Technical Proposal for a 600 kW Three-Phase Utility-Frequency Off-Grid Photovoltaic Energy Storage System
Germany: Three-Phase Off-Grid Photovoltaic Energy Storage System
I. Project Overview
How a 600 kW Three-Phase Utility-Frequency Off-Grid Photovoltaic Energy Storage System Works
II. System Design Principles
Safe and reliable
The system features comprehensive protection across the entire power chain, including overvoltage, undervoltage, overload, short circuit, overtemperature, reverse connection, and lightning protection. The equipment is equipped with robust electrical and thermal protection capabilities to eliminate safety hazards.
High Efficiency and Energy Savings
The core equipment boasts excellent conversion efficiency, with MPPT tracking efficiency of at least 99% and inverter efficiency of at least 93%. The battery charging and discharging efficiency is high, minimizing power loss to the greatest extent possible.
Modular Expansion
The PV array, energy storage batteries, controller, and inverter all utilize standardized modular combinations, allowing for flexible expansion to meet future power demands with minimal retrofitting effort.
Environmental Adaptability
The equipment supports wide-temperature operation and can adapt to complex conditions such as high and low temperatures and high humidity, ensuring stable performance in both outdoor and indoor installation environments.
Intelligent Management
Equipped with RS485 communication and a centralized monitoring system, it collects real-time operational data and automatically switches operating modes, thereby reducing manual maintenance costs.
III. Photovoltaic Power Generation System
3.1 Equipment Configuration
3.2 Array Layout Scheme
This design offers significant advantages: if a single array experiences shading, a malfunction, or panel damage, it will not affect the normal power generation of the remaining arrays, greatly enhancing overall power generation stability. The PV mounting structures are made of corrosion-resistant materials and are equipped with a complete lightning protection and grounding system, ensuring safe outdoor operation.
3.3 High-Voltage Distribution Panel
The combiner boxes integrate DC circuit breakers, fuses, surge protection modules, and current/voltage sensing units, combining power consolidation, distribution, protection, and status monitoring functions into a single unit. Each PV string, controller, and battery branch is equipped with an independent protection circuit, allowing for rapid disconnection and isolation of faulty circuits. Additionally, real-time operational parameters from each branch are uploaded, enabling O&M personnel to quickly troubleshoot issues. These combiner boxes serve as the core distribution hub for the entire DC side.
IV. Energy Storage Battery Subsystem
4.1 Battery Selection and Specifications
The energy storage unit utilizes the SW-G10-160KWH high-voltage rack-mounted lithium iron phosphate (LiFePO₄) battery pack. LiFePO₄ battery cells offer advantages such as high safety, long cycle life, excellent low-temperature performance, and stable charging and discharging, making them the mainstream choice for off-grid energy storage in commercial and industrial applications.
Key parameters of the battery pack: Rated voltage: 512 V; capacity: 314 Ah; single-unit capacity: 160 kWh; supports expansion through series connection of multiple units, with a maximum output voltage of up to 819 V; charge/discharge cycle life of no less than 6,000 cycles; operating temperature range: 0°C to 55°C for charging and -20°C to 55°C for discharging; IP20 protection rating; suitable for indoor rack-mounted installation. The battery features a built-in BMS (Battery Management System) that provides comprehensive protection, including individual cell monitoring, voltage balancing, and safeguards against overcharging, over-discharging, overcurrent, overheating, and short circuits. It is also compatible with communication protocols from multiple inverter brands, enabling integrated system control and management.
4.2 Energy Storage System Architecture
The project is equipped with a total of 10 SW-G10-160KWH battery banks, providing a total energy storage capacity of 1,600 kWh. Each battery bank is connected to the high-voltage distribution combiner box associated with the corresponding PV array, with the combiner box handling the centralized collection and control of the battery circuits.
