Thermal imaging and IV curve testing are the two main diagnostic tools for finding faults in solar arrays, and they answer different questions. A thermal camera shows where something is wrong by revealing cells, panels or connections that run hotter than their neighbours. An IV curve tracer shows what kind of problem a string has, and how much power it is losing, by measuring its full current-voltage characteristic. Used together, and interpreted by trained professionals, they turn a vague "the system seems low" into a specific, fixable cause.

Why faults create heat

A normally working cell turns part of the light it absorbs into electrical energy and carries it away as current. Some light always becomes heat, which is why panels run well above air temperature in full sun. When something disrupts the electrical path, more of that energy stays in the panel as heat:

• A cracked or shaded cell that cannot carry the string's current can be driven into reverse bias, dissipating power instead of producing it.
• A high-resistance connection, such as a corroded connector or a failing solder bond, heats up in proportion to the square of the current flowing through it.
• A disconnected panel or open string produces no electrical output, so all absorbed light becomes heat and the whole panel runs warmer.

The fault finder is not looking for absolute temperature but for temperature differences between similar components under the same conditions.

How a thermal camera sees a solar panel

Every object emits infrared radiation, and the amount rises with temperature. Thermal cameras used for solar work detect long-wave infrared, roughly 8 to 14 micrometres in wavelength, and convert it into a temperature map.

Glass is opaque at those wavelengths, so the camera does not see the cells directly. It sees the front surface of the glass, which is warmed by heat conducted from the cells beneath. Glass also reflects infrared from the sky, the sun and nearby objects, particularly at shallow viewing angles. Good practice therefore includes:

• Scanning in strong, stable sunshine, commonly at least around 600 W/m² of irradiance, so faulty cells carry enough current to stand out.
• Viewing from an angle that avoids reflections of the sun and surrounding structures.
• Recording irradiance, air temperature and wind, because wind cools panels and softens contrast.
• Checking suspect areas from a second angle to rule out reflections.

What thermal images typically show

Large commercial arrays are often scanned by drone, which covers hundreds of panels quickly. Residential and roof-level scans must only be done by trained professionals with proper roof safety measures.

What an IV curve measures

An IV curve plots the current a panel or string delivers against its voltage, across every operating point from short circuit to open circuit. At one end, the terminals are shorted: voltage is zero and current is at its maximum (Isc). At the other, the circuit is open: current is zero and voltage is at its maximum (Voc). Between them sits the "knee" of the curve, where the product of voltage and current, the power, is highest. That point is the maximum power point the inverter tries to track.

An IV curve tracer disconnects a string from the inverter and sweeps it through that full range in a fraction of a second, while a reference sensor records irradiance and cell temperature. Software then translates the measurement to standard conditions and overlays the curve that the panel datasheets predict. The concept of how cells produce current and voltage is covered in how solar power works.

The quality of those reference readings matters as much as the curve itself. Current scales almost directly with irradiance, so a sensor tilted differently from the array, or shaded for a moment, makes a sound string look faulty or a faulty one look sound. Voltage depends strongly on cell temperature, so a sensor stuck to a cooler part of a panel can mislead the comparison. Testers therefore measure several strings in quick succession under steady sky conditions and compare them with each other as well as with the model.

Reading the shape of a curve

• Current lower across the whole curve: uniform soiling, uniform shading, optical degradation, or an irradiance sensor that is not reading the same light as the array.
• Voltage lower than expected: fewer working panels or substrings than designed, shorted bypass diodes, or higher cell temperatures than recorded.
• Steps or notches in the curve: partial shading or mismatched cells activating bypass diodes.
• A rounded, sagging knee: increased series resistance from corroded connectors, damaged cabling or solder bond failure.
• A sloping line near short circuit: reduced shunt resistance, which can indicate cell defects or potential-induced degradation.

A useful single number is the fill factor: maximum power divided by the product of Voc and Isc. A falling fill factor signals losses that a simple power reading would not explain. Gradual, uniform decline across all strings is more consistent with normal ageing, described in solar panel degradation explained.

How the two methods work together

1. Monitoring data flags a string or inverter producing less than similar ones.
2. IV curves confirm the loss, measure its size and classify its likely type.
3. Thermal imaging locates the specific panel, cell or connector responsible.
4. A targeted inspection confirms the cause and informs repair or a warranty claim.

Both methods involve live DC circuits that stay energised whenever light reaches the panels, so testing must be carried out by licensed electricians and accredited solar professionals, never as a DIY task.

Next steps

If monitoring suggests an array is underperforming, systematic testing is far more reliable than guessing. To have a system assessed, request a free assessment from Blue Energy Solar. For larger systems, the energy market lists a Thermal Imaging Inspection from $990 and IV Curve Testing from $1,290, each for systems up to 100 kW; prices are indicative and confirmed after a site assessment.

Frequently asked questions

Can an inverter monitoring app replace these tests?

Monitoring is the best early-warning tool, and inverters with several trackers or string-level data can show which part of an array is producing less. However, an app cannot see a single cracked cell, a warm connector or the shape of a string's curve. It points to where a problem might be, while thermal imaging and IV curve testing locate and characterise it.

How often should a solar system be thermally scanned or IV tested?

There is no single rule. Commercial and industrial owners often schedule testing at commissioning, near the end of workmanship warranty periods and at regular intervals set by their maintenance plan. For homes, testing is usually triggered by a specific concern, such as unexplained low output, storm exposure or a recurring inverter fault, rather than on a fixed timetable.

Can test results support a warranty claim?

They can help. Manufacturers typically want evidence that a panel is underperforming or defective under defined conditions, and thermal images and IV curves recorded with irradiance and temperature data provide objective measurements. Each manufacturer sets its own claim process and evidence requirements, so results do not ensure a claim will be accepted, but well-documented testing makes the assessment clearer.