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Comment by alanh | Hacker News Reader

It is so annoying when people tell me their genius idea, putting solar panels on a Tesla. Why doesn’t Tesla already do this, they wonder? Because the amount of energy captured by such a minuscule surface area would barely recoup the inefficiencies of the added weight... That, and a Tesla is sexy in a way that a vehicle plastered with solar panels would have a hard time replicating.

BTW, if you take the ferry to Alcatraz, they will try to impress with you solar panels and a helical wind turbine on the ferry itself. But pay attention, and they admit it doesn’t do anything more than power the loudspeaker. The boat runs on diesel. Because of course it does. If a few panels could power a ferry, we'd have gotten off oil long ago!

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> Because the amount of energy captured by such a minuscule surface area would barely recoup the inefficiencies of the added weight

Is this actually true? Solar Panels don't have to power 100% (or even 20%) of the car to still be super useful on an EV.

An EV with a solar array that generated just ~0.7kwh during 6 hours of daylight, would still be charging itself an extra ~20 miles of range per day while parked. That's significant enough to be worth it to me. And that range can add up (imagine being parked at the airport for 3 or 4 days, and having an extra 60+ miles of "free" range sitting on your car when you return)

Alternatively, that electricity could power an AC outlet or an air conditioner for camping trips or remote work while parked or whatever. "Dog mode" could keep parked cars safely cooled without draining any range.

My EV sits outside an office, in direct sunlight, nearly every business day. And it's battery covers 70% (but not all) of my daily commute. Even if solar panels aren't the most efficient use of that space, surely they're better than nothing, right? Every watt from that solar panel, is a watt I didn't have to pull off the grid, or an ounce of petrol I did not have to burn.

You're not far off on the math for the most efficient cars, but I can't even get that much solar on top of a 23' camper, and that's with full sun and assuming I can park directionally. You're talking about 80 sq ft. Even taking into account these more efficient panels, you're looking at maybe 10 mi a day range added, best case.

And that's assuming you're parking outside at all while at work. In suburbia you might be. Good luck in any big city.

Overall I don't see how this is going to be economically efficient any time soon, even in the best use cases. It seems better to have fixed solar and a plug. But I hope I'm wrong.

There's also the extra weight involved. If you used that extra weight for more batteries instead of solar panels, you might have even more range.

If they could paint the solar cells directly into the surface of the car, it would add little additional weight. Most of the weight of a solar panel is the backing and frame to provide stiffness, and you could use the car body for that.

That's a big "if", though. Photovoltaic paint is currently around half as efficient as commercial solar panels.

It doesn't have to be a paint, it could be a film.

Something like this might be what you want. Hangs on the window and is solar powered.

https://www.walmart.com/ip/Solar-Sun-Powered-Power-Window-Fa...

That was proven to be useless. However, I found this project https://acool.global/. Anyone have any insights on this?

You can plug your car in so that it charges while it's parked. The same solar panels taken off the car and put on your works roof would be far more efficient because they face the sun.

Yes, this exactly. Put the same panel on your roof and charge your car at home (which you do anyway.) You won't mar the car's appearance and you'll get more out of it.

What I would love to see is a Tesla that can act as a powerwall and power your house when the grid fails. Some people hack them to do that but it doesn't look simple or without risk.

This already exists, although not for Teslas. It's called V2G (vehicle to grid) and it's already happening in the UK with the Nissan Leaf.

Not only is this a backup for a rare outage but it makes you money by charging when power is cheap and selling back when expensive. Occasionally the price of power goes negative and you are paid to charge.

https://electricinsights.co.uk/ is good for exploring the energy data and pricing.

If you are in the UK and interested in participating in a trial, see https://www.ovoenergy.com/electric-cars/vehicle-to-grid-char...

A car park with bays with solar panels could be better in that it provides shade/shelter and leaves the nearby building roofs clear to harvest photons to aid in lowering the building.

I'd want solar panels on my car for the sole purpose of running a ventilation fan while parked under the hot sun, so I don't come back to a scorching hot car. More appealingly, it might also prevent the death of pet or child (still incorrectly) left in there.

Well you’re in luck. Go down to your local used car lot and pick up a used 2010 Prius. https://youtu.be/CchHIy7JgvA

Teslas do this just running off of the battery pack. In my experience it doesn't use a ton of power to do it.

A solar panel to make it net neutral energy to keep cool would still be nice.

That would be ideal. At the moment (and hopefully not for much longer) gas engines meet my needs better, so the solar panels would be an interim solution.

This is somewhat easy to do if you have a roof-rack or somewhere similar on your vehicle to mount a small-ish panel, and you are handy and understand your vehicle's electrical system (though this may be tough with newer models since everything isn't controlled by simple switches any longer).

Basically, mount your panel, and install a block diode if it doesn't already have one, then run the wires (positive and negative) to your battery to keep it charged.

Then, all you need to do is hook up a switch to your blower motor inside the vehicle, along with a simple speed controller (for this, it's best to use a cheap 12 vdc PWM controller - don't try to use the "low speed" resistor if your car uses a resistor pack, as it might not keep it cool enough) - so you can turn it off and on, and control the speed of the fan - while the car is parked and "off" (no-key).

