Topology Diagram of a 50 kW / 128 kWh Three-Phase Hybrid Energy Storage PV System (American Standard)

2.2 Design Principles
Principle of Electrical Compatibility

The voltage, current, and power parameters of the inverter, PV modules, and energy storage batteries were verified one by one. The SW3P50K-H 50K hybrid inverter has a DC MPPT voltage operating range of 150–850 V. The selected 630 W N-type modules have an open-circuit voltage of 49.49 V per module. and the open-circuit voltage of a single string of 10 modules in series is 494.9 V, which falls within the inverter’s optimal MPPT operating voltage range, thereby preventing power generation efficiency losses caused by overvoltage or undervoltage; on the energy storage side, the SW-314 battery supports high-voltage series networking and is compatible with the inverter’s battery connection voltage range of 150–800 V.

Principle of Capacity Redundancy

The customer required a storage capacity of at least 100 kWh. The proposed solution includes a 128 kWh storage system, providing a 28% capacity margin. This not only allows for the full storage of surplus solar power but also ensures extended runtime for critical loads during nighttime grid outages, thereby preventing curtailment of solar power due to insufficient storage capacity.

Principles of Environmental Adaptation

The equipment selection fully accounts for South America’s high temperatures, significant diurnal temperature variations, and high humidity in certain regions. The inverters feature intelligent air-cooling and a wide-temperature operating range, while the lithium iron phosphate batteries operate within a temperature range of -20°C to 60°C, making them suitable for both outdoor and indoor temperature and humidity conditions at project sites. Compared to traditional monocrystalline products, N-type photovoltaic modules exhibit lower high-temperature degradation and superior low-light performance, making them well-suited for the intense sunlight and high-temperature conditions typical of South America.

Security Compliance Principles

The complete system integrates multiple protective features, including anti-islanding protection, DC surge protection, AC/DC overcurrent and short-circuit protection, and battery overcharge and over-discharge protection. It complies with local South American grid connection certification standards and can successfully complete the grid connection registration process.

2.3 Basis for Calculating System Power and Electricity Generation

The system has a total installed photovoltaic capacity of 50.4 kWp, consisting of 8 series strings, with each string comprising 10 630 W modules (8 × 10 × 630 W = 50,400 W). Based on an average daily equivalent peak sunlight duration of 5 hours at the project site, the system’s theoretical average daily power generation is 50.4 kW × 5 hours = 252 kWh. This generated power is prioritized for on-site AC loads during daylight hours. Any surplus energy not consumed by the loads is stored in a 128 kWh lithium iron phosphate (LiFePO₄) energy storage battery. During evening and nighttime hours when there is no sunlight, the battery discharges to continue supplying the loads. In the event of a utility power outage, the inverter automatically switches to off-grid backup mode, with the energy storage battery providing continuous power to critical loads on its own, thereby ensuring the efficient, round-the-clock utilization of photovoltaic energy.

III. Detailed Technical Specifications and Selection Guidelines for Core Equipment

3.1 SW3P50K-H 50 kW Three-Phase Hybrid Energy Storage Inverter (System Inverter Core)

This system is configured with a single SW3P50K-H model 50kW three-phase grid-tied inverter, which serves as the energy management hub for the entire system. It is fully compatible with the South American grid standard of 230/120 VAC, three-phase, 60 Hz. The equipment specifications fully meet the project’s design requirements. The following is a detailed description of the four main interfaces: PV DC input, energy storage battery interface, grid-side AC, and off-grid backup output.

