A solar panel looks simple from the roof: glass, a frame, a grid of blue-black cells. Inside, it is a sandwich of about a dozen layers. Each one was placed, soldered, sealed and tested to tolerances measured in fractions of a millimetre. The quality of that assembly decides whether the panel gives you 30 years of output or starts failing in year six.
This post explains how solar panels are manufactured, using Atal Solar's plant at Mitana, near Tankara in Rajkot district, Gujarat, as the working example. We start with the silicon cell, then follow a module through the automated line, stage by stage, to the final tests before dispatch.
If you want the physics of why N-type cells behave differently from P-type, read our guide to P-type and N-type semiconductors first. This post is about the making.
Atal Solar's solar panel manufacturing plant in Gujarat
Atal Solar grew out of a manufacturing group that has made ceramic tiles, vitrified tiles and laminates since 2008. The solar business began in 2021 with a 100 MW module line. Capacity rose to 300 MW in 2023 and reached 1.44 GW in 2026.
| Detail | Figure |
| Location | Mitana, Tankara, Rajkot district, Gujarat |
| Annual module capacity | 1.44 GW |
| Cell technology | N-Type TOPCon, half-cut, 16 busbar |
| Module types | Dual-glass bifacial, G12R and M10R formats |
| Power range | 600Wp to 650Wp |
| Top module efficiency | 23.51% (G12R 132 Series) |
At 1.44 GW a year, that works out to roughly 2.3 million modules of around 620Wp each. At that volume, consistency matters more than any single clever step. A small error repeated a million times becomes a warranty problem. That is why the line is built around automation and inspection at every stage.
How Solar Panels Are Manufactured
Stage 1: From silicon to TOPCon cell
Every module starts as a solar cell, and every cell starts as a thin slice of silicon. Cell making happens in a separate, cleanroom-style facility called a cell fab. Atal does not make cells itself: it sources N-Type TOPCon cells from specialist cell manufacturers and turns them into modules at Mitana. Here is what happens to a cell before it reaches the module line:
Polysilicon to ingot. Purified silicon is melted and grown into a single crystal ingot. For N-type cells, the silicon is doped with phosphorus.
Ingot to wafer. The ingot is sliced with diamond wire into wafers thinner than a fingernail. The G12R wafers Atal uses measure 182.2 x 210 mm. M10R wafers measure 182.2 x 183.75 mm. The "R" means rectangular.
Texturing. A chemical etch roughens the surface into tiny pyramids that trap light instead of reflecting it.
Emitter. Boron is diffused into the front to form the junction that separates charge.
The TOPCon layer. This is the step that names the technology. An ultra-thin tunnel oxide, about 1 to 2 nanometres thick, is grown on the rear, then covered with doped polysilicon. Together they let current out while blocking the recombination losses that limit older PERC cells.
Coating and metallisation. An anti-reflective coating goes on, fine silver lines are screen-printed, and the cell is fired in a furnace.
Testing and sorting. Each cell is measured and sorted into efficiency bins.
The tunnel oxide layer is why TOPCon modules show zero light-induced degradation and hold output better in Indian heat. Our TOPCon vs PERC comparison covers the performance difference in detail. For the underlying physics, the Wikipedia article on solar cells is a good independent starting point.
From here on, everything happens on the module line at Mitana.
Stage 2: Cell inspection and laser cutting
Cells arrive in sealed, sorted batches. Before any cell enters the line, it is inspected for chips, cracks and colour variation, because a single cracked cell can create a hot spot in the finished panel.
Each full cell is then cut in half by a laser. Half-cut cells carry half the current, which cuts resistive losses and lowers operating temperature. They also improve shade tolerance: if one half of the panel is shaded, the other half keeps producing. This is why every Atal module has an even cell count in two mirrored halves. The 132-cell G12R panel is laid out as 11 x 6 cells on each side, and the 144-cell M10R as 12 x 6.
