When Are Bifacial Solar Panels Worth It?

Bifacial solar modules are considered an innovative solution to efficiently convert more sunlight into electricity. They use not only the front but also the back to generate energy. But does this also make sense on the roof of the house? Economic viability and efficiency are particularly questionable on pitched roofs. In this article you will find out when it is worth using them, how bifacial modules work, what you need to pay attention to – and why the surface is crucial.

Key facts at a glance

• Double power generation: Bifacial modules use front and back.
• Not ideal for pitched roofs: Reflected light is often missing.
• High yield on flat roofs and open spaces: There they benefit from the albedo effect.
• More expensive than monofacial modules: Higher acquisition costs due to more complex technology.
• Reflective surfaces increase efficiency: Light-colored surfaces such as gravel or snow are ideal.

When do bifacial solar panels make sense?

Bifacial solar modules are particularly useful when they are installed on surfaces that reflect additional light onto the back – e.g. B. in solar parks, carports or flat roofs with light-colored surfaces.

How bifacial solar panels work

Bifacial solar modules differ from conventional modules in one crucial way: they generate electricity on both sides. While the front absorbs direct sunlight as usual, the back uses reflected or diffused light. This property makes them significantly more efficient in the right environment.

Bifacial modules are constructed almost exclusively as so-called glass-glass modules. Both sides are made of transparent glass, with solar cells made of mono- or polycrystalline silicon in between. A robust aluminum or stainless steel frame additionally protects the structure from environmental influences.

Their resistance to wind, snow, moisture and temperature changes is higher than conventional modules. This makes them particularly durable. Depending on the location conditions, the electricity yield increases by up to 20 percent – provided that the back is properly illuminated.

Applications: when are bifacial modules worthwhile?

Bifacial solar modules are particularly efficient where the back can also absorb light. This is particularly the case with freestanding or inclined installations. The modules can be mounted on flat roofs so that light is reflected from light-colored roof coverings. The same applies to carports or roofs with light-colored floors.

In solar parks, the modules also benefit from open terrain and reflective surfaces such as gravel or sand. Vertical facade systems in urban areas can also offer advantages – walls and surrounding surfaces reflect additional light onto the back.

However, they are less useful on classic pitched roofs. There is no light reflection on the back, so the additional yield is hardly significant.

Why the surface below the modules matters

A decisive factor for the electricity yield of bifacial modules is the subsurface. The brighter and more reflective the surface under the modules, the more light reaches the back. Technically speaking, this is called the albedo value – the measure of the reflectivity of a surface.

Here is an overview of typical reflection values:

Advantages and disadvantages compared with conventional panels

Bifacial modules offer some clear advantages over monofacial PV modules – but only under optimal conditions. In the following table you can see an overview of the most important points:

Energy yield and cost-effectiveness

How much electricity bifacial modules generate depends largely on the location and type of installation. On reflective surfaces or with an optimal tilt angle, they can produce up to 20% more energy than standard modules. This is particularly worthwhile on flat roofs, carports or open spaces.

An example: A 40m² usable roof area with 20 PV modules can deliver an electricity yield of around 9,831kWh per year with ideal use of bifacial technology. In combination with a storage unit, this results in a monthly savings potential of over 100 euros. CO₂ emissions are also reduced – by up to 4,800kg per year.

But be careful: on a pitched roof with a small distance to the roof surface, the increase in yield is significantly lower. In such cases, a monofacial module can ultimately be more economical.

Optimal conditions for bifacial solar panels

For maximum energy yield, bifacial modules require special conditions. The installation angle is particularly crucial as it determines how much light reaches the back. An angle between 15 and 30 degrees is often ideal as it allows both direct radiation and reflection to be used.

The distance to the surface is another key: the higher the modules are mounted, the better the reflected light from below is captured. In addition, the back must not be shaded – for example by greenery, walls or technical structures. The choice of mounting system also plays a role: open frames enable better back exposure than flat structures. Ultimately, cables, inverters or storage devices should be appropriately sized so that the additional yield can be used efficiently.

