Guides · Faisalabad, Lahore, Punjab
PID and LID: Why Some Solar Panels Lose Power Early
Short answer
Potential induced degradation (PID) and light induced degradation (LID) are the two main reasons a solar panel can lose noticeably more power in its early years than its datasheet suggests. LID is a small, fast loss in the first hours of sunlight, mostly in older P-type panels. PID is a slower loss caused by high system voltage pushing current where it should not go; it can be large if ignored, but it is usually preventable and often reversible.
Normal ageing is covered in our average lifespan of solar panels guide. This article covers the two specific effects behind early or uneven power loss, and what you can do about them.
Quick comparison
| LID (light induced degradation) | LeTID (light and elevated temperature) | PID (potential induced degradation) | |
|---|---|---|---|
| What triggers it | First exposure to sunlight | Sunlight plus high cell temperature | High voltage between cells and the earthed frame, made worse by heat and moisture |
| When it shows | First hours to days | Over months | Months to years |
| Typical size | Small, a few percent at most | Small to moderate | Can be large on badly affected panels |
| Panels most at risk | Boron-doped P-type | P-type PERC | Panels at the negative end of long strings, on transformerless inverters |
| Reversible? | No, but it stops early | Partly, slowly | Usually, if caught early |
The percentages behind these descriptions are general industry figures, not numbers for any particular model.
PID and LID
LID
Small first-year loss
PID
Voltage-driven loss in humid heat
LID: the loss in the first days of sunlight
What happens
In a boron-doped (P-type) silicon cell, small amounts of oxygen are trapped in the wafer during manufacture. When sunlight first hits the cell, boron and oxygen form defects that trap some of the electrons the cell would otherwise deliver. Output drops a little, then levels off.
One technical review puts this boron-oxygen loss at roughly 1 to 3 percent of rated power, mostly within the first 100 hours of sun. That is why many panel warranties allow a larger drop in year one than in later years.
LeTID: the slower cousin
LeTID (light and elevated temperature induced degradation) appears when cells run hot in sunlight, above about 50°C. It mainly affected PERC panels, the type sold widely a few years ago. It builds over months and can partly recover over a long period.
On a Punjab roof in May and June, cell temperatures easily pass that threshold, so heat-related losses matter here more than in cooler countries. See our guide to N-type vs P-type panels for the basics of cell types.
Why modern N-type panels largely avoid it
N-type wafers do not use boron in the same way, so boron-oxygen LID is essentially absent. Heterojunction and back-contact cells show very little LeTID; TOPCon shows a small effect but far less than older PERC. Manufacturers also use gallium instead of boron in some P-type wafers, and light-and-heat "regeneration" treatment in the factory, to reduce these losses. For the differences between modern cell designs, see TOPCon vs HJT vs back-contact panels.
PID: when system voltage works against the panel
What happens
Panels in a string are connected in series, so the voltage adds up. A home string can reach several hundred volts DC, and commercial strings more. The aluminium frame, meanwhile, is earthed at zero volts.
On many transformerless inverters, panels towards the negative end of the string sit at a large negative voltage compared with the frame. That voltage difference can drive a tiny leakage current from the cells, through the encapsulant and glass, to the frame. Over time, ions move into the cell surface and create leakage paths inside the cell. The cell can still make current, but more of it is lost internally.
What makes it worse
- Heat and moisture. The standard PID test runs panels at 60°C and 85% humidity for this reason. Punjab's hot summers and humid monsoon are both on the list.
- Long, high-voltage strings. The more panels in a string, the larger the voltage at the negative end.
- Panel materials. Encapsulant, glass and cell coatings make a big difference. This is a matter of manufacturing quality, not something an installer can fix later.
- Dirt and condensation along the frame can make the leakage path easier.
How PID shows up
- A gradual drop in output that is worse on some panels than others, often those at one end of each string.
- In a thermal or electroluminescence image, affected panels show a patchwork of dark cells, often near the frame edges.
