Every solar quote you’ve seen probably had a line buried somewhere near the bottom: “25-year performance warranty.” What it usually doesn’t explain is why your panels will produce less power in year twenty than they did on day one, or how much less. That gap is where a lot of confusion — and a lot of overselling — happens.

The truth is that “degradation” isn’t one thing. It’s at least three separate processes, each with its own cause, its own timeline, and its own severity. Two of them are completely normal and nothing to worry about. One of them can genuinely wreck a system’s output if it isn’t caught early. Knowing the difference is the single most useful thing you can take from a module datasheet before you sign a contract.

The Baseline: General Module Degradation

This is the one every solar panel experiences, everywhere, without exception. It’s simply the slow wear that comes from twenty-five-plus years of sitting outside — UV exposure, daily heating and cooling (thermal cycling), and moisture working its way into the module over time.

For standard crystalline silicon panels, this typically works out to about 0.5% to 1% loss per year, once the panel has settled in after its first year. It’s cumulative and, practically speaking, permanent — you’re not going to reverse it. But it’s also predictable, which is exactly why manufacturers can put a number on it and back it with a warranty.

If you’ve ever wondered why a panel rated at 450W new might be putting out closer to 400W after twenty years, this is almost entirely the answer. Nothing has gone wrong. That’s just the material aging the way glass, EVA encapsulant, and silicon cells age.

The One That Happens Almost Immediately: Light-Induced Degradation (LID)

Here’s something that surprises a lot of first-time buyers: some of a panel’s lifetime power loss happens in the first few hours or days of sunlight exposure, not gradually over years.

This is Light-Induced Degradation, and it happens because of a defect that forms in the cell material itself — specifically, a reaction between boron and oxygen inside p-type silicon cells, which slightly shortens how long the charge carriers (the electrons doing the actual work) survive inside the cell. The result is a one-time efficiency drop, usually in the 1% to 3% range.

The good news is twofold. First, LID stabilizes quickly — once it’s happened, it’s done, and the panel settles into its normal long-term degradation curve. Second, it’s largely avoidable with newer cell technology: N-type cells and gallium-doped wafers don’t have the same boron-oxygen defect, so they’re essentially immune to LID. If you’ve seen “N-type” on a spec sheet and wondered why manufacturers highlight it, this is one of the reasons.

The One Actually Worth Watching: Potential-Induced Degradation (PID)

PID is the mechanism that actually deserves your attention, because unlike the other two, it isn’t a fixed, predictable percentage — it can range from a barely-noticeable dip to a genuinely serious 5% to 30% or more loss in output.

PID is driven by voltage, not just sunlight or time. In a solar array, individual panels are wired together in series to build up system voltage, often exceeding 1000V. That voltage stress, combined with heat and humidity, can cause sodium ions to migrate out of the panel’s glass and into the solar cells themselves. This migration creates unwanted current paths (called shunts) inside the cell, which quietly bleed away power.

A few things make PID different from the other two degradation types:

• It develops over months to years, not hours or a fixed annual rate — so a panel can look completely fine for a while before PID becomes noticeable.
• It’s often reversible, at least partially, using specialized equipment (bias controllers that essentially run the voltage stress in the opposite direction overnight). This isn’t guaranteed and depends on how advanced the degradation is and what equipment is available, but it’s a meaningful difference from LID or general aging, which you simply can’t undo.
• It’s largely preventable. PID-resistant modules, correct system grounding, and (in some designs) bias controllers built into the inverter all reduce the risk significantly.

This is why PID is the one degradation type worth actually asking your installer about, rather than just reading past it on a datasheet.

A Newer Name You Might Come Across: LeTID

If you’ve been reading module manufacturer literature, you may have seen LeTID — Light and Elevated Temperature-Induced Degradation. It’s a related but distinct phenomenon, showing up mainly in p-type cells operating under high temperatures, and it can cause an additional sudden loss of around 3% to 6% in affected technologies.

It’s worth knowing the term exists, but treat it as a newer and less universally quantified issue compared to PID and LID — the industry’s understanding of it is still evolving, and its real-world impact varies significantly by cell technology and manufacturer. If a supplier tells you their modules are specifically tested against LeTID, that’s a reasonable question to ask about, not something to take purely on faith.