Park it in the sun (of course), set the vent controls to allow air in from the outside (hopefully it stays this way when the car shuts down - if not, you'll have to figure out a way around that), crack your windows slightly (1/4-1/2 inch), then shut off the car. Flip the switch and set the speed control for the fan to something "low" - the fan should run, but not at hurricane speed.

Then get out and close/lock the doors. Air will be drawn in from the cooler outside, blown into the cabin, and exhausted out the windows.

The battery will stay charged from the solar panel.

If you are concerned about the battery being run down when the sun sets, then:

1. You can optionally use a separate battery to the fan, with a blocking diode to keep the fan from using energy from the car's battery.

2. Or you can add a thermostat to detect and only run when the sun is beating down hot (this could be in addition to the PWM control - so the fan doesn't run all the time, only when the cabin gets too hot).

3. Add a photoelectric switch to disconnect the fan from the battery, when the sun goes down.

4. A simple way would be by just wiring a standard Bosch SPST automotive relay (the coil) in series with the panel, and the fan across the contacts - when the sun goes down, the relay would open up, and shut off the fan.

Note that this car ventilation mod does not require an Arduino, so you might not become popular or upvoted on the tubes, but your car might be cooler in the summer...

I'm pretty pro-solar and would be interested in seeing this on cars, but I'm very doubtful rooftop solar could ever run an AC continuously. Cooling air requires A LOT of energy.

Assuming 0.7kwh in 6 hours of daylight, that means the solar cells are outputting ~115W. It's hard to estimate exactly how much power is needed to cool a Prius, but 115W seems far less than sufficient. Traditional car air conditioners run directly off of mechanical power from the engine for efficiency. Home window air conditioners typically draw 1000W-1800W. A Tesla user reports [1] that the Tesla electric AC takes 2.4kW when starting up and then switches to a steady state of ~600W. Looks like [2] the Prius climate fans on medium take up 100W without the AC even being on. Coming at this another way, using this online calculator if we plug in 250 cubic ft for an estimate of the Prius internal air volume, assume high-quality insulation, and a 25°F temperature drop, this online calculator says that requires 1500 BTUs or 450Watts. [3]

That said, solar panels would still help somewhat! I also like the idea of exposing more people to solar and increasing general awareness around energy consumption (and how energy-hungry ACs are). Hope they do make it market in some form.

[1] https://teslamotorsclub.com/tmc/threads/how-many-watts-does-...

[2] https://priuschat.com/threads/power-consumption.14026/

[3] https://www.calculator.net/btu-calculator.html?roomwidth=6.2...

>> An EV with a solar array that generated just ~0.7kwh during 6 hours of daylight, would still be charging itself an extra ~20 miles of range per day while parked.

An EV uses ~250wh/mile. This varies a bit for some, but none of them are going to come close to 20 miles in .7kwh. Maybe 3-4 at most.

The ability to use something like this when left parked at an airport would be nice, though. Though I suspect that readily available 120V outlets is actually a cheaper option in the long run, relative to deploying panels on every car.

Sorry, I mixed up my units, I meant "average of ~0.7kw per hour, for 6 hours, for a total of 4.2kwh per sunlight-day". That should get you 16 miles in climates like mine, or up to 20 miles in clearer/warmer weather.

That seems like a very realistic/feasible figure. (Lightyear One's claims their prototype car can pull almost 2kw per hour (7.5 miles of charge per hour), which at 6 hours, earns you 12kWh per sunlight-day)

Pedantic note:

It’s not “.7kW per hour”.

Watts is a measure of power, it’s already Joules/second.

You just want “.7kW”.

For 6 hours, you still won’t get 4kWh, because you need to adjust for less than ideal angle, and less than full sun days.

But if you got 3kWh on a good day, that’s still 10-12 miles of additional range.

I think that is incredibly optimistic for a production vehicle. I think it is likely that production vehicles with setups like this will have one 350 Watt panel on the roof. A typical house roofmount of the same would produce ~1.5 KWh per day.

Car environments tend to be worse than that due to the angle and likely regular proximity of even mild shading. Its certainly enough to eliminate vampire drain, which is helpful at times, but I don't see how it will add an appreciable amount of mileage otherwise.

This isn't new in the least. My 2010 Prius had solar panels that did "dog mode" - running the fan.

Why Teslas don’t—and can’t—have solar roofs [1]

The top of an electric car has maybe 3–5 square meters of flat space.

Solar panels, even at high noon, usually only produce about 200 watt-hours per square meter.

The most efficient production electric vehicles today (probably the Hyundai Ioniq and the Tesla Mod 3) would only be able to travel 2–4 miles on that amount of electricity…in an hour. Most people could walk faster.

Financially, the cost of the panels and electronics, R&D and assembly would never pay for itself in the life of the vehicle, compared to charging from the wall in your garage.

