The patent outlines a design that would allow Tesla to offer colored variants of the solar tiles without compromising any functionality.
The Tesla Solar Roof is one of the most highly expected products of this decade. If Elon Musk can produce roof tiles that look exactly the same as current, terracotta or slate tiles, but which produce electricity on a substantial level, a lot of environmental issues of electricity production and transportation could be alleviated. Just imagine having the entire roof covered in electricity producing tiles, paired up with a Tesla Powerwall battery in your basement, charging up your vehicles and powering up your home - for free and with almost zero Co2 emissions. That, if used on a grand scale, could really make a difference.
Right now, Tesla is prioritizing the production of its Solar Roof tiles this coming 2019 - especially at their Buffalo, NY located Tesla Gigafactory 2. Alongside Tesla continually preparing to ramp up the Solar Roof tiles production next year, the U.S based company recently filed a patent for what could allow them to produce stunning colored Solar Roof tiles with zero compromises. Published last Thursday, the patent is titled: "Uniformly and Directionally Colored Photovoltaic Modules."
An illustration of Tesla’s patent for its colored Solar Roof tiles.
The document contains a note by Tesla that states that PV (Photo Voltaic) modules are usually blue, dark blue, or black because these are the natural color of solar cells. However, for homeowners, having the option to choose their color or to match it to current, terracotta tiles, is necessary to keep the visual appeal. While there are currently several ways of colorizing PV modules, almost all of them (like for example using tinted glass and/or encapsulation sheets) absorb huge amounts of sunlight, resulting in PV power loss. Furthermore, the standard PV modules also visually degrade over time, making them a no-go solution for most modern homes.
“Shading, or absorption of incident sunlight, causes PV power loss, a consequential problem of existing coloring techniques. In addition, colored PV modules manufactured with these techniques, and colored glass more generally, commonly suffer from: sparkle, or glint; flop, or angle-dependent color appearance; and graininess. Note that sparkle refers to glint or localized bright spots. Flop, on the other hand, usually refers to angle-dependent color, i.e. an angular dependence of the peak reflected wavelength. The term flop, or light-dark flop, can also refer to angle-dependent brightness, i.e. an angular dependence of total reflectivity.”
The patent filed by Tesla outlines a system that uses a rather clever solution to avoid any known drawbacks of conventional PV module coloration methods. Instead of using traditional methods like tinted glass, Tesla's design uses a texturized surface for the glass cover that comes with a color filter layer. Furthermore, it uses a “transparent material with a predetermined refractive index.” Below you will find a detailed description by Tesla of its colored Solar Roof tiles design.
“Embodiments of the present invention can produce PV roof tiles with a uniform color with little light absorption. As a result, a high proportion of the incident light (of colors other than the module’s intended color) is transmitted to the PV cells. To facilitate uniform coloring of PV modules and roof tiles, the inside surface of a top glass cover can be texturized, and a transparent material with a predetermined refractive index or combination of refractive indices can be deposited on the texturized surface. Such a micro-textured or frosted glass cover can display significantly less sparkle, flop, and graininess than conventional glass covers, thus improving color uniformity and appearance. Customizable directional coloring, and intentionally controlled angle-dependent color, can provide further aesthetic options, while still performing efficiently for solar conversion. It is also possible to produce a layer of sphere-shaped metal nanoparticles on the inside surface of the glass cover.
“These nanoparticles can produce colors efficiently while absorbing little light. Another feature described herein is directional coloring of PV modules or roof tiles. The texturized surface of a glass cover can have a color filter layer covering one or more facets of the texture. This color filter can include multiple thin film layers formed using a directional thin film deposition technique, such as chemical or physical vapor deposition (CVD or PVD), e.g. sputtering. The coating layer can be deposited by coating the textured glass surface in one or more directions. Such directional coating can reduce unwanted light absorption by the color filter, while still providing a uniform color appearance to viewers at a certain viewing angle.”
The textured micro-structured glass that Tesla uses to colorize their Solar Roof tiles features a feature surface roughness on the order of 100 nm to 10 μιη. In turn, this allows their colored Solar Roof tiles to showcase a uniformed color with little to none light absorption and a lot less sparkle, flop and graininess when compared to conventional colored glass. The design also allows for a customizable directional and multi-directional coating. This both improves the aesthetics of the Solar Roof tiles, but also, makes them optimized for solar conversion as well.
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If Tesla can figure out how to combat all of these issues and start volume production next year, we might see this solution on literally thousands of roofs within a short timeframe. While the long development cycle left plenty room for all the negative talk in recent years, for something that's supposed to both produce electricity and last 30 years, we don't think it was that long. And judging by almost the same thing happening with the Model 3, plenty were questioning whether Tesla could actually produce an affordable electric vehicle on a grand scale, and now, they've all been left waiting in line to buy it.