Solar PV on electric cars

[hendorog]

So, say I'm buying an EV in Auckland. One has solar panels and the other doesn't.

The one with solar panels states that it is on average, 25% more efficient than the other one, during the summer if it is parked in the sun. That statement is fair.

P.S. This isn't the final answer, its just something that has occurred to me as this thread has gone on.
P.P.S. General reminder that this thread is a puzzle. It says so in the first line of the OP. I want to see who is open minded enough to figure it out. Confirmation bias is the enemy in this thread.

Your statement is not fair because it includes unstated and unjustified assumptions based on speculation and zero real world experience, as far as I can tell.

I'm sure you think yourself very clever, puzzles and all.  I'm amazed at the strength of opinions expressed here contrasted with scarcity and incorrectness of information.

I actually own a solar system that I designed and planned myself. to make my net electric bill virtually zero  I also actually own an electric car--which happened to be the most efficient (kWh/mi) one on the market when purchased.  I've sat down and figured out (roughly) how to implement solar panels on two different vehicles--the Focus and the old Ford Ranger Electric (pickup truck).  The Focus is impossible and the old Ranger maybe might have worked a little bit because it would have been a lot easier--it could essentially use two regular 60-cell panels cut up and reconfigured.  I ended up not pursuing the Ranger because they are scarce, old, not cheap, and I didn't need more projects (it would have required redesigning the battery as well).

My point is not that I'm smarter than you or that I know everything.  It is that this subject has been considered by many and actually implemented in few cases.  As of yet, nobody has shown me a system that has any meaningful technical advantage at anything remotely close to a viable price.  If a 5% (or less) increase in range or reduction in electricity costs is worth $5000 to you, great.  Please note that even Tesla, who are able to sell very expensive cars with expensive options, haven't offered anything like this, despite clearly having the technical capability--if anyone does--to implement car solar charging.

It is not about who is smarter. I also thought it was a stupid idea. So did tautech initially.
But then was simply a random thought that occurred to me and I thought would stick my neck out and challenge the general 'common wisdom'. What has come to light is that there are even more benefits than I originally realised. Clear proof that I'm not that smart

And yes, this is pretty abstract. It's all a bit loosey goosey.

And I agree, that 5% increase in range is not that important. But the PV benefit is per day, and you don't need a full charge every day. How far is the average daily commute? Work out that as a percentage.
What could you do to your EV to get that sort of gain? You said you got the most efficient one on the market, so it was something you valued. I would too. But the solar one will eat its lunch all day long and twice on Sundays.

Tautech sent me this link, which has already been mentioned in the thread.
These bleeding edge multi junction cells might cost $5k at volume to slap on the car if/when they ever get to production. I have no idea what these cost, but I'm sure they are very expensive at 34% efficiency. Does anyone know what the state of play is with multi-junction cells getting to production?

But the point is, this thing gets a range of more than 40kms on solar alone. That $5k-ish and my sunny car park would get me to work and back at zero fuel cost.
https://techxplore.com/news/2019-07-toyota-solar-panels-electric-cars.html

Yet at the bottom the editor still felt the need to say:
"As we always like to point out with these solar car efforts, a car's roof is not the most ideal place to install solar cells. They would most likely be more efficient installed on the rooftop of a home and then, you can use the power to charge your vehicle."

Really?! They have just seen a working (albeit experimental) example of a commuter car which for most people potentially would very rarely if ever need to be filled up or charged, and yet they still think putting solar panels on the car is the wrong thing to do. I'll try very hard not to be judgmental on that one.

And that wasn't even the benefit I was thinking of when I started the thread actually. I had no idea that they were getting that sort of range out of solar on a road car. I had something else entirely in mind.

But anyway, if you don't want to participate, then don't.

[tautech]

It is that this subject has been considered by many and actually implemented in few cases.  As of yet, nobody has shown me a system that has any meaningful technical advantage at anything remotely close to a viable price.  If a 5% (or less) increase in range or reduction in electricity costs is worth $5000 to you, great.  Please note that even Tesla, who are able to sell very expensive cars with expensive options, haven't offered anything like this, despite clearly having the technical capability--if anyone does--to implement car solar charging.