While it might be nice to have for cars that sit there for a while or in the apocalypse. Right now it is better to use home solar panels or charging, as they have more surface area. Or maybe build parking structures with panels that can charge with more area. Maybe one day when they are small enough or can pull in sun into a smaller surface areas it will make sense.

Solar panel cars would probably also really up insurance rates and add more safety work/R&D.

[1] https://qz.com/1482588/why-teslas-dont-and-cant-have-solar-r...

I have issue with this: these panels would still capture enough energy to drive at least 2-3k kilometers annually - that's at least 10% of your typical annual mileage, so nothing to sneer at.

It doesn't get around the fact that it still makes way more sense to put those panels on your house roof and charge from that. The house roof is in direct sunlight for much longer than a car.

> It doesn't get around the fact that it still makes way more sense to put those panels on your house roof and charge from that.

On a car it also acts as a range extender and emergency backup (if you're out of battery and the car is engineered for, you can crawl along at the charge rate or wait a bit for a better charge). It's not great, but being to "walk" with your car might save your ass.

And if the car is designed around this idea (à la lightyear one), you can increase things further (the LY1 folks advertise a solar charge rate of up to 7.5mi/h WLTP with no A/C).

If solar panels are the bottleneck then they shouldn't be wasted on people's rooves, either. They should put them in a big field where the electricity company can point them in the optimal direction, perhaps with a device to redirect them during the day, or mirrors, and look after them properly: clean them, if that helps, or whatever.

Tracking and concentration is not cost effective, so it’s just a tilt advantage.

Solar panels in a remote location need to be converted from DC to AC for transmission, then transmitted long distances with associated losses, then converted to DC again to charge the car, stored in batteries in the car with associated losses. A solar roof could actually be a net gain assuming the energy is used while the car is in motion, and it’s used near the equator so no tilt required.

That is an excellent point - if you have a house. It might make more sense for people who have to live with streetside parking?

Why not do both?

Because resources are scarce. If solar panels were free, then yeah let's plaster them everywhere. But let's start with where they make the most difference.

Because very few people have covered every last spot on their roof so you would be designing a product suitable for very few people

Or for people who don't own a roof at all - plenty of such people in cities.

Those people also have their cars in multi level car parks with no sun so that doesn't work for them either. In that case they would be better having the car park have solar and the local government building solar farms. A panel on something almost always undercover makes no sense.

I live in an average residential street in Europe full of 3 story residential houses. Our house with 6 apartments has 3 garages, the majority park on the street.

Sure, the government or the electricity company could just install car chargers and put a solar plant to power that in some rural area. But if I want something now then buying a car is much simpler than lobbying for that.

Very few people have electric cars to begin with, and they're really expensive compared to ICE vehicles so you're already talking about a demographic that's demonstrated a willingness to pay a premium for driving an electric car.

If Tesla offered a "Solar Panel Kit" that made their cars even a few percent more efficient it would sell like hot cakes.

And on every parking lots...

put the panels on your roof, where they are in the sun more often, and cheaper to install.

I don't drive to work, but 2 miles per hour would be crazy good for me, as I live inside a city and my total commute is exactly 18 miles, which would mean my commute would be "free" (not taking into account the cost of the panels or the vehicle).

It's also unrealistically good as you don't get high noon insolation for 9 hours a day.

You do however get some power for more than 9 hours per day. Also, panels can go well past 200w/m at a theoretically possible 600w/m the numbers look rather different. Cars are only going 12-15k miles a year so hit 40miles a day and you generally stop needing charging stations.

The amount of power incident from the sun is roughly 1000 W/m^2 in a sunny area. Good Silicon PV panels will capture 20% of that power generating 200 W/m^2 at peak. Getting anything more than that is going to be too expensive for a car application.

Pulling 600 W/m^2 from a PV panel may be theoretically possible, but the world record efficiency for a PV device is still less than 50%. To get above 40% efficiency you need to use very expensive multijunction devices and solar concentrators (i.e. not going to work on a car).

I generally agree today, but that says little about the long term.

As solar panels have gotten cheaper installation costs have become more important which has pushed up panel efficiency. Cheap but good panels are up to ~23% efficiency where they where ~18% fairly recently. What’s interesting is these trends seem to be continuing with serious research into various affordable multi junction cells going on.

That means it has to sit directly under the sun all the time.

If you get the plugin Prius, you can already not pay for gas at all with short commutes. And it cost almost half of Tesla Model 3.

Yeah how many people want to park their car in the sun all day long?

The better way is parking it in a garage of small to large size, that has solar on the roof, with a much bigger surface area, that you could plug into.

Another bad part is that since solar is still in heavy innovation phases, you'd need to be able to swap out panels for replacement and newer tech so there would need to be standards there or else it becomes highly cost prohibitive. It would add so much to testing that it would add layers of cost. This would also limit design options and weight.

Even when efficient, you still want to park your car in or under a cover/garage. That is the best place to put the panels because noone wants a hot car.

Isn't it a case of the better killing the good ?

From your excerpt is seems electric panels still give 2-4 miles of range per hour of charge. Even taking into account the added weight, it's a net positive so why dismiss the idea completely ?

