Bifacial and Glass-Glass Solar Panels

Most solar panels collect light on one face only. A bifacial panel carries photovoltaic material on both faces, so the rear side can generate electricity from light that bounces off the surface behind the module. Jinko Solar, one of the brands sold in the UK, lists bifacial panels alongside its conventional range, and they work on the same principle as any solar photovoltaic module: converting the sun's energy into electricity, with output rising as the intensity and duration of sunlight increase¹.

The rear face only earns its keep if light actually reaches it. On a flat roof, where panels sit tilted on frames with open space beneath, or on a ground mount above grass, gravel or a pale membrane, reflected light can add meaningfully to output. On a typical pitched roof, where panels sit a few centimetres above dark tiles, almost none does. The one firm gain figure in circulation is a maker's claim: EcoFlow states that its 220W bifacial panel, with 155W on the back, captures 25% more energy than a traditional single-sided panel³.

Most bifacial modules are also glass-glass modules, and that second pane of glass changes more than the warranty. It changes how the panel ages, how it behaves in a fire, how much it weighs and how long the maker will stand behind it. This page sets out what bifacial and glass-glass construction actually do, where the designs earn their keep on British homes, and what they mean for a household trying to generate more of its own electricity.

The meaning of a bifacial panel

Solar electricity panels, also known as photovoltaics (PV), convert daylight into electricity. The greater the intensity and duration of the sunlight, the more electricity is produced². A conventional module does this with a single active face: a layer of photovoltaic cells behind a sheet of glass, with an opaque backsheet behind the cells to protect them from moisture and damage.

A bifacial module replaces that opaque backsheet with a second transparent face, so the same cells, or a second set of cells, can collect light arriving from behind. Jinko Solar, reviewed among the solar panel brands sold in the UK, sells bifacial panels that can generate electricity on both sides¹. The idea is simple: light that would otherwise be wasted, reflected off the roof, the ground or a wall, becomes additional output.

Two points follow from the design. First, the panel is not doubling its power rating. The nameplate wattage refers to front-side performance under standard test conditions, and the rear contribution is a bonus that varies with the site. Second, the rear face needs to see light, which makes the surface behind the panel, and the gap between panel and surface, part of the system's design rather than an afterthought.

Bifacial modules should not be confused with hybrid PV-T panels, which combine photovoltaic cells with solar thermal collectors so one panel generates both heat and electricity. That is a different technology with a different purpose, covered in PVT panels. Bifacial modules generate electricity only, from two faces instead of one.

What determines rear-side gain

The extra energy a bifacial module produces, often called bifacial gain, depends on how much light reaches its rear face, and that depends almost entirely on the installation. The only specific figure available from the sources here is a manufacturer's claim: EcoFlow states that its 220W bifacial panel, with a primary side of 220W and 155W on the back, captures 25% more energy than a traditional solar panel³. That is a maker's figure for one portable product, not an independent measurement, and it should be read as a best case for a panel used in the open.

For context, a typical residential solar panel produces around 250 to 400 watts under ideal conditions, with more efficient panels reaching up to 450 watts⁴. Whatever the panel type, total output depends on several factors⁸:

• geographical location
• the season and therefore hours of daylight
• the roof's compass direction and slope
• any shading that blocks the panels at certain times of day
• the efficiency of the system

Most PV panels absorb up to 70% of the solar energy available to them, which is why coatings and cell technologies that raise absorption are a continuing area of development⁹. What this means for bifacial gain is that the rear face is subject to the same physics as the front. Reflected light is weaker than direct light, so the rear contribution is always a fraction of the front-side output, and the fraction shrinks whenever the surface behind the panel is dark, close or shaded. A panel tilted high above white gravel or a light-coloured flat roof membrane sees far more rear light than one fixed flush to dark slate.

Why glass-glass build affects the guarantee

Most bifacial modules on the market are built as glass-glass, sometimes called double-glass, modules. In this construction the solar cells are encapsulated on both sides with a robust glass pane, rather than glass on the front and a polymer backsheet behind⁵. Solarwatt, whose glass-glass modules have been installed in UK family homes, builds its panels this way⁵. BISOL's bifacial BDO module uses tempered glass with an anti-reflective coating, high transparency and low iron content on the front face⁶.

