Alectrona
Commercial guideBifacial modules pick up reflected light on their rear face, so on a commercial flat roof the gain is real where the surface, the row spacing and the panel height let it be, and negligible where they do not. We model it for your roof rather than quote a marketing figure.
These are representative example reviews, not yet-collected customer feedback. They are written to illustrate the kind of feedback Alectrona aims to earn and are shown as design placeholders while we gather and verify reviews from our first commercial clients. Alectrona is the commercial solar trading brand of RVTC LTD.
What set Alectrona apart was the documented design pack. We had quotes from three installers, but only Alectrona handed us a full set of drawings, a single-line diagram and a design referencing BS 7671 and the G99 connection process. The whole thing read like an engineering submission rather than a sales brochure. Our M&E consultant reviewed it and signed it off without a single query. That gave the board the confidence to release the capital.
Other firms priced our roof off a satellite image and a desktop guess. Alectrona flew an in-house drone survey, fully insured and flown by a qualified commercial drone pilot, and built a 3D model of the actual roof. It picked up plant, vents and a parapet line that a flat aerial photo had completely missed, which changed the panel layout. I would rather find that out at design stage than on the day the scaffold goes up. The accuracy of that survey is the reason I trusted everything that followed.
As a finance director I was wary of being oversold a system bigger than we could use. Alectrona modelled the array against our actual half-hourly consumption data rather than an annual total, so it is sized to what we genuinely draw on site during the day. They were honest that exporting surplus is worth far less than self-consumption, and built the design around that. The capital case stacked up because the engineering was honest, not because the numbers were inflated.
We were undecided between buying outright, leasing and a PPA. Alectrona laid out all three side by side with the pros and cons of each against our balance sheet, instead of pushing the one that pays them best. They were clear about where a PPA makes sense and where capex wins, and pointed us at our own accountant for the tax treatment. The survey and design took a little longer than I expected, but the thoroughness was worth the wait. Genuinely consultative.
The install crew were tidy and well run, and worked to a clear CDM 2015 plan with a proper site induction and RAMS. What impressed me most was the handover. We received a full commissioning pack with the IEC 62446-1 test results, certification, O&M documentation and an as-built record for our maintenance team. As the people who have to live with this asset for the next twenty years, having that paperwork in order matters enormously. Nothing was left loose.
I expected the usual hard sell and got the opposite. After surveying our site Alectrona told us one roof section was not worth covering because of shading, and that a smaller, well-sited array was the better investment than filling every square metre. There was no commission-driven upselling and no pressure. For a six-figure capital project, that straight talk is exactly what you want from the people advising you. We will be using them again on our second site.
A bifacial panel generates from both faces. The front works like any module; the rear collects light that has reflected off the surface beneath and behind the array. On a commercial flat roof that rear-gain can be worth specifying, because a flat roof often has the two things that feed it: a large, open expanse of membrane and the room to raise and space the rows. The honest position is that the gain is roof-specific. It is governed by how reflective the surface is, how far apart the rows sit and how high the panels stand, so it has to be modelled for your roof, not assumed from a brochure percentage.
This page sets out the engineering principles that decide whether bifacial pays on a given flat roof, and how the rear-gain is established for your building. A commercial array above 50 kWp sits outside the MCS scheme, so the assurance here is the structural survey, the PV*SOL yield model and CDM 2015 duties, not a domestic accreditation badge. RVTC LTD holds the contract.
Rear-gain is the extra output a bifacial module produces from light striking its back face. It is not a free uplift that applies everywhere. Three roof-specific factors decide how much of it you actually see, and all three are properties of your roof rather than of the panel:
Because all three vary roof by roof, the rear-gain for your building is established in the PV*SOL model against the real surface, layout and panel height, not carried over from a figure quoted for a different roof.
The strongest case is a flat roof with a bright, reflective single-ply membrane and the area to raise and space the rows. Here the surface feeds the rear face, the layout lets the light in, and the gain is worth specifying. The weaker case is a dark or gravel-ballasted surface, or a layout packed tight for panel count, where the rear face sees little reflected light and the premium for the dual-glass module is harder to justify.
An east-west layout, where rows face in opposite directions across the roof to flatten the generation curve through the day, changes the picture again, because the inter-row geometry and self-shading differ from a south-facing pitch. None of this rules bifacial in or out on sight. It means the surface, the layout and the orientation are assessed together for your roof, and bifacial is specified only where the model shows it earns its place.
