Monocrystalline vs Bifacial Solar Panels for a Balcony

Monocrystalline vs bifacial solar panels isn’t a real either/or: nearly every panel sold today is monocrystalline, and most bifacial panels are monocrystalline too. The real choice is monofacial vs bifacial, one-sided or two-sided. On a balcony, a bifacial panel adds little when it hangs against a wall or solid railing, and more when it stands free with light, open space behind it.

The second choice that comes with it is construction: glass-foil (glass front, plastic backsheet) or glass-glass, which most bifacial panels use.

Are bifacial panels monocrystalline?

Bifacial solar panels are almost always monocrystalline, because nearly all panels are now. “Monocrystalline” describes the silicon wafer, while “bifacial” describes whether the back of the panel also collects light.

Fraunhofer ISE’s Photovoltaics Report counts 690 of the 706 GWp of modules made in 2025 as mono-Si, about 98% by my math. It says multicrystalline technology “has disappeared from the market” and that monocrystalline n-type TOPCon has become dominant.

The cells inside bifacial panels follow the same path. NREL’s bifacial seminar slides list how well each cell type uses rear light, its “bifaciality”:

Cell type	Bifaciality (rear vs front)
p-type PERC	0.65 to 0.80
n-type PERT	0.75 to 0.90
Silicon heterojunction	0.85 to 0.95

Fraunhofer reports that n-type TOPCon and heterojunction are replacing p-type PERC.

Monofacial vs bifacial: the differences that matter on a balcony

The differences between monofacial and bifacial panels that change a balcony decision are rear-side gain, weight, and how easy the output is to predict. Front-side efficiency is about the same.

	Monofacial (usually glass-foil)	Bifacial (usually glass-glass)
Cells	Monocrystalline	Monocrystalline
Rear-side gain	None	Depends on what’s behind the panel
Fixed-tilt gain in NREL models	Baseline	+4% to 8% over open ground
Weight	Lighter	Heavier (second glass pane)
Output modeled by PVGIS	Yes	Front side only
Factory cost (NREL model)	Same	Same
Best spot	Against a wall or solid railing	Free-standing, open rail, light floor

Efficiency doesn’t separate them. Fraunhofer puts the weighted average for silicon modules at 22.7%, with a range of 18.9% to 24.8%, and both kinds sit inside it. The 430 W glass-glass bifacial module used in our weight post lists 22.02% on its sheet.

How much extra power does a bifacial panel make?

A bifacial panel’s extra power, called bifacial gain, is usually a few percent to the mid-teens, and it depends on the site more than the panel. NREL’s slides show fixed-tilt bifacial systems making 4% to 8% more energy than monofacial ones in its simulations, driven by ground albedo (reflectance).

Other neutral figures agree on the scale:

NREL and Sandia say bifacial performance “depends greatly on the installed conditions.” Their 2019 study found bifacial modules can still pay off at gains of 4% to 9%.
Fraunhofer ISE’s Christian Reise called 5% to 15% a realistic target for large plants, pv magazine reported. He said the gain “depends mainly on system design.”
NREL’s tracker field test measured annual gains of 6.5% for PERC and 9% for heterojunction modules.

The big numbers in some ads need ideal conditions. A global NREL-led study found gains under 10% at a low albedo of 0.25. Raising albedo to 0.5 and lifting panels 1 m off the ground can push it to 30%.

Do bifacial solar panels work better on a balcony?

Bifacial solar panels work better on a balcony only when the back of the panel sees open sky and a bright surface. Hung flat against a wall, a solid parapet or a privacy screen, a bifacial panel behaves almost like a monofacial one, because little light reaches its rear.

Height and albedo “have a direct impact” on bifacial output, NREL and Sandia researchers found. Their reference panel sat about 1 m off the ground. Fraunhofer’s Reise warned that mounting panels only a few centimeters from a pitched roof wastes the bifacial potential. A panel on a solid railing is in the same spot, just turned vertical.

Here’s how common balcony setups compare:

Balcony setup	What the rear side sees	Bifacial gain
Flat against a solid concrete or brick parapet	The wall, inches away	Little to none
On an open bar railing over a dark floor	Some sky, a dark surface	Small
On an open railing over a light concrete floor	Sky and a brighter floor	Small to moderate
Tilted floor stand with space behind	Sky, floor and walls	Best case for a balcony
Vertical east/west rail, open both sides	Morning sun on one face, afternoon on the other	Real, but trails a tilted south panel

None of these rows comes with a published number. No neutral lab has measured bifacial gain on apartment balconies.

Balcony factors: railing, wall color, direction and rear shade

Four balcony details decide whether the back of a bifacial panel earns its keep. Check each one before you pay for two-sided glass.

Solid vs open railing. A solid parapet blocks the rear. An open bar or cable railing lets light reach it. If you can’t see daylight through your railing, buy monofacial.
Wall and floor reflectance. NREL’s slides rank surfaces from asphalt (lowest rear light) through soil and concrete to white roofing membrane (highest). NREL modeling used 21% for light soil and 28% for concrete. A white wall behind an open rail helps; a dark one doesn’t.
Vertical east or west rails. The NREL-led global study found vertical east-west bifacial panels beat tilted south-facing ones by up to 15% below 30 degrees latitude, at albedo 0.5. Above 30 degrees the result reversed.
Rear shading. Mounting brackets, planters, bikes and the balcony slab above all shade the back. NREL found interior rows of a large array lose about half their rear light to self-shading, so clutter matters.

Which way your railing faces still matters more than the panel type. Our guide to which direction a balcony solar panel should face covers that first.

