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TT97
Active Member
The Karma has a solar panel roof, I asked how much energy it can produce and was told just over 1 kWh on a good day - good for 2 miles on that car.
RFernatt
Solar/EV Owner/Enthusiast
Yeah, it's just a little more practical to put those panels on your home's roof if possible. I can offset the energy needs of the house and two EVs that way whereas panels on a car would rarely be at an optimal position to maximize power output.
On my best day, I've generated 83kWh which could completely recharge the Model 3. This month, I've averaged over 58kWh per day. To offset the power needed by EVs, you have to be generating a lot of power which just isn't possible with current tech limited to the top surface area of a car. The surface area of a roof is another story.
On my best day, I've generated 83kWh which could completely recharge the Model 3. This month, I've averaged over 58kWh per day. To offset the power needed by EVs, you have to be generating a lot of power which just isn't possible with current tech limited to the top surface area of a car. The surface area of a roof is another story.
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It’s a “concept” car. It won’t be solar powered for more than a kilometer or two if it ever gets to market. Solar cells covering the roof/hood of a car can only generate very small amounts of power, far less than any EV needs to go any useful distance. This is unlikely to change for a long time...
Even with 100% efficient solar cells that cover 100% of the area of the car, it’s unlikely to be terribly practical for most people. You’d also need to leave the car parked outside all the time, unshaded, in a sunny area. Even then most people would need to charge occasionally. So for the cost and complexity this adds, I don’t see it making much sense unless EV’s dip closer to 100wh/mi, which sounds unlikely. And then with current solar cells on a car not designed for efficiency and roof area above all else, it’s absurdly impractical.
Panels on the roof would be massively cheaper and work better. And you can easily make enough energy to charge a standard off the shelf EV with a rooftop solar system today. Although that does mean you’d need a roof... So there is that.
Panels on the roof would be massively cheaper and work better. And you can easily make enough energy to charge a standard off the shelf EV with a rooftop solar system today. Although that does mean you’d need a roof... So there is that.
Vickh, you're a genius! Yes, it would be perfect for dealing with phantom drain parked at locations where there is no charging infrastructure or "off grid" such as a camp site.
This has been brought up about every week since Teslas were around. And the amount of power is barely enough to ventilate the heat that the sun on the roof adds to the car. Elon made some joke about it once and it has never died.
It might fight phantom drain. Maybe. Still need a lot of surface area.
It might fight phantom drain. Maybe. Still need a lot of surface area.
Rothgarr
Active Member
Solar-powered cars, even though they exist and new models are coming out, are just too inefficient and impractical. Solar belongs where it is most efficient, and that's on a roof or solar farms, etc.
Below is our solar array (50 LG 360 W panels) and my new M3 Dual Motor Long Range.
On our best day, we produced over 121 kWh. We produce so much power that even charging the Tesla at home we'll never ever have to pay for electricity.
Below is our solar array (50 LG 360 W panels) and my new M3 Dual Motor Long Range.
On our best day, we produced over 121 kWh. We produce so much power that even charging the Tesla at home we'll never ever have to pay for electricity.
These comments sound like the BEV comments from 20+ years ago. These guys have won multiple international competitions for pure solar powered vehicles. IIRC, their goal is 400 mile range with a small plug in battery with an extremely efficient car and the current price is something like 150k euro. A new model S LR is 370 range, but uses more charge. Bring that down to Tesla model 3 prices and I would try it. God bless them and hope it pans out and becomes mainstream worth it. Hope solar panels become orders of magnitude more efficient. We need it.
The issue with solar powered cars is the amount of energy that hits the vehicle is less than most people tend to assume. BEV's were mocked for the perception that batteries will never be able to hold enough energy at a low enough cost for them to replace an ICE vehicle. This was really a perception issue, not a physical limitation. BEV's could have been made long before Tesla made the first Roadster, but the cost was so far off no sane person would dare.
The solar radiance hitting the average cars roof over the course of a day is in the neighborhood of a handful of kWh. This depends on the day, assumes no shading or obstructions, and 100% conversion to electricity. Current solar cells are capable of mid to upper 20% efficiency, best case. So you're in the ballpark of 1-2kWh in great weather and ideal conditions. This could get you maybe 10 miles driving gently in a M3 assuming you have an exceptionally efficient MPPT SMPS to charge the pack direct. This is very possible today, id imagine anyone in the EV industry knows this. The issue is the value of that energy is around $0.20/day, and it only works when the car is parked outside during the daytime, unobstructed. Having even seemingly minor obstructions can easily halve this energy. Less than ideal solar irradiance will also have massive variability. In the winter, even in a great area, the energy captured might be 1/4 to 1/2 as much as summer. Averaged over the course of the year, my best guess is you would be lucky to get 1kwh a day. So maybe $40 worth of electric a year, and the setup would likely cost at least 200x that.
It's not that its not possible, it very much is. It just makes absolutely zero financial sense, and so is unlikely to be practically implemented. The only use case is when the vehicle has to be totally offgrid, and will be parked outdoors in sunny weather anyways. But with the M3, the energy generated wouldn't even be enough to offset the losses associated from keeping the cell temperatures in check when parked in the sun. The only way for this to work is to design a car around a massive roof area for more PV area, and absurdly efficient aero. Then, if you drive slow, im sure some people can get by without ever charging. But its super impractical for the average person. and it makes absolutely no financial sense.