Honestly it seems like a nice idea. The idea that a car can go _entirely_ on solar on it's roof is clearly off-limits for now, but that doesn't disqualify the idea entirely.

Say I use my car for the daily commute and I'm some 10 miles away from office. I work 8 hours in the office in daytime, and leave my car in the parking. For when I'm going back home, my battery would be topped up.

I'd need to recharge my car much less, once a month maybe.

Also, say you can do 300 miles with a full charge. Depending on how fast you go, you'll do those 300 miles in 5 to 10 hours. So on average, a the solar aid would give you some additional 15 to 30 miles, ie 5%-10%. Which sounds nice to me.

All with the current technology. Obviously there are tradeoffs, in R&D, price and weight.

But it seems like worth pursing, log-term.

The folk building Lightyear One [0], a fully solar powered prototype car, would disagree with the assertion that it is off limits for now. Obviously the car is quite different from a Prius or any other modern car.

[0] https://en.m.wikipedia.org/wiki/Lightyear_One

I would be very surprised if that car could meet crash-test standards to be sold at large scale. If you don't have to meet crash test standards, you can make a much lighter car than you can today.

That actually sounds pretty useful - say the car gets 10 hours of perfect iradiation on a good day, that's 20-40 miles, that could be a sizeable part of a daily commute, not to mention cases where you have the car standing still for a few days.

That would be more like 4 hours. A car solar panel would be horizontal, and it wouldn't track the sun when it's lower on the horizon. The 200W figure is only for noon.

Solar panels in Germany produce about 10% of peak power if you average over the year. Those panels are generally installed in the correct orientation to maximize efficiency. Panels on a car will likely perform much worse.

> Even taking into account the added weight, it's a net positive

You just gloss over the most important part of the question right there. At a charging rate that low, even a small amount of added weight may completely destroy the plausibility of this idea.

If it can generate enough energy to move the 1 ton vehicle for 2~4 miles, it seems it's pulling its weight, literally.

If your daily commute is short, solar panels could provide enough energy to not worry about charging

Or if you don't have a daily commute at all. Perfect for those who could switch to the occasional taxi or rental but stick to owning a car due to cultural inertia, perfect as that fallback family car that only gets used when the family fleet is fully saturated, perfect for the plugin hybrid that never gets plugged in due to the inconvenience of keeping two kinds of energy storage stocked.

Read it again:

> would only be able to travel 2–4 miles on that amount of electricity… in an hour. Most people could walk faster.

I got it wrong the first time, then got it at the second take, thought I had it wrong again reading your comment and turned around again. The writing was weirdly misleading.

> Solar panels, even at high noon, usually only produce about 200 watt-hours per square meter.

> The most efficient production electric vehicles today (probably the Hyundai Ioniq and the Tesla Mod 3) would only be able to travel 2–4 miles on that amount of electricity…in an hour. Most people could walk faster.

From what I get:

- in the best conditions the panels could produce 200W in an hour

- 200W would allow for 2-4miles on the most efficient cars

The author's point seems to be that if the solar panel was the only source of energy the car would be slower that walking. It's different from seeing it as an additional source of electricity, just like regenerative braking is for instance.

> - 200W would allow for 2-4miles on the most efficient cars

Sorry, but that's wrong. They meant 2-4 miles per 1 kWh, not per 200 Wh.

Very good EVs get about 4-4.5 miles / kWh at optimal speed (usually between 25 and 35 mi/hr). So, best case, 200 Wh is good for about 1 mile, assuming you can deliver the 200 Wh over a period of 2 minutes.

However, 200 W can't push the car at 1 mi/hr because of "vampire" losses: Power for accessories and vehicle systems (like power-assisted steering, power-assisted friction brakes, the ABS controller, the airbag monitor, etc). 200 W of power isn't just slower than walking: In a normal-sized car, you will literally go 0 mi/hr.

More importantly, 200 W/m^2 is the best-case scenario at noon, in the tropics, on a cloudless day, with no shadows, using expensive, high-efficiency panels aimed squarely at the sun. As soon as any of those qualifiers is not met, power drops precipitously.

In particular, the atmosphere absorbs a large amount of light: In space, solar insolation is about 1300 W/m^2. At earth's surface in the tropics, solar insolation is about 1000 W/m^2 at noon. At higher latitudes, or other times of the day, solar insolation is lower.

A good rule of thumb is that (for Europe and North America) the total insolation over a full day is about 5000 Wh/m^2. So, a solar panel on a sun-following mount is limited to about 1000 Wh/m^2/day, again assuming no clouds. For a fixed solar panel, such as on the hood of a car, you'll get about half of that: 500 Wh/m^2/day. Remember, you need 1000 Wh to go 4-5 miles.

"Remember, you need 1000 Wh to go 4-5 miles."

That "4-5" implies a lot of accuracy, but I would have thought that the distance you can travel on 1000 Wh would vary by orders of magnitude depending on the speed, terrain and road surface.

However, if you are moving a 1 tonne vehicle up a 5% gradient then you won't do more than 4.5 miles on 1000 Wh, if I've calculated that correctly.