3.1.1 Photovoltaic (PV) DC Input Parameters

The inverter has a rated available input power of 50 kW on the PV side and a maximum connectable PV power of 60 kW, providing a 20% margin for PV over-provisioning to accommodate potential future customer demand for minor PV system expansions; The MPPT voltage operating range is 150V to 850V. A single string of 10 630W N-type modules connected in series has an open-circuit voltage of 494.99V, which falls within the MPPT high-efficiency operating range. Even when the module open-circuit voltage rises in low-temperature environments, it remains below the 850V upper limit and will not trigger overvoltage protection shutdown; The device is configured with 4 MPPT channels, each with a maximum input current of 40A and a peak current of 60A; The project’s PV array is designed with 8 strings of modules, with 2 strings connected in parallel to a single MPPT channel. The 4 MPPT channels evenly distribute the current from the 8 strings, ensuring balanced branch currents with no unbalanced current losses. The MPPT connection configuration is 4 inputs and 8 outputs, precisely matching the project’s 8-string PV layout.

3.1.2 Parameters on the Energy Storage Battery Input Side

The inverter’s battery input voltage range is 150–800 V, making it compatible with the SW-314 high-voltage lithium iron phosphate battery pack in a series configuration. The device has a rated battery charge/discharge power of 55 kW, which meets the 0.5C charge/discharge requirements for a 50 kW system and 128 kWh of energy storage (128 kWh × 0.5 = 64 kW; the inverter’s 55 kW charging and discharging power can reliably handle standard battery charging and discharging conditions); the device is equipped with 2 battery connection terminals, with a maximum charging and discharging current of 70 A per channel; connecting both channels in parallel supports high-current battery charging and discharging, Standard communication ports include CAN and RS485, enabling real-time communication with the SW-314 battery BMS management system to monitor battery voltage, current, temperature, and SOC data online. The inverter can automatically adjust charging and discharging power based on feedback from the battery BMS to prevent overcharging, over-discharging, and overcurrent faults.

3.1.3 Parameters for the Grid-Connected Side & Off-Grid Backup Output Side

Grid-side rated grid-connected output power: 50 kW; three-phase 3/N/PE, 120 V per phase / 230 V per line, 60 Hz output; rated grid-connected output current: 76 A; precisely compatible with South American 120/230 V three-phase power distribution; In off-grid backup mode, the unit supports a short-term overload of 1.6 times the rated power for 2 seconds, capable of handling the inrush current during load startup. The rated backup output is also 50 kW, with an off-grid THD (Total Harmonic Distortion) of <3%. The waveform remains stable even with nonlinear loads, ensuring high-quality power for precision equipment; The grid bypass AC input supports connection to the same power source as the utility grid. When the utility grid is operational, the unit operates in grid-tied mode; in the event of a utility grid failure, it switches to off-grid mode in less than 10 ms, ensuring uninterrupted power supply to the load.

3.1.4 Efficiency, Environmental, and Safety Parameters

The PV inverter achieves a maximum efficiency of 97.9%. The full-chain efficiency—from PV charging to battery charging and from battery discharging to AC output—reaches 97.9%, delivering excellent energy efficiency across all operating conditions; The unit measures 530 × 880 × 290 mm and weighs 73 kg. It features a transformerless topology and intelligent air-cooling, with an operating temperature range of -25°C to +60°C and relative humidity of 0–95% (non-condensing). With an IP65 protection rating, it is suitable for outdoor wall mounting. For this project, the inverter is installed in a nearby rooftop electrical room to avoid damage from sun exposure and rain; electrical protection features include islanding protection, AC/DC overcurrent protection, insulation fault monitoring, DC lightning protection (DC Type II/AC Type II), DC reverse connection protection, and AFCI arc fault protection; a lightning protection module is optional, meeting South American grid connection safety standards; Human-machine interaction features a 7-inch LCD display + Bluetooth + APP remote monitoring. Communication options include CAN, RS485, Ethernet, and optional 4G/WiFi, allowing customers to remotely view power generation, battery charge levels, and equipment operating status via their mobile devices.

3.2 SW-314 High-Voltage Rack-Mounted Lithium Iron Phosphate Energy Storage Battery (128 kWh Energy Storage Unit)

Based on the customer’s energy storage requirement of ≥100 kWh, this project utilizes SW-314 51.2V 314Ah rack-mounted lithium iron phosphate (LiFePO4) cells. Each cell has a rated capacity of 16.08 kWh, and by connecting them in series at high voltage, the system achieves a total energy storage capacity of 128 kWh. The cells are centrally arranged in an indoor energy storage distribution cabinet using a floor-standing rack installation method. The equipment utilizes the LiFePO4 lithium iron phosphate system, which offers an exceptionally long cycle life and high safety characteristics, making it the mainstream choice for commercial and industrial energy storage applications.

