Mercedes-Benz says its testing solar power generating vehicle-paint that could coat vehicles, and generate 100% of their power requirements in sunny cities like Los Angeles.
Mercedes-Benz says its testing solar power generating vehicle-paint that could coat vehicles, and generate 100% of their power requirements in sunny cities like Los Angeles.
Revolutionary! Mercedes-Benz solar paint could mean Australians never have to plug their EVs in again
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Yeah this is total BS.
The sun delivers about 1.3kW of energy per square meter and an average car takes up about 8 square meters of space. So that's about 11kW to work with, but even very efficient solar panels only harvest about 20% of that. So that leaves us with about 2.2kW to work with. Now in order to convert that energy into something usable and charge the battery, more losses are added, depending on the situation this would be around 20%, leaving 1.76kW. This means charging a 50kWh battery would take around 28 hours. Obviously we can only expect around 6 hours of really good sun on an average day, with the rest of the day having much less energy available. So charging the car would take several days in perfect conditions. If it's cloudy, if it's raining, if you've got shade over the car, if you drive the car etc. it will take more time to charge it.
In reality however, this is with modern commercial grade equipment, oriented perfectly to the sun at the proper angle. Putting that in a car isn't possible. Stuff is going to get hot, which leads to reduced efficiency, active cooling costs energy so that's probably not a good solution. The car isn't going to have all of it's surface facing the sun, by definition a part of it is going to be in it's own shade. If the sun is perfectly overhead for max efficiency on the roof, the sides aren't going to get anything. Angles are going to be wrong and people prefer to park their cars in the shade or under cover. Cars also tend to be used, so they get pretty dirty driving around, that reduces efficiency further. So if they get half of what I described, they would be doing real good. Just takes a week to charge the car, but still, doing good.
But then there's the real kicker. It isn't possible to get anywhere near 20% out of a paint or surface finish. Modern solar panels have many tricks to get their efficiency as high as 20% (and even nearing 30% with the newest techniques, but that isn't commercially viable at the moment). Solar paints are way worse and do badly even in perfect lab settings. One of the issues is the energy generation isn't as optimal to begin with, but another issue is getting the energy transported out of the material is problematic. This leads to efficiency numbers in the 1% range. This means going from charging in a week, it will take months, if it charges at all.
Except for niche use cases, putting solar on anything except roofs usually makes no sense at all. It's handy for camping, on top of the RV or for example on a boat, where having a little bit of DC is handy when no other sources is available. But when there is a roof available, just put it on the roof and use the power from there.
Well, "they did the math". If you read the article, they're saying 32km/day in Stuttgart and 47/day in LA, and then extrapolating to 55/day in Australia. This is from their practical trials.
The kicker to the kicker is that they are claiming >20% efficiency here. It's apparently a very revolutionary new paint. The main thing they didn't cover is how fast it degrades, which has been a huge problem with perovskite-based systems like I bet this is.
Yeah I don't really see how that's possible. Even if you get a material that's able to harvest at 20% efficiency, getting the energy out is a big issue. It's a lot of power and transporting it through a layer a few micron thick is very rough and leads to huge losses.
I also don't know what "math" they actually did. I think it was some back of the napkin extrapolations and not actual data. For example they state: "one scientist suggested covering an entire car with the new solar paint, ramping up the surface area to more than 11m2" That leads me to believe they didn't actually do anything but were just extrapolating and speculating for the press.
They also state: "scientists hardwired the body panels to the Benz’s high-voltage battery". This makes zero sense. In order for energy to flow from a solar panel into for example a battery, the voltage of the panel needs to be higher than the voltage of the battery. Otherwise the current will flow in the wrong direction. But Mercedes EQS batteries run at 400 volt, you can't connect "directly" to the battery unless you want the panel to explode and the car to catch fire. And even if you connect it directly into some charger system that can convert the voltage from the panel into something the battery can use to charge, you wouldn't want to do it like that. Including a voltage optimizer in the system is key for getting efficiency out of a solar panel.
I think some journalist misunderstood some Merc tech demo and made up this BS story.
"They" here was you. You did the math. That was a bit ambiguous, sorry.
Journalistic misunderstanding is possible, I guess. There's no way it's just a wire to the high-voltage motor output - it doesn't trickle charge off the grid directly either - although omitting the charging system is arguably more of a wording choice.
Here's another one where they go into more detail, and even mention the possibility of perovskites independently: https://newatlas.com/automotive/mercedes-benz-solar-paint/
Unfortunately the press release itself doesn't seem to be accessible, after a quick search.