I drive a gen1 Chevrolet Volt. Plugged into a 110V outlet it adds about 4 miles range in an hour. This is enough to make its benefits worthwhile.

>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.

50km is just as many kms as I commute to work during a week. Perfect prototype for me already. For longer trips I prefer motorcycle.

50km a day in charge capacity is the absolute best-case scenario. In reality you should count on half of that.

What you gain in additional charge will offset the AC power draw you need to cool down your car after you parked it in the sun for a full day.

A more effective solution would be to have a carport with a solar panel roof (10~15m2) that way you have shade, affordable panels, and an actual charge capacity of about 50km. It doesn't move with the car, but since we are talking about work commute your car will probably be parked at the same location for 5 days/week during peak sun output.

Mind you that the panels used on the Toyota prototype are still very expensive. At current prices they probably don't make economic sense.

> A more effective solution would be to have a carport with a solar panel roof (10~15m2)

Right. Or from a pure economics point of view, put the solar panels literally anywhere else in the world other than on top of the moving vehicle that is sensitive to aerodynamics, weight and structural integrity. Deal with the small transmission losses from the grid. Rely on charging stations at home, work or other businesses. The last part is the only piece that isn't reliable at the moment, but is only getting more so.

Parent's point with the carport is that it would also keep the car from heating up in the sun. "Anywhere else" doesn't necessarily provide the benefits he's talking about.

Sure, build carports where they make sense, and put solar panels on roofs where those are economically worthwhile. There are not especially large synergies between solar power and carports compared to other permanent structures, it's just an example of something that is still superior to solar panels on cars.

To be fair, on top of moving vehicle is still better than under moving vehicles ala Solar Roads

Not only they got publicity and kick-starter funding they even got cobtracts from local government! And there are copycats also with government money.

Can someone explain this to me a bit? How one manages to not only promote such an obvious flawed idea to implement, but actually inspore others to copy them?

Are there any lesson to learn from that for projects that actually work?

>50km a day in charge capacity is the absolute best-case scenario. In reality you should count on half of that.

I'd count on even less than that. Industrial solar farms average a capacity factor of around 20-25%, dropping as low as 10%. And that's with farms built for maximizing sunlight. A car is likely to do far worse, especially when you consider imperfect conditions, and how frequently people park indoors. If it's a tossup between protecting my car from the elements, and getting a few miles a day of charge, I'm going to choose the former.

If you read the sentence closely, it's actually claiming ~25km/day of charging, to drive 50km 4 days a week.

I wish more people would respond to this comment rather than debate the benefits of putting solar on a ferry. Is there data on the avg commute distance in different cities? 50km seems like a significant distance and could cover a large number of commuters.

cars are used around 10000 km per year in Germany by what I found online. That’s around 30 km per day.

Americans drive around twice that much. The latest number I could find was 13,476 miles per year for the US.

I use my car for 6km per day, but I do 700km in a day on motorcycle on a weekend day.

Anecdotally 140km between Glasgow and Edinburgh (round trip) so it seems like inter-city commuting is probably out.

Virtually no one in the UK is doing this, this is an absurd answer.

80 miles (128km) a day is a pretty harsh commute I used to do, the vast vast majority are doing significantly less than this.

When I used to regularly visit Bristol, I got to learn quite a few that used to commute to London from Bristol and Bath surrounding areas.

The vast majority of people don't commute 140km a day.

That’s an extremely specific single example. Can we really usefully generalise from it? Maybe some cities are closer than these two?

Glasgow also has only 1201 annual hours of sunshine, less than 3.5/day. What a strange example to choose...

Anecdotally I live 8km from work (same city, Europe), making a 16km/day commute.

That seems on the high end of a traditional commute; given traffic that takes, what, nearly two hours each way?

I used to do 80miles (128km) a day with harsh traffic and that was 1.5 hours each way(40miles). so yes you are right it's much closer to 2hrs than 1hr.

It's closer to an hour, than it is to two.

You also need to remember that the Prius Prime has just a laughable battery capacity relative to a Tesla. Like less than a twentieth of the batteries.

Among other things this means you can meaningfully charge the Prius's battery from the solar hitting it on a daily basis, even though it would take weeks to fully charge a Tesla.

if you park and drive in the sun all day. No clouds, no garages, no trees, etc. It would usually be more sensible to put the panels on your roof, to plug your car into.

I think the appeal of solar panels on a car roof is that you don't need any infrastructure at all. Just park you car wherever and it automagically recharges.

But you cannot rely on that every day. On cloudy day it’s not going to help you. So while it maybe fine for a PHEV, I still think than having PV installations over every parking lot makes more sense.

>I still think than having PV installations over every parking lot makes more

If this was a planned economy I would agree and vote in the next party meeting to put chargers in every parking lot and power them with transparent PV over the parking spaces.

But since I live in a capitalist country I can't make other people invest tens of thousands of dollars just because it makes more sense than putting solar panels on my car. I mean, in some cases I still can, but there's a significant market for the people that can't effect such a change and have to make due with the less efficient solar powered car.

