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Comment by mdorazio | Hacker News Reader

The title doesn't really tell you what they're actually doing. Toyota is basically running a program to put 34% efficient solar panels on a Prius to charge the battery during the day.

Using typical panels on roof, hood, and trunk only nets you 4-6 miles / day of solar energy if you do the math. They're increasing surface area of panels here and using what are probably multi-junction (i.e. really expensive) cells for a fair boost in potential range / day. The claim of 18 miles per day of sun seems like a stretch and in actual production and real-world conditions you'd be more likely to get three quarters of that, but I could be wrong. Still impressive, though.

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Ok, we'll use your wording for the title above. Thanks!

5 * 365 > 1500 miles. I'd take that. And if I perchance ran out of fuel and battery, it'd be nice to know I could eat at a cafe for an hour in the afternoon and probably get it to hobble to a gas station.

That's the kind of peace of mind that's worth maybe an extra grand.

I'd expect full solar panels to cost significantly more than $1000.

Well retail, sure. You think the largest auto maker in the world is paying retail on everything?

But the public will be paying retail.

No, the public will pay much more than that because it is now a car part. Brand specific car parts are sold way above what an equivalent part would cost at retail. There was an interesting business model that consisted of buying brand new cars and breaking them up for parts.

Why did you say "No"? Clearly it will only be more expensive if you buy it as a part instead of as a car. Your own line explains it to yourself if you think about it: "There was an interesting business model that consisted of buying brand new cars and breaking them up for parts."

What happens when it gets hit by a bit of flying debris on the highway? Screwdriver, piece of wood, rock, etc? Do I have to call insurance to get the panel replaced? Or just hail. Can I own this car in the midwest?

That's what killed the Solar Road: https://www.google.com/amp/s/amp.businessinsider.com/worlds-...

That and pretty much everything else about it

Underrated comment!!

Less than what happens when you take a rock or brick through a windshield. For one, you don't die when your solar panel gets a scratch or a dent.

Seems like an odd complaint to me. What happens if your mirror gets hit by a rock on the highway? Or the front windshield? The solar panel is just another part of the vehicle that can be damaged, no?

If your car is being assaulted by solid objects at highway speeds so often that it becomes a serious concern to factor into your next car purchase, I very strongly suggest moving somewhere safer.

Cracks on windshields and dinged paint are cheaper to repair than high efficiency solar panels.

That's only assuming the external glass of the panel cannot be replaced without also replacing the actual energy generating panel beneath.

Windows ... generally ... aren't high-power electrical equipment.

Solar cells aren't simply inert panels of glass or silicon, but circuits of cells for which damage may affect a large portion of a panel. Solar panels as it is suffer degredation and a lifespan of ~20-25 years, in stationary mounts, due to sunlight, UV, wind, rain, hail, sand, dust, stones, and other forms of degradation.

Road debris, rocks, falling tree limbs, pine cones, other vehicles, birds, insects, and more, could impact or degrade solar panels.

A chipped windshield can be filled or replaced, at fairly modest cost. Trailing-edge rear windows might have integrated defogger wires or radio aerials, generally front glazing doesn't. Solar panels are rather more fussy.

Body nicks and dings can be effectively ignored. PV damage, not so much.

Good point, but would you leave your car without solar panels out in the hail?

If it really breaks, then you have a car just as useful as before, until you get the solar panel fixed.

Whether this is good or bad comes down to how much the panels will add to the cost.

In hail, you worry more about windshields than anything else. Hail is pretty random, and baseball size does occasionally happen. So for most people, I'm guessing that would just mean throwing a larger blanket on the car to try and prevent impact damage.

The car would not rely on the solar panel for constant operation, so the same thing that happens to escalators when they stop working and becomes stairs—-the solar powered car just becomes a normal hybrid or electric vehicle. Then you get it fixed.

