Best thermal cameras for solar inspection

What the camera needs to reveal on a solar installation

A solar panel turns part of the light into electricity and the rest into heat. When a cell no longer works properly (crack, degradation, shading, poor solder joint), it stops contributing and can even dissipate its neighbours’ energy: it becomes a hot spot. Thermography finds these anomalies panel by panel, without removing anything or shutting the installation down.

The most common targets are isolated hot cells, whole substrings running warmer (often linked to an active or failed bypass diode), disconnected panels that appear uniformly warmer than their neighbours, and hot connections in junction boxes, connectors and combiner boxes. Outdoor thermography of PV modules and plants is described in the technical specification IEC TS 62446-3.

Getting the measurement conditions right

• Measure while producing, under a clear sky with stable sunshine: a fault only heats up when the panel is producing. IEC TS 62446-3 notably recommends sufficient irradiance, commonly quoted as at least around 600 W/m². Passing clouds distort comparisons.
• Mind the viewing angle: the panel glass reflects the sky, the sun and the operator. Avoid aiming strictly perpendicular, which returns your own reflection, and very shallow angles, where reflection dominates. Change position to tell a reflection from a real hot spot.
• Compare panels with one another: they are identical and under the same sunshine. Comparison reveals the anomaly more than the absolute value does.
• Record the conditions: irradiance, ambient temperature, wind and time of day. They determine how severe a fault appears.

Distance, target size and resolution

The typical situation used by the selector is an area of about 15 cm seen from 5 m: a cell viewed from the ground or from the edge of a roof. A cell is usually 16 to 21 cm across, and half-cut cells are half as wide. For a defect to be located unambiguously, a cell must cover several pixels in each direction.

Example: with a 256 × 192 sensor and a 50° field of view (IFOV about 3.4 mrad), one pixel covers about 1.7 cm at 5 m. The measurable area with our five-pixel margin is about 8.5 cm, smaller than a cell. At 10 m that area grows to 17 cm: you can still spot a faulty panel, but no longer a specific cell. For inaccessible roofs and large plants, drone thermography changes the scale; that equipment has its own specialized ranking and the article thermal cameras for drones.

What matters, and what matters less

• Spatial resolution: the decisive criterion, because distance is often dictated by access. A 320 × 240 sensor or better, or a narrower field of view, is comfortable for inspecting from the ground.
• Temperature range: hot spots can exceed 100 °C on a panel in full sun; a range reaching at least 150 °C is prudent.
• Radiometric images and reporting: to document a warranty defect or monitor a fleet, images must be re-analysable and linked to the measurement conditions.
• Overlay with the visible image: it identifies the exact panel and rules out dirt, bird droppings or cast shadows.
• What matters less: very high sensitivity (faults usually produce differences of several degrees) and, for ground-level inspection, frame rate.

Common pitfalls

Reflection is the number one pitfall: a reflection of the sun or a warm cloud on the glass looks like a hot spot. A reflection moves when you move; a real defect stays attached to its cell. The second pitfall is shading and soiling: a chimney shadow or a bird dropping causes real but temporary heating, which is not a panel defect. The third is measuring through the glass while believing you measure the cell: the camera sees the glass surface, slightly cooler than the cell beneath. Values are therefore indications, and comparison between panels remains the safest method. Finally, an inspection on an overcast day may show no defects even though they exist.

Phone attachment or standalone camera?

For a homeowner checking their own accessible installation, a module with good resolution can be enough, but a phone screen is hard to read in full sun, which is exactly when you need to measure. For installers and maintenance teams, a standalone camera with a bright screen or viewfinder, visible overlay and reporting software is far better suited. Both formats are ranked separately above.

What budget should you plan?

To check a small accessible installation, the €€ to €€€ bands (€200 to €1,000) are suitable, provided you choose a native sensor of at least 256 × 192 and stay close to the panels. For installation or maintenance work, aim for €€€€ to €€€€€ (€1,000 and above): high resolution, reporting software and, if needed, a lens suited to longer distances. Large plants are better served by drone inspection. See the price ranges page.

Frequently asked questions

Can I inspect panels from the ground?

Yes, if the distance stays reasonable and the angle is favourable. Beyond about ten metres, or for a low-pitched roof seen from below, resolution and reflections become limiting, and a thermal drone takes over.

Does a hot spot always mean a faulty panel?

No. A shadow, dirt or a reflection produce similar images. Check that the anomaly persists, does not move with your viewpoint and is not caused by an external object.

Should I inspect at a particular time?

Preferably during hours of strong, stable sunshine, often around midday. Avoid early morning, evening and cloudy days, when production is too low or too variable.

What resolution do I need to see a cell?

It depends on the distance. The selector calculates, for your distance and cell size, whether a device can resolve them.