This past November, Tesla CEO Elon Musk took to Twitter and floated the idea of offering a solar roof option for the Model 3. When asked outright if Tesla had plans to “embed solar panels in the roof,” Musk replied that they would “probably offer that as an option.”

Right off the bat, Musk’s tweet seemed overly optimistic, if not downright absurd. While a solar roof capable of harnessing the sun’s power and charging a car as it drives is certainly intriguing, such a design is far from practical given the current state of solar technology. At the core, the size of the Model 3’s roof would only be big enough for a solar panel that would, at best, manage to tack on an extra mile or two of range per day. In effect, implementing a solar roof would be far more trouble than it’s worth.

Earlier this week, however, Panasonic unveiled a new a type of solar panel technology designed specifically for cars. Dubbed the “HITPhotovoltaic Module for Automobile”, the solar roof design is currently available for the Toyota Prius PHV exclusively, but that may change in the coming years.

What makes Panasonic’s work here so intriguing is that the design houses new technology which makes it possible to actually charge lithium-ion batteries, the very same which power Tesla’s fleet of vehicles.

Panasonic’s press release reads:

Panasonic’s solar cells have a unique structure that combines a crystalline silicon substrate and an amorphous silicon film, and feature high conversion efficiency and excellent temperature characteristics.

Conventional automotive solar cells can output up to several tens of watts and have been used only for the auxiliary charging of 12 V batteries and ventilation power sources for parked cars; however, the use of the features of Panasonic’s solar cells allow a high output (approx.180 W) in a limited area on a car’s roof, enabling the charging of the drive lithium-ion batteries as well as 12 V batteries, resulting in a possible extension of an EV’s travel distance and increased in fuel economy.

An added bonus is that Panasonic’s solar roof can be designed to match a car’s existing design, thereby enabling an efficient installation process.

That said, a lot more work still needs to be done before solar roofs become an add-on worth paying for, or even considering. Even with Panasonic’s solar roof advancements, a parked car equipped with a solar roof panel might still only be able to eek out an additional 3-4 miles of range per day. While that could certainly add up over time, it’s hardly a game-changer. Additionally, consider this: the aforementioned Toyota Prius PHV would reportedly need about a full week to go from empty to full charge via a solar roof alone.

In the meantime, Tesla owners can look forward to next-gen Supercharger technology which Musk last year hinted would be a huge leap forward.

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