Off-Grid Solar-Wind-Storage Hybrid for Industrial Gatehouse — 7.15kWp PV + 5kW Wind + 50kWh LFP

Abstract

This case study documents a pilot off-grid solar-wind-battery hybrid system deployed at an industrial gatehouse in southern China. The system combines a 7.15 kWp monocrystalline PV array, a 5 kW horizontal-axis permanent-magnet wind turbine, and a 50 kWh DC512V lithium iron phosphate (LFP) battery cluster on a common high-voltage DC bus, powering a 0.8 kW gatehouse load and a 7 kW single-phase AC EV charger with a combined daily consumption of 45.5 kWh. An EMS implements tiered load shedding because the 50 kWh battery cannot sustain two full days of autonomous operation. The project demonstrates a scalable, diesel-free approach to remote-site electrification with integrated EV charging.

1. Project Overview

The client operates a manufacturing facility in an industrial park in southern China and selected the factory gatehouse as a pilot site for an entirely islanded, off-grid energy system with no utility grid interconnection. The objective was to validate a self-sufficient power supply that covers both the gatehouse baseload and a 7 kW AC EV charging station, eliminating diesel generator runtime and demonstrating a replicable model for remote or weak-grid locations.

The site has approximately 40 m² of usable rooftop area for PV installation and adequate wind exposure for a small horizontal-axis turbine. The system architecture is built around a DC512V high-voltage common DC bus, which simplifies the integration of multiple DC sources and reduces conversion stages compared to an AC-coupled topology.

2. Project Challenges

2.1 No Grid Connection — Full Autonomy Required

The site operates as a pure islanded system with no utility grid interface. Unlike grid-tied storage that can rely on the grid as a backup, every watt consumed must come from PV, wind, or battery discharge. This places strict requirements on generation diversity and battery sizing to avoid load shedding during extended cloudy or calm periods.

2.2 Battery-to-Load Ratio Constraints

With a 50 kWh battery serving a 45.5 kWh daily load, the battery provides slightly more than one day of autonomy at full load. This is insufficient for two consecutive days of poor renewable generation. The EMS must therefore implement tiered load management, prioritizing critical gatehouse loads (lighting, CCTV, communication) while throttling or deferring EV charging when battery state of charge (SOC) drops below predefined thresholds.

2.3 High-Power DC Load on a Modest Battery

The 7 kW EV charger represents a significant instantaneous load relative to the 50 kWh battery (approximately 0.14C discharge rate during charging). While not extreme, the simultaneous operation of the charger and gatehouse loads requires careful DC bus voltage regulation and inverter capacity sizing. The DC512V bus architecture helps by allowing multiple DC sources to share the load directly on the DC side before inversion.

3. Engineering Analysis

3.1 Load Profile Analysis

The gatehouse baseload is relatively flat throughout the day, dominated by CCTV (24/7), a router, and LED lighting with a combined peak of 0.8 kW and daily consumption of 3.5 kWh. The EV charger is an intermittent, high-power load: a single full charge consumes approximately 42 kWh, typically scheduled during daylight hours when PV generation is available. This load characteristic aligns well with a PV-priority dispatch strategy, where the charger directly absorbs surplus solar generation rather than cycling it through the battery.

3.2 Renewable Resource Assessment

Southern China receives approximately 1,100–1,400 kWh/kWp of annual solar irradiation, with the highest yields from May through September. The 7.15 kWp array can generate an estimated 25–35 kWh on a clear summer day and 8–15 kWh on an overcast winter day. The 5 kW wind turbine provides complementary generation, particularly during nighttime and cloudy periods when PV is unavailable, though small wind output is highly variable and site-dependent. According to the International Renewable Energy Agency (IRENA), hybrid PV-wind systems with battery storage can achieve significantly higher capacity factors than single-source renewable systems, especially when the two resources are temporally complementary.

3.3 DC512V Bus Architecture Rationale

The system uses a DC512V high-voltage common DC bus as the central coupling point. PV connects via MPPT DC/DC converters, wind via a rectifier and DC/DC stage, and the LFP battery via a bidirectional DC/DC converter. AC loads (gatehouse and EV charger) draw power through DC/AC inverters. This architecture offers several advantages: reduced conversion stages for DC-to-DC power transfer, higher overall efficiency, simplified coordination of multiple sources, and the ability to add or remove DC sources without reconfiguring the AC side. Per IEC 62619 (secondary lithium-ion cells for industrial applications), the 512V DC bus falls within the standard voltage ranges for stationary storage systems, and proper insulation monitoring is essential for personnel safety.

Figure 1: System topology — DC512V common DC bus architecture with PV, wind, battery, and dual AC loads.

4. Solution Design

4.1 Dispatch Strategy: PV Priority → Battery → Wind Assist

The energy management strategy follows a clear priority hierarchy:

• PV direct supply (priority 1): Solar generation first feeds the gatehouse baseload and the EV charger directly through the DC bus, minimizing battery cycling and round-trip losses.
• Surplus PV to battery (priority 2): When PV output exceeds the instantaneous load, excess energy charges the LFP battery via the bidirectional DC/DC converter.
• Battery discharge (priority 3): When PV is insufficient (nighttime, heavy cloud cover), the battery discharges to meet the load deficit.
• Wind real-time assist (priority 4): The wind turbine provides supplementary generation whenever wind speed is above the cut-in threshold (~3 m/s), directly offsetting load or charging the battery.