128 kWh energy storage unit

3.2.1 Basic Parameters of Individual Cells

The SW-314 single module has a rated voltage of 51.2V, a rated capacity of 314Ah, a single-module energy storage capacity of 16.08kWh, a unit weight of 115kg, and dimensions of 801×532×233mm; it is configured into rack units through modular stacking; The recommended charge and discharge current for a single module is 157A (0.5C standard charge/discharge rate), consistent with the industry-standard 0.5C energy storage design specification; battery charge/discharge lifespan is optimized under 0.5C operating conditions. The cell charging temperature range is 0–55°C, the discharge temperature range is –20–60°C, the storage temperature range is –10–40°C, and the operating humidity range is 10%–95% (non-condensing), making it suitable for South America’s variable climates.

3.2.2 High-Voltage Series and Parallel System Configurations and Capacity Calculations

SW-314: Minimum of 3 cells and maximum of 15 cells per string, This project, in conjunction with the inverter’s 150–800 V battery voltage range, employs 3 series strings to form a single high-voltage battery cluster (3 × 51.2 V = 153.6 V, single-cluster capacity 48.24 kWh, voltage 134.4–172.8 V), Three battery clusters are connected in parallel to form the complete energy storage system, with a total capacity of 3 × 48.24 ≈ 128 kWh, perfectly achieving the 128 kWh system storage capacity. The total voltage of the battery clusters falls within the inverter’s optimal battery connection voltage range, eliminating any voltage mismatch issues. The entire battery cluster measures 530 × 800 × 2420 mm and weighs 1060 kg. It is installed in a standardized rack-mounted cabinet with neat wiring, facilitating future operation, maintenance, and repairs.

3.2.3 Product Performance and Safety Benefits

The cycle life of individual battery cells exceeds 6,000 cycles (at 25°C and 90% DOD), and the system is designed for a 15-year service life—far exceeding the 3–5-year lifespan of conventional lead-acid batteries—thereby reducing long-term replacement costs; The built-in BMS (Battery Management System) monitors the voltage and temperature of the entire battery pack in real time, performs equalization management, and provides overcurrent protection. The CAN bus communication port connects directly to the SW3P50K-H inverter, allowing the inverter to retrieve real-time battery SOC, fault codes, and temperature data, and intelligently control charging and discharging start/stop operations; The product is compatible with mainstream energy storage inverters on the market. It is fully compatible with the SW3P50K-H inverter in terms of both hardware and software protocols, enabling plug-and-play installation without the need for additional communication adapters; The lithium iron phosphate (LFP) chemistry offers excellent thermal stability with no risk of fire or explosion. With an IP20 indoor protection rating, the batteries are centrally housed in a rack within the electrical room, shielding them from sun and rain to extend their service life.

3.2.4 Summary of Selection Advantages

The final configuration of 128 kWh provides 28 kWh of excess capacity compared to the customer’s minimum requirement of 100 kWh. With an average daily generation of 252 kWh during the day, after deducting the electricity consumed for daytime loads, the surplus solar power can be fully stored in the battery. At night, when there is no solar generation, the battery discharges steadily. Even during 1–2 consecutive days of cloudy, rainy, or low-light conditions, the energy storage system can still support the base load, significantly enhancing system reliability.

3.3 630W High-Power N-Type Monocrystalline Silicon Photovoltaic Module (PV Module)

The photovoltaic array for this project utilizes high-efficiency N-type monocrystalline silicon modules with a power output of 630 W per module, meeting the client’s mandatory requirement of a module power rating of ≥600 W. The open-circuit voltage (Voc) of each module is 49.49 V, which serves as the key parameter for the series and parallel design of the photovoltaic array.