You assume viable based on your own metric and that's fine however I ask why you've gone solar to the degree to reach zero cost ?
Surely the investment required means the cost is indeed not zero so you must have done it as your contribution to reducing pollution, correct or is there another reason ?
If the presumption that it's your contribution to the environment and obviously at some cost to you would you not agree that the cost of adding PV to EV is also a contribution to the environment and also not without some cost.
It would seem wrt EV PV's you can't see also the benefits of less generation requirement that might seem insignificant for a single EV it's not for a country full of them.

Sure, those that use EV's are doing their bit along with some substantial purchase incentives of which could well reduce any additional cost of a PV equipped EV for further benefit of the environment.

[David Hess]

Is solar PV worth it on cars?  What is the opportunity cost?

The solar PV adds a couple kilometers to the range per day, assuming good conditions.  But the same cost placed into larger battery capacity adds even more range under any conditions.  So solar PV is not worth it.

[tautech]

Is solar PV worth it on cars?  What is the opportunity cost?

The solar PV adds a couple kilometers to the range per day, assuming good conditions.  But the same cost placed into larger battery capacity adds even more range under any conditions.  So solar PV is not worth it.

David, that's a very short sighted and selfish view.
There is a very much bigger picture to consider here.

[David Hess]

Is solar PV worth it on cars?  What is the opportunity cost?

The solar PV adds a couple kilometers to the range per day, assuming good conditions.  But the same cost placed into larger battery capacity adds even more range under any conditions.  So solar PV is not worth it.

David, that's a very short sighted and selfish view.
There is a very much bigger picture to consider here.

What bigger picture?

It is a waste of money which is better spent on either larger battery capacity or a fixed solar installation.

The exception is if you expect to park your car for long periods in the sun without using it like if you were camping out.  After a few days, you might have enough energy stored to get to a charger.

[bdunham7]

So, say I'm buying an EV in Auckland. One has solar panels and the other doesn't.

The one with solar panels states that it is on average, 25% more efficient than the other one, during the summer if it is parked in the sun. That statement is fair.

P.S. This isn't the final answer, its just something that has occurred to me as this thread has gone on.
P.P.S. General reminder that this thread is a puzzle. It says so in the first line of the OP. I want to see who is open minded enough to figure it out. Confirmation bias is the enemy in this thread.

Your statement is not fair because it includes unstated and unjustified assumptions based on speculation and zero real world experience, as far as I can tell.

I'm sure you think yourself very clever, puzzles and all.  I'm amazed at the strength of opinions expressed here contrasted with scarcity and incorrectness of information.

I actually own a solar system that I designed and planned myself. to make my net electric bill virtually zero  I also actually own an electric car--which happened to be the most efficient (kWh/mi) one on the market when purchased.  I've sat down and figured out (roughly) how to implement solar panels on two different vehicles--the Focus and the old Ford Ranger Electric (pickup truck).  The Focus is impossible and the old Ranger maybe might have worked a little bit because it would have been a lot easier--it could essentially use two regular 60-cell panels cut up and reconfigured.  I ended up not pursuing the Ranger because they are scarce, old, not cheap, and I didn't need more projects (it would have required redesigning the battery as well).

My point is not that I'm smarter than you or that I know everything.  It is that this subject has been considered by many and actually implemented in few cases.  As of yet, nobody has shown me a system that has any meaningful technical advantage at anything remotely close to a viable price.  If a 5% (or less) increase in range or reduction in electricity costs is worth $5000 to you, great.  Please note that even Tesla, who are able to sell very expensive cars with expensive options, haven't offered anything like this, despite clearly having the technical capability--if anyone does--to implement car solar charging.

It is not about who is smarter. I also thought it was a stupid idea. So did tautech initially.
But then was simply a random thought that occurred to me and I thought would stick my neck out and challenge the general 'common wisdom'. What has come to light is that there are even more benefits than I originally realised. Clear proof that I'm not that smart

And yes, this is pretty abstract. It's all a bit loosey goosey.

And I agree, that 5% increase in range is not that important. But the PV benefit is per day, and you don't need a full charge every day. How far is the average daily commute? Work out that as a percentage.
What could you do to your EV to get that sort of gain? You said you got the most efficient one on the market, so it was something you valued. I would too. But the solar one will eat its lunch all day long and twice on Sundays.

