The UK product standard for solar panels recognises three cell technologies: monocrystalline silicon, polycrystalline silicon and thin film. On a domestic roof in 2026 you will be quoted crystalline silicon in practically every case, so the useful question is not mono versus poly but what else on that datasheet is doing the work.
Most guides to this subject reprint a table of efficiency ranges by cell type and stop there. That table settles nothing, because the panel you are actually being offered is one of a few hundred crystalline silicon modules certified for use in the UK, and the things separating them are rated power, physical size, the power tolerance and whether the module is bifacial. Everything below was verified on 15 August 2026 against the MCS solar PV product standard MCS 005, the MCS Product Directory and the Energy Saving Trust.
Ask each installer for the module make, model and rated watts in writing, then check the model against the MCS Product Directory yourself. Quotes come from MCS-certified installers covering your area.
Get My Free Quotes →The three solar panel types the UK certification scheme recognises
MCS 005, the product standard a panel has to pass before an MCS installer can fit it, defines exactly three cell technologies. These are its own definitions, from Issue 4.0 of the standard.
- Monocrystalline silicon. "Often referred to as single-crystal silicon. Consists of silicon, where the entire solid's crystal lattice is continuous, unbroken to its edges, and free from grain limits."
- Polycrystalline silicon. "Consists of several fragments of silicon crystals melted together to form a single PV cell."
- Thin film. "Generic term for a range of different technologies alternative to crystalline silicon solar PV cells, typically formed by the deposition of a photovoltaic material onto a glass or other substrate."
That is the whole taxonomy, and it is worth noting how plain it is. Monocrystalline and polycrystalline are the same material handled two different ways at the point of manufacture. Thin film is not one technology at all, it is a bucket.
Issue 4.0 is also newly binding. The standard sets its own implementation date: compliance "is mandatory for products to be certified in accordance with MCS 005 from the date of implementation 01/08/2026". So every panel newly certified from the start of this month has been tested against this version.
You can see how much of a bucket from the test standards MCS 005 requires a module to meet. Section 6.1.1 lists a general test standard, BS EN IEC 61215-1:2021 and 61215-2:2021, then four technology-specific parts underneath it: 61215-1-1 for crystalline silicon modules, 61215-1-2 for thin-film cadmium telluride, 61215-1-3 for thin-film amorphous silicon, and 61215-1-4 for thin-film copper indium gallium selenide, the family usually written as CIGS. So the UK regime treats crystalline silicon as a single test category and splits thin film into three separate ones.
Why your quote will say crystalline silicon
The panels UK installers actually fit are crystalline silicon, and the module efficiencies on the certified register are the giveaway. The Energy Saving Trust describes the cells in a domestic panel as "made from layers of semi-conducting material, most commonly silicon".
When we worked through the MCS Product Directory on 13 August 2026, dividing rated watts by listed panel area, certified solar PV modules came out at roughly 19.5% to 24% efficient. That is crystalline silicon territory. The best thin-film modules on the market are not far off the bottom of it, with First Solar's Series 7 cadmium telluride range quoted at up to 19.7%, but those are large-format modules built for solar farms rather than products a UK installer will offer for a semi in Leeds. Thin film is a real technology with a real market. That market is not domestic rooftops. Our guide to solar panel efficiency works through the calculation and what the number does and does not buy you.
Be careful with anyone who gives you a precise market share for mono against poly in the UK. Nobody can, and the next section explains why.
What the MCS Product Directory can and cannot tell you
The directory does not record cell technology, so you cannot look up whether a certified panel is monocrystalline, polycrystalline or thin film. This surprises people who have been told to check the directory before signing.
Checked on 15 August 2026, a solar PV product record in the directory carries the certification number, the manufacturer, the certification body, the model number, the technology, the certification period and the current certification status. The technology field holds "Solar PV", meaning the product category, not the cell type. Some manufacturers put the word into the model name, which is why a handful of older polycrystalline listings are findable by searching the model text, but that is a naming habit rather than a field you can filter on.
What the directory is genuinely good for is narrower and more useful: confirming that the exact model on your quote is certified, by whom, and that its certification is current. The certification period has an end date, and some entries are flagged as being in a grace period. If the model on your quote is not on the register, that is the conversation to have before you sign, not the cell technology. Our guide to choosing a solar installer covers the rest of those checks.
Bifacial panels are rated on a different test
A bifacial module generates from both faces, and MCS 005 rates it under test conditions that assume light hitting the back, which makes its headline wattage not directly comparable to an ordinary panel's. This is the single most likely way to misread a quote on panel type.
