Quick answer
Polycrystalline Solar Panel A polycrystalline solar panel (also called multicrystalline) is a panel built from cells cut from a block of silicon that cooled into many small crystals, which gives the cells their blue, speckled look and makes them a little less efficient than single-crystal cells.
Poly was once the cheaper mainstream choice. The industry roadmap now reports only monocrystalline wafers on the market, so poly is mostly found on roofs installed years ago.
Quick facts
The key facts about polycrystalline solar panel, with sources:
- Also called
- Multicrystalline, multi-Si, mc-Si, "poly"
- How the silicon is made
- Melted silicon cast in a mould and cooled into a block of many crystals
- Example module efficiency
- 16.89%–17.39% (Canadian Solar KuMax CS3U-P, 2018) 1
- Example temp. coefficient
- −0.38%/°C (same sheet) 1
- Market status
- Only Cz-mono wafers present in the 2025 market 3
- Mono share of global shipments, 2022
- 96%, with the rest mostly cadmium telluride 5
- Wear rate
- Crystalline silicon showed similarly low degradation before and after 2000 in NREL’s review 7
Key takeaways
- Poly cells are cut from cast silicon made of many crystals. You can spot them by their blue, flaky look.
- They convert less light than mono cells, because electrons get lost where crystals meet.
- Poly has left the market. The 2025 ITRPV roadmap found only mono wafers in production.
- If you own poly panels, they still work. Track output against the warranty.
- Adding or swapping panels is the hard part, because new panels have different electrical ratings.
What "polycrystalline" means
A crystal is a solid whose atoms sit in a neat, repeating pattern. In poly silicon, that pattern runs in many directions at once, in small patches. Each patch is one crystal, called a grain.
You can see the grains with your eye. A poly panel looks blue, with a shiny, flaky pattern like frost on glass. A monocrystalline panel looks an even black, because the whole cell is one crystal.
The names get mixed up. "Poly", "multi" and "multicrystalline" all mean the same panel. "Polysilicon" is different. It is the purified raw silicon that both mono and poly wafers start from.
How polycrystalline cells are made
Instead of pulling one crystal slowly out of the melt, poly makers pour molten silicon into a square mould and let it cool. Many crystals start growing at once. They meet at boundaries, which are the lines you see as the flake pattern.
The square block is sawn into bricks and then thin wafers. Little silicon is wasted, because the block is already square. A round mono ingot has to be trimmed first.
The crystal boundaries are the trade-off. Electrons freed by sunlight can get trapped there before they reach the wiring. So a poly cell turns a smaller share of light into power than a mono one.
Types of poly panels you may find on a roof
| Type | What it means | How to spot it |
|---|---|---|
| Standard multicrystalline | Cast silicon cells with the classic flake pattern | Blue cells, square corners, "poly" on the label |
| Poly PERC | A poly cell with a back layer that reflects light for a second pass, like PERC on mono | Label says "poly PERC" or "multi PERC" |
| Half-cut poly | Each cell cut in two to lower electrical losses | Panel split into two halves with a line across the middle |
| Cast mono (quasi-mono) | Cast like poly but grown to be mostly one crystal | Darker cells; data sheet names it |
Poly vs mono, from two Canadian Solar data sheets
| Spec | KuMax CS3U-P, poly (2018) | HiKu6 CS6R-MS, mono PERC (2022) |
|---|---|---|
| Module efficiency | 16.89%–17.39% 1 | 20.2%–21.5% 2 |
| Temperature coefficient (Pmax) | −0.38%/°C 1 | −0.34%/°C 2 |
| Nominal operating temperature (NMOT) | 42 ± 3°C 1 | 41 ± 3°C 2 |
| Cell type line | "Poly-crystalline" | "Mono-crystalline" |
Example: how much roof the efficiency gap costs you
Efficiency is the share of sunlight a panel turns into power. Lab ratings use 1,000 watts of light per square metre. This example uses each sheet’s top efficiency. It is simple math, not a production estimate.
| Step | Poly KuMax, 17.39% 1 | Mono HiKu6, 21.5% 2 |
|---|---|---|
| Watts per m² at test conditions | 1,000 × 17.39% ≈ 174 W | 1,000 × 21.5% = 215 W |
| Roof area for 6 kW of panels | 6,000 ÷ 174 ≈ 34.5 m² | 6,000 ÷ 215 ≈ 27.9 m² |
| Difference | About 6.6 m² more roof for poly |
On a big roof that gap may not matter. On a small one it can decide whether the system fits. Yearly kWh still depends on tilt, shade and weather, which a model such as PVWatts estimates 10.
Where you still see poly panels
Mostly on systems built years ago, on homes, farms and small businesses. Many of them still run well.
You will rarely see poly on a new quote. The DOE says mono silicon made up 96% of global solar shipments in 2022. The ITRPV roadmap found only Cz-mono wafers in the 2025 market.
Poly also turns up in used-panel listings and cheap off-grid kits. Check the age and the warranty before you buy one.
Why poly disappeared
Two things happened. Mono wafer costs fell until poly’s cheaper casting no longer made up for its lower output. And newer cell designs such as PERC and TOPCon gain more from a clean, single-crystal wafer than from a cast one.
