Inside a solar panel: seven layers, one laminate
From the roof a panel is one flat dark rectangle. It is actually seven layers laminated into a single sealed unit, and almost every difference between a good panel and a cheap one is in the layers you cannot see.
The seven layers
Drag the slider to separate the stack, or select any layer to read what it does. Every layer is described in full below regardless.
A powder-coated aluminium extrusion runs around the perimeter, tying every internal layer into one rigid unit and giving the mounting structure something to clamp onto.
- Provides the structural rigidity that lets a panel span a mounting rail
- Protects the laminate edges from impact and handling damage
- Carries wind and snow loading into the racking
- Provides the earthing path for the module frame
A low-iron tempered glass sheet sits over the cells. Low-iron because ordinary glass has a green cast that absorbs part of the spectrum the cells want; tempered because it has to survive hail, wind-borne debris and two decades of thermal cycling.
- Transmits sunlight to the cells with minimal absorption
- Shields the laminate from rain, dust and impact
- Toughened so it fractures into blunt granules rather than shards
- The surface that soiling accumulates on, and the one you clean
A clear sheet of ethylene-vinyl acetate laminated under heat and vacuum. It flows around the cells and cures, fusing glass to cells and sealing the assembly against moisture.
- Bonds the glass to the cell layer
- Cushions the wafers against mechanical and thermal stress
- Forms the front half of the moisture barrier
Wafers of crystalline silicon, wired into strings by thin metal ribbons. When photons strike the silicon they free electrons, and the junction inside the wafer pushes them in one direction. That directed flow is direct current.
- Convert sunlight to DC electricity through the photovoltaic effect
- Wired in series to build voltage, and in parallel to build current
- Wired in strings, which is why shading one part of a panel affects more than that part
- The most valuable layer, and the reason every other layer exists
A matching sheet beneath the cells. The wafers are brittle and only a fraction of a millimetre thick, so they are encapsulated on both faces rather than merely backed.
- Completes the moisture seal around the cell layer
- Bonds the cells to the backsheet
A multi-layer polymer sheet closes the rear face. It is the electrical insulation between a live circuit and whatever the panel is mounted on, and it has to stay intact through decades of UV and heat.
- Provides electrical insulation on the rear face
- Blocks moisture ingress from behind
- Reflects light that missed the cells back into the laminate
Bonded to the backsheet, the junction box terminates the cell strings and carries the output to the array wiring. It also houses the bypass diodes, which is the part most people have never heard of and which matters most on a shaded roof.
- Houses bypass diodes that let current route around a shaded string
- Terminates the internal circuit and connects the external DC cables
- Sealed against water ingress, because it sits outdoors for the panel's life
Why it is laminated rather than assembled
A panel is not screwed together. The glass, the two encapsulant sheets, the cell strings and the backsheet are stacked, then pressed under heat and vacuum until the encapsulant melts, flows around the cells and cures into a solid block. What comes out is one sealed laminate with no internal air gaps.
That process is doing two jobs at once. It excludes moisture (the enemy of a silicon cell and its metal interconnects) and it supports wafers that are only a fraction of a millimetre thick and would otherwise crack under their own handling. The frame and junction box are attached afterwards; everything else is committed permanently at lamination.
This is why panels are not repairable and why manufacturing quality matters more than it does for components you can open. A void left in the encapsulant, or a backsheet that embrittles under UV, is a fault you cannot inspect for and cannot fix. It shows up years later as declining output.
What to ask about the layers you cannot see
Glass
Is it low-iron and tempered?
Low-iron glass transmits more of the spectrum the cells use. Tempering is what makes it survive hail and thermal cycling, and makes it fail safely if it ever does.EVA
What is the encapsulant rated for?
Encapsulant is where slow degradation shows up first, as yellowing. It is rarely on a spec sheet by name, but the question tells a supplier you know where quality hides.Cells
Mono or poly, and how many busbars?
More busbars means shorter paths for current across the cell and lower resistive loss. It is a real engineering difference rather than a marketing number.Backsheet
Is it a rated multi-layer backsheet?
The backsheet is the electrical insulation between a live circuit and your roof, exposed to UV and heat for decades. Cracking here is a safety issue, not a performance one.J-box
What is the ingress protection rating?
The junction box sits outdoors for the life of the panel. Its sealing rating is printed on it, and it is the one part of the laminate assembly you can actually inspect.Frame
Anodised, and how thick?
The frame carries wind loading into the mounting structure. Thin or poorly finished extrusion is a false economy on a roof that sees real wind.
None of these questions require you to be an engineer, just a supplier willing to answer them. One check needs no question at all: whether the panel is on the government’s Approved List of Models and Manufacturers (ALMM) and BIS-certified, since those are also the panels eligible for the PM Surya Ghar subsidy — an unlisted panel loses you the subsidy regardless of how good the panel itself is. If you want to see where the panel then sits in the wider installation, that is the system components page, and maintenance covers keeping the outer layer, the one you can reach, doing its job.
Common questions
Can a solar panel be repaired if one layer fails?
Generally not. The seven layers are laminated into a single sealed unit under heat and vacuum, so they cannot be separated without destroying the panel. The junction box on the rear is the one serviceable part: a failed bypass diode can sometimes be replaced. Anything inside the laminate is a warranty claim, not a repair.
What is the difference between monocrystalline and polycrystalline panels?
It is a difference in the cell layer only; every other layer is the same. Monocrystalline cells are cut from a single silicon crystal, giving a uniform dark appearance and higher efficiency per square metre. Polycrystalline cells are cast from multiple crystals, which is cheaper but slightly less efficient. On a constrained roof the extra efficiency buys you capacity you could not otherwise fit; on a large open roof it may simply cost more.
What is the difference between Mono PERC, TOPCon and Bifacial panels?
They are refinements of the monocrystalline cell, not separate products. PERC (Passivated Emitter Rear Cell) adds a reflective rear layer that recaptures light a standard cell would otherwise lose, lifting efficiency. TOPCon (Tunnel Oxide Passivated Contact) is a newer cell structure that cuts electrical losses further and typically degrades more slowly over 25 years than older designs. Bifacial panels generate from both faces, picking up extra output from light reflecting off a light-coloured roof or ground beneath the array — though how much depends heavily on what is actually underneath. Which one suits a given roof is a specification decision, not a rule of thumb.
Why do some panels turn yellow or brown with age?
That is usually discolouration of the EVA encapsulant. Ultraviolet light and heat can degrade the polymer over many years, and as it yellows it transmits less light to the cells beneath. It is a visible symptom of encapsulant quality, and it is one reason the layers you cannot inspect from the ground are worth asking about.
What does a bypass diode in the junction box do?
Cells are wired in series, so current through a string is limited by its weakest cell: a single shaded cell would otherwise drag down every cell wired with it. A bypass diode gives the current a path around the affected group. It does not recover the shaded output, but it stops one shaded corner from disproportionately reducing the whole panel. It is also why panel-level shading behaviour is not simply proportional to the shaded area.
Does the aluminium frame need earthing?
Yes. The frame is a conductive surface on a structure carrying live DC circuits, and it must be bonded to the installation earth. Frame earthing and array earthing are part of a compliant installation, not an optional extra, and they are worth confirming appear on any quotation you are comparing.
Ask us these questions
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