Tautech sent me this link, which has already been mentioned in the thread.
These bleeding edge multi junction cells might cost $5k at volume to slap on the car if/when they ever get to production. I have no idea what these cost, but I'm sure they are very expensive at 34% efficiency. Does anyone know what the state of play is with multi-junction cells getting to production?

But the point is, this thing gets a range of more than 40kms on solar alone. That $5k-ish and my sunny car park would get me to work and back at zero fuel cost.
https://techxplore.com/news/2019-07-toyota-solar-panels-electric-cars.html

Yet at the bottom the editor still felt the need to say:
"As we always like to point out with these solar car efforts, a car's roof is not the most ideal place to install solar cells. They would most likely be more efficient installed on the rooftop of a home and then, you can use the power to charge your vehicle."

Really?! They have just seen a working (albeit experimental) example of a commuter car which for most people potentially would very rarely if ever need to be filled up or charged, and yet they still think putting solar panels on the car is the wrong thing to do. I'll try very hard not to be judgmental on that one.

And that wasn't even the benefit I was thinking of when I started the thread actually. I had no idea that they were getting that sort of range out of solar on a road car. I had something else entirely in mind.

But anyway, if you don't want to participate, then don't.

You sound like a slick salesman--or someone who has been sold by one.

I didn't say efficiency was important to me, it just happened that way.  Range is much more important, as well as cost, reliability and ease of use--my wife drives it to work.

You are assuming the assertion that the car can gain 27 miles per day is supportable in a realistic use scenario.  If that's true, then that is a big step forward--even if the cost is astronomical.  So I figured I could put about 0.9 m^2 of panels on the roof of the Focus.  1.2 or so if I used the hood.  I see they've covered the back window as well, so let's assume they have somehow put on 1.5 m^2 of panels.  Or, provide your own estimate and justify it.  So my panels are about 1.5 m^2 each, they're about half as efficient as the VERY EXPENSIVE cells on the Toyota and they produce 1.2 to 1.3 kWh in the summer here in one of the highest insolation areas in the inhabited world, installed on a roof facing south and tilted at an angle that nearly maximizes annual production.  So if you parked your car on the south-facing elevated ramp that I posited earlier, perhaps you could get 2.5kWh per day.  For my car, that's 10 miles.  That is certainly something.  It certainly isn't 27 miles and I'd like to see their math--something's got to give.

Now, lets have a realistic look at costs and realistic output scenarios. Am I mistaken that this is a forum of engineers?  Is this math and economics not relevant?  So I'd like to compare your "free" energy with the more traditional concept of adding rooftop solar power and a bit of battery.  If you don't have a roof, then you'll have to do your model using purchased electricity. 

The first issue is that the car cannot and will not produce as much electricity as a the ideal model would indicate.  The panels will at times be shaded, not at an ideal angle--since they are at different angles, they simply cannot all be at the ideal angle at the same time and most places don't have as much sun as we do here--of course this last one applies to roof panels as well.  The car may be inside or shaded at times, a truck may be driving next to it, etc.  I think you'd be doing really really well to get 2.0 kWh on average and I'd like to see evidence to the contrary.

The second issue is that sometimes the car will be fully charged, especially shorter range models.  So figure out how often a fully charged EV sits in the sun (mine does quite often) and put that power in the wasted energy column.

So, as I said, my panels produce about 1.2-1.3kWh/day, and since they are half as efficient as the triple-junction ones here, it makes sense that it would take two of them to be somewhat equivalent.  My NET COST per panel of an installed system was about $500/panel and I contracted out most of the labor.  I actually have room (theoretically) to add 6 more panels and I could do it for the same price or less.  So $1000 (and I can actually do it MUCH cheaper, but I'm trying to be evenhanded).  To be fair, I have to cost in the additional battery capacity, so perhaps another $1000?  At this point, I'll have the rough equivalent of your solar roof. They each have some advantages and disadvantages, but I think they're close enough to compare. 

A very similar debate arose over the Tesla solar roofing product for homes--and it appears to be a complete failure in the market place. So how much for the solar roof? 