The standard defines bifacial modules as those "that can produce power from both their front side, as per a traditional module, but also from the back of the cells", and clause 6.1.2 says that for these modules "the power output should be determined at BNPI test conditions". BNPI stands for Bifacial Name Plate Irradiance, and the difference from the usual rating is set out in the standard's definitions:
- Standard Test Conditions. 1000 W/m2 on the front of the panel, 0 W/m2 on the rear.
- Bifacial Name Plate Irradiance. 1000 W/m2 on the front, plus 135 W/m2 on the rear.
A bifacial module quoted at its BNPI figure has been credited with rear-side light that a panel mounted flush to a pitched roof will never see much of. That is not a trick, it is the correct rating for the product, but it means a 500W bifacial module and a 500W conventional module are not the same claim. If a bifacial panel appears on your quote, ask for the STC rating alongside the BNPI one, and ask what mounting arrangement the installer expects will deliver rear-side gain on your roof.
Panels with the electronics built in
Some modules arrive with power electronics already attached, and MCS certifies them on the panel underneath. MCS 005 defines module-level power electronics as devices incorporated into a solar PV system "to improve its performance in certain conditions (especially where shade is present)", the category that covers microinverters and DC power optimisers.
The standard is specific about how these are handled: modules with integrated module-level power electronics, "e.g. those which utilise an integrated microinverter on the panel itself, allowing for both an AC and DC output directly from the panel", are eligible for MCS certification "given that the DC PV panel with the relevant junction box itself passes the relevant part(s) of BS EN IEC 61215". In other words the certification is testing the panel, not the electronics bolted to it.
Whether you want per-panel electronics at all is a shading question rather than a panel-type question, and it belongs in the inverter conversation. Our guide to solar inverters covers string, hybrid, optimiser and microinverter setups and the grid paperwork each one triggers.
Roof tiles are a shape, not a cell type
Solar roof tiles are not a fourth technology. They are crystalline silicon in a different form factor, and they route to the same product standard as ordinary panels.
MCS has a separate standard, MCS 017, for bespoke building-integrated photovoltaics, meaning products "tailored and manufactured for a specific project" such as PV glazing or facade units. Mass-market solar tiles are standardised products rather than bespoke ones, and MCS 017 sends them elsewhere explicitly: "PV modules and tiles which do not meet the BBIPV product definition require certification under MCS 005." So the tile on a brochure and the panel on a brochure are certified against the same document. The differences are cost, appearance and installation, which our guide to solar roof tiles goes through in full.
The line on the datasheet worth reading
Power tolerance tells you how far the panel you receive is allowed to differ from the wattage you were sold, and MCS 005 constrains how a manufacturer may state it. Clause 6.2.1 requires the maximum power tolerance to be declared either as "a value either side of zero (e.g. +/- 5%)" or "a value relative to zero (e.g. 0% to +3%)".
The rule underneath that is what protects you. The minimum and maximum cannot both sit on the same side of zero, so a manufacturer cannot advertise a tolerance of +5% to +10% and quietly move the real baseline. And the standard states that "a tolerance range of greater than 10% between the minima and maxima is not permitted", which caps how vague the claim can get.
A tolerance of 0% to +3% means every panel meets or beats its label. A tolerance of plus or minus 5% on a 450W panel means you might receive 427.5W. Across a dozen panels that is the difference between two rated system sizes, and it costs nothing to ask for.
What actually changes your output more than the panel type
Orientation, shading and system size move your generation far more than the cell technology does. The Energy Saving Trust puts a typical domestic system at around 4.5 kWp costing around £7,600, using roughly 12 panels over 20 to 30 square metres of roof. MCS, working from its own installation data, reports that "the average cost of installing a certified solar PV system for the home in 2025, according to the MCS Data Dashboard, is just over £7,000", around £500 down on 2024.
Against those numbers, here is the order of magnitude of the things you can still decide:
- Which way the roof faces. The Energy Saving Trust says an east or west facing system "tends to get around 15-20% less energy than one facing directly south", and it does not recommend north-facing roofs at all. Our guide to which direction solar panels should face covers the split-array case.
- Shading. A chimney or a neighbour's tree over part of the array costs you more than any plausible efficiency difference between two crystalline silicon modules.
- How many panels fit. Efficiency only becomes a spending decision when the roof runs out before the kWp does. Our guide to how many solar panels you need works through sizing from your actual consumption.
- What you do with the electricity. Using a unit yourself is worth considerably more than exporting it, which is why self-consumption drives payback. Our guide to what solar panels cost in the UK sets out the full cost and payback picture.
