Roof panels for electric cars

I wonder why none of the current electric car models have solar panels on the roof  ?
I know it would not increace range a great deal but every little helps .

David

I've wondered the same thing myself. Why not put panels on the hood, roof and trunk? Seems logical to me.

They used to be too inefficient and/or expensive to make any sense. Nowadays, though, if not today, sometime soon. Combine hood/roof/trunk mounted solar panels with transparent PV film on the windows, regenerative braking and perhaps regenerative shocks, and incremental improvements make a huge difference.

-CK

Maybe we could suggest thus to Mr Musk maybe he will give us a free car / battery / trip to mars out of gratitude :-)

David

David Livingston wrote:Maybe we could suggest thus to Mr Musk maybe / trip to mars out of gratitude :-)

David

I would wait on the trip to mars. Reports are that they crashed one recently with some mega $ spy gear on board.

https://youtu.be/-2PWKdQzuU8

He suggested a massive nuclear explosion to set up a breathable atmosphere, so either now or never, i suppose.

Generally for the cost of (good looking, effective and integrated) pv on a vehicle, you might double or quadruple a home charging capacity or grid power offset of home charging.
I would still want pv though, if most of the ev batteries get low, you cannot fire up the controller or connect the traction battery to move it until charged, so a module would definitely offset consumption from communications and computing hardware that are always on, along with climate control and other functions while driving.

Pv watts are more effective when consumed directly, rather than stored, and this works great on small projects or specialty vehicles a like people moving trolly train photos i found that were being used for european tourism and sight-seeing, boats, buses, semis, things with alot of room, tall and having less priority on aerodynamics.

The roof of a car is quite small, but there are also going to be alot of cars, so watts are watts and as long as it gets consumed to offset consumption of material, it is likely better than not. Hopefully the cars will all or most all be electric and the coating or body or skin material will be pv.

When Elon Musk first announced the Tesla Model 3 he had included the concept of solar panels on the roof as something they would probably offer. When put up to the task, his engineers said that it wasn't worth it and that you'd only get a couple of miles of extra driving each day if you're parked in a location conducive to having sunlight strike your car roof. A couple of extra miles with a 200+ mile range car really is a drop in the bucket. I'd rather they make the car slightly cheaper. :)

Here is my crazy idea. Its one step beyond a solar trailer.
A flexible panel,that can unroll behind the vehical on a pair of wheels. This would be for highway driving, during city driving it would be retracted.

being environmentally responsible is about directing resources in an efficient manner.
For the same resource cost as putting solar panels on a car roof, you could install solar for a static non vehicle application and save more hydrocarbons from being burned in the power station than the on car panels would offset. Plus your static panels might last 20+ years. Battery powered cars make very little environmental sense until we are not using fossil fuels to power homes and industry.

@Steve: It depends on where you are and what sort of generation is in the mix. In NZ over 80% of our generation is renewable and carbon neutral, so electric vehicles make a lot of sense and that is why we recently got one. Until our regional grid operators sort out their antiquated infrastructure and mindset, grid-tied rooftop PV is going to be hampered in this country. After the electric car, the next quickest payback on investment for us would be to install a battery bank to charge with the cheap nighttime tariff, then use during the day. PV panels are the last cab off the rank for us in economic terms, as much as I'd like to get some.

Adding solar panels directly to the vehicle is very inefficient, and introduces a whole host of competing design priorities.

Solar panels are quite heavy, and when they are added to the vehicle they make the whole vehicle less energy efficient while in motion. Thus you are trading a possible energy gain (on a sunny day, in good conditions) against a definite efficiency loss (added weight).

Solar panels work best when they are angled towards the sun. Cars have lots of different surfaces, pointing in different directions. Optimising the benefits from the panels means looking at the design of the whole vehicle shell and manipulating the layout. On top of that solar panel technology is predominantly based on silicon wafer technology - flat rigid sheets that don't play nicely with the smooth curves needed for an aerodynamic vehicle. Manufacturing custom panels to fit is probably possible, but hugely more expensive than simply using existing flat panel technology. If you do use flat panels the you have directly trade aerodynamic efficiency of the vehicle with efficiency of the panels.

