Comment by janosch_123 | Hacker News Reader

Comment by janosch_123 | Hacker News Reader

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Of course. It is an intriguing idea, but a local maximum.

- The panel sits at open-circuit voltage of 48V

- That then needs to be converted/boosted to 400V (conversion loss)

- The converter needs to talk to the BMS to make sure batteries can be charged at this moment (component that is live all the time and is a current draw)

- Need to think about it, but you want another set of contactors between panel and HV-Bus where the battery sits (current draw)

1km of driving is 150Wh so 1kWh gets you 6.6km or 4.1 mi

Let's be generous and say you have a 500W panel(punchy) for 8 hours at full blast (doesn't happen), you get 500W x 8 hrs = 4kWh. Lets say isolated converter loses you 10% so you are at 3.6kWh Thats 24km or 15mi of driving in perfect conditions.

2x Gigavac contactors, keep them closed costs you 24W, so that lowers the input further to 476W * 8hrs = 3.8kWh, less 10% = 3.42kWh ...

Someone who studied EE might be able to make this more accurate. Back of the napkin math, not totally impossible, but not worth adding it for a trickle charge. Adding components that can break, adding weight etc.

There are interesting solar cars out there where you reduce the weight heavily and fold out big solar sails. Then you are getting somewhere, for a city car you don't have enough surface. For an SUV or American Style Flatbed truck you have so much weight it's not worth it either.

> not totally impossible, but not worth adding it

I don't drive 24km per day, and don't have a good way to get to the train station other than by car. The bus is too tight, they miss each other often. Cycling isn't safe between towns, you have to basically go on a highway without any separation (yes that's legal in Germany to cycle on, as there is no other way than perhaps a farmer's grass path to go between towns, so they don't call them highways but cars drive highway speeds - or more, if they don't stick to the limit). I also don't have charging infrastructure or a driveway. A vehicle that does those couple km a few times per week without needing to drive elsewhere to charge gets me a long way. Charge me up, Scotty

I've looked into this and the moment the Aptera ships (probably never but here's for hoping) I'm buying my first car. I've looked critically at the range they assume you get at my latitude and it would keep topped up for enough months of the year that it's totally worth it (maybe it was even year-round because they're so efficient, I don't remember now, but I'm also okay charging it thrice a year)

But 24 km per day is under ideal conditions (perfectly sunny day, mid-latitude, panels angled southward) and 500W requires 2 square meters of panels[1].

Unless you own a big American pickup truck, it's hard to see where those panels fit on the car. And if you do own a big American pickup truck, you will not achieve the 150 Wh/km assumed by the GP (it will be more like double that). GP also used quite optimistic loss figures for conversion.

It begs the question: Why not a Nissan Leaf and solar panels on your (home) roof?

[1] Only 1000 W of solar energy falls on each square meter of the earth's surface at noon. The best commercially available solar panels have about 25% efficiency converting light to low voltage DC. This means you need a flat surface of about 2 square meters directly facing the sun to collect 2000 W of light, which will achieve 500 W of electrical power.

Why not on your home roof: because I don't have a home roof or a place to run the cable to the car. I could ask the landlord if they'll allow me to pay for solar panels on their building but I still don't have a driveway as mentioned

Why doesn't the Leaf have it: afaik the leaf is a normal car, not like the Aptera that I'd be looking to buy. Even the Lightyear One was claiming to be more efficient than normal but pretty disappointing in how much range you get from the solar roof. Still more than zero though, so yeah ask them why they don't sell that variant ¯\_:|_/¯ While we're at it, let's find out why there isn't a smartphone that fits my niche (modern chipset with dual frequency GNSS for less than twice the price that competitors charge for it, operable with one average-sized hand, sdcard slot, and ideally a headphone jack but at this point I'd settle just for a bit of storage and really don't feel like it should be a hard-to-find device) or a laptop that makes sense (arrow keys and no annoying tapered edges that don't fit a network port, for example, already limits your options to a tiny percentage of the available systems)

Thanks! That helps clarify the engineering challenges. There’s never a free lunch!

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