A bifacial module generates from both faces, the rear collecting light reflected off the surface beneath and behind the array. On a flat roof the gain is real where a bright single-ply membrane, room to space the rows and elevation off the deck let it be, and negligible where they do not. It carries a higher module cost and usually more ballast, so it is specified only where the PV*SOL model shows the rear-gain pays for its premium on your roof.
A monofacial module generates from its front face alone, the way any standard panel does. It is the honest choice on a dark or gravel-ballasted surface, or a layout packed tight for panel count, where the rear face sees little reflected light and the premium for a dual-glass module is harder to justify. The cell technology inside, PERC, TOPCon or HJT, is a separate decision either way.
Most commercial flat roofs are covered by a single-ply waterproof membrane, and the warranty on that membrane usually depends on it not being pierced. The standard method here is a ballasted mounting system: the frames are held down by weight, typically concrete blocks or pavers, so the array resists wind uplift without any fixing penetrating the roof. That keeps the waterproofing and its warranty intact.
This pairs naturally with bifacial, because a ballasted frame already raises and tilts the panels off the deck, which is exactly the elevation that feeds the rear face. The constraint is weight. The ballast needed to hold the array against wind uplift is a real load the roof has to carry, and it is calculated for your roof from the wind exposure and the layout, then checked against what the structure can take in the survey. On a standing-seam metal roof the method is different again: the array is clamped to the raised seams, so it is fixed without penetrating the deck, and the seam profile and panel height drive what rear-gain is available. The mounting method follows the roof; we describe the method rather than tie you to one manufacturer's kit.
Bifacial describes the module's construction, a rear face that generates, usually with glass on both sides. It is not the same choice as the cell technology inside, and the two are decided separately. The common commercial cell types each have an honest trade-off, and none is the right answer for every roof:
Which cell type suits your roof depends on the area available, the load profile, the temperature behaviour you are designing for and the funding route. We choose it from the survey and the model, name the specific module, its scheme, grade and quarter, and re-verify that status for the exact module before contract.
On a flat roof you choose the tilt and the inter-row pitch, which is not true on a fixed pitched roof, and both choices change the rear-gain. The angle that maximises front-face yield in the UK sits broadly in the south-facing band, but a steeper tilt lifts the rear face higher off the membrane and lets more reflected light reach it, while a shallower tilt packs more capacity onto the roof and reduces self-shading. There is no universal best angle, because the optimum trades front yield, rear-gain, ballast weight and panel count against each other for your specific roof.
Row spacing is the second lever and it pulls in two directions at once. Wider rows cut the inter-row shading that starves both faces in winter, when the sun is low, and they let more reflected light onto the back of the panel behind. Tighter rows fit more kilowatts on the same membrane. The pitch that suits your roof comes out of the PV*SOL yield model in our feasibility study, run against your latitude, your shading and your capacity target, and it feeds directly into how much roof space the array needs. We model the tilt and pitch together rather than apply a default, because on a bifacial flat-roof array the two are not separable from the rear-gain they produce.
It can, and the weight is the binding constraint on most flat-roof bifacial designs. A raised, tilted module presents more surface to the wind, so the ballast needed to hold it down against uplift is a genuine dead load the roof has to carry, and a steeper tilt or a more exposed roof edge needs more of it. That load is not assumed. It is calculated from the wind exposure for your site under the relevant Eurocode wind loading standard, BS EN 1991-1-4, with the elevated array and its turbulence taken into account, then set against what the structure can take.
The verdict on whether the roof can carry it comes from a structural roof survey by a chartered engineer, who checks the existing dead and imposed loads against the array and ballast and confirms the load paths down to the supporting steel. Where the survey shows headroom is tight, the design is adjusted, by lowering the tilt to cut wind load, redistributing ballast toward stronger bays, or trimming the array, rather than forced onto a roof that cannot take it. Because a commercial array above 50 kWp sits outside MCS, this structural verification and the CDM 2015 duties that sit over the works are the assurance, set out in our CDM 2015 guide.
Bifacial changes what soiling costs you, because dirt on the surface beneath the array matters as well as dirt on the glass. Rear-gain depends on light reflecting off a clean, bright membrane, so a membrane that greens over with algae, collects dust or pools standing water loses reflectance and the rear-gain falls with it. The front-face soiling question is the same as for any module, but the reflective surface is an extra thing to keep clean, and a low-tilt flat-roof array sheds rain less freely than a steep pitch, so soiling can build up. Our cleaning and bird-proofing guide covers how that is managed, and bird fouling under a raised flat-roof array is a specific risk worth designing out.
