Operating Mechanism of the 6.5kW Single-Phase Hybrid Grid-Tied PV-Storage Integrated System

The power generation unit of the system adopts high-efficiency N-type TOPCon double-glass monocrystalline modules. Based on mature half-cut cell technology, it features high conversion efficiency and low attenuation over the full lifecycle, making it the mainstream preferred product for residential PV-storage scenarios. Core electrical parameters under Standard Test Conditions (STC: 1000W/m² irradiance, 25°C cell temperature, AM1.5 spectrum):

• Maximum Power (Pmax): 590Wp
• Maximum Power Voltage (Vmp): 42.65V
• Operating Current (Imp): 13.60A
• Open-Circuit Voltage (Voc): 51.86V
• Short-Circuit Current (Isc): 14.50A
• Module conversion efficiency: 22.80%

As the core of energy conversion and intelligent control for the entire system, the 6.5kW single-phase hybrid inverter integrates four core functions: PV MPPT tracking, bidirectional battery charging & discharging, grid-tied inversion and off-grid emergency power supply, specially customized for 48V low-voltage energy storage systems.

• Rated AC output power: 6.5kW; maximum conversion efficiency up to 97%; MPPT tracking efficiency over 99%, capturing maximum PV DC power.
• DC MPPT operating voltage range: 60V~500VDC, covering the voltage range of most residential PV strings with wide compatibility.
• Built-in multi-layer electrical protection logic: DC overvoltage, undervoltage, overcurrent, short circuit and overtemperature protection. Its charging voltage regulation range perfectly matches the standard operating voltage of LFP energy storage batteries.
• The unit outputs pure sine wave AC power, compatible with all household loads including refrigerators, air conditioners, motors and digital devices.
• Equipped with mobile APP remote monitoring, users can view real-time PV generation, battery SOC, load power consumption and grid interaction data, and conduct remote parameter debugging for convenient operation & maintenance.
• Supports automatic switching between grid-tied and off-grid modes; it switches to off-grid power supply within milliseconds upon grid failure to guarantee continuous power for critical loads.

The prerequisite for stable operation of a PV-storage system is that the PV string voltage across all temperature ranges falls within the inverter’s MPPT operating range of 60V~500VDC. This scheme adopts a single string of 6 pieces of 590Wp modules in series; total voltages under standard temperature, extreme low temperature and extreme high temperature are calculated separately to verify rational matching.

1. Voltage Calculation under Standard 25°C STC Conditions

Single module Voc=51.86V, Vmp=42.65V Total open-circuit voltage of 6 modules in series: 51.86V × 6 = 311.16V Total maximum power voltage of 6 modules in series: 42.65V × 6 = 255.9V Under conventional illumination at 25°C, the string operating voltage stays steadily between 255.9V~311.16V, fully within the inverter’s 60V~500V MPPT range. The inverter can continuously track the maximum power point accurately without power generation loss.

2. Voltage Check under Extreme Low Temperature (-10°C)

PV open-circuit voltage rises as temperature drops under low-temperature conditions, which is the main risk factor triggering overvoltage protection. Voc temperature coefficient of modules: -0.25%/°C, temperature difference ΔT=25-(-10)=35°C Single module open-circuit voltage increase: 51.86 × 0.25% × 35 = 4.53V Maximum single module Voc under low temperature: 51.86 + 4.53 = 56.39V Total open-circuit voltage of 6 modules in series: 56.39 × 6 = 338.34V 338.34V is far lower than the inverter’s MPPT upper limit of 500V, reserving sufficient safety margin. No DC overvoltage protection will be triggered under low temperature, enabling continuous and stable power generation of the system.

3. Voltage Check under Extreme High Temperature (70°C)

High temperature reduces module voltage, bringing hidden risks of falling below the MPPT lower limit and failing to track maximum power. Temperature difference ΔT=70-25=45°C Single module open-circuit voltage drop: 51.86 × 0.25% × 45 = 5.83V Minimum single module Voc under high temperature: 51.86 - 5.83 = 46.03V Total open-circuit voltage of 6 modules in series: 46.03 × 6 = 276.18V Meanwhile, the total string Vmp voltage under high temperature is approximately 227V. Both values are much higher than the inverter’s minimum MPPT voltage of 60V. The inverter can still stably capture PV power during high-temperature noon periods with high power output, without power loss.

Based on full-temperature range calculation results, the voltage range of the 6×590Wp series module configuration is 227V~338.34V, fully covered by the inverter’s 60V~500VDC MPPT operating window. The string design is scientific and reasonable without voltage matching defects.

The whole system is designed for a daily power generation of 17.7kWh and a daily energy storage capacity of 10kWh, operating under two modes: normal grid-tied mode and off-grid emergency mode.

Grid-Tied Operating Logic

The system follows the strategy of "PV power for self-consumption first, surplus power stored, full battery power exported to grid": During daytime, electricity generated by PV modules prioritizes household loads including air conditioners, lighting and kitchen appliances. Remaining power after consumption is automatically stored in the 10kWh energy storage battery. During nighttime or cloudy days with insufficient PV generation, the storage battery discharges to supply loads first; the system only switches to grid power when the battery is fully depleted. In regions with large peak-valley electricity price gaps, users can configure the system to charge the battery via grid power during low-price off-peak hours and discharge the battery during expensive peak hours to realize peak-valley arbitrage and drastically cut monthly electricity bills.

Off-Grid Emergency Operating Logic

When the grid loses power, the system automatically switches to off-grid mode. PV modules and the 10kWh storage battery jointly supply power to guarantee uninterrupted operation of critical loads such as lighting, refrigerators and surveillance cameras, ideal for rural areas, old residential compounds and remote regions with unstable grid power supply.

Long-Term Investment Value

N-type PV modules come with a 20-year power output warranty, and the energy storage battery boasts ultra-long cycle life, making the full equipment lifecycle exceed 20 years. Only minimal operation & maintenance costs are required after upfront investment, realizing massive electricity bill reduction or even zero electricity expenditure in the long run. Modular equipment design supports later expansion; users can add PV modules or parallel storage batteries to scale up power generation and storage capacity, catering to the growing household power consumption demand year by year.