3.3.1 Array Layout and Capacity Calculation

The total installed capacity of the PV system is 50.4 kWp, consisting of 80 630 W modules divided into 8 series strings, with 10 modules in series per string: voltage per string = 10 × 49.49 V = 494.9 V. This voltage falls within the 150–850V MPPT operating range of the SW3P50K-H inverter. Even under low-temperature winter conditions where the open-circuit voltage of the modules increases by 15%, the maximum voltage per string is approximately 569V, which remains well below the MPPT upper limit of 850V, thereby preventing shutdown due to DC overvoltage protection; The 8 strings of modules are evenly distributed across the inverter’s 4 MPPT channels, with every 2 strings connected in parallel to a single MPPT channel. The power input per MPPT channel is ≈12.6 kW, and the current remains within the 40 A rated input limit. Current distribution is balanced, maximizing MPPT tracking efficiency.

3.3.2 Electricity Generation and Roof Installation Compatibility

Each 630W N-type module is sized to fit standard rooftop PV mounting systems. With 80 modules installed on a building roof and based on South America’s average annual equivalent peak sunlight duration of 5 hours, the system’s average daily power generation is 50.4 kW × 5 hours = 252 kWh; During the day, solar power is prioritized to directly supply on-site three-phase loads, with excess electricity stored in a 128 kWh SW series lithium iron phosphate battery. This enables on-site consumption of electricity, reduces the cost of purchasing power from the grid, and serves as the core source of the project’s return on investment. N-type solar cells feature low degradation, strong low-light performance, and minimal high-temperature losses. The modules are encapsulated in high-weather-resistant aluminum frames and double-layered tempered glass, offering resistance to hail and UV aging. They are designed to withstand the high-temperature, rainy outdoor rooftop environments of South America and come with a 25-year warranty against power degradation.

IV. Detailed Explanation of the System’s Overall Operating Mode

The complete 50kW three-phase hybrid energy storage system supports four operating modes: grid-connected self-consumption, peak shaving and valley filling, off-grid backup during power outages, and standalone PV operation. The SW3P50K-H inverter automatically switches between these four modes based on grid voltage signals, battery SOC, and real-time PV generation, eliminating the need for manual intervention.

4.1 Grid-connected self-consumption (main operating condition during normal grid power supply hours)

During daylight hours, the 630W N-type photovoltaic array generates DC power, which is converted by the MPPT inverter into three-phase AC power with a phase voltage of 120V, a line voltage of 230V, and a frequency of 60Hz. This power is supplied directly to on-site loads at the facility as the first priority; When the PV power generation exceeds the real-time power consumption of the loads, the excess energy is converted back to DC via the inverter’s bidirectional power conversion module to charge the SW-314 lithium iron phosphate energy storage batteries. Once the battery SOC reaches the full-charge threshold, the system automatically feeds the excess power back into the South American public grid to generate revenue from grid-connected power sales; When PV generation is insufficient to meet load consumption, the grid automatically supplements the shortfall, enabling a combined PV and grid power supply.

4.2 Nighttime Energy Storage Discharge for Peak Shaving and Valley Filling (Under No-Light Conditions)

At night, when the photovoltaic system stops generating power, the inverter detects the load’s power demand and directs the energy storage battery to discharge. The battery’s DC power is converted and stepped up by the inverter to produce three-phase AC power (phase voltage 120V, line voltage 230V) to supply the load. This reduces nighttime grid power consumption, avoids using electricity during local peak-rate periods, and achieves peak shaving and cost reduction; When the battery’s State of Charge (SOC) drops to the minimum protection threshold, the inverter automatically cuts off battery discharge and switches to grid power alone to prevent deep discharge damage to the battery cells.

