The question no longer needs settling, it has been settled. In its Photovoltaics Report updated on 14 July 2026, Fraunhofer ISE puts world production of multicrystalline modules at 0 GWp for 2025, out of a total of 706 GWp, and states that the technology has disappeared from the market; the ITRPV confirms for its part that only Czochralski-grown monocrystalline material is still on sale. Polycrystalline is therefore no longer something you compare at the point of purchase, it is something you meet on a roof, on arrays installed before 2020 that you are called in to extend or repair. That is what the comparison below is for: knowing what the existing array is worth, and what it costs to complete it with mono.
Understanding monocrystalline and polycrystalline solar panels
Monocrystalline: principle, appearance and most common uses
A monocrystalline module is made from a single silicon crystal. The cells are usually a uniform black, with sometimes rounded corners. In solar, it's the most common choice in 2026, because efficiency is high. You'd recommend it when roof area is limited, or to reach a given power rating with fewer panels.
Polycrystalline: how it works, how to spot it, and its strengths
Polycrystalline combines several silicon crystals rather than one. You can spot it by its marbled blue appearance and, almost always, by a 60-cell format of roughly 1,650 x 990 mm for 250 to 285 Wp. What you need to take from it is no longer a purchasing decision but a diagnosis: a blue array on a roof predates 2020, its unit power is low, and its commercial reference is no longer manufactured. Check the availability of spare modules before promising a like-for-like extension.
What's the same: inverter, installation, protections and connection
Mono or poly, the job follows the same logic. Central inverter or micro-inverters, DC wiring, earthing, disconnect switch, a surge arrester depending on the site, and AC-side protections at the consumer unit. Grid connection follows the same procedure, with a declaration and commissioning by the grid operator.
Efficiency, roof space and output: comparing what matters on site
Power, efficiency and low-light behaviour: how to read technical data sheets
On a module's data sheet, look at the Wp rating (STC), then the efficiency (%). To compare real-world output, add the temperature coefficient (Pmax) and the NOCT, which are closer to actual conditions than the 25°C test. A "low irradiance" note or the I-V curves show whether the module performs better in the morning, in winter, or under overcast skies.
Two data sheets are enough to measure the gap. On the left, a multicrystalline module representative of what went onto houses until the late 2010s; on the right, a TOPCon assembled in France, current data sheet.
| Data sheet entry | Trina TSM-285 PD05, 2017 data sheet | DualSun FLASH 500 TOPCon, v1.2 of March 2026 |
|---|---|---|
| Cell technology | multicrystalline 156.75 mm | monocrystalline n-type TOPCon, half-cut |
| Peak power | 285 Wp | 500 Wp |
| Module efficiency | 17.4% | 22.61% |
| Dimensions | 1,650 x 992 x 35 mm | 1,950 x 1,134 x 30 mm |
| Power density | 174 W/m² | 226 W/m² |
| Area for 1 kWp | 5.75 m² | 4.42 m² |
| Pmax temperature coefficient | -0.41 %/°C | -0.31 %/°C |
| NOCT or NMOT | 44 °C | 45 °C |
Translate that into site terms. For 3 kWp, the poly array needs 17.3 m² of pitch, the TOPCon array 13.3 m²: four square metres apart, which is two modules and a run of rail fewer. And at a cell temperature of 60 °C, an ordinary state of affairs on a roof in August, the poly loses 14.4% of its power where the TOPCon loses 10.9%. Those 3.5 points never show on the quote, only on the July output curve, when the client compares it with the one you gave him.
One methodological warning, because it comes up often: PVGIS cannot simulate this gap. The JRC models a single "crystalline silicon" category, with no split between mono and multi, on one set of coefficients. A PVGIS simulation will therefore never separate two technologies: only the data sheet does.
Small or constrained roofs: when monocrystalline makes the difference
When surface area is limited, every square metre counts. A monocrystalline module, usually denser in Wp/m², lets you hit the target power with fewer panels, less rail, and sometimes a single array. It's often the simplest choice in solar for dormers, parapets or complex roofs. On such roofs, Argile lays the panels out on the chosen pitch and estimates output from orientation and tilt.
The ITRPV publishes each year the average module efficiency in mass production by cell technology. Converted into area, that gives the square metres needed for 1 kWp, the only figure that matters when you lay out the array.
| Cell technology | 2025 module efficiency | Power density | Area for 1 kWp |
|---|---|---|---|
| PERC p-type mono | 21.7% | 217 W/m² | 4.61 m² |
| TOPCon n-type | 23.5% | 235 W/m² | 4.26 m² |
| SHJ, heterojunction | 23.5% | 235 W/m² | 4.26 m² |
| TBC, back contact on TOPCon | 24.1% | 241 W/m² | 4.15 m² |
| HBC, back contact on heterojunction | 24.4% | 244 W/m² | 4.10 m² |
Between PERC and HBC, the gap is half a square metre per kWp, two square metres on a 4 kWp installation. That is rarely decisive on a clear pitch, and it is what makes or breaks a project on a roof cluttered with rooflights and stacks.
Temperature, shading, orientation: where the gap widens (or doesn't)
The gap widens mainly in high heat, partial shading and mixed orientations. A good temperature coefficient limits summer losses. Bypass diodes and, depending on the case, optimisers or micro-inverters reduce the impact of shade. On a due-south orientation with no shading, however, the efficiency gap between comparable modules stays modest.
One case deserves separating out, because it comes up more and more: the mixed array, when you add recent mono alongside an existing poly array. Never mix two technologies on the same series string. The short-circuit currents differ, the MPPT settles on the weakest module, and you lose more than the efficiency difference. Two separate MPPT inputs, or micro-inverters, are the only clean answer.