4.2 EMS Tiered Load Shedding

Because the 50 kWh battery cannot sustain two full days of autonomous operation, the EMS implements a tiered load management protocol based on battery SOC thresholds:

Figure 2: EMS control logic — real-time source/load monitoring with PV-priority dispatch and SOC-based tiered load shedding.

4.3 Key Equipment Configuration

5. Implementation & Results

5.1 Commissioning and Initial Performance

The system was commissioned as a pilot installation at the gatehouse. Initial testing verified the DC512V bus voltage stability under varying PV and wind conditions, the MPPT tracking efficiency, and the seamless transition between PV direct supply and battery discharge. The EMS load shedding logic was validated by simulating low-SOC conditions and confirming that EV charging was throttled or suspended while critical gatehouse loads remained powered.

5.2 Expected Energy Balance

The pilot demonstrates that for the majority of days in southern China, the combined PV-wind-battery system can meet the full 45.5 kWh daily load. During extended periods of poor renewable generation, the EMS load shedding ensures that critical gatehouse functions (security, lighting, communication) remain operational, while EV charging is deferred — an acceptable tradeoff for a pilot site that does not require 24/7 charging availability.

6. Key Takeaways

• DC bus architecture simplifies multi-source integration: The DC512V common bus allows PV, wind, and battery to share power on the DC side, reducing conversion stages and improving overall system efficiency compared to AC-coupled alternatives.
• PV-priority EV charging minimizes battery cycling: By directing surplus PV directly to the EV charger rather than through charge-discharge cycles, the system reduces battery throughput and extends calendar life.
• Tiered load shedding is essential for modest battery sizes: A 50 kWh battery serving a 45.5 kWh daily load cannot guarantee multi-day autonomy. SOC-based load prioritization (critical loads first, EV charging deferrable) is a practical and cost-effective approach.
• Wind provides valuable temporal diversity: Small wind generation, though variable, complements PV by producing during nighttime and cloudy periods, reducing the depth of battery discharge and improving overall system reliability.
• Pilot-validated scalability: The gatehouse pilot serves as a proof-of-concept that can be scaled to larger sites by increasing PV capacity, adding wind turbines, expanding battery capacity, or parallelizing multiple DC bus systems.

7. Frequently Asked Questions (FAQ)

Q1: Can this off-grid system power a 7kW EV charger without a grid connection?

Yes. The 7kW EV charger draws power from the DC512V bus through a dedicated DC/AC inverter. During daylight hours, PV generation directly supplies the charger; during nighttime or low-PV periods, the 50kWh LFP battery discharges to meet the demand. The EMS may throttle or suspend EV charging when battery SOC drops below 30% to preserve power for critical gatehouse loads.

Q2: Why use a DC512V common bus instead of an AC-coupled architecture?

A high-voltage DC common bus reduces the number of AC/DC conversion stages when multiple DC sources (PV, wind, battery) share the same load. Power can transfer directly between DC sources without double inversion, improving efficiency. The DC512V level is compatible with standard LFP battery cluster voltages and industrial DC/DC converter ranges, and it reduces line losses compared to lower-voltage DC buses.

Q3: How many days of autonomy does the 50kWh battery provide?

The 50kWh battery provides approximately 1.1 days of autonomy at the full 45.5 kWh daily load, assuming no renewable generation. In practice, PV and wind generation supplement the battery on most days, so the effective autonomy is significantly longer. The EMS tiered load shedding extends critical-load autonomy to approximately 14+ days by suspending EV charging and reducing to the 3.5 kWh/day gatehouse baseload when SOC is critically low.

Q4: Is a small 5kW wind turbine worth adding to a PV-dominant system?

Yes, for off-grid applications. While small wind turbines have lower capacity factors than utility-scale machines, they provide valuable temporal diversity by generating during nighttime, early morning, and cloudy periods when PV is unavailable. According to IRENA, hybrid PV-wind systems with storage can achieve 20–40% higher overall capacity factors than PV-only systems in locations with moderate wind resources. For an off-grid site with no diesel backup, every additional kWh of renewable generation reduces battery depth of discharge and extends system reliability.

Q5: Can this system be scaled up for a full manufacturing facility?

The architecture is inherently scalable. For larger loads, the system can be expanded by adding more PV arrays (up to the MPPT capacity), increasing wind turbine count or size, expanding battery capacity in 50kWh increments, and parallelizing multiple DC bus sections with interconnection controllers. ImaxPWR offers scalable hybrid microgrid solutions ranging from this 12kW-class gatehouse pilot to 500kW+ industrial microgrids with PV, storage, and diesel backup. The EMS software supports multi-node coordination for expanded systems.

8. Related Reading

Related Reading: 8 C&I Energy Storage Architectures Guide · AC Coupled vs Series Coupled PV-Diesel-Battery Hybrid Topology · PV-Diesel-Storage Microgrid for Southeast Asia · 500kW PV-Storage-Diesel Microgrid System · Sunlight Series PV-Storage Off-Grid Cabinet · Product Center

9. About the Author

10. About ImaxPWR

ImaxPWR Power Co., Ltd. (Brand: ImaxPWR) is a National High-Tech Enterprise and source manufacturer, covering bidirectional converters, DC/DC, energy management, and energy storage cabinet integration, providing design, delivery, and O&M services. Products are CE, UL, and ROHS certified. Our off-grid and hybrid microgrid solutions are deployed across Southeast Asia, Africa, and the Middle East, enabling reliable power for remote industrial sites, island resorts, and weak-grid communities.

© 2026 ImaxPWR Power Co., Ltd. · This article is for engineering practice and case study purposes. Data sourced from project documentation, IRENA industry reports, and IEC 62619 standards.