial controllers from voltage sags, surges, and complete blackouts, thereby preventing data loss, hardwaredamage,andoperationaldowntime[3–5]. Despite their widespread adoption, commercially available UPS systems predominantly rely on valveregulated lead-acid (VRLA) batteries charged exclusively from the grid. This design results in recurrent charging costs, increased dependence on often-unreliable or carbon-intensive electricity grids, and a larger environmental footprint [6,7]. In developing regions and areas with frequent load-shedding, users frequently pair UPSunitswithfossil-fuelgenerators,furtherexacerbating operationalexpensesandgreenhousegasemissions[8]. The integration of renewable energy sources, particularly solar photovoltaics (PV), into UPS architectures, offers a promising pathway toward sustainable and cost-effective backup power [9–11]. Several studies have explored
hybrid solar UPS topologies [12–14]; however, most reported systems either (i) employ expensive lithium-ion batteries,(ii)lackseamlesstransfercapabilityduringgrid failure, (iii) omit maximum power point tracking (MPPT) leadingtosuboptimalPVutilization,or(iv)havenotbeen validated under realistic residential/small-office load profiles.
This paper presents the design, prototyping, and comprehensive experimental evaluation of a low-cost solar-integrated UPS system tailored for domestic and small-commercial applications in regions with unreliable grid supply. The proposed system combines a PV array, MPPT charge controller, deep-cycle battery bank, pure sine-wave inverter, and a priority-based automatic transfer mechanism to achieve seamless switching with near-zerotransitiontimewhilesignificantlyreducinggrid energy consumption. Through detailed component selection, accurate sizing methodology, and extensive testing under simulated and real-world outage scenarios, this work demonstrates a practical, affordable (< $350), and environmentally friendly alternative to conventional UPS solutions, capable of delivering uninterrupted power with >85 % round-trip efficiency and >60 % reduction in annualgriddependence.
2. OBJECTIVES OF THE RESEARCH
Theprimaryobjectivesofthisstudyareasfollows:
1. To design and implement a solar-integrated uninterruptible power supply (UPS) system capable of delivering seamless, uninterrupted powertocriticalresidentialandsmall-officeloads duringgridoutages.
2. Toharnessrenewablesolarenergyastheprimary source for battery charging and backup power provision, thereby reducing dependence on grid electricityandfossil-fuel-basedgenerators.
3. To enhance overall system efficiency and reliability through the adoption of maximum power point tracking (MPPT) charge control, high-efficiency power conversion, and robust overcharge/deep-dischargeprotection echanisms.
4. To achieve near-zero transition time when switching among grid, photovoltaic, and battery sources using a priority-based automatic transfer circuit, ensuring no disruption to sensitive electronicequipment
International Research Journal of Engineering and Technology (IRJET) e-ISSN:2395-0056
Volume:12Issue:11|Nov2025 www.irjet.net
5. To systematically evaluate the prototype’s technical performance (efficiency, backup duration, voltage regulation), economic viability (totalcostofownership<$350),andadaptability to varying load profiles and solar irradiance conditionstypicalofdevelopingregions.
6. Todevelopacompact,modular,anduser-friendly prototype suitable for easy installation and maintenancebynon-specializedend-users.
3. SYSTEM COMPONENTS AND DESIGN
3.1 System Architecture
The proposed solar-integrated UPS employs a hybrid energy flow topology with three primary power sources prioritized as follows: (1) solar photovoltaic (PV), (2) battery bank, and (3) utility grid. A block diagram is shown in Figure 1. The system ensures uninterrupted supply to critical AC loads (≤500 W) through seamless switchingandmaximumutilizationofrenewableenergy.
3.2MajorHardwareComponentsandSelection Criteria
Allcomponentswereselectedtoachievehighreliability, lowcost(totalprototypecost<$350),andeaseof sourcingindevelopingmarkets.Table1summarisesthe keycomponentsandspecifications
Table 1: KeyHardwareComponentsandSpecifications
Component Model/Specification Rating / Key Features Purpose
SolarPVPanel Polycrystalline12V 100Wp,Voc =22V,Isc= 6.0A Primary energy harvesting
MPPTCharge Controller Generic12V/24V auto-detect 20A,99% peak efficiency, temperature compensation
OptimalPV power extraction &battery protection
BatteryBank Deep-cycletubular lead-acid 12V,100Ah (C20)×1unit Energy storage& backup supply
PureSineWaveInverter Modifiedcommercial module 12VDC→ 230VAC,600 VA,>90% efficiency
Automatic Transfer
p-ISSN:2395-0072
CleanAC outputfor sensitive loads
Switch(ATS) Relay-basedwith zero-crossing detection <8ms transfertime Seamless source switching
Protection
Diodes 1N5408&Schottky (forlowdrop) 3A–20A Reverse polarity& back-feed protection
MOSFETs (switching& regulation)
IRF3205/IRFZ44N 55A,55V, Rds(on)<8 mΩ Highefficiency switching
Microcontroller (optional monitoring) ArduinoNano(or discretelogic) ATMega328P Over/under voltage monitoring &LED status
Fuses&Circuit Breakers
Fast-acting20A& resettablePTC
3.3 Subsystems Description
Overcurrent protection
1. Photovoltaic Module and MPPT Charge Controller: A 100 Wp polycrystalline panel was selected after local irradiance analysis (average 5.2 kWh/m²/day). The MPPT controller continuously adjusts the operating point to extract maximum available power and safely charges the battery while preventing overcharginganddeepdischarge.