Overall cost and equipment choice: think in price per watt and durability
Price per watt, availability and ranges: avoiding misleading comparisons
Compare in €/Wp installed, not the price of the panel alone. On a solar project, the inverter, mounting structure, wiring, electrical protection and installation carry a lot of weight. At equal power, also check the technology and range (efficiency, bifacial, glass-glass). And keep an eye on availability, a reference you can't find complicates after-sales service.
The only public European index split by technology is pvXchange's, recorded monthly on the spot market, duty paid and excluding tax. Here is its August 2026 reading.
| pvXchange category | Definition | Module price | Change since January 2026 |
|---|---|---|---|
| High Efficiency | HJT, n-type TOPCon or xBC, efficiency above 23.5% | €0.150/Wp | +30.4% |
| Full Black | black frame and backsheet | €0.160/Wp | +23.1% |
| Mainstream | same technologies, efficiency at or below 23.5% | €0.135/Wp | +28.6% |
| Low Cost | end of stock, seconds, limited warranty | €0.075/Wp | +27.3% |
Two readings, both pointing the same way. The index carries no polycrystalline line at all: the only category where poly survives at that broker is spare modules, which says a great deal about what this market has become. And the module price has been rising in all four categories since January 2026, by between 23 and 30%. If you are still working from a price list built in late 2025, the module line is out by a quarter.
Those cents do not make the quote, though. At €0.15/Wp, the modules on a 3 kWp installation come to €450, while the complete job runs into thousands: it is the installation, the structure, the inverter and the grid connection that set the price, and the choice of technology barely moves it.
Product warranty and performance warranty: points to check before signing
The product warranty covers material defects; the performance warranty governs the power decline over time. Ask for the detail of the linear degradation profile, the threshold at 25 years, and who pays for transport and labour. Check there's a contact in Europe, and keep invoices, serial numbers and the commissioning report.
Manufacturing quality: frames, glass, junction boxes, certifications and traceability
A good module has a rigid frame, suitable tempered glass, and a sealed junction box. Check for IEC 61215 and IEC 61730 certifications, plus any relevant tests for the site (salt mist, ammonia). Require clear traceability, marking and unique serial numbers, and a declared recycling channel.
Solar in 2026: grants, standards and requirements to anticipate for a clean file
2026 grants and schemes: what to check before costing a solar project
Before costing the job, check the rates in force: the French order of 1 June 2026, which applies to complete connection requests filed from 5 June 2026, removed the investment premium and introduced a single feed-in tariff of €0.011/kWh excluding tax up to 100 kWp, indexed by 2% a year over the 20 years of the contract, with no payment for injection beyond 1,600 kWh/kWp/year. Contracts and complete requests predating 5 June 2026 keep their terms. Also check eligibility: the property, the power rating in kWp, installation by a qualified professional, town hall procedures and grid connection. The surplus valuation arrangements are covered in our article on self-consumption with a virtual battery.
Installation rules and compliance: DTU standards, electrical safety, Consuel and inspection points
On the roof, installation must comply with the roofing DTU standards and module ventilation requirements, or you risk leaks. On the electrical side, apply NF C 15-100 and the dedicated PV rules. For commissioning, the Consuel certificate is often a mandatory step. Protections, cable cross-section, labelling, surge arrester as needed.
Self-consumption, selling the surplus, building integration: choosing the right setup
In self-consumption, you can aim for surplus sale (purchase contract) or zero export (dedicated agreement). In full sale, meters and connection change. Building-integrated mounting isn't mandatory. On-roof mounting is often simpler and limits waterproofing risks. Confirm the approach with the insurer and Enedis.
Quick decision method: choosing between monocrystalline and polycrystalline for your client
Site checklist: technical criteria, budget, appearance and roof constraints
On a solar project, start from the available surface area and the target power rating. Efficiency decides the number of modules, and therefore the rails, the labour hours and the roof penetrations. The question is no longer mono or poly but which generation of mono: at 21.7% for a PERC and 23.5% for a TOPCon, the difference in area per kWp is already 0.35 m². The pre-project benchmarks are set out in our method for sizing a self-consumption installation, and the effect of aspect in the orientation coefficient tables.
- Usable surface area, shading, orientation and tilt.
- Loads and fixings, steel deck roofing, tiles, waterproofing.
- Ventilation under the modules, especially in summer.
- Overall budget (modules, installation, connection), not just the price of the panel.
- Appearance. Uniform black for mono, "speckled" blue for poly.
Example cases: single-family home, agricultural building, small surface area, high heat
A house with 25 m² usable: at 4.26 m² per kWp in TOPCon, you fit 5.8 kWp, against only 4.3 kWp with the poly modules of the previous generation. An agricultural building with a large roof: area is not the constraint, so decide on price per Wp and on the availability of the reference for after-sales. A small roof area with a complex shape: the highest efficiency available, and take care with the layout. High heat or a poorly ventilated roof: compare the Pmax temperature coefficient, the closer to zero the less output drops, and remember that 0.10 point of difference is worth 3.5% of power at a cell temperature of 60 °C.
Simple talking points: explaining the difference to your client without jargon
Mono is a more uniform "block" of silicon; it converts light better for the same surface area. Poly is an assembly of crystals, less efficient, and no longer manufactured. If a client brings up poly, it is usually because he is comparing your quote with prices found online on end-of-stock batches: tell him the question no longer arises at the point of purchase, and bring the discussion back to what really sets the price, the installation, the structure, the inverter and the grid connection. In both cases, lifespan and warranties mostly come down to the manufacturer's quality and a clean installation.