I have a Gen 3 Prius with the "solar roof" option that is used to run ventilation when parked, so you don't come back to a uncomfortably hot car. The solar panels are covered by thick glass (I guess toughened), so there is no more chance of them being damaged than a window.

At 35mpg that’s essentially 43 gallons of gas a year or $111 worth at $2.50/gallon (~national average). So yeah, $1000 seems about right but likely people would pay more just to use less fossil fuels. I would.

And if gas prices in USA come closer to the rest of the industrialized world the savings would be much more.

43 gallons of gas is 162 litres.

In Europe that’s about €240 or $265

The Europe price doesn’t even cover the externalities of burning oil.

But price of solar panels is decreasing rapidly right? Spending the R&D now such that your cars have solar in 10 years, when it might be profitable.

I live in Santa Monica and even here doesn't get 365 days of sunlight.

> Using typical panels on roof, hood, and trunk only nets you 4-6 miles / day of solar energy if you do the math.

FWIW there's a project to actually do that: https://lightyear.one

This is an outgrowth from the WSC, the founders are alumni from TU/e.

Now the car is really covered in panels (~5 sqm), it looks like they just replaced the rear window by panels (as well as panelling the hood, trunk and roof obviously).

IIRC they were claiming up to 12km/h solar charging (as in you could crawl along on solar alone on sunny days). According to their calculator thingie, they're expecting about 5km/day in midwinter aberdeen (on average obviously).

The claimed range would meet easily meet my mileage five days of the week – it's a big win! I'm in a fairly sunny city in Australia so I imagine I'd get a decent charge much of the time. I don't think this'd work so well in say, Vancouver, but then every place has to use the renewable energy sources locally available :-)

If you don't park in the shade. If your parking space doesn't tilt slightly away from the the sun.

For the same money you would be far better off installing some solar panels permanently somewhere along with a battery that can transfer that power into the car when you get home. Or, better yet, skip the batteries and plug the solar panels into the grid. The more solar panels attached to the grid the better. Anyone who cares about the environment would put panels on their house, lawn, driveway and pets long before their car. This is a fashion statement, a fancy paint job.

(And most people would be shocked at how much solar power is available in Vancouver. Without dust in the air, droughts most summers, and the lack of mountains to the south, Vancouver does fairly well in terms of solar.)

+1 for the idea of putting solar panels on the pets. Pretty sure of the same marketing people who think putting solar cells on a car roof will be cost effective would love that idea.

Most people who live in big cities in the EU dont have a house (and they make up >50% of the population). They live in apartments. Isnt this the case for the USA too?

And those cars would be parked underground, or at least on city streets ... not the best places for solar.

If your commute is 5 miles/day, that's also bikeable, even walkable.

> in a fairly sunny city in Australia

nope, not doing that -- too hot.

If you need AC, then your EV range will also suffer.

That's about a 90-minute walk each way. Even in the age of podcasts and earbuds, that's a supremely unappealing way to cover 5 miles.

I don't know how fast they walk down in Australia, but in the USA, that's around 45 minutes each way.

5 miles at 45 minutes is 6.66 miles/hour. Unless most Americans are professional speed walkers I think that's jogging speed.

I think you’re confusing 5 miles / day with 5 miles each way. 5 miles per day is 2.5m each way which is about 45 minutes each way of walking and 90 minutes total walking per day (not each way)

Average walking speed is 3.2 miles/hour or less [1]. That's 94 minutes for 5 miles.

[1] https://www.healthline.com/health/exercise-fitness/average-w...

So 47 each way... splitting hairs.

Or 20 minute cycle

90 minutes per day not each way if the commute is 5 miles per day. That’s walking distance of you’re motivated, but if I lived 2.5 miles from work I think I’d commute on my OneWheel at least when it’s not raining.