[bdunham7]

It is that this subject has been considered by many and actually implemented in few cases.  As of yet, nobody has shown me a system that has any meaningful technical advantage at anything remotely close to a viable price.  If a 5% (or less) increase in range or reduction in electricity costs is worth $5000 to you, great.  Please note that even Tesla, who are able to sell very expensive cars with expensive options, haven't offered anything like this, despite clearly having the technical capability--if anyone does--to implement car solar charging.

You assume viable based on your own metric and that's fine however I ask why you've gone solar to the degree to reach zero cost ?
Surely the investment required means the cost is indeed not zero so you must have done it as your contribution to reducing pollution, correct or is there another reason ?
If the presumption that it's your contribution to the environment and obviously at some cost to you would you not agree that the cost of adding PV to EV is also a contribution to the environment and also not without some cost.
It would seem wrt EV PV's you can't see also the benefits of less generation requirement that might seem insignificant for a single EV it's not for a country full of them.

Sure, those that use EV's are doing their bit along with some substantial purchase incentives of which could well reduce any additional cost of a PV equipped EV for further benefit of the environment.

Buying into bleeding edge  "green" technology at greater cost to "save the environment" generally is both expensive....and doesn't help the environment.  I went solar because electricity is expensive here and we have a lot of sun.  I did the math and once costs came down enough--they're even lower today--I bought in.  The system I have has more than paid for itself and I'll have recouped double my investment in about another two years.  Many people that bought in too early got vastly more expensive systems with not-fully-developed technology that had high failure rates.  So their systems have either been scrapped or are sitting on their roofs not doing anything.  That wastes money and doesn't help the environment. 

Everything you do has a cost--both environmental and economic.  According to some economic theories, the two are actually closely related--the more something costs to make, the more impact it has on the environment.  So you have to balance the costs--both types--of producing your solar auto roof with the benefits of it.  And then you have to compare those costs with the alternatives.  The last time I looked at it the idea was not viable.  Eventually this may change, but I don't think it has yet.

If anyone wants to call and price out those triple-junction modules, here's the manufacturer.  If you have any experience with procurement, you'll know not to guess at the price.

https://www.spectrolab.com/photovoltaics.html

[hendorog]

Is solar PV worth it on cars?  What is the opportunity cost?

The solar PV adds a couple kilometers to the range per day, assuming good conditions.  But the same cost placed into larger battery capacity adds even more range under any conditions.  So solar PV is not worth it.

Adding to the range is not much help for a commuter car, and most EV's are - at least in this country. Putting the same cost into the battery gives you more range, but what use is that when you are only doing 20km's a day? The average daily commute by car in Auckland is around that figure.

But that extra power is power you don't need to pay for. So it makes the car more efficient by 25% if the solar gives you 5kms per day and your commute is 20kms. That is worth having instead of extra battery you are just lugging around for the lifetime of the vehicle. Could you do anything else to an EV that would get an efficiency boost like that?

As tautech alluded to, that power you don't need to put into the car is power that doesn't need to be generated. That is particularly relevant if it is generated from fossil fuels. 18% of the power in this country is generated from fossil fuels.
It is also power that doesn't need to be moved from the generator to the load. It is already there.

[tautech]

It is that this subject has been considered by many and actually implemented in few cases.  As of yet, nobody has shown me a system that has any meaningful technical advantage at anything remotely close to a viable price.  If a 5% (or less) increase in range or reduction in electricity costs is worth $5000 to you, great.  Please note that even Tesla, who are able to sell very expensive cars with expensive options, haven't offered anything like this, despite clearly having the technical capability--if anyone does--to implement car solar charging.

You assume viable based on your own metric and that's fine however I ask why you've gone solar to the degree to reach zero cost ?
Surely the investment required means the cost is indeed not zero so you must have done it as your contribution to reducing pollution, correct or is there another reason ?
If the presumption that it's your contribution to the environment and obviously at some cost to you would you not agree that the cost of adding PV to EV is also a contribution to the environment and also not without some cost.
It would seem wrt EV PV's you can't see also the benefits of less generation requirement that might seem insignificant for a single EV it's not for a country full of them.