Putting It Side by Side

Feature	Potential-Induced Degradation (PID)	Light-Induced Degradation (LID)	General Aging
Primary cause	High voltage stress + ion migration	Sunlight exposure (boron-oxygen defect)	UV, thermal cycling, moisture
Timing	Months to years	First hours/days	Continuous over 25+ years
Severity	5%–30%+ loss	1%–3% loss	~0.5%–1% per year
Reversibility	Often reversible (with equipment)	Permanent	Irreversible
Prevention	Grounding, PID-resistant modules	N-type / gallium-doped cells	High-quality encapsulation

Why This Matters More in a Climate Like Bangladesh’s

PID is specifically accelerated by heat and humidity — and Bangladesh has plenty of both, for a large part of the year. That doesn’t mean every system here suffers from PID; a properly grounded installation using PID-resistant modules is designed to handle exactly these conditions. But it does mean the climate here gives you slightly less margin for a poorly designed or poorly grounded system than, say, a cooler, drier market would.

The same logic applies to general aging: heat, humidity, and monsoon-season moisture are the exact stressors that drive that baseline 0.5–1% annual decline. Again, this isn’t a Bangladesh-specific number — no reliable local dataset exists to say panels here degrade faster than the industry-standard range — but it’s a reasonable reason to take module quality and installation practices seriously rather than choosing purely on upfront price.

This is also where checking whether a module appears on Bangladesh’s SREDA-approved product list is useful groundwork — though it’s worth being clear-eyed that approval on that list is a quality and compliance signal, not a specific guarantee against PID or LID on its own.

What to Actually Ask Your Installer

If you take one practical thing from this article, make it this list of questions:

• Are the modules you’re quoting PID-resistant, and is that documented on the datasheet?
• Is proper grounding included in the installation design — not just mentioned, but actually specified?
• What does the performance warranty guarantee, in writing, at year 10 and year 25 — not just “25-year warranty” as a headline figure?
• Is there a difference between the product warranty (covers manufacturing defects) and the performance warranty (covers output decline) in what you’re being quoted?

Muspana factors PID resistance and grounding practice into how modules are selected and installed, precisely because a system that looks identical on paper can perform very differently over twenty-five years depending on these details. If you’re evaluating a quote and unsure how to read the degradation or warranty terms, that’s a reasonable thing to bring to a consultation before you commit.

For Commercial and Industrial Buyers Specifically

If you’re specifying a larger rooftop or ground-mount system for a factory or commercial facility, PID risk deserves a bit more attention than it does for a small residential setup. Larger arrays typically run higher system voltages to reduce cabling losses, and higher voltage is one of the two core ingredients PID needs (the other being heat and humidity, which Bangladesh supplies regardless of system size). This doesn’t mean industrial systems are inherently riskier — it means grounding design and PID-resistant module selection are worth explicitly confirming in procurement specifications, not just assumed.

None of this means solar panels are fragile or unreliable — quite the opposite. The fact that manufacturers can quantify these degradation mechanisms this precisely, and design around most of them, is exactly why 25-year performance warranties are a realistic promise rather than marketing fluff. The point of understanding PID, LID, and general aging isn’t to worry about your system — it’s to know which numbers on a quote are guaranteed physics, and which ones depend on getting the installation right.

FAQs

Is PID (potential-induced degradation) reversible? 

Often, yes — at least partially — using specialized equipment such as bias controllers, but it depends on how advanced the degradation is and whether the right equipment is used. Prevention through grounding and PID-resistant modules is far more reliable than counting on a fix later.

Do all solar panels experience LID? 

Most standard p-type silicon panels experience some LID, typically a 1–3% one-time loss shortly after installation. N-type and gallium-doped cells are largely immune to it, which is why some manufacturers highlight this as a selling point.

What is LeTID and should I worry about it? 

LeTID (Light and Elevated Temperature-Induced Degradation) is a newer, less universally quantified degradation type that can cause an additional 3–6% loss in some p-type technologies under high heat. It’s worth asking your supplier about, but treat it as an area of ongoing industry research rather than a settled, fixed figure.

How much will my solar panels degrade over 20 years? 

For a well-installed system using PID-resistant, quality modules, expect roughly 0.5–1% annual loss from general aging plus a one-time 1–3% LID loss in the first year — meaning most panels should still be producing somewhere in the 80–90% range of their original output after two decades. This is a general industry range, not a guarantee tied to any specific brand or installation.

Does Bangladesh’s climate make solar panel degradation worse? 

Heat and humidity are known accelerants for PID and general module aging, and Bangladesh has both for large parts of the year. This is a reason to prioritize PID-resistant modules and correct grounding rather than a reason to expect worse performance automatically — a properly designed and installed system is built to handle these conditions.