4.3 Off-Grid Backup Power Supply in the Event of a Mains Power Failure (Emergency Power Outage Conditions)

When power outages, malfunctions, or scheduled maintenance occur in the South American grid, the inverter rapidly disconnects the grid connection switch in less than 10 milliseconds and switches to standalone off-grid operation mode, with the entire system powered solely by a 128kWh energy storage battery, continuously outputting 50kW of rated three-phase AC power (120V per phase / 230V per line) to critical loads, ensuring uninterrupted operation of production equipment, security systems, and key office loads; Once the utility grid returns to normal, the inverter automatically verifies that grid parameters are within specifications and smoothly switches back to grid-connected operation mode, simultaneously resuming the photovoltaic charging and utility grid complementary logic. The entire switching process occurs without any power interruption or momentary outage.

4.4 Operation Mode for Isolated Sites in Overcast, Rainy, and Low-Light Conditions

During prolonged periods of rainy weather, the average daily power generation from the photovoltaic system drops significantly. The inverter prioritizes drawing on stored energy from the battery to support the load. Once the battery charge level drops to the lower limit, the utility grid steps in to provide backup power, preventing the system from shutting down. The redundant design of the 128 kWh high-capacity energy storage system significantly enhances the system’s self-sufficiency during adverse weather conditions.

V. Construction Standards for Rooftop Photovoltaic Installation and Indoor Energy Storage Installation

5.1 Installation Specifications for Rooftop Photovoltaic Modules

All 630W N-type photovoltaic modules are installed on the customer’s building roof. Aluminum alloy mounting brackets are selected based on the roof material (color-coated steel tiles or concrete roof). For color-coated steel tile roofs, clamp-based mounting is used to avoid drilling holes, thereby preventing damage to the roof’s waterproofing layer and potential leaks; For concrete roofs, counterweight-type mounts were used, eliminating the need for drilling holes for chemical anchors; modules were arranged with ventilation gaps to allow for heat dissipation, utilizing air convection to lower module operating temperatures and increase actual power generation; PV DC cables are selected from specialized flame-retardant PV1-F cables, which are routed through flame-retardant corrugated conduits along the roof structural beams for concealed installation. DC cables from 8 strings of modules are routed directly to the DC terminals of the inverter in the distribution room, minimizing voltage drop losses; protective fencing is installed around the perimeter of the rooftop PV array to mitigate risks of falling objects and accidental contact by personnel.

5.2 SW-314 Rack-Mounted Energy Storage Battery Installation Specifications

The 128kWh lithium iron phosphate energy storage batteries are mounted on standardized steel battery racks and installed on the floor of a dedicated indoor energy storage distribution room. The distribution room is equipped with ventilation, heat dissipation, moisture protection, and fire safety systems, and the ambient temperature and humidity are maintained within the batteries’ optimal operating range; Each cluster consists of three SW-314 battery modules stacked in a modular configuration on the rack. The high-voltage DC busbar is securely connected using copper busbars, and the three-phase AC output lines are connected to the inverter’s backup power distribution terminal; The battery BMS communication lines use shielded twisted-pair cables for point-to-point connection to the CAN communication port of the SW3P50K-H inverter. Shielded cabling prevents electromagnetic interference from power cables, ensuring stable communication data. The energy storage substation is equipped with fire suppression aerosol devices and temperature/smoke detectors, complying with fire safety regulations for energy storage facilities.

5.3 Installation Specifications for Inverter Power Distribution

The SW3P50K-H grid-tied inverter is wall-mounted in a nearby energy storage distribution room. The grid-connected AC side is equipped with a three-phase molded-case circuit breaker and a surge arrester to connect to the South American municipal 120/230V three-phase grid. The off-grid backup output side is independently configured with a feeder distribution cabinet to supply power to critical on-site loads via branch circuits; Each string branch on the inverter’s PV DC input is equipped with a DC fuse to provide individual protection for single-string faults, ensuring that normal power generation from the remaining seven strings is unaffected; the entire unit’s grounding system is connected to the building’s lightning protection grounding network, with a grounding resistance of <4 Ω, meeting electrical safety grounding standards.

