How to Use a Drone to Do EL Testing (Electroluminescence) for Solar Panels

What is Electroluminescence?

Electroluminescence (EL) is a special kind of light that Solar Panels give off when electricity is applied to them. It’s not the kind of light we can see with our eyes—it’s usually in the near-infrared range—but special cameras can detect it.

When a solar panel is connected to a power source that applies a small forward voltage, it starts to emit this faint light from inside the Solar Cells. If the solar panel has cracks, broken connections, or other hidden problems, some areas won't shine as brightly—or may not shine at all. These "dark spots" on the EL image show exactly where the defects are.

EL testing is super helpful because it doesn’t damage the panel and shows problems that the human eye, or even basic cameras, can’t detect. It’s like giving the solar panel an X-ray!

Methods of Applying EL Solar Testing

There are two main ways to do EL testing:

1. Indoor EL Testing

This is done in a lab or factory. The solar panels are placed in a dark room where conditions like lighting and temperature are carefully controlled. High-resolution cameras take EL images while electricity is passed through the panel. This method is great for research, quality control, and checking new panels before they leave the factory.

2. Outdoor EL Testing

Outdoor EL testing is used on installed solar panels in fields or rooftops. Since you can’t move those panels into a lab, technicians bring the EL testing to the site. It’s a bit trickier outdoors because sunlight, wind, and uneven terrain can affect image quality and safety. There are two main types of outdoor EL testing equipment: portable devices and drones.

Portable EL Testing Devices

Portable EL testing devices are small, mobile kits that include a power supply, EL camera, and sometimes a foldable dark cover. These are usually mounted on tripods or handheld stands and used by technicians to inspect one panel at a time.

The benefit of this method is its low cost and relatively simple setup. It allows close-up inspection and detailed imaging. However, it’s time-consuming. Technicians must manually move the equipment from one panel to the next, which can take hours or even days for large solar farms. This makes it better for spot-checking or inspecting small systems like rooftop installations.

It’s also usually done at night or in low light, because strong sunlight can overpower the faint EL glow.

Drone-Based EL Testing

Drones offer a high-tech and efficient way to perform EL testing over large solar installations. These drones are equipped with specialized EL cameras and sometimes include onboard power sources. They fly above the panels, taking infrared images while the system is energized.

This method can scan hundreds of solar panels in a short time and access hard-to-reach places safely—like tall rooftops or remote desert farms. The flight path is pre-programmed or guided manually, and results are analyzed using software after the flight.

Drone-based EL testing does require trained operators who understand both drones and solar systems. Also, external conditions like wind, rain, or bright sunlight can affect the clarity of images. And because standard testing rules for drones are still developing, accuracy can vary depending on who’s flying and how well the environment is controlled.

Still, drones are becoming more popular because of their speed and flexibility. Many solar companies now use drone EL testing as part of regular solar panel maintenance and troubleshooting.

What is an EL Testing Drone?

An EL testing drone is a flying robot specially designed to inspect solar panels using EL technology. It carries a lightweight EL camera and a small power source to apply voltage to the panels while flying over them. The drone captures EL images from above, showing which panels are healthy and which ones need repair.

These drones are built to fly steadily and take sharp images, even in tricky conditions like strong sunlight or wind. They are controlled by trained operators who understand both drone flight and how EL works.

Using drones makes EL testing much faster and safer—especially when inspecting large fields of solar panels that would take days to check manually.

How to Apply EL Testing with an EL Testing Drone

To use a drone for EL testing, follow these main steps:

Step 1: Preparation

First, technicians plan the flight path using mapping software. The area to be inspected is divided into grid zones so the drone can cover every solar panel. Batteries, the EL camera, and control systems are all checked to make sure they’re working properly.

Step 2: Power Connection

To make the solar panels emit electroluminescent light, a current needs to be applied. This can be done by connecting the panels to a power supply before the drone flight. The timing must match the drone’s imaging so that the EL light can be recorded clearly.

Step 3: Drone Flight and Image Capture

The drone flies over the solar panels at a low altitude, taking EL images with its specialized camera. It follows the planned route automatically or with manual guidance, depending on the system used. The flight is usually done at night or in low-light conditions, so ambient sunlight doesn’t interfere with the EL signal.

Step 4: Image Processing

After the drone lands, the EL images are uploaded into software that processes and analyzes them. Dark spots or irregularities in the images point to defects like cracks, weak cells, or poor electrical connections.

Step 5: Maintenance and Reporting

Based on the analysis, technicians can decide which panels need fixing or replacing. This helps solar farms stay efficient and avoid bigger problems later. Reports with the EL images and findings are often shared with maintenance teams or sent to the solar plant operators.

The Pros and Cons of EL Testing Drones

The Pros of EL Testing Drones

High Efficiency: Drones can cover large solar farms much faster than manual inspections, saving time and labor costs.

Non-Invasive and Safe: Since no physical contact is required with the panels, there's less risk of damage or accidents during inspections.

Detailed Imaging: Drones equipped with EL cameras can capture high-resolution images, revealing defects invisible to the naked eye or standard cameras.

Accessibility: Drones can easily reach areas that are hard to access for technicians, like tall rooftops or remote desert farms.

Reduced Downtime: Because drone inspections are quicker, solar panel systems experience less operational downtime during testing.

The Cons of EL Testing Drones

Weather Dependent: Wind, rain, and bright sunlight can affect flight stability and image quality. EL testing typically needs to be done at night or in low-light conditions.

High Initial Cost: Specialized drones and EL imaging equipment can be expensive, which may be a barrier for small businesses or schools.

Requires Expertise: Operators need to understand both drone flight and EL testing procedures, including synchronization of power supply and camera settings.

Limited by Battery Life: Drones can only fly for a limited time before needing to recharge, which may require multiple flights for large areas.

Lack of Standardization: Industry-wide standards for drone-based EL testing are still being developed, which can result in inconsistent data quality and interpretation.