Why PVGIS and most calculators can’t show bifacial gain

PVGIS, the free tool most balcony guides use, does not model bifacial panels. Its methods page says plainly that “PVGIS doesn’t make dedicated calculations for bifacial modules at present.”

PVGIS does describe the bifacial rating condition: 1,000 W/m² on the front and 135 W/m² on the rear, assuming an albedo of 0.2, like light sandy soil. By my math, that’s 13.5% of the front light. It’s a lab label, not a balcony forecast.

That’s why a bifacial panel’s “boosted” wattage is a guess for your spot. The glass-glass sheet in our example lists 451 W at a 5% rear gain and 494 W at 15%, on top of its 430 W rating. Use the 430 W figure when you compare panels or check your state’s wattage cap.

By my math: a bifacial panel on a vertical New York railing

A bifacial upgrade on a vertical railing adds a few dozen kWh a year at most, by my math. That’s well short of what tilting the panel does.

Our balcony solar output analysis ran PVGIS for an 800 W kit hung vertically on a south railing in New York City: 725 kWh a year. Apply NREL’s fixed-tilt bifacial range of 4% to 8%:

725 × 1.04 = 754 kWh
725 × 1.08 = 783 kWh

That’s 29 to 58 extra kWh a year, and it’s an upper bound. NREL’s range is for panels over open ground, not against a wall. The same kit tilted 35 degrees south made 1,074 kWh in PVGIS, which is 291 kWh more than even the bifacial best case.

Our balcony solar calculator doesn’t add bifacial gain either, and it already runs above PVGIS, so treat its result as an upper estimate.

Weight and cost: glass-glass vs glass-foil

Glass-glass panels weigh more than glass-foil panels of the same size, because a second pane of glass replaces the plastic backsheet. Our panel weight guide puts the 430 W glass-glass example at 24.3 kg and compares it with glass-foil panels, so check your railing there before you buy.

As of October 2026, EcoFlow’s 400 W rigid panel lists monocrystalline cells and weighs 21.8 kg. By my math, the glass-glass example is 2.5 kg heavier at the same footprint. On a railing that’s near its limit, that difference can decide it.

Cost barely differs at the factory. NREL’s slides found that a bifacial PERC module “costs the same as monofacial” to make, using 2019 pricing. Retail prices still vary, so compare price per front-side watt.

Durability and warranty

Glass-glass construction ages in much the same ways as glass-foil in lab studies, and some glass-glass bifacial panels carry longer power warranties. Neither type has decades of balcony-specific field data.

An NREL and SLAC study found glass-glass degradation mechanisms “appear to be similar” to those of glass-backsheet modules. Bifacial panels with a clear plastic back fared worse: encapsulants degraded more than in glass-glass.

The glass-glass example sheet lists a 30-year power warranty to 87.4% and a 25-year materials warranty, longer than the usual 25-year performance warranty in the Australian Government’s solar guide. Check what a warranty covers and how panels age in our guide to how long balcony solar panels last.

Which should you buy? A decision table

The right panel depends on what sits behind it.

Your situation	Pick	Why
Railing is solid concrete, brick or opaque panels	Monofacial glass-foil	No light reaches the rear; save the weight
Weak, glass or load-limited railing	Lightest monofacial you can find	Weight matters more than a few percent
Open bar railing, dark floor	Either; monofacial if cheaper	Small gain at best
Open railing, light floor or white wall	Bifacial glass-glass	Some rear light, plus a sturdier build
Tilted floor stand with space behind	Bifacial	Closest to the setups where gain was measured
Price per front-side watt is lower for bifacial	Bifacial	You lose nothing if the rear gain is small

Whatever you pick, secure it properly. Our guide to mounting panels on a railing without drilling covers wind and load.

My take, and the limits of this evidence

My take: on most balconies I’d buy whichever monocrystalline panel gives the most front-side watts per dollar and per kilogram, and treat bifacial gain as a free bonus, never a reason to pay more. The exception is an open railing or floor stand with a light floor, where the bifacial glass-glass panel is the one I’d pick.

Every gain figure here comes from ground-mounted arrays and simulations, not balconies. PVGIS can’t model the rear side, and NREL found that common rear-side models “appear to be conservative by ~30%.” Your monitoring app, not a datasheet, will tell you what the back of your panel adds.

FAQ

Are bifacial solar panels monocrystalline?

Almost always. Fraunhofer ISE counts 690 of the 706 GWp of modules made in 2025 as mono-Si and says multicrystalline has practically disappeared. So a bifacial panel you buy today is, in practice, a monocrystalline panel that also collects light on its back.

What is the disadvantage of bifacial solar panels?

The extra output depends on light reaching the back, so it shrinks to little or nothing when the panel sits close to a wall, roof or solid railing. Most bifacial panels are glass-glass, which makes them heavier, and output tools such as PVGIS don’t model the rear side, so you can’t easily predict the gain.

Which solar panel is better, mono or bifacial?

It’s not either/or, since most bifacial panels are mono. The real choice is one-sided (monofacial) or two-sided (bifacial). Pick bifacial only when the back of the panel sees open sky and a light surface; against a wall or solid railing, a monofacial panel does the same job and weighs less.

Do bifacial solar panels cost more?

Not much at the factory. An NREL cost model found a bifacial PERC module costs the same to make as a monofacial one. Retail prices vary by seller, so compare cost per rated front-side watt, not the bifacial ‘boosted’ wattage on the label.

Monocrystalline vs Bifacial Panels: Which Is Better for Balcony Solar?