Stage 3: Stringing and tabbing
Stringing is where cells become a circuit. Robotic stringers lay thin copper ribbons across each cell and solder them to the next, forming long strings. Atal's cells use a 16-busbar design. More, thinner busbars mean each electron travels a shorter distance to a conductor, which reduces losses and spreads the stress if a micro-crack develops later.
Manual soldering introduces variation in heat, pressure and alignment. A robot applies the same temperature for the same time in the same place on every joint. On a line making over a million modules a year, that repeatability shows up directly in lower failure rates.
Stage 4: Layup, bussing and inspection
Now the sandwich comes together. On Atal's dual-glass modules, the layup goes like this, from the sun-facing side down:
- Front glass: 2 mm low-iron, semi-tempered glass with an anti-reflective coating
- Encapsulant: A PID-resistant, UV-resistant film that bonds and cushions the cells
- Cell strings: Placed and spaced by robot
- Encapsulant: A second layer
- Rear glass: 2 mm low-iron printed glass, which lets reflected light reach the back of the cells
Once the strings are placed, bus ribbons join them into the full circuit. Then comes an important check: automated optical inspection (AOI) and an electroluminescence (EL) scan before lamination. EL imaging sends current through the cells so they glow in infrared, which reveals micro-cracks, broken fingers and bad solder joints the eye cannot see. Anything caught here can be fixed. After lamination, it is sealed in for good.
Stage 5: Lamination
The laminator turns the loose stack into a single solid part. The module goes into a vacuum chamber, air is pulled out so no bubbles remain, and heat melts and cures the encapsulant around the cells. The exact temperature and timing are set by the encapsulant maker's specification. The result is a sealed unit that keeps moisture and oxygen away from the cells for decades.
Lamination is where cheap panels often fail years later. Trapped air, uneven curing or a poorly matched encapsulant show up in the field as bubbles, yellowing and delamination. Glass on both sides helps here: two sheets of glass let far less moisture through than a plastic backsheet, which is one reason dual-glass modules suit humid coastal India.
Stage 6: Framing and junction box
After lamination and edge trimming, the module gets its frame and its electrical exit point.
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Frame: anodised aluminium alloy, sealed to the glass edge. The frame is what lets the module handle rated loads of 5,400 Pa of snow pressure on the front and 2,400 Pa of wind suction on the rear.
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Junction box: IP68-rated, made of weatherproof PPO, with bypass diodes that route current around a shaded or damaged section. It comes with 4 mm² cables and connectors.
The junction box is potted (filled with sealant) and the module is left to cure before testing.
Stage 7: Final testing on every module
This is the stage buyers should ask about most, because it separates a module that was built from one that was checked. Every Atal module goes through four tests before dispatch:
| Test | What it checks | Why it matters |
| Flash test (IV curve) | Actual power output under standard test conditions: 1,000 W/m² light, 25°C | Confirms the module delivers its label rating. Each panel is graded by measured wattage. |
| EL test | Micro-cracks, broken cells and faulty joints after lamination | Catches damage caused during lamination and framing |
| HiPot test | Insulation strength at high voltage | Confirms the module is safe at 1,500 V system voltage |
| Leakage test | Current leaking to the frame | Checks insulation and electrical safety |
The flash test result is why the label on your panel means something. A 635Wp panel is one that measured 635Wp on the simulator, within the stated tolerance.
Solar panel reliability testing to IEC standards
Line tests check every module as it is built. The reliability lab asks a different question: will this design survive 30 years outdoors? Samples are pulled from production and pushed well beyond normal conditions:
- Thermal cycling: repeated swings between deep cold and high heat to stress solder joints
- Damp heat and humidity freeze: long exposure to heat and moisture to test the lamination seal
- PID and LeTID testing: checks for the two degradation mechanisms that quietly eat output in hot, humid climates
- Salt mist and ammonia: for coastal sites and for farms or dairies
- Mechanical load, hail and UV: for storms, impacts and years of strong sun
These tests follow the IEC standards that module designs are certified against: IEC 61215 for design qualification and IEC 61730 for safety. Atal's quality systems are certified to ISO 9001, ISO 14001 and ISO 45001. You can read more on our quality and reliability pages.
