Drones Aren't Good Enough. Change My Mind

Thermal imaging makes a visual inspection MUCH more effective. Normally, destructive testing would be necessary to understand the internal health of a connector, but with thermal imaging, we can have a sense of what’s going on inside the connector casing by measuring its temperature.

Why do we care about connector temperature?

We care about the temperature because we care about resistance. We care about resistance because it reduces current flow. We care about current flow because we care about performance and reliability. And the more resistance we have, the more heat we generate therein converting electricity to heat rather than using it / selling it.

Power (heat lost) ?= ?(Current) 2 ?x ?Resistance >> Reduce resistance, reduce power lost to heat

Ideally, our connectors would have the same resistance as any cross-section of wire in the array, but that’s not the case. Bad connectors will have a higher-than-normal resistance, leading to high connector temperatures which can potentially melt connectors, create arc faults, and result in fires.

Find these issues with thermal imaging before connectors fail.

How does thermal imaging work?

Thanks to Max Planck and Gus Kirchhoff we know that, in radiative heat transfer, the electromagnetic wavelength of emitted photons from an object correlates directly with the temperature of that object. This occurs in the infrared spectrum, so we need a special camera. ?Effectively, with an infrared camera, we can measure the surface temperature of an object.

Original image owned by?PROTHERM

NOTE: Thermal cameras show the surface temperature of an object, not the internal temperature! So remove that combiner box cover and open that inverter door to image the connections!

Importantly with connectors, we’re just seeing the surface temperature of the connector, the internal connection is the source of that heat and would be hotter than the surface temperature.

Also, this imaging relies on the flow of electrons, so make sure your system is energized and a minimum amount of current is flowing.

DON’T SEND IN THE DRONES

?Drones can be an excellent addition for site assessments, but not when you’re looking at connectors. Good wire management involves limiting UV exposure, so naturally, aerial photography would not be a great way to see connectors! Getting under modules and taking a really close look at connectors is usually beyond the capability of drones.

We operate in a young industry and the lack of standards is apparent. So, what do industry best practices have to say about how we should conduct thermal imaging of connectors?

We have seen 3 approaches to thermal imaging module connectors in the field. Consider these approaches for both field-made and factory-made connector samples:

1. ?Define a temperature threshold as pass/ fail criteria. For example, connector manufacturers may define 85°C as a maximum allowable temperature for a connector. Connectors above this temperature should be rejected.
2. Define pass/ fail criteria based on specific irradiance and ambient temperature ranges. For example, connector temperature should not exceed 70°C when irradiance is between 800 – 1,000 W/m2 and Tamb is between 30 – 35°C.
3. Create a baseline average for set conditions and define pass/ fail criteria based on a deviation from that baseline average. For example, establish a baseline temperature average of 10 connectors, consider this baseline average valid for 1 hour, fail connectors that deviate by +20°C from the baseline temperature.

We have found that a combination of Approaches 1 and 3 result in a high confidence in connector inspections. Catching the manufacturer-defined extreme temperature is a must (Approach 1). Understanding connector temperature relative to like-connectors in like-conditions gives a great sense of connector abnormalities (Approach 3).

When you find those connectors, make sure you take appropriate corrective actions and flag where you found the issue! We built SolarGrade to do just that and track these issues over time. Test drive SolarGrade for free at SolarGrade.io and be more effective with your fieldwork.