Exactly. Home ownership is at 64% in 2018 in the US. Solar roof installation requires landlord/HOA permission and permits in apartments/condo units. Lots of cars in the southeastern/southwestern US are parked in direct sunlight. At the very least, getting into an ambient temperature car is a great feeling in these places

There would be a lot of permits though, delays, etc. I like the idea of having smaller panels as one offs.

Unless you park in a garage, which a lot of people do.

And a lot of people don't. There's way more cars than there is garage space.

So everyone will park in the sun and not near trees or buildings.

Garage is just one example where there is no sun.

Yes, and since this is a product specifically marketed to people who live in the area of the world where 100% of parking spaces is shaded it's obviously a bad idea.

What if they instead sold it to people who usually park in non-shaded parking spaces? Would that work, do you think?

Parking garage at my office park doesn’t even have open-air spaces on the top floor: the deck is covered with solar panels.

The Prius used to have an option for a solar panel roof before (the article mentions this) - and all the tiny panel was used for was to run the cabin fan to keep the cabin a bit cooler if you ended up parking in the sun.

The difference with the cells in the article is they are 0.03mm thick so they don't weigh as much and can be curved around more car body parts.

To gain an understanding of what a near-useless idea it is to put solar panels on a tesla, go here:

https://pvwatts.nrel.gov/

plug in a prototypical 1000W PV system at your latitude and longitude, as if it's on the roof of your house. That would be four 250W panels.

Look at the kWH produced per month in mid summer, and again in mid winter.

Using Seattle as an example, estimated production of 147kWh per month in mid summer, and 34kWh in the worst month of winter.

Now look at how many kWh the capacity of a tesla battery (70 or 90 or 100kWh) is for a single full charge.

147, divide by 31 = 4.74kWh per day

Those estimate figures for pvwatts are pretty rough, but they also calculate based on having near direct sunlight from sunrise to sunset, as if the PV panels are on the roof of a building or an unobstructed ground mount. Cars are frequently in the shade.

Realistically, if you were to somehow magically cover a Tesla in 1000W of PV, and it was all flat-angled optimally to catch the sun, you might get 3kWh a day if you were really lucky.

There is really no practical reason why the photovoltaics needs to be ON the car. Putting high efficiency pv cells on curving surface is expensive and hard. The PV can be on a roof mount covering your closest grocery store, home depot, car repair garage, public school, and so on, feeding the grid.

If, on the other hand the solar panel would unfold during parking over the parking space (like spacecraft unfold their solar panels in orbit), you could get about 5 times more power... and you car would always be in the shade.

That sounds heavy

> It is so annoying when people tell me their genius idea, putting solar panels on a Tesla.

Why? People are wrong about stuff all the time. Often more committed to worse ideas than this. What about this particular instance of them being wrong annoys you so?

> What about this particular instance of them being wrong annoys you so?

While I can't speak for the person to whom you're replying, I can tell you why it is annoying to me, and that is very simple. In this thread there are basically two kinds of posts:

1. Posts about the physics of why solar on cars is basically a bad idea (or at least a massive waste of money in the face of much better alternatives).

2. "Yes, but have you tried turning your head sideways and squinting at it like this [...]"

For some reason, solar-on-cars brings out the #2 in many otherwise smart people, and it's extremely tiresome to constantly slap down the nonsense. Because, I think, they really, really, really want to believe it can work.

> People are wrong about stuff all the time. Often more committed to worse ideas than this.

Yes, but when you show them why those ideas can't work, using numbers and science, they abandon those ideas.

> Yes, but when you show them why those ideas can't work, using numbers and science, they abandon those ideas.

This is empirically not true: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.357...

There is probably selection bias in the sort of person who would think it's a genius idea and an oversight by thousands of engineers for decades. Then account for the type of person that would make such a statement to a stranger. I'm guessing this set of people can be a bit annoying in general.

Yeah, what Tesla is doing instead is investing heavily in the infrastructure - charging stations, batteries, and I don't know if they operate solar power fields but they also do solar panels and installation. So if anything, Tesla is doing a lot with solar panels already - just not on their cars for the aforementioned reasons.

We have a few electric ferrys in Denmark, so it’s certainly possible, but they obviously aren’t charged by onboard solar or wind power.

Wind power ferries. I think they tried that in the days before electrical motors.

There's an article in a recent issue of IEEE Spectrum about a plug-in hybrid ferry:

https://spectrum.ieee.org/transportation/marine/happiness-is...

It can cruise purely electric, although with just 100 kWh of battery capacity, the net result is a 30% reduction in diesel consumption.

There's a good video on a Denmark to Sweden ferry that is fully electric: https://www.youtube.com/watch?v=rE_M1n-ClOA

One way of helping people internalise this is to point out that 1ph is, to a first order approximation, 1kw. The same as many electric heaters.

A typical solar panel is 100w in peak conditions. It's then easy to visualise what powering something with solar panels might entail if you can make a guess at the engine HP.

Even a small ferry is likely 2000hp+.