Each battery module is an independent unit equipped with its own on/off switch and fault isolation device. If a single battery module fails, it can be isolated individually without affecting the operation of the entire energy storage system. Leveraging the central distribution capabilities of the combiner box, the system coordinates the charging and discharging logic for all batteries. By automatically adjusting operating modes based on PV generation, load power, and remaining battery capacity, it ensures balanced charging and discharging, thereby slowing cell degradation and extending service life. The entire energy storage system serves as an energy buffer unit, storing surplus solar power during the day and releasing it at night or on cloudy and rainy days, providing the core guarantee for continuous power supply in off-grid systems.
V. Power Conversion and Control System
5.1 Selection Calculations and Instructions for the SW1-100 MPPT Controller
This system utilizes SW1-100 MPPT solar charge controllers, all of which are connected to a high-voltage distribution cabinet. The selection process involved rigorous calculations of power, current, and voltage, as outlined below:
Calculation of Total Power for a Single Array
A single PV array consists of 14 modules connected in series to form one string, with a total of 8 strings connected in parallel. Each module has a power rating of 620W. Total power calculation: 14 × 8 × 620 = 69,440 W, which converts to 69.44 kW.
Operating Current Calculation (Including Safety Margin)
The energy storage system has a rated voltage of 512 V. The base operating current of the array is: 69,440 ÷ 512 ≈ 135.6 A. To account for extreme operating conditions such as low temperatures and intense sunlight, a 25% safety margin is incorporated into the design. The maximum operating current for the array is: 135.6 × 1.25 ≈ 169.5 A.
Single Controller Load Verification
A single PV array is configured with two SW1-100 controllers operating in parallel; the current shared by each unit is: 169.5 ÷ 2 ≈ 84.75A. The SW1-100 controller has a rated current of 100A, with an actual operating load factor of approximately 84.8%. The load range is reasonable, and there is sufficient current redundancy.
Voltage Compatibility Verification
Operating voltage per string: 14 × 33.8 = 473.2 V Open-circuit voltage per string: 14 × 41.5 = 581 V The SW1-100 high-voltage model has a maximum PV input voltage of 800 V and an MPPT voltage tracking range of 480 V to 640 V, making it fully compatible with the string voltages in this project. Additionally, the equipment is compatible with 512V high-voltage energy storage systems, and its charging logic meets the requirements for lithium iron phosphate (LiFePO₄) batteries.
Total Number of Controllers
The project consists of a total of 10 independent PV arrays, with 2 controllers configured for each array, for a total of 10 × 2 = 20 units.
This selection is scientifically sound and reasonable, with equipment parameters highly matched to system operating conditions. All controllers are connected to a high-voltage distribution combiner box for centralized power collection, featuring comprehensive electrical protection and communication monitoring functions to ensure long-term stable system operation.
5.2 Three-Phase Off-Grid Inverters Operating at Utility Frequency
The inverter unit consists of two 300 kW three-phase utility-frequency off-grid inverters operating in parallel, with a total rated output power of 600 kW, sufficient to meet the system’s rated load requirements. The utility-frequency inverters output standard three-phase 380V/50Hz sinusoidal AC power with low waveform distortion, making them suitable for various loads such as industrial motors and general-purpose equipment. The equipment features high inverter conversion efficiency and strong overload capacity, capable of handling load startup surges.
The inverter’s DC input voltage range is perfectly matched to the 512V energy storage batteries, accommodating voltage fluctuations throughout the entire battery charging and discharging process. The equipment features a comprehensive set of built-in electrical protection functions, supporting synchronized parallel operation of two units with load sharing. In the event of a single-unit failure, the affected unit can be isolated and shut down independently while the other continues to operate, ensuring uninterrupted power supply. Additionally, it offers remote communication, fault alarm, and parameter logging capabilities, demonstrating a high level of intelligence.
