Comment by pinkmuffinere
2 days ago
> Even on an overcast day, the team saw over 545 watts of solar input
Let’s (generously) assume that was the minimum they saw, and let’s (generously) say they charged for 14 hours. That’s 7.63 kWh gained over the day, in almost ideal conditions. Flagstaff’s high altitude means stronger sunlight, and they can do regenerative braking as they come down the mountain. In my Nissan leaf, 6 kWh would get me about 20 miles. If they are much more efficient, they maybe got 50 miles from the charging on that day, and the other 250 from the charge they started with.
I’d love to be wrong about any of the above! Solar panels on cars would be so cool! It just doesn’t seem useful. Please correct me if I’m mistaken.
For roadtrips, you're absolutely right.
The average car travels less than 50 miles on the average day though (more like 30 I believe). This means you don't have to charge except on roadtrips (provided you can park outside in the sun, and don't drive more than average. The battery can provide some smoothing out of day-to-day variability though).
Whether not having to plug in at home is particularly useful... hard to know if it's something consumers want.
If you are parked outside in the sun, you'll need to spend some amount of energy keeping the battery at a healthy operating temperature.
Fully agree. The physics of solar panels on cars just doesn't work. It's bizarre that this is actively pursued by startups and concept cars from large manufacturers when it takes just quick back-of-the-napkin math to see.
A car has about 5 m^2 of flat space on the roof/hood/trunk so that's the maximum surface area that can capture solar energy at any given time.
The total energy to hit the area is 1000 w/m^2.
The panels can't rotate to track the sun so the effective area is the cosine of the angle. So you end up with about half the amount of effective sunlight hours as the actual daylight hours. So in summer you get about 6 hours of effective sunlight.
Good panels in real world conditions can give you 22% efficiency.
So in optimal conditions you get: 5 * 1000 * 6 * 0.22 = 6.6 kwh
That will reflect your best days. It can be dramatically less if it's cloudy, overcast, winter, far from the equator, car is dirty, parked in shade, etc.
6.6 kwh is about one tenth of the battery in my Hyundai Kona EV. With very conservative highway driving, 6.6 kwh can get about 40km of range and about 50km in city driving. It's what I get from plugging into my home charger for 30 min and what you get from a fast charger in about 3 minutes.
So besides some very niche uses, there's no sense in massively increasing the cost and complexity of a car by installing solar panels. Far better to put the panel on the roof of parking and just plug in for a few minutes while you park.
Have you looked at the thing? I wouldn't be surprised if it's an order of magnitude more efficient than most electric cars out there.
The energy dynamics will be closer to a heavy ebike or light motorcycle.
500-600 watts is plenty for moving along at 30-40mph, and with such a light bodyshell, you don't want to be going a lot faster than that.
Standard automobiles are something of a vicious cycle energy-wise - weight, range and speed aren't a linear relationship, so on short-range trips we're paying a huge efficiency penalty for long-range capability. Golf buggies, ebikes and so on can be 1/10th the weight and 1/10th the energy consumption.
50 miles of free driving a day sounds incredible, but you're implying that's a bad thing? I'm confused.
With how cheap solar panels are getting, why not slap a few of them on the roof of every EV? Some days they get you 10 free miles, other days 20 or 30. If you’re a commuter, you’re basically driving for free at that point.
Sure it’s not enough on road trips, but why is that a problem?
The solar cells themselves may be cheap, I don't think putting them on the roof of a car (without ruining the aerodynamics) is particularly cheap, yet. Most people would be better served putting the solar panels on the roof of their house.
Their marketing and reserve page claims "up to 40 miles per day": https://aptera.us/vehicle/
Yes also any one with a ev knows speed matters. Its not stated how long it took or average speed over the course. Not to mention a nice draft from the film car. Besides all that I would still love to have one.
You are not wrong, you are just missing the point. This is the ultimate commuter vehicle. Most commutes fall in the 10-30 miles range. On an average day, you might drive 30-40 miles. If so, you basically are powered by the sun on most days.
> they maybe got 50 miles from the charging on that day
They claim it's up to 40.
Best case you charge more than you drive; so your car has a enough in the battery every morning to make it back home after work. Worst case, you delay the moment when you have to charge by plugging in by some large percentage. The difference between charging your car once or twice per week and once or twice every few months top top it up. Perfect if you don't have a charger at home. Removes a lot of the hassle and cost related to charging.
Road trips are not something people do on a daily basis. Especially not in light/small vehicles. But when you do, a light vehicle with a longish range is a nice thing to have. And this thing is very efficient by design (light, teardrop shaped) and the relatively small battery probably charges pretty quickly. And you get a few tens of miles extra because of the solar. So it can do a 300 mile journey despite having a smallish battery. Which is what they just demonstrated. 300 miles is pretty good. Most EVs don't do any better than that.