Sure, those that use EV's are doing their bit along with some substantial purchase incentives of which could well reduce any additional cost of a PV equipped EV for further benefit of the environment.

Buying into bleeding edge  "green" technology at greater cost to "save the environment" generally is both expensive....and doesn't help the environment.  I went solar because electricity is expensive here and we have a lot of sun.  I did the math and once costs came down enough--they're even lower today--I bought in.  The system I have has more than paid for itself and I'll have recouped double my investment in about another two years.  Many people that bought in too early got vastly more expensive systems with not-fully-developed technology that had high failure rates.  So their systems have either been scrapped or are sitting on their roofs not doing anything.  That wastes money and doesn't help the environment. 

Everything you do has a cost--both environmental and economic.  According to some economic theories, the two are actually closely related--the more something costs to make, the more impact it has on the environment.  So you have to balance the costs--both types--of producing your solar auto roof with the benefits of it.  And then you have to compare those costs with the alternatives.  The last time I looked at it the idea was not viable.  Eventually this may change, but I don't think it has yet.

Yep, right with you up until the last bit when big picture thinking that seems absent in this thread should be a important part of the cost viability.
Let's for a moment think we we are heading with the subsidisation of EV's to enhance their uptake that btw has been rightly pointed out might be nearer to zero if it wasn't for EV buying incentives.

So those that have the power to have implemented this artificial EV uptake in some attempt to meet their countries Paris accord commitments have totally missed a double barrel opportunity to insist PV's are a mandatory part of EV technology and production in order have a further positive impact on their electrical grid charging demands that can only grow in the future, notwithstanding the lesser environmental cost of burning fossil fuels to charge EV's.
So who might pay for this, an arguably nonviable mandatory PV on a EV, pretty simple, it's those that are already paying for the artificial uptake of EV's.......the taxpayer.
A few hundred $/EV, no big deal when spread over all the taxpayers/country and at the the current uptake of EV's might amount to bugger all in the big picture.

In my thoughts of our leaders and forward thinking planners......the words dumb and dumber come instantly to mind !

[nctnico]

And self discharge of EVs is a serious issue if you don't use the car that often. Money is evaporating into thin air if you park the car:
https://www.reddit.com/r/teslamotors/comments/5pd6fm/how_long_can_a_tesla_reasonably_hold_a_charge/

According to this posting the loss is about 10kWh per week which translates into 520kWh per year (that is as much as a big refridgerator!). I pay about .22 euro per kWh so the monetary loss is 114 euro per year. At fast charging stations the electricity price is likely double of that. If you own the car for 10 years then spending 500 euro on the solar roof to keep the battery topped up while the car is parked is well worth it.

You guys are making these wild conclusions with pretty skimpy evidence.  One Reddit post?  Here's the facts:

1.  Li-Ion batteries of the kind in cars generally don't self-discharge very much.  Rather they are discharged by the car using power to do things when parked.  As stated right in the response you are cherry-picking, this is very simple to change--it's just a setting.  Sort of like shutting your computer down as opposed to putting it to sleep.

2.  I don't own a Tesla, but my car doesn't lose ANY significant power from the main battery when parked, even if I leave for a month.  In fact, I generally try to leave it partially discharged if it will be parked because it is less stress on the batteries if it gets warm out.  This is a design feature where the main batteries are completely disconnected when the car is not running and all power is drawn from the accessory battery.  Some cars actually have a small panel to keep the accessory battery charged, which is a gimmick but one I do like.

3.  That solar roof is going to cost you 5000 Euro, not 500, if you want even so much as a peak kilowatt out of it.  And for that you'll need a large car to boot.  You might do a bit better if you could park the car on an elevated ramp facing south with an inclination equal to your latitude, but I'm sure you'll agree that is not a generally practical solution.

That solar roof costs 5k if you are using experimental stage solar cells. That is not relevant for a commercial product. Based on commercially available solar cells a solar roof for a car can be made for 500 euro. And perhaps the Tesla is a poor example but having to put a car in deep sleep (and likely disabling stuff like remote monitoring / software updates) before parking it for a longer period is something I'd typically forget / don't care about so for me it would be nice to have a feature which just makes the car easier to use. Especially since I can't keep an EV plugged in at home.