None of that is an argument for ignoring the panel on your quote. It is an argument for reading past the word monocrystalline to the model number, the rated watts, the tolerance and the certification status, which are the parts that differ between the quotes on your kitchen table.
Ask each installer for the module make, model, rated watts and power tolerance in writing. Quotes from MCS-certified installers covering your area, in about 60 seconds.
Get My Free Quotes →Solar panel types: frequently asked questions
Three cell technologies are recognised by MCS 005, the UK product standard for solar panels: monocrystalline silicon, polycrystalline silicon and thin film. The standard defines monocrystalline as "single-crystal silicon" where the crystal lattice is "continuous, unbroken to its edges", polycrystalline as "several fragments of silicon crystals melted together to form a single PV cell", and thin film as a "generic term for a range of different technologies alternative to crystalline silicon". Thin film is itself split into three test categories in the standard: cadmium telluride, amorphous silicon and CIGS. On a UK domestic roof you will be quoted crystalline silicon in practically every case.
In practice the question rarely arises now, because domestic quotes in the UK are overwhelmingly monocrystalline. Certified modules on the MCS Product Directory work out at roughly 19.5% to 24% efficient when checked in August 2026, which is the crystalline silicon band, and polycrystalline listings are increasingly historic. If you are choosing between two live quotes, compare the rated watts, the physical size, the power tolerance and the certification status of the specific model rather than the cell type, because those are the figures that differ.
Not from the MCS Product Directory, which does not record cell technology. Checked on 15 August 2026, a solar PV record in the directory holds the certification number, manufacturer, certification body, model number, technology field, certification period and certification status, and the technology field says "Solar PV" rather than the cell type. Some manufacturers include the word in the model name, but that is not a searchable field. To find the cell type you need the manufacturer's datasheet for the exact model, which your installer should provide on request. Use the directory for what it is good at, which is confirming that the model quoted is certified and that its certification is current.
A bifacial panel generates from both faces. MCS 005 describes them as modules that "can produce power from both their front side, as per a traditional module, but also from the back of the cells". The catch is the rating. Ordinary panels are rated at Standard Test Conditions, which is 1000 W/m2 on the front and 0 W/m2 on the rear. Bifacial modules are rated at Bifacial Name Plate Irradiance, which adds 135 W/m2 on the rear. A bifacial panel's headline watts therefore include rear-side light that a panel mounted flush to a pitched roof will see very little of. Ask for the Standard Test Conditions rating as well, and ask what mounting arrangement would actually deliver the rear-side gain on your roof.
No. Solar tiles are a different shape, not a different cell technology, and mass-market tiles are certified under the same product standard as ordinary panels. MCS has a separate standard, MCS 017, for bespoke building-integrated photovoltaics such as PV glazing and facade units made for a specific project, and it states that "PV modules and tiles which do not meet the BBIPV product definition require certification under MCS 005". Standardised tiles are not bespoke, so they route to MCS 005 alongside conventional panels. The real differences are cost, appearance and how the roof is built.
It is how far the panel you receive may differ from the wattage on the label. MCS 005 clause 6.2.1 requires the tolerance to be declared either as "a value either side of zero (e.g. +/- 5%)" or as "a value relative to zero (e.g. 0% to +3%)", and it does not allow both ends to sit on the same side of zero, so a manufacturer cannot state a tolerance of +5% to +10%. The standard also caps the spread: "a tolerance range of greater than 10% between the minima and maxima is not permitted". A 0% to +3% tolerance means every panel meets or beats its rating. A tolerance of plus or minus 5% on a 450W panel means an individual panel could be 427.5W.
Less than the size of the system and the state of your roof do. The Energy Saving Trust puts a typical domestic system at around 4.5 kWp costing around £7,600, using around 12 panels over 20 to 30 square metres, and MCS reports the average certified domestic install in 2025 at "just over £7,000", around £500 down on 2024. Within crystalline silicon, a higher efficiency module costs more per watt and mainly buys you the ability to fit more kWp onto a roof that has run out of space. If your roof has room, the cheaper module of the same rated power generates the same electricity.
Figures and quotations on this page were verified against MCS standard MCS 005 Issue 4.0 (dated 1 August 2024), MCS 017 Issue 2.0, the MCS Product Directory, the MCS consumer solar guidance and the Energy Saving Trust on 15 August 2026. Note that the MCS website's own standard page for MCS 005 still renders the superseded Issue 2.5 of 2017, so check the issue number on the document itself. Product standards, certified product listings and costs change. Check the linked primary sources before making a decision.