The practical consequence of encapsulating cells between two panes of glass is durability. A backsheet is a polymer layer that can delaminate, yellow and let moisture in over decades; glass does neither. That is why glass-glass modules generally carry longer product warranties:

Which? likewise notes that solar panels can have warranties of up to 20 or 25 years¹⁰. EcoFlow makes a related durability claim for its bifacial product, stating that its thin tempered glass construction is five times tougher than other panels on the market³. That is a maker's claim and applies to a portable panel rather than a rooftop module, but it points the same way: glass on both faces changes how a module ages and how it resists impact.

Longer warranties are worth reading closely before relying on them. On cracked panel claims in particular¹⁰:

• the cost of labour for replacing the panel and any scaffolding may not be covered
• the replacement panel may look different from the original
• some manufacturers require independent testing to prove underperformance

A 25-year guarantee on the product is not the same as 25 years of free replacements. The detail is covered in solar panel warranties, degradation and lifespan.

The settings where bifacial modules pay off

Bifacial gain needs light behind the panel, and that shapes where the technology works. Solar panels can be installed on both pitched and flat roofs; on a flat roof the panels need to be tilted and spaced to avoid shading one another¹¹. That tilting and spacing is precisely what a bifacial module wants: an air gap beneath the panel, and a surface below that reflects light up into the rear face. Energy Saving Trust confirms that panels on flat roofs are normally tilted up to help maximise energy production¹², and Which? notes that, contrary to popular belief, solar panels can be installed on flat roofs too¹³.

Flat roof installations carry their own costs and checks. They can be more complex because the panels may need additional mounting systems and the roof must support the extra weight, so a flat roof installation might cost more than a pitched roof one¹². The additional loading on the roof structure and the associated electrical works are also why building regulations come into play¹⁴. Ground mounts are the other natural home for bifacial modules, with open space beneath the array and a reflective ground surface; see ground-mounted solar for homes.

A typical pitched roof is the weakest site for bifacial working. Panels sit close above the roof covering, which blocks rear light almost entirely, and planning guidance adds constraints of its own: on pitched roofs, panels should be located to the rear of the property and should match the colour of the existing roof covering as closely as possible¹⁵. None of that stops a bifacial module working on a pitched roof; it simply means the rear face contributes little, and the household is paying a premium for glass it cannot fully use.

Orientation and shading matter as they do for any array. An unshaded, south-facing roof is ideal for maximum performance¹⁶, a south-west or west-facing roof is also suitable though a little less productive¹⁷, and north-facing roofs are not recommended because they do not receive enough sunlight to make installation worthwhile¹². If a roof is heavily shaded, solar panels may not be the most suitable option at all¹⁴. Where shading is unavoidable, an installer might recommend microinverters or power optimisers, which let each panel work independently, or trimming the trees causing partial shade¹².

Choosing between bifacial and monofacial for your home

For most homes with a conventional pitched roof, the comparison comes down to a straightforward question: does the rear face of a bifacial panel see enough light to justify its price premium? On the evidence available, on a flush-mounted pitched array it does not, and a high-quality monofacial panel is the rational choice. Monofacial panels have reached high outputs in their own right: Which? records an Aiko panel at 640W and 23.7% efficiency, the most efficient domestic monofacial panel from its test results¹⁸.

Bifacial modules suit homes and sites where the array is tilted with space beneath it: flat roofs with framed mounting, ground mounts, canopies and pergolas. They also suit households whose priority is longevity, because the glass-glass construction that most bifacial modules use carries the longer product guarantees described above. If a flat roof installation is already planned, specifying bifacial modules adds rear-side gain to a design that already has the right geometry.

Cost cuts across the comparison. Monocrystalline panels, the type most bifacial and high-efficiency modules are built from, are described by Which? as very pricey¹⁹, and the upfront cost of rooftop photovoltaics remains a significant barrier to more widespread adoption by homeowners and businesses alike²⁰. A bifacial premium sits on top of an already significant outlay, which strengthens the case for spending it only where the geometry delivers. The general choice between panel types is covered in types of solar panel sold in the UK.