It's 2.5 miles each way, pretty walkable if weather is ok. Probably not even uphill each way. :-)

In my particular case I work from home, and my 'commute' is back and forth from church in the morning; I give a lift to a friend who isn't terribly mobile, so the car is necessary – otherwise I'd be on the bicycle. Unusual, I'll grant :-)

I just bought a new car. I was interested in a Tesla but don’t have a parking spot with an outlet, among other deterrents, that kept me from spending the initial $10k.

My commute is about 8 miles per day. If a solar panel on a Prius could give me an almost free commute I would have bought it in a heartbeat.

It seems like this could be useful for making electric cars more practical for apartment dwellers, in that a car in an open lot would stay indefinitely topped up when unattended and unplugged instead of the omnipresent worry of the battery running down.

Yeah, a lot of people inner city won't drive everyday and often only have on street parking. Or they'll be renting somewhere that has garages without charging stations.

Anything that can minimize the number necessary trips to a charging station or eliminate them completely for people that only drive once or twice would a week be a big win.

"renting somewhere that has garages"

I still don't think solar panels will help in this situation.

A lot of city garages have an open roof level.

Getting those people to use a shared pool of electric cars would be a bigger win. That low utilisation means the initial environmental cost of producing the car is not amortised over nearly as many trips.

Yea, if you've got a 15 minutes commute then you charge your Leaf2/Zoe/Ioniq not twice a month but once in three weeks.

I think any bit helps. If solar panels will ROI over the lifetime of vehicle ownership, then that’s awesome!

How far is the average commute? There are a lot of places where this level of additional range for "free" could potentially halve your charging needs.

Might also mean that people start looking for uncovered airport parking. Or that it's a lot harder to get really stranded with an electric car.

Even at 100% efficiency (which we'll never get) I think electric cars will still have to charge off of something. But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable.

> But dragging the panels around with you so that you always have some kind of charging seem pretty reasonable.

It might prevent the worst case scenario of being stranded in a desert without fuel. But for everyday driving, dragging around that extra weight has a real cost, which could quite plausibly outweigh the benefits to everyday driving.

Remember, our auto industry has moved to the point where spare tires are starting to become uncommon and full-size spares are almost unheard of. The market isn't trying to optimize for the worst case scenario.

You may be underestimating how much people dread chores like manually plugging their car to the electric outlet, and many people don't have those special garages with chargers on them, and if the house is a rented one modifying it is out of question (and renting is not only a poor people problem, a lot of people pay an insane amount of money renting, ask anyone in NYC).

> You may be underestimating how much people dread chores like manually plugging their car to the electric outlet,

I'm simply assuming that, for the foreseeable future, solar panels on your car won't put a noticeable dent in the frequency of those chores compared to with a current production Prius. If you can already go for two weeks of commuting and grocery runs without topping off the gas tank in your hybrid, stretching that by another day or two doesn't meaningfully change the ownership experience even if it does have a long-term impact on the economics of owning that vehicle.

When I first read your comment, I thought that there was no way that solar panels could be heavy enough to affect your mileage. So I did some quick calculations.

Estimates of solar panel weight I found say that solar panels tend to weigh 2-4 lb per sqft.[1] Note that estimate is for roof-mounted solar panels, but if anything, car-based solar panels should be lighter.

A Prius has dimensions of 180"x69".[2] The sqft of the solar panels will be less than that, since the panels don't cover the windshield, and they don't go all the way to the edge of the hood, etc. That's 86.25 sqft, so that puts an upper bound on the weight of the solar panels at 345 lb. If we assume the lighter end of the scale for solar panel weight, that becomes 172.5 lb. That's 6-11% of the curb weight of a Prius. That's pretty substantial! For reference, a 50 lb spare tire kit can reduce fuel economy (and presumably mileage, for EVs) by 1%.[3]

Although that does imply that you're breaking even if the solar panels can increase your range by ~5%, not accounting for the weight. If you live somewhere like Arizona, that might work out. If you live in Seattle, maybe not.

[1] https://sunmetrix.com/is-my-roof-suitable-for-solar-panels-a....