How to judge a solar panel manufacturer: 5 questions to ask
You will probably never visit a module factory, but you can still judge one. Five questions to ask any manufacturer or installer:
1. Is every module EL tested after lamination, or only a sample? "100% EL" should mean after lamination, not just before.
2. Can I see the flash test data for the modules supplied to my project? Good manufacturers keep it by serial number.
3. Is the module on MNRE's ALMM list, and are its cells on ALMM List-II? Since June 2026, subsidy and net-metering projects need both. Check the exact model number on the official ALMM list.
4. What does the power warranty guarantee in year one and year 30? Atal's N-Type TOPCon warranty guarantees at least 99% of rated output after year one, no more than 0.4% loss a year after that, and at least 87.4% after 30 years.
5. Is the module dual-glass or glass-backsheet? For humid, coastal or high-dust sites, dual-glass lasts longer.
Our solar panel warranty guide explains how to read the fine print, and the G12R vs M10R guide helps you pick a format once you trust the factory.
How solar panels are manufactured, in one line
Silicon becomes a wafer, the wafer becomes a TOPCon cell, and the module line turns about 132 to 156 half-cells into a sealed, framed and tested panel through stringing, layup, lamination and final tests. Each stage has one job: make sure the panel on your roof produces what its label says, for 30 years.
At Atal's plant in Mitana, that process runs on an automated line with AI-based process monitoring and optical inspection, and electrical tests on every module before it leaves. If you are a developer, EPC or distributor and want to see it, get in touch to arrange a plant visit or explore the full module range.
Frequently asked questions
How are solar panels manufactured, step by step?
There are two phases. First, a cell fab turns silicon into cells: ingot, wafer, texturing, junction, TOPCon passivation layers, metallisation and testing. Then a module line turns cells into panels: laser cutting, stringing, layup with glass and encapsulant, EL inspection, lamination, framing, junction box fitting and final flash, EL, HiPot and leakage tests. Atal Solar runs the second phase at its Mitana plant, using cells from specialist cell makers.
What materials are used in a solar panel?
A modern dual-glass panel uses silicon cells, copper ribbons, silver contacts, two layers of encapsulant film, two sheets of low-iron tempered glass, an aluminium frame and a junction box with bypass diodes and cables. Glass and aluminium make up most of the weight.
How long does it take to manufacture one solar panel?
On an automated line, the process from cell stringing to a tested module takes a few hours. The slowest steps are lamination and curing. Because modules move through the line in a continuous flow, a 1.44 GW factory finishes thousands of panels each day.
What is an EL test in solar panel manufacturing?
An electroluminescence test passes current through the module so the cells glow in infrared. A special camera photographs the glow, and cracks, broken fingers or dead cells show up as dark areas. It is the most reliable way to find damage invisible to the eye.
Where is Atal Solar's manufacturing plant?
Atal Solar's plant is at Survey No. 177 P3, Mitana-Ganeshpar Road, Mitana, Tankara taluka, Rajkot district, Gujarat. It has an annual module manufacturing capacity of 1.44 GW and makes N-Type TOPCon modules from 600Wp to 650Wp.
Why are half-cut cells used in solar panels?
Cutting each cell in half halves the current each piece carries, which reduces resistive losses and heat. It also splits the panel into two independent halves, so shade on one part costs less output. The result is more energy from the same area.
Is solar panel manufacturing fully automated?
Modern lines automate the steps where human variation causes defects: stringing, tabbing, layup, lamination handling and inspection. People still supervise the line, handle materials, run the reliability lab and review test data. Automation is about repeatability across millions of panels.