VI. Electrical Safety Protection Design for the System

The entire system features multi-level electrical protection across the entire chain—from the PV DC side, through the energy storage battery side, to the AC grid-connection side and the backup load side—and is fully compliant with local electrical safety standards in South America:

DC-side protection

Each string in the PV array is equipped with a DC fuse. The inverter features built-in DC reverse connection protection, DC Type II surge protection, and arc fault circuit interrupter (AFCI) protection, which instantly disconnects the circuit in the event of lightning surges, reverse wiring, or line arc faults to protect the modules and the inverter;

Side protection for energy storage batteries

The SW-314 cell features built-in BMS protection against overcharge, over-discharge, overcurrent, and overtemperature at the cell level. The battery pack’s main output cable is equipped with a high-voltage DC circuit breaker, and the inverter side is configured with synchronized software protection against overcurrent during battery charging and discharging. This dual-layer protection effectively prevents battery thermal runaway;

AC Grid-Connected Side Protection

The inverter features built-in anti-islanding protection, which instantly disconnects from the grid in the event of an abnormal islanding condition, thereby preventing PV backfeed from causing harm to grid maintenance personnel; the AC side is equipped with AC Type II surge protection and plastic-case circuit breakers rated for overvoltage and overcurrent, which help mitigate damage to the inverter caused by grid surges;

Off-Grid Load-Side Protection

The backup power distribution cabinet is equipped with branch-specific ground-fault circuit interrupters (GFCIs) and overload circuit breakers; in the event of a short circuit in a single circuit, only the corresponding branch is disconnected, preventing a system-wide shutdown.

VII. Overview of System Operations, Maintenance, Monitoring, and Return on Investment

7.1 Remote Intelligent Monitoring and Maintenance

The SW3P50K-H inverter features built-in Bluetooth, Wi-Fi, and Ethernet connectivity. Customers can use a mobile app or web browser to remotely monitor the system 24/7, tracking real-time power output, daily generation, cumulative generation, battery SOC (State of Charge), battery temperature, and equipment fault alerts. In the event of a malfunction, the system automatically sends SMS or app alerts, enabling maintenance personnel to quickly diagnose and resolve issues; The SW series battery BMS synchronously uploads data to the monitoring platform, providing full visualization of battery string voltage, cell temperature, and charge/discharge currents, thereby simplifying the troubleshooting of energy storage system faults.

7.2 Project Revenue Forecast

The system generates an average of 252 kWh per day. Self-generated electricity is prioritized to offset grid purchases, while surplus electricity is fed into the grid to generate revenue. Combined with a 128 kWh energy storage system for nighttime peak-shaving, the system leverages South America’s tiered commercial and industrial electricity rates to reduce electricity costs year by year; With a 25-year power output warranty for N-type solar modules, a 15-year design life for the SW-314 lithium iron phosphate battery, and low lifecycle O&M costs for the SW3P50K-H inverter, the project typically recoups the initial equipment investment within approximately 5 years, with all solar power generation revenue for the remaining years constituting pure profit.

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VIII. Summary of the Proposal

This 50kW three-phase 120/230V, 60Hz rooftop hybrid solar-storage system was designed and implemented in strict accordance with all six of the customer’s custom requirements. The SW3P50K-H three-phase grid-tied inverter was selected to match the local voltage and frequency specifications of 120V phase-to-phase, 230V line-to-line, and 60Hz. The PV system utilizes 630W high-power N-type modules to meet the ≥600W power requirement, while the 128kWh rack-mounted SW-314 lithium iron phosphate (LFP) energy storage unit far exceeds the minimum 100kWh capacity standard. The entire system is installed across both the rooftop and indoor zones to accommodate on-site construction conditions. System parameters have undergone triple verification for voltage, current, and power. The PV MPPT voltage, battery connection voltage, and AC/DC output specifications are all precisely matched. The system balances power generation efficiency, energy storage stability, electrical safety, and future expansion potential. Leveraging the superior high-temperature performance of N-type modules, it is optimized for South American power grids and climatic conditions, making it a mature commercial and industrial PV-storage solution that integrates self-consumption, emergency backup, and cost-saving efficiency.