[wraper]

A very similar debate arose over the Tesla solar roofing product for homes--and it appears to be a complete failure in the market place. So how much for the solar roof?

It's not a failure in market. It just was never really released to wide public until now as it just starts ramping up.

[james_s]

There are always going to be more sensible places to locate the panels than on the cars themselves....

Interesting. Why is that?

Because math.

Calculate the area available on a typical car body and work out the maximum typical power you'd get by covering the entire thing with the most efficient solar panels available. Now compare that to the amount of energy required to propel a car and you'll find that even under ideal circumstances the contribution is going to be underwhelming and most of the time we do not have ideal circumstances. Once you factor in the additional weight, cost, maintenance and repair challenges, etc I think you'll find it cannot possibly be cost effective. A stationary installation is cheaper, lasts longer, is not married to one specific car for life, the panels can be optimally placed and using them does not require you always to park your car outside under the scorching sun which damages the interior and degrades plastics like lamp lenses and trim.


I really don't understand why a few people latch on to these silly ideas like solar panels in roads or on cars when there are SO many superior as of yet untapped options.

[klunkerbus]

As a Bolt EV owner, the thread is interesting to follow.  I wouldn't have wanted to pay anything extra for a solar rooftop, because
 
a) I haven't measured it, but the Bolt rooftop seems pretty small and cells would be flat to the ground - not angled towards the sun for optimal efficiency.  On the Bolt, the hood is really small, so very little to be gained by PV there.  Optimizing the orientation and even tracking the sun can be a benefit of building-rooftop or freestanding solar that our Bolt couldn't achieve. 
b) For us, achieving a few extra miles or km range on a daily basis is insignificant. If that was a substantial portion of our daily driving, I'd have likely bought an e-bike instead.
c) We garage our Bolt every chance we can to reduce exposure to what seems like daily summer hail storms here, and when it isn't raining the sun at our higher elevation can be a killer on plastics and vinyl.  Besides, if we were to park the car in the sun instead of the garage, how much gain from PV would we then lose in then having to cool or heat the vehicle when we got in to drive somewhere? 

Also, as I recall, Elon Musk has said he had Tesla engineers study vehicle rooftop PV, and their conclusion is that it just doesn't make sense.  The way I look at it, if Musk can't find a creative way to hype it, odds are no one can. Well, perhaps except for certain, limited scope use cases. 

[hendorog]

There are always going to be more sensible places to locate the panels than on the cars themselves....

Interesting. Why is that?

Because math.

Calculate the area available on a typical car body and work out the maximum typical power you'd get by covering the entire thing with the most efficient solar panels available. Now compare that to the amount of energy required to propel a car and you'll find that even under ideal circumstances the contribution is going to be underwhelming and most of the time we do not have ideal circumstances. Once you factor in the additional weight, cost, maintenance and repair challenges, etc I think you'll find it cannot possibly be cost effective. A stationary installation is cheaper, lasts longer, is not married to one specific car for life, the panels can be optimally placed and using them does not require you always to park your car outside under the scorching sun which damages the interior and degrades plastics like lamp lenses and trim.


I really don't understand why a few people latch on to these silly ideas like solar panels in roads or on cars when there are SO many superior as of yet untapped options.

So, on the car:

No need to buy a battery
No need to buy an inverter
No fees to pay to setup feed into the grid.
No electrician to pay
No certification required
No installer to pay - assuming the panel is purchased already integrated with a part of the car such as the moon roof.
One panel system is viable.
No need to transport power. It is produced directly on the load
Mass produced, every system is the same
Nothing to arrange. It just comes with the car. Your granny can do it.
Design is one time cost.
No need to seek additional funding. It is included with the car
Makes the car more efficient
Allows the battery to be maintained while disconnected

The house install can be larger. It will be more expensive per kW for the simple reason that the non-generating one off costs are significant.
Cost breakdown of a typical professional quote I have is very roughly 33% Panels, 33% Inverter/Charger and Hardware, 33% install and misc.
That is a system without a battery. A battery is hugely beneficial, but it makes the costing much worse. Big win for the car.

