Finding Faults – I-V Curve Tracing & Thermography

I-V Curve Tracing & Thermography

Current vs voltage (I-V) curve tracing is a useful diagnostic method for isolating problems with your PV array. We recently received some advanced training from the guys over at Seaward Ltd, so we thought we’d pass on some of the knowledge.

An I-V curve represents the relationship between current and voltage, and if your PV is operating correctly, you will see a nice regular curve like the one shown to the right.

If there is a fault in your PV system, however, you will be able to spot it from an irregularity in the I-V curve (continue reading for example).

I-V curves are a great way of diagnosing a problem within your system because, although it is possible to discover an issue through a fluctuation in your system’s total output (accessible through things like inverter screens, generation meters, and personal display units), an I-V curve will give you detailed information about a module or string. Interpreting this information will not only indicate that there is a fault, but it will also point towards what that problem could be.

The kind of things that can be spotted and diagnosed by reading an I-V curve are reduced current, reduced voltage, shunt losses, series losses, operator errors, irradiance measurement issues, shading, micro-cracks and shorted bypass diodes. (to see the risks of not spotting faults like these, click here)

The benefit of using an I-V curve to find a fault in this way, is being able to read the problem from one graph, rather than running individual time consuming tests to find the issue.

As an example of how I-V curve tracing can be put to use, see the case study below…

Case study

When monitoring a string of modules for one of our O&M contracted sites we came across a curve that looked like this… (right)

The shape of this curve indicated to us that there could be a micro-crack in one or some of the cells. Micro-cracks will cause current to build up in one area and cause hotspots on the panel, so we took our thermal camera to the site and took a number of pictures including the one displayed below.

As clearly shown in the thermal image, the string’s I-V curve helped us to correctly discover and diagnose the fault. The panel in question had two hotspots which were significantly affecting its yield. Hot spots are very important to watch out for, as they are not only detrimental to energy production, if left, they will cause severe damage to the panels.

Below is another image (which you may have seen in our PV Fire Safety blog) of some PV suffering from long-standing hotspots on a site we were contracted to do some maintenance on. We got there just in time…

As you can see, the damage is fairly substantial, and in extreme cases, hotspots have the potential to start a fire which could destroy your entire PV array. – don’t believe us, take a look at this article: PV Fires.

Thanks to I-V curve tracing along with thermography, we were able to prevent any injuries or large scale destruction. But these cases make it clear why regular maintenance of your PV system is imperative – to protect your investment and maintain a safe surrounding environment.

If site maintenance is not something you have the time for or wish to conduct yourself, Solar South West offer cost effective bespoke O&M maintenance plans. These plans are tailored to your individual needs, they will ensure the safety and operation of your PV array, and usually pay for themselves by the optimisation of your generation. Don’t let your site end up like this one we serviced recently!

For more information on the O&M services we offer, follow the link below, or get in touch via our Facebook or Twitter pages.

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