5.2 Module Types and Building Integration

Quick Answer: Handbook v1.3, 3.1.1(c), names four module types you must be able to describe: standard, bifacial, PV roof tiles, and bespoke building integrated PV (BBIPV). The everyday 2922 job is still a framed glass-backsheet or glass-glass module on rails above the existing covering, normally using an MCS 012 pitched-roof installation kit. Bifacial modules add rear-side current from albedo. Tiles and BBIPV replace or form the roof covering, so rain, fire and the correct MCS 012 in-roof kit or MCS 017 BBIPV route sit on the design, not just the electrical schematic.

Standard framed modules — still the domestic default

A standard module is a factory laminate of series-connected cells, encapsulant, front glass, and either a polymer backsheet or a second sheet of glass, held in an aluminium frame. It is certified as a PV module (MCS 005 for products used on MCS installations) and is then mounted on a pitched-roof installation kit certified to MCS 012. MIS 3002 requires those product routes for MCS-certificated work: modules to MCS 005 or, where the product is truly bespoke and building-integrated, MCS 017; pitched-roof kits to MCS 012.

Glass-backsheet construction is lighter and has been the volume domestic product for years. Glass-glass is heavier, generally more moisture-robust, and is the usual platform for bifacial cells because light can enter from the rear. Both sit on rails above the tiles or slates in an above-roof (on-roof) arrangement: the original covering stays, the kit carries wind uplift and keeps the penetrations weathertight, and rain still sheds on the existing tiles. That is why framed modules on rails remain the domestic default — known loads, known flashings, known replacement of a failed module, and a fire/weathertightness story that still belongs to the original covering plus a tested kit.

Construction details that matter on 2922

Look at a module as an electrical accessory, not just a wattage sticker.

• Junction box — usually on the rear, IP-rated, potted or gasketed, containing the outgoing leads and the bypass diodes. Diodes protect substrings under shade and mismatch; their number, rating and failure modes are taught in a later chapter. For this chapter, know that they live in the box and that a cooked box is a hot-spot or diode-failure clue.
• Connectors — locking, polarised, typically MC4 or a manufacturer-stated compatible type. They are not a load-break isolator unless the datasheet says they are. Keep them dry, fully mated, and of one compatible family.
• Frames — anodised aluminium, the clamp interface to the rails, and a possible earthing / bonding path. Module frames are exposed-conductive-parts. Depending on the earthing arrangement and BS 7671 Section 712 design, you may bond via the mounting system, a dedicated earth lug, or both. Do not assume the anodised surface is a connection; use the kit's bonding method.
• Leads — double-insulated, UV-resistant, usually factory-fitted. Strain-relieve them; do not use the connector as a cable clamp.

None of that construction disappears when you switch to tiles or BBIPV. The junction box may move, the frame may vanish, and the bonding path may become a curtain-wall mullion — the design duty grows, it does not shrink.

Bifacial modules — using the rear face

A bifacial module has an optically useful rear: typically glass-glass, with cells that collect light from both faces. The extra current comes from rear irradiance, not from a different band-gap miracle. Rear irradiance is albedo — light reflected from the surface behind or below the array — plus some diffuse sky seen from the back.

Rear current shows up where the designer has actually given the rear a view:

• Bright membranes (white TPO/PVC) on commercial flat roofs
• Light gravel, concrete, or snow
• Ground-mount over grass, sand, or pale ground, with enough height and row spacing
• Some flat-roof ballasted systems with a high-albedo field and an open rear

A dark concrete tile pitch with the module almost sitting on the covering offers little rear light. Raising the array, painting a membrane white, or going ground-mount is what makes bifacial worth the extra glass. Do not quote a single "rear gain percentage" as a 2922 rule: gain depends on albedo, height, tilt, rear shading from rails and junction boxes, and soiling. Stay qualitative here; yield software and the datasheet's bifaciality factor belong to design, not to a handbook pass mark.

Bifacial modules are still often standard framed products electrically. They may need glass-glass handling, higher mass on the roof structure, and clamp zones that do not shade the rear. The I–V curve still has an Isc, Voc and Pmax; the rear simply adds to the current at a given irradiance on the front.

PV roof tiles — the covering is the product

PV roof tiles (and similar slate-format products) are intended to look like roof covering and to replace a run of tiles or slates rather than sit above them. Active area is usually a smaller fraction of the plan area than a framed module field: more gaps, more flashing, more "roof" and less cell. Conversion efficiency of the semiconductor may be respectable; system watts per square metre of roof are often lower than a packed framed array. That is why a customer who wants maximum kWh on 20 m² of south roof (section 5.1) and a customer who wants the roof to still look like a roof are asking for different products.

Because the product is the covering, you inherit covering duties:

• Weathertightness — laps, underlay, valleys, abutments, and replacement of a failed tile without wrecking the course
• Fire performance of the roof as built, not just of a module hanging in air
• Ventilation and heat — in-roof cells often run hotter than a racked above-roof array, which trims power (section 5.3)
• MCS product route — many tile systems are MCS 005 modules used inside an MCS 012 in-roof kit; they are not automatically MCS 017

MCS 012 exists precisely so a kit can be tested as a structurally stable fixing that keeps the roof weathertight and supports the fire performance expected under the building regulations. An in-roof kit is still MCS 012 territory when it is a defined mounting kit. Treat "tile" as a covering decision, then prove the kit and module listings.

Bespoke building integrated PV (BBIPV)

BBIPV in the handbook sense is bespoke: manufactured in project-specific sizes and configurations to be built into the fabric — façade units, PV glazing, brise-soleil, custom roof elements. MCS 017 is the product-certification route for those bespoke building-integrated products. Repeat catalogue tiles that are not tailored to one project are usually not MCS 017; they stay on MCS 005 (and an MCS 012 kit if they sit in a pitched roof).

BBIPV pulls the PV designer into curtain-wall, glazing, and fire-engineered façade territory. Electrical construction is still cells, a junction arrangement, connectors, and a bonding path, but the "frame" may be a structural transom. Do not treat BBIPV as a cosmetic extra on a standard string design. The later string-voltage and isolation chapters still apply; the building-physics duties are additional.

Conservation-area roof: tiles versus MCS 012 on-roof

A conservation officer or planning condition often wants the roof to keep reading as a tiled roof. That is an appearance and planning brief. It is not a statement that on-roof MCS 012 is electrically inferior.

MCS 012 on-roof (above-roof) keeps the original covering, uses a listed kit, and is the faster, more maintainable, usually cheaper 2922 default. Modules are visible. Rain still runs on the existing tiles. Bonding and DC isolation are textbook.

Tiles or other in-roof / BBIPV can satisfy the appearance brief, but you now own weathertightness, fire, hotter cells, lower packing density, and the correct MCS 012 in-roof or MCS 017 listing. You may also need listed-building or conservation-area consent even when permitted-development would have covered a standard on-roof array elsewhere. Electrical competence does not replace that planning step.

Choose on-roof MCS 012 when visibility is accepted and the customer wants energy, serviceability and a known kit. Choose tiles or BBIPV when the covering itself is the design, and then budget the extra design duty instead of pretending a tile is "just a black module."

Type versus use versus extra design duty

The electrical heart is the same: cells, a DC source that is live in daylight, connectors you must not unmate under load, and frames or metalwork that may need bonding. What changes is whether you are hanging a listed module on a listed kit above a roof, or making the building the module.