On the house:

Design simpler, but is required each time - every system is different.
Inverter/inverters/inverter charger
Battery - depends on power company terms whether you need it. Eventually if enough solar is installed it will be essential.
Installation - every installation is different. Its expensive to get people onto your roof.
Grid tie setup costs
Certification costs
Funding costs/opportunity costs - nobody (professionally) installs a tiny PV system. Average size (based on my observations and quotes) I estimate somewhere around $5-10K

I think the panel on the car will win the cost effective argument every time.

Rooftop solar is less likely to be shaded and will be better aligned, so on average the same panel will generate more power. However that power is used up paying back the one off install and hardware costs.

Rooftop solar does have the ability to scale up, by adding a couple more panels to a roof.

However consider there are thousands of EV cars coming off production lines every week. That scales up pretty good.

If each one had a PV panel then that is a significant capacity being installed every year.
This is a virtual power station that requires zero infrastructure, zero management. It just quietly offsets other generation.

[Nauris]

If you think typical city bus, like a MB Citaro 12 meters long, 2.5 wide that is 30 m2 quite flat roof you can put maybe 6 kW solar array there. It provides about 5 MWh electricity annually in central Europe enough for about 4000 km city driving that is like two or three weeks maybe. Quite small help but might actually make economic sense as electricity from battery is expensive and panels are cheap.

[nctnico]

Rooftop solar does have the ability to scale up, by adding a couple more panels to a roof.

However consider there are thousands of EV cars coming off production lines every week. That scales up pretty good.

If each one had a PV panel then that is a significant capacity being installed every year.
This is a virtual power station that requires zero infrastructure, zero management. It just quietly offsets other generation.

I think this pretty much sums up the 'problems' with solar panels on roofs. Roof top solar just doesn't scale because every home owner has different priorities (and may not even want to use the roof for solar panels).

[David Hess]

But that extra power is power you don't need to pay for. So it makes the car more efficient by 25% if the solar gives you 5kms per day and your commute is 20kms. That is worth having instead of extra battery you are just lugging around for the lifetime of the vehicle. Could you do anything else to an EV that would get an efficiency boost like that?

As tautech alluded to, that power you don't need to put into the car is power that doesn't need to be generated. That is particularly relevant if it is generated from fossil fuels. 18% of the power in this country is generated from fossil fuels.
It is also power that doesn't need to be moved from the generator to the load. It is already there.

And the same cost put into a fixed solar installation delivers even more energy and lasts longer as well.

There are some unusual use cases where solar on a vehicle makes sense but energy economy and range are not them.

[hendorog]

But that extra power is power you don't need to pay for. So it makes the car more efficient by 25% if the solar gives you 5kms per day and your commute is 20kms. That is worth having instead of extra battery you are just lugging around for the lifetime of the vehicle. Could you do anything else to an EV that would get an efficiency boost like that?

As tautech alluded to, that power you don't need to put into the car is power that doesn't need to be generated. That is particularly relevant if it is generated from fossil fuels. 18% of the power in this country is generated from fossil fuels.
It is also power that doesn't need to be moved from the generator to the load. It is already there.

And the same cost put into a fixed solar installation delivers even more energy and lasts longer as well.

There are some unusual use cases where solar on a vehicle makes sense but energy economy and range are not them.

The same cost put into fixed solar will get you nothing - unless of course you happen to already have a fixed solar installation handy that you can add a panel to, or you DIY something and you account your time as very cheap or free. The DIY approach is great, but it doesn't scale up like PV cars would.

Now if there was a solar farm that existed somewhere you could just buy a panel and add to their infrastructure then it gets more interesting.

However if you attempt to get that power from the solar farm to your car, in my country at least, it loses about 2/3 of its value.
The retail cost of power here is very roughly 3 times the wholesale power price. About 1/3 is the wholesale price the generator gets, 1/3 is transmission, 1/3 is margins, fees and taxes.
So when you feed power into the grid, you get paid the wholesale price. When you pull it out you pay the retail price.

I know this won't be the same for everyone. Some people will be able to get a special deal, and that's great, good for them. But a great deal in California isn't much use here.

The point there is, the panel on the car is right on top of the battery and the load. So no need to move the power and so no extra cost.