The solar radiance hitting the average cars roof over the course of a day is in the neighborhood of a handful of kWh. This depends on the day, assumes no shading or obstructions, and 100% conversion to electricity. Current solar cells are capable of mid to upper 20% efficiency, best case. So you're in the ballpark of 1-2kWh in great weather and ideal conditions. This could get you maybe 10 miles driving gently in a M3 assuming you have an exceptionally efficient MPPT SMPS to charge the pack direct. This is very possible today, id imagine anyone in the EV industry knows this. The issue is the value of that energy is around $0.20/day, and it only works when the car is parked outside during the daytime, unobstructed. Having even seemingly minor obstructions can easily halve this energy. Less than ideal solar irradiance will also have massive variability. In the winter, even in a great area, the energy captured might be 1/4 to 1/2 as much as summer. Averaged over the course of the year, my best guess is you would be lucky to get 1kwh a day. So maybe $40 worth of electric a year, and the setup would likely cost at least 200x that.
It's not that its not possible, it very much is. It just makes absolutely zero financial sense, and so is unlikely to be practically implemented. The only use case is when the vehicle has to be totally offgrid, and will be parked outdoors in sunny weather anyways. But with the M3, the energy generated wouldn't even be enough to offset the losses associated from keeping the cell temperatures in check when parked in the sun. The only way for this to work is to design a car around a massive roof area for more PV area, and absurdly efficient aero. Then, if you drive slow, im sure some people can get by without ever charging. But its super impractical for the average person. and it makes absolutely no financial sense.
That is exactly what they are doing , except - as I noted - the car is not 100% solar, it can be plugged in; the solar augments the charge. Impractical sure, except for the super wealthy early adopters, I still hope it works out for them.
I think its super cool and I would certainly love for it to work. Unfortunately the physics of it indicate its barely possible, so they have an extreme challenge. Typically those hyper efficient cars have massive compromises to occupant comfort, safety, vehicle performance, and likely durability. So it would be interesting for sure to see if they ship and what impressions early adopters have. At the stage they're at now, they made no claims on the vehicles performance. They just anticipate its possible to have some conditions exist in which the vehicle wont need to be charged. This isn't the first group to try a solar car, and they showed no innovation or results.
And to be clear, its not that it won't work or can't work. Its just so absurdly ridiculous compared to the massively improved performance, lower cost, and likely drastically reduced environmental impact of putting conventional panels on a roof. That's very well proven, has good scale, is robust, reliable, makes no compromises to the vehicle, and can be scaled to meet essentially any needs in all conditions. And then you can park the car near trees, in a garage, underground parking, or next to a building without being concerned with shading. The complexity of that solar panel is quite significant as well. I wonder how practical it is for a small team to ensure long term durability with the significant thermal cycling and vibration it will be exposed to. This inst an off the shelf panel that's made in large volumes, flat, and easy to replace.
And to be clear, its not that it won't work or can't work. Its just so absurdly ridiculous compared to the massively improved performance, lower cost, and likely drastically reduced environmental impact of putting conventional panels on a roof. That's very well proven, has good scale, is robust, reliable, makes no compromises to the vehicle, and can be scaled to meet essentially any needs in all conditions. And then you can park the car near trees, in a garage, underground parking, or next to a building without being concerned with shading. The complexity of that solar panel is quite significant as well. I wonder how practical it is for a small team to ensure long term durability with the significant thermal cycling and vibration it will be exposed to. This inst an off the shelf panel that's made in large volumes, flat, and easy to replace.
They claim the solar panels can produce 1.25 kW peak. So on a sunny day that would average out to about 4 kWh/day (more in the summer, less in the winter), or about 16 miles/day in a Model 3. That would actually cover a lot of my daily driving.
It would be interesting to know how they actually implement it. The Japanese version of the Prius Prime has an optional, and much smaller, 180 watt solar panel that can charge the main battery pack. They use a small intermediate pack to accumulate charge from the panel, then burst power into the main pack.
It would be interesting to know how they actually implement it. The Japanese version of the Prius Prime has an optional, and much smaller, 180 watt solar panel that can charge the main battery pack. They use a small intermediate pack to accumulate charge from the panel, then burst power into the main pack.
Yes, if it was parked outdoors fully exposed. In summer. Under clear skies, no clouds.
All of which only occur a small fraction of the time.
Really, the idea that car roof solar cells can offer any practical benefit is unrealistic, and they add significantly to the cost of the car.
As @boaterva notes, this idea comes up regularly. I first saw it years ago. It made no sense then, and it still makes no sense. I say this as someone who is passionate about solar power; I have 9.8kW of panels on my roof.
In my case, that is the normal situation. My old 2 seater convertible got first dibs for garage space. Sadly not enough room for both cars.
Rothgarr
Active Member
At least it's not "Solar Freakin' Roadways!!!1!11!!"
(It takes all my power to hold back when someone tells me that's a good idea)
(It takes all my power to hold back when someone tells me that's a good idea)
I still wonder how much ‘solar energy’ is being added to the car as heat that COP will need to spend to cool the car down. 
There’s a calculation for someone...
There’s a calculation for someone...
