Bifacial solar cells
Double-sided, or bifacial (from the Latin: “double surface”) of the photovoltaic cells are capable of harnessing the solar energy from both sides of the panel. At first glance, this idea may seem a bit misguided.
The idea of a typical installation of photovoltaic cells counts with pointing the active side of the panel to the Sun and the shadows that are cast shadow, which itself bar creates. Shadow so seemingly condemns the other hand, to stay in the shadows.
But the areas for the installation of the other panels is not an infinite amount. At the same time the efficiency of conventional silicon panels close to the theoretical physical limit, which is approximately 29%. Usable is less than a third of the solar energy incident on the PV panel. The rest is transformed into heat an overheating panels and part of the energy is reflected into the surroundings.
New non silicon technology, like perovskit. It is still, however, about the music of the future, at least as massive deployment of the technology concerned. Let's stay even a moment with silicon.
Classic one-sided (monofacial) panels generate electricity from direct sunlight. Therefore, it is the frontal panel side is protected by a transparent materials – glazing and films. The back side of these panels is generally provided with a solid (opaque) materials.
In contrast, bifacial panels have articles from both sides and the front and back side of the panel is then protected by a transparent material. The junction box, which is unilateral always on the back side of the panel, is also a two-sided as a rule, on the rear side. Power rear side is way lower at least on the surface, which occupies the box.
There are commonly three variants
- Full duplex panel
- Panel with spaces
- Semi-permeable
Full duplex panel
Has an active area equipped with a double-sided photovoltaic cells. The only exception is the space for the derivation box, which is used to connect the panel to the photovoltaic network. This mount box is installed on the bottom side of the panel.
The space, which occupies a box, can be fitted with photovoltaic cells, therefore, the performance of the rear panel always lower than the performance of the front panel. Both sides of the panel are protected with a transparent glass, or plastic wrap.
Front panel is turned to the Sun and back side relies on the reflection light and diffuse, or scattered solar light. The so-called albedo effect, where the area of the panel and what is under the panel, although imperfectly, but reflects the sun's rays on the back side of the panel.
Another option is to install the panel vertically, as will be mentioned later.
Panels with gaps
each double-sided photovoltaic cells aligned in a matrix, with the exposed gap. Spaces after penetrating part of the sun shine behind the frontal articles and reflective (reflecting) surface, affixed with the appropriate distance from the rear side of the panel, headed these rays back to back articles.
Semi-permeable (semi transparent) bifacial panels
Are the panels, whose articles are of a material partially permeable sunshine. Can be compared to a darker glass. These bifacial panels are rather an extension of semi-permeable unilateral panel. You lead the way to install the type of roof panels greenhouse, glazed winter garden, enlightened the interior of the blocks and the like. But this type of articles is not made of silicon, so it's a different technology type perovskit and more.
Note: the Definition of panels with gaps and panels polopropustných is sometimes misleading. Sometimes they are semi-permeable understood and panels with gaps, because the partially released, though gaps and not thanks to the characteristics of the articles.
Install or how to provide light for the other side panel
Most of the installation relies in the direction of the front side towards the Sun, and the rear side of the draws of the solar energy from the reflection of the (called albedo effect). To install the policy applies to the location of the one-sided panel, but with the difference that we need to ensure the best conditions for the back side.
Panels placed for example in the field must rely on the reflection from the surface of the earth and also the reflection from the other panels, clouds and other large objects placed in the location.
For semi-permeable double-sided panels offers solutions in the installation of the reflective surface, for example the wall of the building which more reflected than absorbs the rays. It is well known that the high reflectivity can achieve a glossy material and the white, silver or other light-colored surface.
Another option is to install a panel offset the reflective surface, which may be the outer wall of the building. The ideal is a highly reflecting surface, or a white coating walls with white paint.
Vertical installation of two-sided panels
What happens when bifacial panel placed vertically, perpendicular to the ground and put parallel to the axis of north-south? We start to bridge the increased production of consumption in the morning and the afternoon. The following chart displays the image of the supreme power monofaciálního panel, then the classical one-sided and bifacial panel, located to the vertical position.
The following chart shows the most favorable orientation of the one-sided photovoltaic panel towards the south (red curve) in comparison with the effective position of the vertically placed a two-sided panel (blue curve), whose axis is directed from south to north.
It is evident, that the greatest power supplies single-sided panel in the midday hours when the Sun is in the south.
On the contrary, the vertically positioned double-sided panel one tops the highest performance the morning and afternoon hours.
A common installation of a two-sided and one-sided panels can complement each other in the cases where we want to be as stable coverage of production during the day.
