Comment by jleyank | Hacker News Reader

Comment by jleyank | Hacker News Reader

People on HN question from time to time about what to do. This article points out several key issues, and battery recycling must be added:

Where do the amps come from? How do they get to the chargers? How much delay is introduced by charger operation/bottleneck? Plug/voltage compatibility? Current safety? Disaster handling (can’t carry a bucket of electrons)?

This suggests material science, power generation, portable aux power sources and real time load balancing are going to be critical. Along with a whole lot of infrastructure that might have difficulty getting built. I’m not an EE - is it possible to create a solar cell that has any impact on an EV? Even enough to move it at trivial speeds? Might portable wind turbines have an effect? Will this force a return to smaller lighter cars?

Would be nice to replace some/much of the medium long haul/intercity travel with trains but that’s a political problem. So is a paying for all the steps in changing from a gas to an electric environment. Man, that Nobel-to-be for high temperature superconducting will be very much appreciated.

Just some back-of-the-napkin math. An electric car uses approx .25 kWh per mile. Household solar gives you 15 watts/sq ft. Assuming a car 5 ft wide, the hood 5 ft long, roof 4 ft, and trunk 3 ft, that's 60 sqft of sky-facing surface. Accounting for rounded edges, let's make that 50 sqft. So 750 watts, or .75 kWh per hour.

That comes out to 3 miles of driving for every 1 hour charge. So your car sitting at work for 8 hours will give you 24 miles of power to drive home.

Adjust up or down based on location, summer vs winter, cloud cover, solar cell efficiency, etc.

Now what you can do is have your garage roof covered in solar, charge a stationary battery, then transfer from there to your car every night. Or swap-able car batteries.

Another possibility is have a design that keeps the solar on the car following the curves of the vehicle when driving, then have a parking mode that would extend / unfold solar to cover more of the car when it is parked. That would be good for people who live in apartments without charging ports, although if parking is provided for tenants then adding charging ports (for a fee) may be a thing.

And, importantly (which you imply, but I feel needs stating outright), this car-roof solar does not have to be the sole source of charging. It can be a convenient (and energy-efficient) supplement to whatever other charging options we can make work.

I was thinking of emergency use but extenders work as well (or commuter parking).

Even converting the whole surface of the car to ideal 100% efficient solar cells world be nowhere close to enough, unfortunately.

Close enough enough for what? For the typical Californian or New Yorker, who drives about 30 miles a day, on-car solar would cut their charging needs in half. That's "close enough" to useful that dismissing it out of hand seems wrong.

You're assuming something like 24 hours a day of having the car parked in full sunlight, which is not realistic (even ignoring that night exists). For it to make sense, you'd need the solar arrays on the car to provide a reasonable percentage of the energy needed during driving. If this isn't the case, you're way better off putting the solar panels somewhere other than the car (where they can work much better), and charging the car when it's not driving.

solar cells can have a decent impact on very exotic efficient designs like the aptera. On a normal sedan it is better to put the solar panel elsewhere than the car

what about power generation at the charging site? i.e. solar on the roof of the charging station. Small scale hydrogen cells? Local battery storage on site so its not all simultaneously drawing from the grid? (I'm not an engineer, just curious)

Article says many sites will need 5 megawatts.

5 megawatts) / ((1000 watts) / (square meter))) / .18 = 27 777.7778 m2

And, of course, this is only when sun is shining with max intensity and certainly not delivered at night.

Figure in the Northeast you get 4 hours times this power on a typical day, and it’s not aligned with peak charging demand.

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