> A typical solar panel is 100w in peak conditions

That doesn't mean anything. A standard panel (1m×1.9m) has a peak power of 300W.

What we must compare is the solar radiance times the efficiency of the panel, and multiplied by the surface, would give you your available power

And 1hp is actually 745.7w. It makes very little difference with regards to the big picture of whether something is feasible. Whether you tell someone the ferry is going to need 20,000 solar panels or 5000 it's still way more than reasonably be put onboard.

The solar factor usually employed in the UK is about 0.1 to get from nameplate capacity to actual production (accounting for hours of darkness and suboptimal atmospheric conditions) so it would be reasonable to assume your 300w is actually more like 30w.

At least some percentage of solar panels on our hypothetical solar power ferry are likely to be in shade or not pointing directly at the sun. Then you have various conversions and charging losses to get the power into a usable form.

I was talking about the assertion, not about if it was feasible or not.

I was talking in broad strokes about how to encourage someone to have an intuition of the power requirements for such an endeavour. I was using easy round numbers not asserting exact numbers.

Note that the solar panels are not necessarily the primary energy source, they can do trickle-charging, range extension and/or emergency recharge / supply (e.g. when you've run out).

These are roughly the use cases lightyear one tends to cover, under a somewhat ideal 12km/h WLTP (that is in good sun the panels can charge 12km worth of WLTP range per hour, which can extend the range during a drive, recharge a parked car or let you drive at 10~12km/h when the batteries have run out).

Yeah, that’s a good way of looking at it. Note that a typical modern solar panel is around 285-340 watt these days.

My favorite "genius idea" that comes up regularly is to have people running on treadmills and pedaling stationary bikes use the power they generate to power the gym or whatever. The amount of energy that treadmills and stationary bikes can generate from human power is absolutely trivial. Even given high electricity rates, it's worth about 3 cents an hour. The energy generated can barely power basic electronics on most self-powered exercise bikes.

My gym actually does that. The elliptical machines actually tell you how much power you're generating. Going at a moderate pace generates about 90 watts. That's enough to light up about 10 modern light bulbs.

You're going to be generating that energy while working out anyway and it has to go somewhere. I think the biggest benefit is being able to direct where that energy dissipates. You can either put those 90 watts into the air as heat through friction, or put it into electricity through some dynamo. The second choice will make it so the place doesn't heat up as quickly.

> My gym actually does that.

Do they really tell you how much energy they are harvesting as electricity or do they just tell you how much energy they are dissipating as heat?

Because it is very common for sports equipment to measure/estimate the power applied by the athlete, in watts, all without the slightest trace of harvesting implied.

The bike trainer I have tells how many watts I produce and how much is sent back to the grid, the number isn't high so is more geek stats than anything else

Don’t ignore aesthetics and installation costs of plug powered gym equipment vs. muscle powered equipment. Customer generated electricity allows to place equipment everywhere in the gym. Gym does not need power outlets for every piece of equipment and to have exact floor plan in the very beginning. Gym can rearrange equipment periodically delivering better experience for clients. You need 20 Watts to power Raspberry Pi running under load. Basic electronics with couple LEDs need only 3-5 Watts. Even less if designed properly, so this way generated energy can very well power gym equipment. I think, I can generate 100 Watts.

> I think, I can generate 100 Watts.

> Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of work.

That's before conversion & transmission losses (especially as the converter will need to handle wildly varying inputs)

And even if we ignore these, according to 10.1109/MSPEC.2011.5910449:

> Let’s assume that the average piece of exercise equipment is in use 5 hours a day, 365 days a year. If each patron generates 100 watts while using it, that machine creates some 183 kilowatt-hours of electricity a year. Commercial power costs about 10 cents per kilowatt-hour on average in the United States, so the electricity produced in a year from one machine is worth about US $18 dollars.

Also, don't forget the gear to capture the electricity isn't free, is more stuff that can break and incur maintenance fees, must contain purified metals and other non-zero carbon emissions, and so on. Trying to break even on all of this off of human labor is a silly game to play when there are so many other better opportunities. And that $18/yr is already inflated by enough factors that $1/yr is probably a much better estimate.

Same for these solar panels on a car, too. Solar panels aren't the nicest things to manufacture right now. Putting them on a platform this poor is silly when you could put them somewhere more effective. If they were dirt cheap and harmless to create, opportunity costs might be less of an issue, but even today, they aren't dirt cheap and the aren't harmless to manufacture. They should be used effectively, not for show or feelings.

A bit off-topic, but I've never exceeded 6w of power with raspberry and I have monitored it out of curiosity a lot.

Also, treadmills aren't powered by the people on them, but rather use a lot of electricity to move the tread (and usually a tiny bit more for the electronics).

They have self-powered treadmills. They're not very popular though: https://www.woodway.com/products/curve/

Yeah, they're really weird an uncomfortable until you get used to them, so people just see them as worse treadmills.

All I really want is a stationary bike that powers a fan pointing at you to cool you down because I'm a sweaty bastard.