On durability, most bifacial modules are dual-glass rather than glass-and-backsheet, which removes the polymer backsheet as a weathering and fire-spread path and tends to carry a lower stated annual degradation rate on the manufacturer datasheet. That is a datasheet figure to verify against the specific module, not a promise. Dual-glass is also heavier, which feeds straight back into the ballast and structural check above. The product and performance warranty terms, the degradation curve and the bankability of the manufacturer are confirmed for the exact module before contract, and the ongoing checks sit within commercial solar maintenance.
The rear-gain the model produces is added into the total modelled yield for the array, so it influences the generation figure that any payback or return estimate is built on. Because the gain is roof-specific, the only honest input is the number PV*SOL produces for your surface, tilt and spacing, not a brochure uplift, and a bifacial design also carries a higher module cost and usually more ballast, both of which sit on the other side of the sum.
Whether the rear-gain earns back that premium on your roof is a modelled outcome, not a promise. Any payback, return or saving estimate we show is modelled for your building on stated assumptions, is sensitive to energy prices, finance terms and tax treatment, and is not a guarantee. We do not publish a per-kWp price, because a genuine figure needs the survey and the design behind it; how cost is established is set out in our commercial solar cost guide, and the funding routes and the assumptions behind any return sit in commercial solar finance. The bifacial decision is made where the model shows the rear-gain pays for its premium on your roof, and recorded against the specific module so the basis is auditable.
Our own insured pilot flies your roof and captures the real geometry and shading, so the design starts from your building instead of a satellite guess.
Booked to suit your operating hours
We model the array in bankable-grade software, size it around your daytime load, and set out generation, savings and payback across three funding routes.
Modelled, not promised
Designed and installed to BS 7671, commissioned to IEC 62446-1, connected under G99 and run under CDM 2015. Alectrona is typically the Principal Contractor.
Outside MCS, assured by the non-MCS stack
A 12-month defects period backed by an Insurance-Backed Guarantee, then ongoing operations and maintenance so the asset keeps earning for its full working life.
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Last updated June 2026
They can, and a flat roof is often a favourable case, but it depends on the roof. The rear face only earns its keep where the surface beneath is reflective, the rows are spaced to let reflected light in and the panels are raised off the deck. On a bright single-ply membrane with room to space the array, the gain is real. On a dark or tightly packed roof it is small. We model the rear-gain for your roof in PV*SOL rather than assume it.
That figure is roof-specific, so we will not quote a universal percentage. The rear-gain depends on your surface reflectance, your row spacing and the panel height, and the only honest number is the one the PV*SOL model produces for your roof and layout. We establish it from the survey and the model, and it forms part of the yield you are quoted.
Albedo is the fraction of light a surface reflects. It is the single biggest lever on bifacial rear-gain, because the rear face generates from reflected light. A bright, clean single-ply membrane reflects a large share and feeds the rear face well; a dark, weathered or gravel-ballasted surface reflects little, so the bifacial premium is harder to justify. The survey records the actual surface for the model.
No. The standard method on a single-ply membrane is a ballasted mounting system, where the frames are held down by weight rather than fixings, so nothing penetrates the roof and the membrane warranty stays intact. On a standing-seam metal roof the frames are clamped to the raised seams, again without penetrating the deck. The ballast weight is a real load, so it is calculated for your roof and checked against the structure in the survey.
No. Bifaciality is the module's construction; the cell technology, whether PERC, TOPCon or HJT, is a separate choice with its own trade-offs, and none is the right answer for every roof. TOPCon and HJT tend to carry a higher bifaciality factor, but we choose the cell type and the module from the survey and the model, then name the specific scheme, grade and quarter and re-verify it before contract.
There is no fixed lead time, because a bifacial flat-roof design hangs on survey work that has to happen first. The structural roof survey, the wind-load and ballast calculation and the PV*SOL rear-gain model all precede a firm programme, and a system above 50 kWp also needs a DNO connection agreement that runs to the network operator's own timescale, not ours. Once the survey and design are settled and the connection is in place, the install itself is a defined site programme under CDM 2015. We set out the realistic timeline for your roof at the design stage; our how long installation takes guide covers the stages.
A guide can only take you so far. The figure you get is modelled from your own half-hourly load and a system sized from the on-site drone survey. No obligation, and systems this size sit outside the domestic MCS scheme, so the assurance is the engineering stack.