Research did not stop. The National Laboratory of the Rockies (formerly NREL) record table lists a 24.4% multicrystalline research cell made by JinkoSolar in 2020 on an n-type "cast mono" wafer. Lab records are single small cells, not panels you can buy.
Benefits and limits of polycrystalline panels
Benefits
- Casting wasted less silicon, which once made poly cheaper to build.
- Proven in the field for decades; NREL found crystalline silicon wear rates low and steady 7.
- Existing poly arrays keep making power for many years.
- Same frame, glass and mounting as mono, so racking is standard.
Limits
- Lower efficiency, so more roof space for the same watts.
- Loses slightly more power per degree of heat than the mono example.
- No longer made in volume, so exact replacements are hard to find.
- Mixing with new mono panels needs careful design.
- Older panels may carry shorter warranties that are close to running out.
Limits that matter if you own poly panels
The biggest limit is age, not crystal type. An NREL review of nearly 2,000 measured rates found a median output loss of 0.5% a year. It found crystalline silicon rates were similarly low for systems built before and after 2000.
A ten- or fifteen-year-old poly array has also lived through more heat, storms and wiring stress. Its inverter may already be due for replacement.
Sources: [7]
Cost drivers for poly systems today
HyreSolar does not publish panel prices. For poly owners, the real costs are repairs, added panels and end-of-life. A replacement may need a different panel model, extra electronics or a new inverter input. See solar repair and panel replacement.
Lifespan sets value. DOE cites a Berkeley Lab finding that average panel life rose from about 20 years in 2007 to 25–35 years in 2025. Check the dates on your panel and workmanship warranties; our workmanship warranty guide explains the second one.
When panels retire, DOE notes that US recycling generally costs more than landfill today. Our panel recycling guide covers options.
Sources: [8]
How a poly system gets repaired or expanded
A licensed installer or electrician handles every step. Never mix panels yourself.
- Pull your original data sheet and panel label. Note the model, wattage, voltage and current.
- Have the installer test the array and check monitoring for weak strings.
- For a broken panel, they find a replacement whose electrical ratings fit the string.
- For added panels, they design a separate inverter input or add module-level electronics.
- They pull a permit if your city or county requires one for the change.
- An inspector checks the work, and the utility is told if system size changes.
Our page on adding panels to an existing system covers the design choices.
Keeping old poly panels productive
Watch the monitoring app. Compare each month with the same month in past years. A slow slide is normal; a sudden drop is not.
Keep the glass clear of heavy dirt, leaves and droppings. Our guide to cleaning solar panels covers safe ways, or book panel cleaning.
Plan for the inverter. On older systems it is often the first part to fail.
Warning signs on older poly panels
Call a licensed installer or electrician if you see any of these. Do not touch the wiring.
- Brown or yellow patches on the cells, a sign of aging film.
- Thin dark lines across cells, often called snail trails, which can mark tiny cracks.
- Hot spots that look scorched or bubbled.
- A string reading far below the others in the app.
- Cracked glass, a corroded frame or a loose junction box on the back.
Safety rule
Old panels still make full voltage in daylight. Damaged ones can shock or start a fire. Leave all work to a licensed pro.
Standards and rules that apply
Product listing. UL says the NEC, IBC and IRC require PV products on or near buildings to be certified by a Nationally Recognized Testing Laboratory. Today’s panel safety standard is UL 61730-1 and -2, harmonized with IEC 61730. Older poly panels were listed under the standards of their day.
Changes to an old system. Your city or county decides if adding or swapping panels needs a permit, under the code edition it has adopted. In South Carolina, the SC Building Codes Council lists the 2021 codes as in force.
Utility. Adding panels changes system size. Your utility may need a new interconnection request. See our interconnection guide.
Poly vs mono vs thin film at a glance
| Polycrystalline | Monocrystalline | Thin film (CdTe) | |
|---|---|---|---|
| Silicon structure | Many crystals | One crystal | No silicon wafer; a thin layer on glass |
| Color | Blue, speckled | Even black | Uniform dark |
| Example efficiency | 16.89%–17.39% 1 | 20.2%–21.5% 2 | Modules above 19% 6 |
| Made today? | Largely no 3 | Yes, the whole wafer market 3 | Yes, mainly for utility farms |
Misconceptions
- Myth Poly panels work better in heat.
- Reality The data sheets say the opposite: −0.38%/°C for the poly KuMax against −0.34%/°C for the mono HiKu6. The poly panel loses slightly more per degree.
- Myth Polysilicon means a polycrystalline panel.
- Reality Polysilicon is the purified raw material for nearly all panels, mono included. Polycrystalline describes how the wafer cooled.
- Myth Poly panels wear out much faster than mono.
- Reality NREL’s review found crystalline silicon types showed similar low wear rates 7. Age and build quality matter more.
- Myth Old poly panels should be swapped for new ones.
- Reality Not if they still produce close to their warranty curve. Replacing working panels adds cost and waste.