- An I-V curve test shows the tell-tale changes; a visual check alone usually cannot identify PID.
Can PID be reversed?
Often, yes, if found early. Some inverters can earth one DC pole where the design allows it, and some offer an anti-PID or PID-recovery function, built in or as an add-on, that applies a reverse voltage to the array at night. Whether a particular inverter can do this depends on the model. Left untreated for years, PID can cause permanent damage to cells and encapsulant.
How to protect yourself from early degradation
- Buy genuine grade-A panels from a reputable maker. Fake and grade-B panels are where PID and early losses most often appear. Check serial numbers with our guide to genuine solar panels and read grade A, grade B and refurbished panels.
- Read the datasheet. Look for PID-resistance testing (the IEC 62804 test series) and the stated first-year and yearly degradation figures. A "PID-free" label on its own is a marketing phrase; a stated test result is more useful. Our guide on how to read a solar panel datasheet explains each line.
- Prefer modern N-type panels where budget allows. They avoid most LID and generally degrade more slowly. Compare brands in best solar panels in Pakistan.
- Let the engineer set string length. Strings should be designed for the inverter's voltage window, not simply made as long as possible.
- Watch the monitoring app. If one string or MPPT steadily falls behind the others, ask for a check. Our monitoring app guide shows how to compare strings, and why is my solar system producing less than expected? lists other common causes.
- Know your warranty. A performance warranty covers degradation beyond the stated curve. Read our solar warranty guide.
Safety note. Panels produce DC voltage whenever there is daylight, even with the grid and inverter off. Do not open junction boxes, unplug connectors or test strings yourself. I-V curve and thermal testing are jobs for a technician.
How Solar Works Pakistan reduces the risk
Our in-house engineers select panels and inverters together, so string voltages, inverter type and panel datasheets are checked as one design rather than separately. We supply panels from LONGi, JinkoSolar, Canadian Solar, JA Solar, AIKO, Cora Dawn and Jasco, and every quotation names the exact brand and model so you can check its datasheet and serial number. The manufacturer's warranty for each product.
New systems are designed with monitoring, which makes uneven string performance easier to spot. After a complaint is registered, we target sending service personnel within 48 hours to start diagnosis; the fix time depends on the fault, parts and manufacturer involvement. Learn more about our solar installation services or check current solar panel prices.
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- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM, daily
We serve customers throughout Punjab. See our Faisalabad and Lahore pages, or contact us. Site surveys are normally free.
Frequently asked questions
What is potential induced degradation in solar panels?
PID is a loss of power caused by high voltage between a panel's cells and its earthed frame. It drives a small leakage current that damages the cell surface over time. Heat, humidity and long strings make it worse.
What is light induced degradation?
LID is a small, one-time loss of power in the first hours of sunlight, caused by boron-oxygen defects in P-type cells. It levels off quickly. Modern N-type panels are largely free of it.
Is PID permanent?
Often not, if found early. Changing the system earthing where the inverter allows it, or using an anti-PID or recovery function, can restore much of the lost power. Left for years, it can cause permanent damage.
Do N-type panels suffer from PID?
N-type panels avoid boron-oxygen LID, but no panel type is completely immune to PID. Resistance depends on materials and manufacturing quality, so check the datasheet for PID test results.
How do I know if my panels have PID?
The usual sign is output that falls steadily on some panels or strings more than others. Confirming it needs a technician with an I-V curve tester or thermal camera; a visual check is not enough.
Does Punjab's heat make degradation worse?
Heat speeds up LeTID and PID, and monsoon humidity adds to PID risk. That makes panel quality and careful system design more important here than in cooler, drier places.
Is early degradation covered by warranty?
Panels carry a performance warranty that allows a stated loss over time. Losses beyond that curve may be claimable. Terms vary by brand and model; we give the manufacturer's warranty in writing with every quote.
Sources
- EEPower, "Causes and solutions of the potential induced degradation effect in PV modules"
- SurgePV, "LID and LeTID in solar cells"