Today, nearly all solar-powered street light manufacturers would opt for monocrystalline solar panels as the power-generating component, considering their higher efficiency while at lower costs than before.
Many manufacturers also keep an eye on the latest panel technologies that can be integrated for a higher power out. One of these is bi-facial technology. This article will walk you through this technology, explain its applications on solar street lights, and discuss the pros and cons and whether it's an ideal choice for your project.
An overview of bi-facial panel technology
An in-depth review of the bi-facial technology is outside the scope of this article. While learning the basics is crucial to judge whether these lights are worth your choice and to understand the trends of solar street lights.
In a nutshell, unlike traditional mono-facial panels that can only absorb sunlight from the front side, bi-facial panels are able to absorb and convert sunlight from both the front and rear sides of the panel. The result is theoretically a higher power yield.
Traditional and bi-facial panels also differ in structure and encapsulation technique. In a traditional mono-facial panel, solar cells are sandwiched between EVA films. A tempered glass is placed on top of the structure, while an opaque back sheet is set below. Finally, an aluminum frame is used to encircle the four sides and fix the different layers tightly. A bi-facial panel typically encompasses similar materials and layers. The most prominent difference is the back sheet, which instead uses transparent tempered glass to allow part of the sunlight to pass through the panel to the ground and enable the absorption of reflected light by the rear panel side.
However, we should be aware that bi-facial panels would only make sense when installed at certain ideal tilting angles and over surfaces with appreciable reflectivity. The decision on an efficient pairing between angles and surfaces could only be determined on a case-by-case basis.
How are bi-facial panels utilized on street lights?
Though the research on bi-facial technology dates back to the 1960s, its applications on solar street lights merely commenced over the past few years. Below are 3 common ways bi-facial panels are utilized on street lights.
Bi-facial all-in-two solar street lights
As explained in our previous articles, all-in-two solar street lights pack the lighting module and battery into one structure while leaving the panel fixed individually.
On this variety, manufacturers replace the conventional mono-facial panel with a bi-facial one. Since the panel and lighting module are separated, adjusting the panel will not induce changes in the lighting angle and projected area.
Bi-facial all-in-one solar-powered street lights
Under the concept of all-in-one lights, the panel covers the upper surface of the housing, in which case reflected light below impossibly arrives on the rear side.
Most bi-facial all-in-one lights would adopt a hollow design to remove as many upper and lower surfaces of the housing as possible to allow light rays to pass through and reflect back.
Furthermore, this bi-facial street light variety uses high-brightness rotatable lighting modules to maximize the area for the rear absorption by the panel. The adjustments to the light and panel are separated, eliminating the potential conflict between the optimal angles for lighting and for light absorption while maintaining a sleek look.
Vertical bi-facial solar street lights
On these lights, the bi-facial solar module is shaped into a stripe or rectangle one and fixed vertically in parallel with the light pole instead of on top of it.
In this manner, the angle of the panel is fixed (perpendicular to the horizon). This design is more like capturing all kinds of light nearby (environmental light, reflected light, etc.) rather than centering on maximum direct and reflected sunlight absorption. The design is also renowned for a subsequent more streamlined and sleek appeal, particularly satisfying the growing desire for aesthetics in urban cities.
However, changing the angle of the panel is basically impossible, which narrows down the application flexibility of the light.
Summing up: Pros and cons of bi-facial solar street lights
We condense the features of bi-facial solar street lights into several points below, categorized by pros and cons.
- Bi-facial street lights can convert energy from both sides and theoretically possess a higher efficiency.
- A potentially higher efficiency brings a higher output to power a brighter light, for a quicker battery charging time and a viable replacement for a larger-capacity battery.
- The light can have a smaller panel size for a more compact look due to the improved efficiency of bi-facial technology.
- The costs of bi-facial modules keep going down, making the integration into street lights more affordable.
- Whether bi-facial panels on street lights yield a definitive higher output is yet to be proved by more projects and statistics.
- Bi-facial is still comparatively a younger technology than the mature mono-facial panel, which can potentially weaken the reliability of these street lights.
Are bi-facial solar street lights worth it?
Overall, bi-facial street lights introduce one of the modern advanced panel technology and provide possibilities for higher power output and more versability for the light design. (Has the vertically set design wowed you?!)
Currently, they may more suit small-to-medium projects in urban, where people have a higher expectation on both efficiency and aesthetics.
However, only a few manufacturers supply this variety. You may not have an extensive choice of design. Until now, there are not many projects of this type worldwide; their reliability has yet got sufficiently proven. If you would like to pick them for a large-scale application, we suggest conducting a more comprehensive assessment to judge whether the desired results are definitely achievable.