Currents, area and standards in system design

Bifacial modules change a system's design in three ways. The first is electrical. All solar photovoltaic output is direct current and needs to pass through a solar inverter to turn it into alternating current (AC) electricity for the home¹¹. Bifacial modules do not need a special category of inverter, but because they can produce more current than a monofacial module of the same dimensions, the inverter, the DC cabling and the isolators have to be sized for the actual current the array can deliver. Oversized strings and undersized components are design errors, and the sizing rules are the installer's responsibility under the relevant standards.

The second is physical. Bifacial modules tend to be large, high-output modules. BISOL's bifacial BDO module is built from 96 half-cut bifacial crystalline silicon cells, each 182.25 x 105 mm⁶, which makes for a bigger, heavier panel than a small domestic module. Rooftop panels are commonly around 1m x 2m and can weigh more than 20 kg²¹, and a typical domestic system of around 3.5 kWp covers between 10 and 20 square metres of roof surface¹¹. Weight and roof loading are exactly why building regulations apply to solar installations¹⁴, covered in building regulations and roof loading for solar panels.

The third is standards. The MCS 005 Solar PV Product Standard, the certification standard behind the Microgeneration Certification Scheme, includes additional information on bifacial modules²². That matters because an MCS-certified installation is what a household needs for export payments, and it means bifacial modules are within the scope of the UK's certification regime rather than an uncertified novelty. The certification route is explained in MCS certification for solar PV installations.

Paying a premium on top of a large investment

Solar panels have a high upfront cost, on average £6,100 according to the Energy Saving Trust²³. Other recent figures put the initial cost of a typical installation between £6,000 and £10,000²⁴. Those are figures for conventional rooftop systems; bifacial and glass-glass modules sit above them, because the second pane of glass and the higher-output cell layouts cost more to make. No published UK price for a domestic bifacial rooftop installation appears in the sources behind this page, so bifacial pricing is installer-quoted, and households should obtain written quotes that state the module type, wattage and warranty.

Two cost signals from adjacent markets show the direction of travel. The UK government's solar roadmap notes that costs for floating solar PV, a bifacial-friendly application, are currently higher than those for conventional ground mount solar²⁵. At the portable end, a UKSOL Duo 890W plug-in solar kit, a two-panel ground-mount product, is listed from £899²⁶. Neither is a like-for-like domestic rooftop price, but both confirm that the technologies that pair panels with open, reflective sites carry a premium.

The honest framing for a household is this: the money question for solar is first whether to install at all, given the average £6,100 outlay²³, and only then whether to pay extra for bifacial glass. The general economics, including payback, are covered in solar panel cost and solar panel savings and payback. Where a flat roof or ground mount is already the plan, the bifacial premium buys real additional generation; where it is not, it buys little.

UK supply and its implications for energy independence

Bifacial and glass-glass modules are available in the UK through the mainstream brands. Jinko Solar sells bifacial panels in its UK range¹, Solarwatt's glass-glass modules have been installed in UK homes⁵, and BISOL publishes UK-market datasheets for its bifacial BDO module⁶. Portable bifacial products, such as EcoFlow's 220W panel, are sold directly to consumers³. Rooftop solar panels themselves are suitable across the UK¹², and the electricity they generate can be used in the building²⁷, stored, or exported.

The plug-in and balcony-solar market, where bifacial portable panels often appear, is expanding quickly. Plug-in photovoltaic panels, also known as balcony solar, are now available to buy and self-install in the UK²¹, with changes to the rules reported from 27 August 2026²⁸. A quarter of UK households, 26% or about seven million, want to get plug-in solar panels as the rules change²⁸. Freestanding and portable panels have been available to buy in the UK for some time, though they were previously only legal for off-grid use²⁹, and the government has said it will make plug-in solar available for the first time in Britain so families can buy a low-cost panel straight from a supermarket³⁰. The detail is in plug-in solar kits in the UK and balcony solar systems.

For household energy independence, bifacial and glass-glass modules are a refinement rather than a step change. They generate more electricity per module on the right site, and they hold their output for longer because the encapsulation resists the ageing that degrades backsheet modules, which means fewer replacement cycles over the life of the system. What they do not change is the structure of dependence that remains: the array still needs an inverter, still needs the grid connection for export and for import when generation falls short, and still depends on the manufacturer's solvency for the warranty that underwrites the longevity claim. The wider picture is set out in solar panels and household energy independence and in the pillar guide to solar PV for UK homes.