Colorful photovoltaic panels are no longer a novelty. Already for years on the market circulate red, brown and even green photovoltaic modules that can camouflag their appearance and improve the integration of solar in the building. Trying to balance performance with a greater focus on aesthetics.
But how valid are these solutions? What coloring technologies are available and how much do they affect the efficiency of converting light to electricity? To better understand the segment and the archery of possibilities made available, we have drawn up a short guide on color photovoltaics.
What color are the solar panels?
Most photovoltaic modules on the market, based on crystalline silicon, appear dark blue or black.
Their color depends largely on the crystalline structure of this semiconductor (which in nature appears blue-grey) and the way it interacts with light. To be precise, in the case of monocrystalline silicon, made from lingots in which the crystalline mesh is continuous, the absorption of light is greater, returning to the human eye a black color. Polycrystalline silicon – consisting of disaligned crystals that are less efficient in light absorption – is responsible for the typical blue color instead.
The anti-reflective coating applied to the modules on the front surface during manufacture also plays a significant role, which can intensify dark colors.
But already moving into market niches like organic photovoltaics it is easy to see panels turning to purple or red in response to different active materials and their interaction with light.
In all these cases, however, the color is not the manufacturer’s aesthetic choice but simply a consequence of the material used.
Red photovoltaic panels, a new trend for the market
In recent years, however, color options based on a precise market strategy have increased. In particular, red and brick color photovoltaic panels have become a true trend that can increase the acceptance of solar technology in the built environment, thanks also to the ability to meet building codes. The ultimate goal of the segment is to have devices that can merge with roofs and building blankets, “disappearing” in the landscape. An ideal solution that can meet the special needs of historic or blocked buildings, where it is necessary to guarantee overall harmony.
Let us remind you that in case of landscape or urban constraints, the photovoltaic on the roof is considered an intervention of free activity, i.e. exempt from permits, authorizations or administrative acts of consent by the public administration, only if made in materials of the local tradition or if not visible from public external spaces. In this context, therefore, having solar panels of a color similar to those of traditional roofs is essential from a regulatory point of view, as well as to ensure aesthetic continuity.
There are already several proposals in this regard on the national market. The most famous? The red photovoltaic from the Italian FuturaSun: the Silk® Nova Red. The color given to the panel, a module of 370 Wp composed of 108 half cells, is in this case the glass. FuturaSun has perfected a coating technology that offers a new aesthetic to the photovoltaic integrated with buildings. Its red photovoltaic panel boasts an efficiency of 18.97% and 25 years guarantee on performance with maximum decay from 2nd year of 0.4%/year. And this is not the only colored option in its portfolio, the Silk® Colour line also offers silver, orange and green solar panels, helping with the new two-faceted technology.
Colorful photovoltaic panels, different technologies and yield
A recent study by the École Polytechnique Fédérale de Lausanne (EPFL), in Switzerland, provided an overview of the different coloring technologies used for building-integrated photovoltaic modules, describing their operation, challenges and advantages. The paper provides an interesting insight into the industry and includes valuable considerations about the prices and output power of colored photovoltaics.
When discussing colored solar panels it is good to start by distinguishing the different approaches. To obtain the color it is possible to use the following:
- colored glass;
- colored encapsulant;
- active semi-transparent and rear-coloured PV layers;
- interference coatings; coloured fv cells;
- special films or adhesives added after manufacture.
The colored glass
The technique is “simple” but varied. It may require mass colored glass, i.e. flat glass with low iron content used to optimize the transmission of light, as in the case of the red, green or orange photovoltaic created by FuturaSun.
Or you can use digital printing on ceramic or silk printing to color the front glass of your solar panels. The colored layer will reduce the light absorbed in the cell and consequently the module’s power. The power loss is directly linked to the print density and the ink or pigment used but is generally between 11% and 30%. Companies active in this field are, for example, Kameleon Solar with its ColorBlast® product line and 3S Swiss Solar Solutions, both dedicated to digital printing on ceramics. And the Swiss Sunage employs a process of coating minerals on the surface of the covering glass at a very high temperature, thus becoming a structural part of the glass.
Coloured encapsulant
The colored encapsulant is obtained through a standard polymer extrusion technique. In this case, organic or inorganic colour pigments and other additives are added to the base resin. This is the case with Lenzing’s ColorQuantTM, which offers theoretically unlimited color versatility, allowing for customized designs. The advantage? Since the processing of this material requires lower temperatures than that of glass the choice of pigments is wider. In this case (but also for graphic printing) it is possible to use interferential pigments that modify the reflection of light, instead of providing color, through a selective absorption of visible light. Performance losses are estimated to be below 20%.
Semitransparent and back colored PV-active layers
Another coloring possibility for the built-in photovoltaic is the use of semi-transparent amorphous silicon in addition to colored encapsulants on the rear. The result are transparent laminates of a myriad of possible colors. In this case, performance losses are minimized but the conversion efficiency of amorphous silicon is very low.
Interference coatings
This technology takes on the concept of interferential pigments but creates transparent multi-layer coatings to be deposited on the panel. These films reflect only a selected wavelength of the light spectrum and thus the cell is colored. Depending on the final color the solar panels work with a different efficiency. Examples of this approach are Fraunhofer ISE’s MorphoColor concept, marketed by Megasol Manufacturer, Swissinso’s KromatixTM technology or the first generation of Solaxess white sheets. This approach is expensive but boasts more limited power losses ranging from a minimum of 4% with Megasol’s green solar panels and 45% of Solarxess’s white photovoltaic panels.
Color photovoltaic cells
Gratzel cells are photovoltaic cells in which the active material is made up of a dye and are the most “old” example of coloured PV. But there are always other possibilities at the cell level. Perovskites with organometallic halogenides, a new class of semiconductors, for example, can give orange, red or yellow cells depending on the internal ratios of cations or anions. The disadvantage? The change of color is accompanied by a significant change in conversion efficiency up to less 11%.
Color photovoltaic, module prices
But one of the most interesting data next to that of performance is definitely the cost. “On the basis of the current market price, the estimated European average for special BIPV products, including the coloring solution chosen, can vary from 100 to 400 €/m2 and depends on parameters such as product type, size, materials used (e.g., glass thickness) and the relatively small production volumes of the BIBV companies”, says the EPFL research.
“Because most BIPV projects are customized, costs can vary greatly. Some products may be cheaper, but for others, such as super-sized products integrated into iconic architectural/BIPV installations, may also cost up to €800/m2”.