⚡ Engineering Design for a Municipal Diesel-to-Solar+Storage Replacement Project: 120kW Load, 10-Hour Daily Operation
📋 1. Project Background & Requirements
A municipal engineering site was previously powered by a 200kW diesel generator, operating 10 hours daily (7:00 – 17:00) to support a 120kW continuous load. The facility required a clean, cost-effective alternative to reduce fuel dependency, lower operational expenses, and minimize carbon emissions. The diesel genset will remain onsite as emergency backup.
Customer requirements:
- Replace diesel generation with solar PV + battery storage for daily operation
- Maintain 120kW load for 10 hours/day (1,200 kWh daily consumption)
- Keep existing 200kW diesel genset as emergency backup
- Minimize capital expenditure while ensuring system reliability
- Provide seamless transition between solar, battery, and genset
🔍 Application scenario: Municipal engineering facility · 120kW continuous load · 10h daily operation · diesel genset retained for emergency · off-grid capable hybrid system
🛠️ 2. Key Engineering Challenges
Challenge 1 — PV & Battery Sizing
Determining the optimal PV array and battery capacity to meet 1,200 kWh daily demand while minimizing cost and ensuring 10-hour continuous operation.
Challenge 2 — System Integration
Integrating solar PV, battery storage, and the existing diesel genset into a seamless hybrid system with automatic transfer and control coordination.
Challenge 3 — Economic Optimization
Balancing system cost vs. long-term fuel savings — avoiding over-sizing while ensuring reliability during low solar days.
📐 3. Engineering Analysis — Why This Design
🔌 PCS Configuration Logic
The 120kW load requires a bidirectional PCS capable of sustained 120kW output with peak handling capacity. IMAXPWR’s MSP100HC 100kW PCS was selected as the core power conversion unit[reference:0]. Two units are configured in parallel to provide 200kW total capacity — covering the 120kW continuous load with sufficient margin for motor startup surges and future load growth.
Why parallel 100kW units instead of a single 200kW PCS? The modular approach offers N+1 redundancy: if one PCS unit requires maintenance, the other can sustain 100kW, keeping critical loads online. The MSP100HC achieves 98.78% peak efficiency with wide DC voltage range (600–950V)[reference:1][reference:2], ideal for LFP battery integration.
🧮 Battery Capacity Design
Daily energy requirement: 120kW × 10h = 1,200 kWh. Battery capacity must support one full day of operation with 80% depth of discharge (DOD) for LFP chemistry[reference:3].
Total nominal capacity = 1,200 kWh ÷ 0.80 = 1,500 kWh
However, considering the 300kWp PV array will recharge the battery during daylight hours, the actual battery capacity can be optimized. The system is designed with 1,320 kWh LFP battery (slightly below 1,500 kWh) — leveraging daytime solar generation to reduce required storage while maintaining 10-hour backup capability[reference:4].
☀️ PV Array Sizing
PV array must generate enough energy to recharge the battery and supply daytime loads. Using the standard formula[reference:5]:
= 1,200 ÷ (4.5 × 0.75) = 355 kWp
Conservative engineering approach: 300 kWp PV array — slightly derated to reduce upfront cost while relying on the battery to cover any shortfall. The diesel genset remains as final backup for extended low-solar periods.
🔄 4. System Architecture
120kW
200kW (Emergency)
⚙️ 5. IMAXPWR Engineering Solution
Hardware Configuration
- PCS: 2 × IMAXPWR MSP100HC 100kW bidirectional AC/DC power converters (parallel operation)[reference:6]
- Battery: 1,320 kWh LFP battery bank, 650–950V DC, 80% DOD
- PV Array: 300 kWp (customer supplied — not in IMAXPWR scope)
- DC/DC Converter: MPPT charge controllers for PV integration
- EMS: IMAXPWR Energy Management System with diesel coordination
- STS: Static Transfer Switch for seamless diesel backup transition
Control Strategy
- Peak Shaving: Battery discharges during high-load periods to reduce diesel consumption
- Load Shifting: Solar energy stored during midday for evening use
- Backup Power: Automatic transfer to diesel genset when battery SOC drops below 20%
- Renewable Integration: PV prioritized for daytime loads; excess stored in battery
🛡️ Safety & Reliability Design
- Electrical Protection: Overcurrent, overvoltage, undervoltage, and short-circuit protection[reference:7]
- Thermal Management: Smart forced air cooling on PCS; battery BMS with temperature monitoring[reference:8]
- Communication Monitoring: CAN/RS485 communication between PCS, BMS, and EMS[reference:9]
- System Safety: High-frequency isolation design ensures battery-grid isolation[reference:10]
Need a Similar Energy Storage System?
