Preface

A car wash in Romania now runs on clean energy. This car wash has numerous machines with high instantaneous power demand. With rising electricity prices, sudden power tripping is a major threat to its business. This solution adopts 100 pieces of 580W high-efficiency PV modules, 2 sets of 30kW solar-storage hybrid inverters and 2 sets of 30kWh high-voltage lithium energy storage batteries, forming an intelligent power supply system integrating on-site consumption of self-generated power, surplus energy storage and off-grid backup power. During daytime, electricity generated by PV modules directly supplies car wash equipment, and excess power is stored in batteries. At night or on cloudy days, batteries take over power supply to ensure non-stop car wash operations. The system achieves an average daily power generation of approximately 290 kWh and a daily stored energy of 60 kWh. The coordinated operation of PV and storage cuts electricity bills and provides reliable backup protection for the car wash against power failures.

Layout Drawing of Key Indoor Equipment

This document elaborates on equipment specifications, string connection design, operating principles and load capacity, delivering a complete, easy-to-understand, calculable and implementable solution for the property owner.

1. System Configuration Overview

Customized for a car wash in Romania, the complete system consists of three core components.

System Configuration Diagram

The photovoltaic power generation side is equipped with 100 pieces of 580W high-efficiency monocrystalline PV modules, with a total installed capacity of 58kW. The energy storage side adopts 2 sets of 30kWh high-voltage stacked lithium battery packs, with a total capacity of 60kWh and a cycle life of ≥8,000 times. The core power conversion equipment includes 2 units of 30kW solar-storage hybrid inverters, with a combined rated power of 60kW.

The three parts work together to form a grid-tied and off-grid dual-mode solar-storage system. In daytime, PV power supplies car wash loads with priority, and surplus electricity charges the batteries. At night, batteries discharge to support equipment operation for energy self-sufficiency. The whole system generates around 290 kWh daily and stores 60 kWh per day, fully meeting the high-power and long-duration power demand of the car wash.

2. Main Equipment Specifications

580W High-Efficiency PV Modules

Outdoor Rooftop PV Installation Drawing

100 pieces of 580W high-efficiency monocrystalline PV modules are deployed, with a conversion efficiency up to 22.5%.

• Open-circuit voltage Voc=51.46V
• Operating voltage Vmp=42.65V
• Operating current Imp=13.60A
• Short-circuit current Isc=14.38A
• Dimensions: 2279×1134×30mm
• Weight: approx. 32kg per module

The half-cut cell design effectively reduces hot spot and shading losses. According to string calculation, the operating voltage of each string falls within the inverter MPPT voltage range (150~850V), and the string current is far below the maximum input current of the inverter, ensuring reliable matching. The modules support wide-temperature operation from -40℃ to +85℃, capable of coping with cold winters and hot summers in Romania, featuring low long-term outdoor power attenuation as the main power generation unit of the system.

30kW Solar-Storage Hybrid Inverter

2 units of 30kW three-phase solar-storage hybrid inverters are used, integrating PV inversion, battery charge-discharge and grid/off-grid switching in one compact unit.

• Rated output power: 30kW
• Maximum apparent output power: 30kVA
• European efficiency: up to 97.8% with low energy loss
• 3 independent MPPT channels, MPPT voltage range: 150~850V
• Maximum PV input voltage: 1000V, flexible for various string designs
• Battery port supports 150~800V high-voltage lithium batteries, max charge/discharge power: 33kW

The highlight is its ultra-fast grid-off switching within <10ms. Once the mains supply fails, the system switches to battery power in milliseconds without interruption or stalling of car wash equipment. The whole unit reaches IP65 protection rating, operating from -25℃ to +60℃. Each unit weighs only 73kg, supporting wall-mounted and floor installation for easy setup and maintenance.

60kWh High-Voltage Energy Storage Lithium Battery

2 sets of 30kWh high-voltage stacked lithium battery packs are deployed, with a total capacity of 60kWh. Adopting lithium iron phosphate cells, the battery features high safety, stability and long service life.

