Solar panel testing: electro­luminescence, I-V curve and thermography

Ecobaterías tests solar panels at the customer’s solar plant or in the lab, with visual inspection, infrared thermography, electroluminescence (EL), I-V curves corrected to standard test conditions, dry and wet insulation tests, bypass diode checks and detection of potential-induced degradation (PID). We deliver a report for every module with its serial number, measured power as a percentage of nameplate and the recommended route: repair, reuse or recycle. In the lab, the base protocol takes 6 minutes per module.

The terms we use on this page. STC are the standard test conditions: 1,000 W/m² of irradiance and a cell temperature of 25 °C, the same conditions behind the nameplate rating. The I-V curve is the relationship between the module’s current and voltage; from it come the maximum power (Pmax), the open-circuit voltage (Voc), the short-circuit current (Isc) and the fill factor (FF). Electroluminescence (EL) is an image taken in the dark while current is injected into the module: healthy cells emit near-infrared light, peaking near 1,150 nm, and cracks show up dark. Bypass diodes sit in the junction box and route current around a group of cells (a substring) when it is shaded or fails. PMGD are Chile’s small distributed generation plants (pequeños medios de generación distribuida). More terms in the technical glossary.

Who is it for and what is it used for?

Testing answers a specific question and ends in a decision. These are its typical uses:

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Sources: test report uses (warranty, insurance, decommissioning and buying used modules) described by 2nd Cycle, PV Module Testing · string tests per IEC 62446-1 · P1–P3 classes: Ecobaterías in-house protocol.

If you plan to file a warranty claim, have the modules tested before anyone works on them. According to the Ministry of Energy’s Hoja de Ruta de Economía Circular en Energía 2026–2030 (Circular Economy in Energy Roadmap), manufacturers’ warranties generally do not allow repair or reuse.

For repowering, see also what to do with the modules removed from a plant. If you are buying, see how we present the measured data sheet for each refurbished panel. And if your plant has storage, we also offer lithium battery testing with an SOH certificate. Every service line is listed under services for batteries and solar panels.

What does each test detect?

Each test sees a different kind of fault, which is why testing combines several: thermography finds the module, electroluminescence shows the crack, the I-V curve measures how much power was lost and the insulation test tells you whether the module is safe.

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Sources: IEC 61215-2:2021 preview and IEC listings for IEC 60904-1, IEC 60891, IEC TS 60904-13, IEC TS 62446-3 and IEC TS 62804-1 · IEA-PVPS T13-10:2018 (EL at Isc and Isc/10) and T13-37:2026 (Voc method for diodes) · insulation thresholds per Millennial Solar and Winaico · full links under “Sources.”

Dry testing alone is not enough. In a 2026 study of 37 modules from utility-scale plants, 8.1% failed the 40 MΩ·m² threshold dry and 21.6% failed it wet: five modules would have passed with a dry test only. In a mass-scale reuse project in Queensland (Australia), 331 of 2,200 modules (15%) failed wet leakage, and about 75% of those failures appeared in the first 10 seconds of the test.

How to read an I-V curve

Which faults are most common?

According to the IEA-PVPS failure review (T13-01:2014), the most important field failures are in the junction box, the glass, cell interconnections, the frame and the encapsulant (delamination). After 8 years in operation, the junction box and cables account for 12% of failures, burn marks for 10% and the encapsulant for 9%. Early in the service life, 5% of cases are transport damage. Snail trails appear 3 months to 1 year after installation and follow cell cracks: electroluminescence and the I-V curve tell you whether they affect power.

At the plant or in the lab?

We test wherever it makes more sense for the batch. At the plant, the module is still installed or freshly removed and nothing is shipped. In the lab, conditions are controlled and the STC measurement is direct.

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Sources: IEC TS 62446-3:2017 (thermography conditions) · Sinovoltaics (nighttime EL) · Ecobaterías test protocol: lab capacity, not a committed lead time.

Drone or ground?

Drone thermography is the simplified inspection of IEC TS 62446-3: it covers the whole plant and flags modules with anomalies. Detailed ground inspection, electroluminescence and the I-V curve confirm the cause and the power loss. If you already have an aerial thermography report, we use it to choose which modules to test. When modules go to the lab, we coordinate pickup and transport.

How do you sample a large plant?

In a plant with tens of thousands of modules, you do not always need to test them all. The draft IEC PAS 63525, the IEC’s first document on photovoltaic module reuse (not yet published), proposes two approaches. IEA-PVPS summarizes them in its T13-37:2026 report:

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Source: IEA-PVPS T13-37:2026, §3.1.2, on the draft IEC PAS 63525 (stage 40.99 as of August 7, 2026).

Sample size changes a lot with the ISO 2859-1 inspection level: in a plant of 125,000 modules, level G1 means 200 modules and level S3 only 32. We propose the level in the quote, based on how the report will be used and the monitoring data available.

Before sampling, we review the background. The guide from the European QUASAR project (2025) starts with a desk review: the plant’s annual loss should be below typical degradation (about 0.8% per year in that guide), and models with serial defects or market recalls are excluded. As a general reference, the median degradation measured by NREL is 0.5% per year.

