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 crystals. You can spot it by its marbled blue appearance. Efficiency is generally a bit lower, but it remains reliable. It can still be worthwhile if the budget is tight, if space isn't an issue, or on projects where appearance matters less than the price per watt.
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.
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.
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.
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.
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: since the order of 5 June 2026, there is no longer an investment premium, but a single feed-in tariff of €0.011/kWh (P+Q ≤ 100 kWp, indexed by 2% a year), locked in at the date of the connection request. Also check eligibility: the property, the power rating in kWp, installation by a qualified professional, town hall procedures and grid connection.
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. If space is tight, the efficiency of monocrystalline helps you get more Wp per m². If the roof is very large and the budget tight, polycrystalline can still hold its own where it's still available.
- 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 scenarios: single-family home, agricultural building, small surface area, high heat
A house with 25 m² usable. Aim for mono to reach the target power. An agricultural building with a large roof: more open choice, favour the best cost per Wp and availability. A small roof area with a complex shape: mono, and take care with the layout. High heat: compare the stated temperature coefficient — the closer to 0, the less output drops.
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, usually a bit less efficient. In both cases, lifespan and warranties mostly come down to the manufacturer's quality and a clean installation.
Key figures
20–22%
Mono efficiency
> 90%
Mono share of the market
15–18%
Poly efficiency
Frequently asked questions
You need to file a connection request with Enedis (or the local grid operator) with a single-line diagram, site plan, non-opposition certificate and a Consuel compliance certificate where required. In practice, allow 4 to 12 weeks depending on the power rating, how complete the file is, and whether grid works are needed. Also plan for a prior declaration at the town hall if the roof's external appearance is changed.
Pierre-Louis Guhur
CEO of Argile