• Rated system voltage: 307V
• Operating voltage range: 252~348V
• Rated DC power: 30kW
• Maximum charge/discharge current: 100A
• Cycle life ≥8,000 times. With one full charge and discharge cycle per day, stable service life can exceed 20 years, bringing extremely low long-term operating cost.

The battery packs support CAN/RS485 communication for seamless coordination with hybrid inverters and automatic charge-discharge strategy execution. Adopting rack-mounted/stacked structure, it occupies limited space. Built-in BMS (Battery Management System) monitors voltage, current and temperature in real time, with multiple protections against overcharge, overdischarge, overcurrent and overheating for reliable and safe operation.

3. PV String Connection Design

100 PV modules are evenly allocated to 2 hybrid inverters, with 50 modules per unit. Considering the rise of open-circuit voltage caused by low temperature in Romanian winters, the string design satisfies two key requirements: successful startup and no overvoltage. Each inverter is divided into 3 strings in the configuration of 17 modules +17 modules +16 modules, connected to 3 MPPT channels respectively. One string connects to one MPPT channel without parallel connection, fundamentally avoiding string mismatch and circulating current issues.

System Topology Diagram

Calculation results:

• String with 17 modules: Vmp≈725V, Voc≈875V
• String with 16 modules: Vmp≈682V, Voc≈823V

All values fall within the inverter MPPT voltage window of 150~850V and exceed the 600V startup voltage. The open-circuit voltage of each string under low-temperature conditions remains below the 1000V upper limit with sufficient safety margin. The string current is only 13.6A, well below the maximum input current of MPPT channels. Each inverter carries a PV capacity of 29kW, lower than the maximum recommended PV access capacity of 60kW, achieving reasonable matching.

4. System Operating Principle

The system operates on the logic: PV power priority, energy storage buffering, off-grid backup.

Animated Video of System Operation Principle

When sunlight is sufficient during daytime, the inverter tracks the maximum power point of PV strings via MPPT, converts DC power to AC power and supplies loads such as car wash machines, water pumps and lighting with priority. When power generation exceeds load consumption, surplus electricity charges the lithium battery until the 60kWh storage is fully charged. When PV output drops or at night, the battery automatically discharges to cover power shortage and guarantee continuous equipment operation.

In case of mains power failure, the inverter completes off-grid switching within 10ms, and PV together with batteries independently support loads to achieve uninterrupted power supply. The system automatically reconnects to the grid once mains power restores.

The whole process is coordinately controlled by BMS and inverters, which intelligently dispatch energy from PV, battery and grid, prioritizing self-consumption, cost saving and uninterrupted operation.

5. Load Power & Duration Table

The table below shows the continuous power supply duration under different load power of the system (60kWh energy storage, 90% depth of discharge, usable energy ≈54kWh):

Supplementary note: A single inverter supports 160% short-time overload (25s), delivering stronger peak load capacity. Actual power supply duration will slightly fluctuate due to equipment starting current, battery SOC and ambient temperature.

Conclusion

This solution builds an integrated intelligent solar-storage system for power generation, energy storage and backup power for the Romanian car wash. Featuring 100 pieces of 580W PV modules (58kW installed capacity) with around 290 kWh daily power generation, 60kWh energy storage with 60 kWh daily stored energy, and 2 sets of 30kW hybrid inverters with total 60kW load capacity, plus <10ms fast grid/off-grid switching, the car wash can cut electricity expenses and maintain operation during power outages.

String calculation verifies that voltage and current of all strings stay within the operating range of inverters with adequate safety margin under low-temperature conditions for reliable operation. With a battery cycle life ≥8,000 times at one charge-discharge cycle per day, the system requires low long-term maintenance cost and features a short payback period. For a car wash with concentrated power consumption and zero tolerance for shutdown, this solution balances energy self-sufficiency and cost reduction, serving as a stable choice for green and low-carbon operation.