How much do bifacial panels cost, and when do they pay off?

The purchase of bifacial PV modules is around 15-25% higher than the cost of monofacial modules – depending on the manufacturer and design. In addition, there are higher installation costs because special assembly systems and careful planning are necessary. However, this additional effort can be worth it: with ideal subsoil and good alignment, the yield advantage is up to 30%.

This leads to a significantly shorter payback period, especially when electricity prices are high. It is important to carry out a precise cost-effectiveness calculation that takes all factors into account – including module price, feed-in tariff, self-consumption rate and maintenance costs. Government funding programs such as KfW grants or regional solar bonuses can make the investment even easier. A consultation with a specialist company or a PV simulation tool will help with the calculation.

Incentives and legal requirements at a glance

Anyone who wants to install bifacial PV modules should also know the legal framework. In Germany, the same regulations apply to them as to conventional modules – for example regarding grid registration, the EEG 2023 or feeding into the power grid. It is important to register in the Federal Network Agency’s market master data register (MaStR). In addition, systems with an output power of over 600W must be installed and approved by a specialist.

Additional building law requirements apply to flat roofs, such as statics and wind load. Funding programs such as the KfW Program 270 or regional grants can make bifacial technology more economically attractive. Anyone who also installs storage often benefits from combined subsidies. The path to funding usually leads through energy consultants or local network operators – they also provide assistance with permits and applications.

Why bifacial panels are rarely worthwhile on pitched roofs

The back of bifacial solar panels is only an advantage if light reaches it. However, this is rarely the case on pitched roofs. The modules lie flat on mounting rails. The distance to the roof surface is small and reflective light is hardly used.

Additionally, roofing materials are often dark and absorb light rather than reflect it. The albedo value for brick or bitumen is low – typically 0.1 to 0.2. This means that the possible additional yield remains far below the potential.

In addition, the higher purchase costs, the more complex installation and the lower effect of the rear side make bifacial modules on pitched roofs usually uneconomical. If you only use the front, you can also use monofacial modules – cheaper and easier to implement.

What homeowners should consider before installation

Before installing bifacial solar panels, homeowners should consider several factors. In addition to the location, roof orientation, roof material and possible shading play an important role. The distance to the ground is particularly important on flat roofs, as this is the only way reflected light can be used optimally. However, if you have a sloping roof, you should keep in mind that dark roof tiles hardly provide any reflection.

The load-bearing capacity of the roof must also be checked, as glass-glass modules are heavier than standard modules. In addition, electricity prices and the planned self-consumption rate should be included in the profitability calculation. A consultation with a specialist company is recommended to avoid a bad investment.

Cleaning and maintenance of bifacial solar panels

An often underestimated point is the cleaning and maintenance of bifacial PV systems. Since both sides of the modules generate power, not only the front but also the back is relevant for performance. Dust, bird droppings or leaves can significantly reduce efficiency.

While standard modules are usually only cleaned superficially, bifacial modules require more thorough care. For installations close to the ground, there is a greater risk of dirt or moss affecting the back. Specialist companies therefore recommend carrying out regular inspections and adapting cleaning intervals to site conditions. Anyone who neglects this risks that the additional yield will quickly evaporate.

Decision checklist: are bifacial panels worthwhile?

To find out whether bifacial solar modules make sense, a simple checklist can help.

• First: Is it an open area such as a flat roof, carport or solar park?
• Secondly: Is the surface light and reflective or can it be retrofitted with gravel or foil?
• Third: Is there enough distance from the surface for light to reach the back?
• Fourth: Are the higher acquisition costs covered by possible additional income and subsidies?
• Fifth, are there any shades that could partially block the back?

If at least four of these points are answered positively, bifacial modules are usually a worthwhile investment.

Conclusion

Bifacial solar modules offer exciting possibilities – but not everywhere. They hardly develop their potential on pitched roofs and are usually not worth it. However, anyone who works on flat roofs, carports or open spaces with reflective surfaces will benefit significantly from the increased yield. If you plan sensibly, you can compensate for the higher acquisition costs in the long term by producing more electricity.