Cost is an added factor. Consumers want low cost vehicles. A body shell stamped from a single piece of steel is cheap and simple. A body panel with a steel frame then manufactured with extra solar panels is substantially more expensive.

The general conclusion of the manufacturers over the years is that solar cells on the vehicles themselves are a bad idea. It is better to invest the same funds in an efficient static system that generates more energy at lower cost, and simply plug into it at home.

Phil Stevens wrote:In NZ over 80% of our generation is renewable and carbon neutral, so electric vehicles make a lot of sense and that is why we recently got one.

With 20% of your grid power non fossil then your electric car is still burning more diesel/gas/coal at  the powerstation than it is saving by not running in its own engine. This is because the combustion chamber to tyre end to end efficiency in a car is far superior to the end to end efficiency of burning fossil fuel in a power station, sending over the grid, charging a battery, discharging a battery and running electric motors. I cant think of how your electric car is reducing the amount of fossil fuels burned per km travelled. A possible positive is if driven in a city an elec car is kinder to people near the road, tho at the expense of people near the power station.

As others have pointed out , it wouldn't offer any significant advantage, but would make the vehicle heavier and possibly less aerodynamic.  It's not cost effective nor is it a good use of resources.
Solar panels work best when they are tilted to face the noon sun, this rarely happens on the surfaces of parked cars.   While some modern panels have relatively good efficiency (~20% or so) these are all solid, FLAT, crystaline panels.  The flexible solar panels have very low efficiency.  So you either use a flat panel and ruin the vehicle's aerodynamics, and get poor performance from the panel since it isn't tilted properly, or you use a flexible panel that provides even lower over-all efficiency.

Someday they might invent a lightweight spray-on solar panel with relatively high efficiency.  At that point it might make sense, but we haven't developed that technology yet.

You are much better off parking the vehicle in the shade (so it doesn't heat up and need energy to cool it down) than parking it in the sun with low efficiency panels.  Put the solar panels on the roof that is providing the shade.
Down here in Arizona I'm seeing more and more businesses installing solar roofs over their parking areas.

FWIW I drive a car that runs on electricity most of the time, and I typically charge it using the surplus power from the solar array that powers my house.

You can but it looks very odd.

Check out this guys website. He's experimented with a lot of different things.
http://aprs.org/my-EVs.html

Be forwarmed that he knows his way around electricity, including dealing with hundreds of volts DC, which is rather more dangerous than house electricity.

I think he was getting about 1 miles of range for every hour of sun charging. So not a lot but if you don't travel a lot of very far it could be useful.

Daniel

The problem with applying solar solutions to problems here is that people do not understand scale.  The very typical mistake is that people grossly underestimate what the power need is, and grossly overestimate the power that solar can produce.

The central problem here that posters are chipping around the edges is that modern electric cars need kWh of electric power, but only hundreds of watts of panels can be fitted onto a car.  It's sort of like needing a thousand gallons of water per day for irrigating your plants, but you have a spring that only puts out 100 hundreds of gallons of water per day.

A workable solution that makes more sense is a solar car-port that the car can be parked under.  The car-port roof could be angled South to face the sun, and the size of the roof could hold the MANY solar panels needed to produce the kW of power needed to charge the car.  All the electronics needed to control the power could then be placed in a secure dry place under the roof that won't get exposed to the weather.

If you can give me specific charging specifications, I can help you design a system that will reliably charge your car.  Most charging stations I've seen are designed around 240VAC.  It's doable, and I have 240VAC at my own cabin, but it ain't gonna happen with a system composed of a 100W panel and an old car battery.

I think Michael is exactly right. Electric cars need power on a much larger scale than what a car-sized set of panels could provide.

I know someone here in Ladakh with an electric car. Their work and residential quarters are at an institute that is solar powered, off-grid. They installed some of their panels as a solar carport that can keep several cars in the shade, and charge the car there. There's only one electric car at the place though and the other vehicles are conventional fuel vehicles.