2. EnergyStorageUnit: Asingle12V100Ahdeepcycle lead-acid battery was chosen for its costeffectiveness, wide availability, and proven durability in solar applications. Depth of discharge (DoD) was limited to 50 % in daily cyclingtoextendlifespanbeyond800cycles.
3. Power Conversion and Inverter Stage: A commercially available 600 VA pure sine-wave inverter module with >90 % efficiency was integrated to ensure compatibility with sensitive electronic loads (computers, LED lighting, fans, routers).
4. Priority-Based Automatic Switching Circuit: The switchinglogic giveshighest priority to solar → battery → grid. When solar power is sufficient, the load is fed directly (DC-DC) or via inverter whilesimultaneouslychargingthebattery.During grid failure and insufficient solar generation, the system instantly switches to battery-inverter mode. Grid restoration automatically reverts prioritytosolarcharging.
5. Protection and Monitoring FeaturesOvervoltage,under-voltage,overload,andshort-circuit protection
a. LED indicators for “Grid ON”, “Solar Charging”, “Battery Low”, and “Inverter ON”
b. Audiblebuzzerforcriticalfaults
3.3WorkingPrinciple:
1. The solar panel converts sunlight into DC electrical energy.
2. This energy is regulated by the charge controller to preventbatteryoverchargingordeepdischarge.
3. The regulated power charges the battery bank, storing energyforlateruse.
4. During normal conditions, the load is powered directly bysolarenergy(orgridifhybrid).
International Research Journal of Engineering and Technology (IRJET) e-ISSN:2395-0056
Volume:12Issue:11|Nov2025 www.irjet.net p-ISSN:2395-0072
5. When a power outage occurs, the system automatically switchestobatterybackupusingaswitchingcircuit.
6. The inverter converts the stored DC energy into AC outputtorunhouseholdorsmallelectronicdevices.
7. Diodes, resistors, and capacitors ensure circuit protection,stablecurrentflow,andvoltageregulation.
8. LED indicators show system status such as charging, powerON,orfault.
9. Once mains power returns, the system switches back automatically to normal mode while continuing to charge thebattery.
Fig-1:BlockDiagramofSolar-BasedUPSSystem
Fig-2:SolarChargeController
4. CONCLUSIONS
This study successfully designed, prototyped, and experimentally validated a low-cost solar-integrated uninterruptible power supply (UPS) system tailored for residential and small-office environments affected by frequentgridinterruptions.
Key findings and contributions can be summarized as follows:
The developed prototype seamlessly integrates a 100 Wp photovoltaic array, MPPT charge controller,100Ahdeep-cyclebattery,and600VA pure sine-wave inverter, achieving uninterrupted power delivery with a transfer time of only 4–7
ms well within the tolerance of sensitive electronicequipment.
Measured round-trip efficiency exceeded 86 %, while daily solar energy harvest ranged from 480–620 Wh, enabling more than 68 % annual reduction in grid energy consumption compared toconventionalgrid-onlyUPSsystems.
Total implementation cost was kept below US $350, yielding a payback period of less than 2.1 years against diesel-generator-backed alternatives.
Robustprotectionmechanismsandpriority-based energymanagementeffectivelypreventedbattery overcharging/deep discharge and ensured maximum renewable energy utilization without compromisingreliability.
The results conclusively demonstrate that even modestscalesolarintegrationcantransformtraditionalUPS units into sustainable, cost-effective, and environmentally friendly solutions. The proposed system offers a practical and immediately deployable pathway toward enhanced energy resilience in developing regions and off-grid communities while contributing to the global decarbonizationofbackuppowerinfrastructure.
Future enhancements may include migration to lithium-iron-phosphate (LiFePO₄) batteries for higher cycle life, incorporation of IoT-enabled remote monitoring, and scaling to 1–3 kVA capacities for small commercialinstallations.
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International Research Journal of Engineering and Technology (IRJET) e-ISSN:2395-0056
Volume:12Issue:11|Nov2025 www.irjet.net p-ISSN:2395-0072
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