Air-oil Finned Tube Coolers Used in Outdoor Solar Plants
Air-oil finned tube coolers are widely used in outdoor solar (PV) plants as the primary cooling solution for PV inverter transformers and auxiliary oil systems. They are well suited to harsh outdoor conditions and fluctuating solar loads.
What they are
An air-oil finned tube cooler is a heat exchanger in which hot transformer oil flows through tubes fitted with external fins, while ambient air is forced across the fins by axial fans. The fins increase surface area, enabling efficient heat rejection from oil to air.
Why they are used in outdoor solar plants
Air-oil finned tube coolers are preferred in PV plants because they:
Do not require water, which is often scarce at solar sites
Perform reliably in high ambient temperatures (typically up to 45–50 °C)
Handle variable thermal loads caused by changing solar irradiance
Are simple, robust, and low-maintenance
Typical applications
PV inverter transformers (medium-voltage step-up transformers)
Auxiliary oil cooling systems in solar substations
Energy storage system (ESS) transformers in hybrid plants
Key design features for outdoor use
- OFAF cooling concept (Oil Forced, Air Forced)
- Carbon steel or stainless steel headers
- Aluminum or copper finned tubes for high heat transfer
- Axial fans with IP55/IP56 motors
- Hot-dip galvanized or powder-coated frames
UV- and corrosion-resistant coatings
Performance characteristics
Cooling capacity: from a few kW to several hundred kW
Oil operating temperature: typically 60–85 °C
Continuous duty with staged or temperature-controlled fan operation
Modular design allows capacity expansion
Advantages in solar plant environments
High reliability in dusty, remote locations
Lower operating cost compared with liquid-to-liquid systems
Easy installation and scalability
Long service life with minimal service intervention
Maintenance considerations
Periodic cleaning of fins to remove dust and sand
Fan inspection and bearing checks
Monitoring oil temperature and pressure drop
Visual inspection for corrosion or oil leakage
Summary
In outdoor solar plants, air-oil finned tube coolers provide an efficient, water-free, and rugged cooling solution for PV inverter transformers. Their ability to withstand high ambient temperatures, variable loads, and harsh environments makes them a standard choice in modern utility-scale photovoltaic installations.