That has been done many times. Products like Racermate Wind Load Simulator in the 1970ies, more recently the CycleOps Wind or the Lemond Revolution. In fact, all "trainer" devices where a regular bike is attached for indoor use are still colloquially called "turbos", in fierce defiance of Elon Musk's sudden love for semantic precision.

They all suffered the same fate: when the hundreds of watts a well-trained athlete will produce during interval training is put into air movement, the noise is just unbearable. Much quieter setups are possible with more direct conversion to heat and even there, noise is still the dominant product metric.

On a related note there's a pretty entertaining NPR video breaking down whether or not you can power your house with a bike - https://www.youtube.com/watch?v=xbUxt2x4InE (spoiler alert - you can't :))

I worked it out and even if I pedal 8 hours / day and somehow convince the wife to join we're only producing 2kWh / day. Our house's power usage is ~11 kWh/day in the winter (worse in summer due to AC)...it's hopeless.

Most of the gym equipment I use, with the exception of treadmills and stair climbers, is powered by the operator. It only turns on after using it for half a minute.

Phones and tablets need 10 watts or less. A notebook somewhere between 25 to 50 watts if it is running at 100% CPU. Why would an exercise machine with a similar screen size need more than that? Even a total beginner can generate far more than 50 watts.

It's a cool DIY project though. I've been wanting to do this for ages (though I might want to get such a bike first and actually use it), and a while ago I saw this big nose YouTuber actually do this and they (barely) managed to run a gaming PC off of it. Which is a neat spin to the whole idea: No workout, no gaming.

> treadmills [...] use the power they generate to power the gym or whatever

That's... not even wrong?

ask a bike courier how much they spend on food each day, to maintain a 5000 calorie per day existence. Calories cost money.

Hardly, you could easily cover any extra energy needs with a few spoonfuls of olive oil worth about $0.005

GP is talking colloquially, they're talking about "large calories" (food calories, Calorie, …) aka 5000kcal. FDA recommendations is 2600kcal RDI for a healthy lightly active adult male.

The "extra energy needs" is 2400kcal, olive oil is 884kcal/100g, that's 270g of olive oil, about 300ml.

That's pounding down half a standard bottle every day, and at least a buck or two. Aside from getting cheap as hell olive oils, you seem to use ladles for spoons.

Slightly different motive though.

If your car is hanging out all day at a parking spot, say in front of your office building, or just on the streets, it might actually charge a large battery enough to get you a chunk of the way through your trip.

It could make plug-in hybrids the norm, even if you don't have a place to plug. For many people, their cars sit idle 80% of the day, if not more. Even if it charges enough for a quarter of the way to your house, that's a quarter more of not needing fuel.

Right now I fill up my regular prius once a month. With this I can see that changing to once every 3-5 months. A potential of course, not saying this will work.

That's the idea behind it. Not to power it as it drives.

Yeah there was a new building built in our city with wind turbines on top that everyone was impressed with because "They could generate their own power." The thing is that I remember hearing that the amount of energy wind turbines can generate depends on how big their blades are and these turbines looked really small. It took some digging but eventually I found an article that said the turbines will generate less than 5% of the buildings energy requirements at full speed. I mean that's not terrible, but then again they spend a lot of time not spinning at all let alone full speed...

I've sailed on ferry type boats in Norway that were electric. However they were charged from the grid when docked via two 415V 3-phase connections at hundreds of Amps. Power from hydro, of course.

I am thinking that this is mostly marketing.

Plus, installing PV on a car is not new. Half the top tier engineering department in the US have a setup for that, some are nearly 20 years old. But PV have come down in price, they’re still not very efficient, and the benefit will be marginal. I’d rather install PV on every parking lot instead, that way it is always connected to the grid. Unlike the car which is only connected when plugged in.

> Tesla is sexy

I found them banal in most cases, at least including 3. Also they are technologically pieces of shit in terms of value for money since it's not worth giving at least $60,000 for a car that isn't even enough for very long trips without stopping to recharge.

This, unfortunately, extends to the rest of the world's energy usage:

https://en.m.wikipedia.org/wiki/World_energy_consumption

Don't buy any coastal property! Unless you're 70 and don't care about leaving anything behind. The sea water will come.

The Intergovernmental Panel on Climate Change's high end estimate is 90cm sea level rise by 2099. So if your costal property is at least 90cm above the water you might still think about it.

You can buy land high enough on the coast so your offsprings will get rich. Obvious you need free money to do that.

Do you know WHY you put solar panels on top of a car? Because everyone has the genius idea of putting them there. It isn't about how well they work, it's that people will pay more to buy a car with them.

> BTW, if you take the ferry to Alcatraz, they will try to impress with you solar panels and a helical wind turbine on the ferry itself.

I missed that the time I went to Alcatraz - but it was probably because it was a night tour...

What about a decent sized solar array + batteries at each ferry terminal, and relatively fast transfer to the ferry of however much power is needed for the trip.

wait until Elon makes car solar tiles. Tesla Scales (c) me.

It's true a car surface is ridiculous. Now on a van, bus or truck .. this could make for some nice juice.

Curious, but would the larger surface area of a bus or a truck be more suitable?

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