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Tesla’s Solarglass Roof tiles are already among the most aesthetically-pleasing PV systems in the market. A Solar Roof installation involves the setup of both PV and non-PV roof tiles, and according to Tesla, this could present some issues. Since some tiles do not have solar cells in them, there will be some angles or times when it is possible to distinguish which tiles have solar cells and which do not.
Tesla described this issue in the background of its patent, titled “System and Method for Improving Color Appearance of Solar Roofs” and published on February 11, 2021.
“When viewed from a shallow angle (e.g., when the roof is viewed from the street), the dark-colored photovoltaic structures can become visible. The color contrast between the photovoltaic structures and the glass cover can create a scene that is not aesthetically pleasing… Although the non-PV roof tiles can include similar glass covers as those of the PV roof tiles, the absence of embedded photovoltaic structures can result in the non-PV roof tiles having a different color appearance than that of the PV roof tiles.”
Tesla notes that these issues are due to several factors, including tiny imperfections during the Solar Roofs’ manufacturing process or the fact that PV roof tiles tend to look different when viewed under different lighting and at different viewing angles. According to Tesla, there are ways to get around these challenges, such as adopting a robust color-management scheme and some adjustments in the Solar Roof tiles’ manufacturing line.
“First, to reduce the color contrast within a PV roof tile, the PV roof tile can encapsulate polycrystalline-Si-based photovoltaic structures. By controlling the size and pattern of the surface texture of the polycrystalline-Si-based photovoltaic structures, one can reduce the “glow” of the photovoltaic structures. While keeping the front cover of the roof tile transparent, the back surface of the back cover can be coated with a layer of paint that matches the color of the textured surface of the photovoltaic structures to reduce the color contrast within the PV roof tile. A similar paint layer can also be deposited onto the back surface of the non-PV roof tiles.”
“As a result, the color appearance of the PV and non-PV roof tiles can be quite similar. Moreover, when assembling the PV roof tiles, the embedded photovoltaic structures are fed into the production line following a predetermined color pattern such that a majority of PV roof tiles contains solar cells of a similar color and PV roof tiles of different colors are evenly or randomly mixed to prevent clustering of colors on a roof.”
Through these methods, Tesla noted that it would be able to create Solar Roof tiles that feature much less “glow” than typical integrated PV systems. The patent also covered how reactive ion etching (RIE) techniques could be utilized to create textured PV roof tiles. These invoke images of the various Solar Roof variants that Elon Musk unveiled in 2016, which included textured tiles that mirrored the appearance of materials like slate and clay.
“The surface of a polycrystalline-Si-based solar cell can be textured using a reactive ion etching (RIE) technique. In further embodiments, the feature size of the RIE-textured surface can be less than 1 micron (i.e., 0.5 micron or less). In alternative embodiments, the surface of the solar cells can have pyramid texturing with the base width of the pyramids being less than 1 micron (e.g., 0.7 micron or less). Compared to the textured surface of a monocrystalline-Si-based solar cell, the RIE-textured surface of the polycrystalline-Si solar cells can have improved surface uniformity. As a result, the PV roof tiles can have reduced color flop and glow.”
“In alternative embodiments, reducing the cell glow can be achieved through specifically designed anti-reflection coating. This specially designed anti-reflective coating (AR) on a monocrystalline-Si-based solar cell surface can include materials with a higher refractive index than a conventional AR coating (e.g., an indium tin oxide (ITO) coating). More precisely, the specifically designed AR coating can include a layer of SiNx or a SiOxNy /SiNy double layer structure. As a result, the cell glow can be reduced by three- to eightfold with low (e.g., less than 5%) power loss.”
Elon Musk has stated that 2021 will be a key year for the Solar Roof, with the CEO noting that its potential would be evident this year. Considering the company’s ongoing rollout of the integrated PV system and the development of better Solar Roof designs, it may only be a matter of time before more customers of Tesla’s flagship residential solar product would have more design options available.
Read Tesla’s recently-published Solar Roof patent could be accessed here.