Poly systems in SC, GA and VA
Older poly systems in South Carolina often date from the net-metering years. Customers who applied before 1 June 2021 keep legacy net metering until 31 May 2029 under Act 62 12.
Ask your utility whether adding panels changes that status before you expand. SC LLR registers solar panel installers as a residential specialty, so check the registration 13.
Georgia Power caps residential renewable systems at 10 kW, which limits how far you can grow 14. Virginia allows residential net metering up to 25 kW on investor-owned utilities 15.
If your roof already has poly panels
- They still work. Compare your monitoring with the warranty’s yearly loss figure; see panel degradation.
- Adding panels is the hard part. New panels are mono with different voltage and current. A licensed installer may give them their own inverter input or use module-level electronics.
- Replacing one broken panel: an exact poly match may no longer be made. Ask for one whose ratings fit the string.
- Selling the house: a buyer’s inspector may note the older technology. Production records matter more than cell type; see buying a house with solar.
- Buying new: you will be quoted mono. Compare cell design, heat loss and warranty instead.
Questions about polycrystalline solar panel
Are polycrystalline solar panels still sold?
Rarely. The ITRPV roadmap reports only monocrystalline wafers in the 2025 market, so any poly panel offered today is likely old stock or used. The DOE also reports that mono silicon made up 96% of global shipments in 2022. If a quote lists poly, ask why and check the panel’s age and warranty.
How do I know if my panels are polycrystalline?
Look at the color and the label. Poly cells are blue with a visible grain or flake pattern and square corners. The panel label on the back, or the data sheet, will say poly, multi or multicrystalline under cell type. Your installer’s original contract usually names the model too.
Can I mix polycrystalline and monocrystalline panels?
Not on the same string without care, because their voltage and current differ. A mismatched panel can hold back the whole string. A licensed installer can put new panels on a separate inverter input or use module-level electronics. Never mix panels yourself.
Is polycrystalline cheaper than monocrystalline?
It used to be, because casting wastes less silicon. That price gap closed as mono production grew, which is why makers stopped making poly. HyreSolar does not publish panel prices. Today the price differences you see are between mono cell designs and brands.
How long do polycrystalline panels last?
Often 25 years or more. DOE cites a Berkeley Lab finding that average panel life reached 25–35 years in 2025. An NREL review found a median output loss of 0.5% a year, with crystalline silicon showing similarly low rates. Your warranty sets what you can claim if output falls faster.
Are polycrystalline panels less efficient?
Yes. The 2018 KuMax poly panel tops out at 17.39% efficiency, while the 2022 mono PERC panel from the same maker reaches 21.5%. Electrons get lost where crystals meet, so less light becomes power. In practice that means more roof space for the same watts.
Should I replace my old poly panels?
Usually not while they still work. Check monitoring against the warranty’s yearly loss figure. Replace a panel only if it is damaged or failing. If you need more power, adding a separate set of new panels is often simpler than swapping the old ones.
Why are polycrystalline panels blue?
Light bounces off the many crystal edges at different angles, which shows as a blue, flaky sheen. The anti-reflective coating used on poly cells also tints them blue. Mono cells look black because the whole cell is one crystal.
Do polycrystalline panels work in cloudy weather?
Yes, at lower output, like any silicon panel. They use scattered light as well as direct sun. A poly array makes somewhat less than a mono array of the same size in any weather, because of its lower efficiency.
Sources
- Canadian Solar, KuMax CS3U-P (poly) data sheet V5.57_E2_NA (June 2018), retrieved .
- Canadian Solar, HiKu6 Mono PERC CS6R-MS data sheet V1.7C25_AU (April 2022), retrieved .
- VDMA, International Technology Roadmap for Photovoltaic (ITRPV), 17th Edition, Results 2025 (June 2026), retrieved .
- National Laboratory of the Rockies (formerly NREL), Best Research-Cell Efficiency data table, retrieved .
- US DOE Solar Energy Technologies Office, Crystalline Silicon Photovoltaics Research, retrieved .
- US DOE Solar Energy Technologies Office, Cadmium Telluride, retrieved .
- Jordan and Kurtz, NREL, Photovoltaic Degradation Rates — An Analytical Review (NREL/JA-5200-51664, 2012), retrieved .
- US DOE Solar Energy Technologies Office, End-of-Life Management for Solar Photovoltaics, retrieved .
- UL Solutions, Building-Integrated Photovoltaic (BIPV) System Testing and Certification (UL 7103, UL 61730), retrieved .
- National Laboratory of the Rockies (NLR, formerly NREL), PVWatts V8 documentation, retrieved .
- SC Building Codes Council, code adoption, retrieved .
- South Carolina Code Title 58 Ch. 40 (Act 62 of 2019, customer-generators), retrieved .
- SC LLR, Residential Specialty Contractor registration (Solar Panel Installer), retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Panel specs were read from the two named Canadian Solar data sheets; market status from ITRPV 17th Edition and DOE SETO; the research-cell record from the NLR data table; wear rates from the NREL review by Jordan and Kurtz. The roof-area example is arithmetic on the data-sheet efficiencies.
Suggest a correction. We fix errors and say what changed.