What does the report contain?

A report for every module and a batch summary. Each module is identified by its serial number, so the result works for a claim, an insurer or a sale.

• Identification: serial number, brand, model and nameplate data (Pmax, Voc, Isc and maximum system voltage); at the plant, the string as well.
• Visual inspection: defects found, with photographs.
• Electroluminescence: module image with defects marked (cracks, inactive cells, PID patterns).
• I-V curve: Pmax, Voc, Isc and FF corrected to STC, and power as a percentage of nameplate.
• Electrical safety: dry insulation and, if performed, wet leakage in MΩ·m²; condition of the bypass diodes.
• Thermography (at the plant): anomaly class 1, 2 or 3 per IEC TS 62446-3.
• Class and route: P1, P2, P3 or recycling, and the recommended action.
• Batch summary: modules by class and by 5 W power bin, defects by type and, if sampling was used, the plan and level applied.

The content follows what reuse schemes require. The R2v3 standard (Appendix G) requires telling the buyer the power measured at STC, its percentage of the design power and every repair performed. The draft IEC PAS 63525 calls for a reuse label that does not cover the original one and lists any repairs, and advises adding the measured I-V parameters. Our report is a technical report: it is not a product certification or an authorization from the SEC (Chile’s Superintendency of Electricity and Fuels).

What happens after testing?

Testing ends in a route for each module. We use an in-house classification by percentage of nameplate power, together with the electroluminescence and insulation results.

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Sources: P1–P3 classes from the Ecobaterías test protocol (in-house classification, not a standard) · IEA-PVPS T13-37:2026 (repairs) · Scientific Reports, 2022 (PID recovery).

Every repair, except replacing cables or connectors, is validated with a new wet leakage test, as IEA-PVPS recommends. PID recovery is not complete: efficiency comes back almost fully at high irradiance, but not at low irradiance. A module with broken glass is neither repaired nor sold. As an outside reference, the European CIRCUSOL project proposed treating a module as functional if it keeps at least 70% of its rated power; IEA-PVPS calls that threshold somewhat arbitrary until regulations exist.

How we work: the step-by-step protocol

1. Request and backgroundYou tell us the quantity, brand, model, nameplate power, year, location and reason for testing, and send any monitoring data or thermography you have. We reply within 48 business hours with the scope, the sampling plan and the quote.
2. On-site inspectionFor field testing: thermography with at least 600 W/m² of irradiance per IEC TS 62446-3, string or module I-V curves corrected to STC with IEC 60891:2021, Voc per module to locate failed diodes and substrings, and electroluminescence at night.
3. Intake and visual inspectionIn the lab, the serial number, model and nameplate data are recorded; visual inspection at a minimum of 1,000 lux per IEC 61215-2:2021 and UV fluorescence.
4. Electrical safetyDry insulation (at least 40 MΩ·m²) and bypass diode testing. Wet leakage by sampling and on every repaired module, except those that only had cables or connectors replaced.
5. ElectroluminescenceEL imaging in a dark cabin per IEC TS 60904-13:2018, at Isc and, when looking for shunts or PID, at Isc/10.
6. I-V curve at STCPmax, Voc, Isc and FF at 1,000 W/m² and 25 °C under a solar simulator with a calibrated reference module. Power is expressed as a percentage of nameplate.
7. Report and decisionA report for every module and a batch summary, with each module’s class and the recommended route: repair, reuse or recycle.

In the lab, steps 3 to 6 take 6 minutes per module, with 50–100 modules per day. That is the lab’s capacity, not a committed lead time: the lead time for each batch is confirmed in the quote.

Which panels do you test?

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Sources: scope of IEC TS 62804-1:2025 (crystalline silicon; excludes thin film, tandem and heterojunction) · Ecobaterías in-house scope.

Which standards do you use as a reference?

We cite these standards as test methods. They are not certifications held by Ecobaterías or by the module.

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Sources: titles as listed on webstore.iec.ch and in the official previews of IEC 61215-2 and IEC 62446-1 · IEC PAS 63525 status as of August 7, 2026 · full links under “Sources.”

What do Chilean rules require?

• SEC, module authorization: the SEC authorizes modules by brand and model, based on IEC 61215 and IEC 61730 certificates for new products (Exempt Resolution 32,427/2020). There is no authorization path for used or refurbished modules. Each module keeps its brand, model and nameplate; the installation declared to the SEC is defined by the licensed electrical installer. We recommend checking with the SEC.
• SEC, damaged modules: Technical Instruction RGR No. 02/2024 prohibits installing modules with breaks or cracks. ITG RIC No. 9.1 requires authorized models in off-grid installations too.
• SEC, array insulation: RGR No. 02/2024 (Table 2) sets the test by system voltage (Voc at STC × 1.25): at 250 V with a minimum of 0.5 MΩ below 120 V; at 500 V with a minimum of 1 MΩ between 120 and 500 V; and at 1,000 V with a minimum of 1 MΩ above 500 V.
• Hazardous waste: according to Chile’s Ministry of Energy, a disused or damaged panel is handled as hazardous waste unless it is declassified under Supreme Decree (DS) 148/2003. If the batch is already waste, we coordinate pickup with licensed hazardous-waste transport.
• Supreme Decree (DS) 22/2025: sets collection and recovery targets for photovoltaic panels, from 10% in the third year up to 50% from the tenth, enforceable 24 months after its publication on May 7, 2026.
• Chile’s Extended Producer Responsibility law (Ley REP, Law No. 20,920): checking, cleaning or repairing a discarded product so it can be reused is preparation for reuse (art. 3 No. 18), and valorization (recovery) includes it alongside recycling (art. 3 No. 30). Testing is the first step to know which one applies.