Many EPC contractors and project developers face similar challenges when designing BESS and microgrid systems.
IMAXPWR engineering team can help evaluate your:
🔋 Energy capacity
🔄 System architecture
⚙️ Integration strategy
📊 6. Engineering Comparison — Design Options
| Parameter | Option A (Conservative) | Option B (Aggressive) | ✅ IMAXPWR Selected |
|---|---|---|---|
| PV Array | 400 kWp | 250 kWp | 300 kWp |
| Battery Capacity | 1,800 kWh | 1,000 kWh | 1,320 kWh |
| PCS Configuration | 2×125kW | 1×120kW | 2×100kW (MSP100HC) |
| Estimated CAPEX | Highest | Lowest | Optimized |
| Diesel Dependency | Minimal | Moderate | Balanced |
📈 7. Expected Engineering Benefits
Diesel Fuel Reduction
Operating Cost Savings
CO₂ Reduction / Year
Note: These are expected engineering benefits based on system design modeling. Actual results may vary with solar irradiance and load profiles.
📝 8. Key Engineering Lessons Learned
- Correct PCS sizing improves system efficiency. Oversizing increases CAPEX without proportional benefit; undersizing risks overload. The 2×100kW parallel configuration provides optimal balance.
- Early load profile analysis prevents costly redesigns. Understanding the 10-hour daily cycle and 120kW continuous load was critical to battery sizing.
- Modular architecture enables future scalability. The parallel PCS design allows additional units to be added as load grows, without replacing existing equipment.
- Diesel integration requires careful EMS logic. The genset must start only when battery SOC drops below threshold — avoiding unnecessary starts that reduce engine life.
- Thermal management is non-negotiable. PCS and battery cooling must be designed for local ambient conditions to maintain efficiency and longevity.
⚠️ 9. Common Mistakes to Avoid in Similar Projects
- Incorrect PCS sizing — Selecting a PCS that cannot handle peak load or motor startup surges leads to system instability.
- Poor thermal design — Inadequate cooling reduces PCS efficiency and battery cycle life, increasing long-term OPEX.
- Ignoring grid requirements — Even in off-grid applications, future grid interconnection should be considered in system architecture.
- Underestimating battery DOD impact — Operating LFP batteries below recommended DOD significantly shortens cycle life[reference:11].
- No diesel coordination strategy — Without proper EMS logic, the genset may start unnecessarily, wasting fuel and reducing engine lifespan.
Need Engineering Support for Your Next Project?
Planning a BESS, microgrid or renewable energy project?
Send us your project requirements, and our engineering team will provide a customized system recommendation.
✓ PCS configuration support
✓ Energy storage solution design
Typical response time: within 24 hours
🏢 About IMAXPWR
ImaxPWR (Imax Power Technology Co., Ltd.) is a national high-tech enterprise specializing in new energy solutions. As an OEM/ODM manufacturer, IMAXPWR focuses on energy storage power conversion equipment, bidirectional PCS, DC/DC converters, V2G modules, energy storage cabinets and integrated microgrid solutions. With professional R&D capabilities and power electronics expertise, IMAXPWR provides reliable and customized energy solutions for global customers in industrial and commercial energy storage, renewable energy integration, smart microgrids and charging infrastructure applications.
📞 Contact IMAXPWR
Ready to Develop Your Energy Storage Project?
Contact IMAXPWR technical team for:
⚡ PCS selection
🔌 Microgrid solutions
⚙️ Customized energy conversion equipment
👨💻 About The Author
This article was reviewed by Ethan Li, an energy storage system specialist focusing on PCS, bidirectional DC/DC converters and microgrid system design.