[2] https://www.toyota.com/prius/features/dimensions/

[3] https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=...

These are thin-film, light-weight, and flexible. Hanergy owned Alta Devices has a Gallium Arsenide lift-off process that produces the world-record efficiency for single junction PV.

172lb is a lot! Thanks for doing that. But I think solar panels meant for rooftops have a lot of weight in the aluminium frame, and are think glass. I can't imagine a car manufacturer putting thick glass above the aluminium skin of the car if they didn't have to.

Maybe we'll get cool solar panel crystal car roofs in the future!

I've often thought these cars should have a small gas generator you could use to charge the car if there's no outlet available.

You are describing the Chevy Volt. Or the BMW i3.

Shame they canceled the Volt. It combined the best things about electric and ICE cars in one vehicle.

The generator in my proposal wouldn't deliver enough power to drive the car, only charge the battery. You'd have to wait while it charged.

It could still be used as a supplement while driving to extend the range. If the battery was fully discharged, you'd have to wait.

So you’d leave the generator running when you park the vehicle, unattended? Would it be safe to allow this in, say, an indoor parking garage?

It would be like leaving a vehicle idling when you park it. Noisy, polluting, and potentially deadly.

> So you’d leave the generator running when you park the vehicle, unattended?

I use a generator frequently. I leave it outside, unattended. So do the neighbors (when the power goes out). I never leave an idling car unattended because I worry about it. It's a much bigger deal than a little gas engine.

> It would be like leaving a vehicle idling when you park it. Noisy, polluting, and potentially deadly.

It certainly is a bad idea to run any sort of combustion engine in a poorly ventilated area. Perhaps I presume too much that people will have some common sense.

As for the noise, that's a design issue. ICE car engines are pretty quiet these days. There's no particular reason why a small ICE has to be loud like a chainsaw.

That's essentially what a plug-in hybrid is, modulo the "small."

> That's essentially what a plug-in hybrid is, modulo the "small."

Not exactly, Prius uses two drive trains and some fancy gearing to be able to use both engines. The gas engine actually propels the vehicle (either alone or together with the electric)

Some 'hybrids' like the Volt only have EV drivetrains. The gas engine is just a generator and does not turn any wheels. Which also means that it can be much simpler – no transmission to worry about, you can run at whatever the ideal RPM is. And so on.

You're incorrect about the Volt's drivetrain: https://en.wikipedia.org/wiki/Chevrolet_Volt#Drivetrain

Yes, the gas engine can turn the wheels.

Most Prius-es are simple hybrids; the car they're testing with is a Prius Prime, a plug-in hybrid with ~25mi of all-electric range from an 8.8kWh battery, that's what they're trying to add range to. If that battery is exhausted you just drive on the gas engine as usual (I have a 2017 Prime). So this would just be a small boost, though to be fair I often can go a few days on a charge (but I don't drive a lot).

Thermo-photovoltaics are a reasonable alternative to the internal combustion engines for the hybrid car of the future. Would probably run off methane or a 90/10 methane/hydrogen mix.

You could just carry one in the trunk. But I doubt the reduced range and space from it would be worth it.

I could also carry a transistor radio with me instead of using the one in the car :-)

That's the thing. Unless the option costs ~$1k extra, you will never ROI until after at least 10 years. In that time you'll be paying for replacing the glass on the solar panel when a rock inevitably cracks it.

That has some value. How many people get stuck for a simple flat battery ? Having a way to avoid that is pretty nice to me. Depending on how costly is the option.

4-6 miles? you only read the first paragraph, where the author summarized previous efforts.

"If the car is driven four days a week for a maximum of 50 kilometers a day, there’s no need to plug into an outlet, NEDO’s Yamazaki said."

This car maintains equilibrium at 124 miles per week, so basically anyone with a commute with a 1-way distance up to 12.4 miles, or 15.5 miles if you work from home one day a week, would not need to use a charger.

I think you didn’t read my full comment.

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