Solar Power Plant Electrical System: Where Is the Power Transformer Used?

Introduction

In a modern solar power plant, the power transformer is one of the most critical components in the entire electrical system. It is responsible for stepping up the voltage generated by photovoltaic (PV) inverters and enabling efficient transmission to the utility grid.

Since solar panels generate low-voltage DC electricity, which is then converted into AC power by inverters, the output voltage is still not suitable for grid transmission. A solar power transformer (step-up transformer) is required to increase voltage levels such as 0.8kV to 10kV or 35kV, depending on the system design.

This article explains where the power transformer is used in a solar power plant, how it fits into the electrical system, and how voltage levels like 10kV and 35kV are applied in real photovoltaic projects.

1. Overview of Solar Power Plant Electrical System

A typical solar power plant electrical system consists of several key stages that convert solar energy into grid-compatible electricity.

Standard Power Flow Structure:

Solar PV Modules → Combiner Box → Inverter → Power Transformer → Switchgear → Grid

Each stage plays a specific role in energy conversion and transmission.

Key Roles of Each Component:

• PV Modules: Generate DC electricity from sunlight
• Combiner Box: Aggregates DC power strings
• Inverter: Converts DC into AC power
• Power Transformer: Steps up voltage for grid transmission
• Switchgear System: Controls and protects electrical flow
• Grid Connection: Final integration into utility network

Among these, the power transformer is the critical bridge between generation and transmission.

2. Where Is the Power Transformer Used in Solar Power Plants?

The power transformer in a solar power system is installed after the inverter stage and before grid connection.

Function Location:

Inverter output → Power Transformer → Medium/High Voltage Switchgear → Grid

Main Functions:

• Step-up low voltage (0.4kV / 0.8kV) to medium voltage (10kV / 35kV)
• Enable long-distance electricity transmission
• Reduce power losses in cables
• Ensure grid compliance standards

Without the power transformer, solar plants cannot safely or efficiently connect to utility grids.

3. Voltage Levels in Solar Power Systems (0.8kV / 10kV / 35kV)

Voltage design is one of the most important engineering decisions in a solar power plant.

3.1 0.8kV (Low Voltage Side)

This is the output voltage from most solar inverters.

• Used inside inverter stations
• Not suitable for grid transmission
• Requires immediate step-up transformation

3.2 10kV Medium Voltage System

The 10kV system is commonly used in:

• Small to medium solar power plants
• Distributed photovoltaic systems
• Industrial solar installations

Characteristics:

• Lower investment cost
• Simpler electrical design
• Short to medium distance transmission

3.3 35kV Medium-to-High Voltage System

The 35kV system is widely used in:

• Utility-scale solar farms
• Large ground-mounted PV projects
• Centralized solar generation systems

Advantages:

• Lower transmission losses
• Higher efficiency for long-distance power delivery
• Reduced number of transformer units per MW

4. Box-Type Substation (Solar Compact Substation)

In modern solar projects, the box-type substation (compact substation) is widely used to integrate multiple functions into one unit.

Typical Structure Includes:

• Step-up Power Transformer (0.8kV → 10kV or 35kV)
• High-voltage switchgear
• Protection and control system
• Measurement and monitoring equipment

Advantages:

• Compact design (space-saving)
• Factory pre-assembled
• Easy transportation and installation
• High reliability for outdoor solar farms

This design is especially common in desert and large-scale utility solar projects.

5. 10kV vs 35kV Transformer Application in Solar Plants

The selection between 10kV and 35kV depends mainly on project scale and grid requirements.

Engineering Insight:

• 10kV systems are often used in distributed or modular solar projects
• 35kV systems are preferred in centralized grid-connected solar farms

6. Role of Power Transformer in Grid Integration

The final and most important role of the power transformer in a solar power plant is grid integration.

Key Functions:

• Voltage matching with utility grid (10kV / 35kV / 110kV)
• Power quality stabilization
• Isolation between generation and grid
• Fault protection and system reliability

By ensuring voltage compatibility, the transformer allows solar energy to be safely injected into the national grid.

7. Why Power Transformers Are Critical in Solar Projects

Without a properly designed transformer system, solar power plants would face:

• High transmission losses
• Grid incompatibility issues
• Equipment overload risks
• Reduced system efficiency

Therefore, selecting the right solar power transformer is essential for:

• EPC contractors
• Project developers
• Utility companies
• Renewable energy investors

FAQ – Solar Power Plant Power Transformer

What is a power transformer in a solar power plant?

A power transformer is used to step up inverter output voltage (0.4kV/0.8kV) to medium or high voltage levels like 10kV or 35kV for grid transmission.

Where is the transformer located in a solar system?

It is installed between the inverter output and the grid connection system.

Why do solar farms use 35kV transformers?

Because 35kV systems reduce transmission losses and improve efficiency in large-scale solar power plants.

What is a box-type substation in solar projects?

It is a compact integrated unit that includes a transformer, switchgear, and protection systems for solar power plants.

Conclusion

In a solar power plant, the power transformer plays a central role in converting inverter output into grid-ready electricity. It is positioned between the inverter and the grid connection system, enabling safe and efficient power transmission.

The choice between 10kV and 35kV systems depends on project scale:

• 10kV for distributed and medium-scale solar plants
• 35kV for utility-scale solar power stations

As solar energy continues to expand globally, the demand for efficient and reliable solar power transformers will continue to grow across EPC and utility sectors.