5.3 Parallel Control Cabinet
VI. Overall System Architecture and Operational Logic
6.1 Overall Architecture
Power Generation and Energy Storage Tier
10 PV arrays + 10 energy storage battery banks, each connected to a corresponding high-voltage distribution combiner box, to convert solar energy into electricity and store the electricity;
Combiner Control Layer
10 high-voltage distribution combiner boxes + 20 MPPT controllers. Controllers, batteries, and PV arrays are all connected to the combiner boxes to perform maximum power point tracking, branch protection, and centralized power collection;
Central Control and Dispatch Layer
A parallel control cabinet aggregates the electrical energy output from all combiner boxes and coordinates the system-wide operational logic;
Inverter Output Layer
2 × 300 kW inverters convert DC power into utility-frequency AC power for external supply.
All system equipment is interconnected via a communication network, forming a closed-loop control and management system.
6.2 Operating Logic
Adequate Sunlight
PV power, after being aggregated via MPPT controllers and combiner boxes, is prioritized for supplying loads; excess power is stored in the energy storage batteries, and charging automatically stops once the batteries are fully charged;
Insufficient sunlight
When PV generation cannot meet load demand, the energy storage batteries discharge simultaneously via the combiner boxes to supplement power, ensuring normal load operation;
No Sunlight
During nighttime or cloudy/rainy weather, when PV generation ceases, the energy storage batteries independently discharge power through the combiner box and control cabinet;
Protection Mode
When battery voltage drops to the minimum threshold or equipment malfunctions, the combiner box branch protection and system-level protection activate sequentially to isolate the faulty circuit and trigger an alarm, ensuring equipment safety.
The entire operation process is fully automated and requires no manual intervention.
Germany: Three-Phase Off-Grid Photovoltaic Energy Storage System
VII. Safety Protection System
Equipment-Level Protection
Photovoltaic modules, MPPT controllers, battery banks, and inverters all feature built-in independent protection functions. In the event of a single-unit failure, the system provides self-protection to prevent the spread of faults; the battery BMS enables cell-level monitoring and protection, eliminating the risk of thermal runaway.
Module-Level Protection
Each high-voltage distribution combiner box functions as an independent unit. Within the box, the PV modules, controllers, and battery branches are electrically isolated from one another. A fault in a single branch is rapidly isolated, ensuring that other branches within the same box and the entire system continue to operate normally.
System-Level Protection
The entire system is equipped with unified lightning protection, grounding, and insulation monitoring devices, and all metal equipment is reliably grounded. Circuit breakers and fuses are installed at various levels in both DC and AC circuits to form a multi-layered protection system; The protection systems of each device are interconnected and operate in coordination during a fault, enhancing overall safety.
Additionally, equipment is selected with appropriate protection ratings based on the installation environment: outdoor equipment is waterproof and dustproof, while indoor equipment is moisture-resistant and well-ventilated, meeting the requirements for long-term continuous operation.
VIII. Installation, Commissioning, and O&M Guidelines
8.1 Installation Standards
8.2 System Commissioning
8.3 Daily Operation and Maintenance
IX. Comprehensive Project Benefits
9.1 Economic Benefits
9.2 Environmental and Social Benefits
X. Summary
This 600 kW three-phase utility-frequency off-grid photovoltaic energy storage system was designed based on the project’s solar irradiation conditions and load requirements. The four major components—photovoltaic, energy storage, control, and inverter—are optimally configured and highly compatible. The solution employs an integrated busbar architecture where the PV array, MPPT controllers, and storage batteries are uniformly connected to a high-voltage distribution busbar box. This design ensures orderly DC-side wiring, centralized protection, and convenient operation and maintenance. Furthermore, through rigorous current and voltage calculations, the W1-100 MPPT controller was determined to be the ideal device for this system, offering reasonable load capacity, sufficient redundancy, and reliable operation.
The entire solution is technically mature and highly practical, making it widely applicable in remote industrial sites, mining areas, rural villages, and islands—regions without grid access or with weak grid infrastructure. By combining solar power with energy storage, it establishes an independent, reliable, and green power supply system, offering significant practical value and promising prospects for widespread adoption.