Sources: SEC, RGR No. 02/2024 · SEC Exempt Resolution 32,427/2020 · ITG RIC No. 9.1/2021 · Circular Economy in Energy Roadmap · Law 20,920 · 2026-09-26

What does it cost and how long does it take?

Price and lead time are confirmed in the quote. They depend on:

• the number of modules, and whether all of them or a sample are tested;
• the tests you request, for example wet leakage or thermography;
• the location: your plant and its region, or our lab;
• the condition of the batch: installed, removed or stacked in a warehouse;
• whether pickup is needed, and with what kind of transport.

We reply within 48 business hours with a proposal. Request your testing here.

Frequently asked questions

How can I tell whether a solar panel is faulty or working properly?

A panel can look fine and still be losing power. Three tests confirm it: an I-V curve corrected to standard test conditions measures how much power it delivers against its nameplate; electroluminescence shows microcracks and inactive cells that the eye cannot see; and an insulation test tells you whether it is safe. If the Voc reads 2/3, 1/3 or 0 of normal, one, two or three substrings are disconnected or bypassed, and the next step is to test the bypass diodes.

What is electroluminescence testing of solar panels?

It is an image of the module taken in the dark while current is injected under forward bias: healthy cells emit near-infrared light, while cracks, broken cells, cut fingers and inactive areas show up dark. Images are taken at the short-circuit current (Isc) and at one tenth of it, which reveals shunts and PID. The method is described in IEC TS 60904-13:2018.

What does a solar panel’s I-V curve show?

It shows the current the panel delivers at each voltage. From it come the maximum power (Pmax), the open-circuit voltage (Voc), the short-circuit current (Isc) and the fill factor (FF). When measured in the field, it is corrected to standard test conditions (1,000 W/m² and 25 °C) with the procedures of IEC 60891:2021 so it can be compared with the manufacturer’s nameplate.

What is thermography for, and what is a hot spot?

Infrared thermography measures the temperature of every cell while the plant is running. A hot spot is a cell or area hotter than its neighbors; the most common cause is a broken cell, but shading, soiling or a diode can also cause it. Under IEC TS 62446-3, a silicon cell 10 to 40 K hotter is a thermal anomaly, and more than 40 K is a safety-relevant anomaly. It requires at least 600 W/m² of irradiance.

What is PID (potential-induced degradation)?

PID is the power loss caused by the high system voltage acting on the module. There are two types, shunting and polarization. It is detected with low-current electroluminescence. Recovery with nighttime reverse voltage, heat or UV light is only partial. The test standard, IEC TS 62804-1:2025, covers crystalline silicon only.

How much does a solar panel degrade per year?

The median NREL found across about 2,000 measurements is 0.5% per year (Jordan and Kurtz). A module with defects, PID or mechanical damage degrades faster, so its real power is measured with an I-V curve at standard test conditions rather than estimated from its age.

How long does a solar panel last?

It depends on the module and its history, which is why it is worth measuring. For reference, 23-year-old polycrystalline modules in Brazil still kept 87–88% of their nameplate power. In an Australian study of 3,749 decommissioned panels, 58% were still fit for a second life, with a median remaining useful life of about 12 years.

How do you detect hail-damaged solar panels?

With module-by-module testing: visual inspection for glass and frame, electroluminescence for cell cracks that cannot be seen, an I-V curve for power loss and an insulation test for safety. The IEC draft on module reuse calls for testing every module in plants damaged by hail or wind. In Chile, the SEC prohibits installing modules with breaks or cracks.

What is an insulation test?

It measures the resistance between the live parts of the panel and its frame to confirm there is no current leakage. In the wet leakage test the module is wetted with a conductive solution and the voltage is held for 2 minutes. A module larger than 0.1 m² passes with at least 40 MΩ·m² (IEC 61215-2). Dry testing alone is not enough: in a 2026 study, 8% failed dry and 22% failed wet.

Drone or ground inspection: which is better?

They complement each other. Drone thermography is the simplified inspection of IEC TS 62446-3: it covers the whole plant and flags modules with anomalies. Detailed ground inspection, electroluminescence and the I-V curve confirm the cause and the power loss of those modules. To decide whether a module is repaired, reused or recycled, you need the detailed testing.

More answers in frequently asked questions about batteries and solar panels.

Sources

Updated September 26, 2026 · Reviewed by the Ecobaterías technical team