[wraper]

The same cost put into fixed solar will get you nothing - unless of course you happen to already have a fixed solar installation handy that you can add a panel to, or you DIY something and you account your time as very cheap or free. The DIY approach is great, but it doesn't scale up like PV cars would.

Your point only works if one is idiot who doesn't plan anything beforehand. And just "needs" to put (additional) solar panels the day car is bought. Also you don't necessarily need to buy any solar panels to begin with. There are thousands of ways ways how to spend your money more efficiently, rather than buying barely working technology. It's not like you are obliged to blow the largest amount of money possible when buying a car.

[hendorog]

The same cost put into fixed solar will get you nothing - unless of course you happen to already have a fixed solar installation handy that you can add a panel to, or you DIY something and you account your time as very cheap or free. The DIY approach is great, but it doesn't scale up like PV cars would.

Your point only works if one is idiot who doesn't plan anything beforehand. And just "needs" to put additional panels the day car is bought. Also you don't necessarily need to buy any solar panels to begin with. There are thousands of ways ways how to spend your money more efficiently, rather than buying barely working technology.

Huh? It is the same solar tech that goes on the roof.
How is that barely working tech?

Of course perhaps a big car company with buying power can certainly do better on price, efficiency or both, than the ordinary panels we mere mortals can afford.

Everyone is talking about rooftop solar like you can just spend a few hundred bucks and make it happen and it will be better than on a car. I've looked into it and that is not the case. Certainly not the case for the same money as are talking about on the car.

You have to pay much more, get a bigger system before it starts to work out on a roof. _Or_ you have to DIY it.

[wraper]

Huh? It is the same solar tech that goes on the roof.
How is that barely working tech?

If it somewhat adds at least noticeable range 5% of the time when you parked your car on sunny spot during a middle of a day, it's barely working.

[ahbushnell]

But that extra power is power you don't need to pay for. So it makes the car more efficient by 25% if the solar gives you 5kms per day and your commute is 20kms. That is worth having instead of extra battery you are just lugging around for the lifetime of the vehicle. Could you do anything else to an EV that would get an efficiency boost like that?

As tautech alluded to, that power you don't need to put into the car is power that doesn't need to be generated. That is particularly relevant if it is generated from fossil fuels. 18% of the power in this country is generated from fossil fuels.
It is also power that doesn't need to be moved from the generator to the load. It is already there.

And the same cost put into a fixed solar installation delivers even more energy and lasts longer as well.

There are some unusual use cases where solar on a vehicle makes sense but energy economy and range are not them.

On Mars

[schmitt trigger]

All this discussion matters depending on your geographical location. In other words, how much YEARLY sunshine on receives on average, not only in the summer.

Case in point: I was in Budapest a few weeks ago. It was hot and very sunny. I saw the many trams in the city, and suggested to my Hungarian engineer friend that they should put solar panels to power the trams.
He replied: you haven't seen a bleak Budapest winter.

[nctnico]

Huh? It is the same solar tech that goes on the roof.
How is that barely working tech?

If it somewhat adds at least noticeable range 5% of the time when you parked your car on sunny spot during a middle of a day, it's barely working.

It is a big numbers game. Take 16 million cars and you have 4 to 6 km^2 worth of solar panels which are mass produced in a shape which fits their environment precisely, can be mounted using robots, don't need any extra space, don't need any infrastructure for connection and/or storage (storage is going to make solar and wind energy really expensive) and are right at the load.

[wraper]

Huh? It is the same solar tech that goes on the roof.
How is that barely working tech?

If it somewhat adds at least noticeable range 5% of the time when you parked your car on sunny spot during a middle of a day, it's barely working.

It is a big numbers game. Take 16 million cars and you have 4 to 6 km^2 worth of solar panels which are mass produced in a shape which fits their environment precisely, can be mounted using robots, don't need any extra space, don't need any infrastructure for connection and/or storage (storage is going to make solar and wind energy really expensive) and are right at the load.

And then sit under shade most of the time. If thing somewhat works when you are lucky, it's basically not working. It has the major problem of regular solar panels squared.

don't need any infrastructure for connection and/or storage (storage is going to make solar and wind energy really expensive) and are right at the load.

The issue is it still needs both of those. And practically to the same extent as regular EV.