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Discussion Starter · #1 · (Edited)
[Updated] :
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I have chosen to add an additional "buffer" battery for the sake of storing more solar power. I am leaving this original post as is, but read ahead to see what my new idea is: [Updated] Crazy idea for extending EV range using solar.

More details and a schematic layout here:
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I had an idea for extending EV range using solar, but without batteries or additional inverters:
Given that almost all EVs have 12v battery for accessory usage, and a DC-DC converter that keeps the battery topped off (at least while driving), what would say about a solar panel connected to this 12v battery?
Of course it would make use of a simple solar charge controller, to match the 12v battery voltage.
I was thinking that this could improve range a little (don't know how much), because it would offload some of the burden from the DC-DC converter, which obviously takes its power from the traction battery.

I have two 100w ETFE (semi-flexible) panels laying around. They weigh less than 2kg each.
The panels could either lay on the dashboard when the car is parked, or somehow attached to the roof when driving.

Let's say that in direct sunlight, the net output of these two panels (in parallel) would be around 150-180w (taking into account inefficiencies, PV panel heat etc...)

If an average EV does about 150Wh/km, that means that for every hour driven (in best conditions), you would save 1km in range. Not much. But, while the car is parked, it would also top-up the 12v battery, and the DC-DC would not have to work as hard to keep it up to proper voltage. I don't know how to estimate this saving in terms of range...

If you had all the parts needed, just laying around, would you do this, or do you think it's totally not worth the trouble?

Of course if you didn't have the parts, it would certainly not be cost effective.
 

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I had an idea for extending EV range using solar, but without batteries or additional inverters:
Given that almost all EVs have 12v battery for accessory usage, and a DC-DC converter that keeps the battery topped off (at least while driving), what would say about a solar panel connected to this 12v battery?
Of course it would make use of a simple solar charge controller, to match the 12v battery voltage.
I was thinking that this could improve range a little (don't know how much), because it would offload some of the burden from the DC-DC converter, which obviously takes its power from the traction battery.

I have two 100w ETFE (semi-flexible) panels laying around. They weigh less than 2kg each.
The panels could either lay on the dashboard when the car is parked, or somehow attached to the roof when driving.

Let's say that in direct sunlight, the net output of these two panels (in parallel) would be around 150-180w (taking into account inefficiencies, PV panel heat etc...)

If an average EV does about 150Wh/km, that means that for every hour driven (in best conditions), you would save 1km in range. Not much. But, while the car is parked, it would also top-up the 12v battery, and the DC-DC would not have to work as hard to keep it up to proper voltage. I don't know how to estimate this saving in terms of range...

If you had all the parts needed, just laying around, would you do this, or do you think it's totally not worth the trouble?

Of course if you didn't have the parts, it would certainly not be cost effective.
The loss of range due to increase in drag of your aftermarket addition of your EFTE SOLAR films would likely exceed the gains, even the drag increase of the wiring...
that would be on a good sunny day.
Best place for these schemes is as a fixed solar static 12v battery top-up, nothing to do with range increase, a la Leaf.
 

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Ioniq 5 has this as an optoin on their top spec cars. I think they say it can add up to 1200 miles a year depending on weather obviously. And that feeds both the 12v and main battery.
 

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Car manufacturers have offered solar roofs as an option, you can buy a Prius Plug-in PHEV with a built in solar roof, but the idea doesn't seem to have taken off yet, probably a combination of extra upfront costs vs limited benefits compared to simply plugging in.
 

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It's too little to make a discernible difference to your driving range, but it might be enough to keep the battery topped up if you leave the car unused for several weeks.
 

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Discussion Starter · #10 ·
Thanks for all of your replies!

At first I thought I was up to something (and after posting, I saw similar ideas in other posts).
But now I understand that it's simply not going to be that beneficial to range, maybe just for battery maintenance.

Well, we will keep on dreaming, maybe some day a good idea will arise :ROFLMAO:
 

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Solar panels attached to an ebike's pannier rack that can be unfurled when parked up can be useful, but that's mostly because an ebike is much more efficient at moving a person than a car, so the small amount of wattage that a solar panel can extract from the sunlight is proportionally more than you'd achieve by attempting to push 1.5 tonnes of car along with the sunlight.
 

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Discussion Starter · #12 ·
Ioniq 5 has this as an optoin on their top spec cars. I think they say it can add up to 1200 miles a year depending on weather obviously. And that feeds both the 12v and main battery.
It's a mystery how they implemented that on the Ioniq 5. I mean there isn't that much space one roof, maybe enough for 200-300w.
But in order to efficiently charge, they would have to do direct DC charging, which would need at least 400v. That means a heck of alot of solar cells connected in series.
Given that a typical solar cell outputs 0.5v, they would need 800 of those!

I wonder if thier patent info is available, just for the curiosity...

Or maybe they don't connect directly to the main battery, just the 12v, like my idea.
 

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It's a mystery how they implemented that on the Ioniq 5. I mean there isn't that much space one roof, maybe enough for 200-300w.
But in order to efficiently charge, they would have to do direct DC charging, which would need at least 400v. That means a heck of alot of solar cells connected in series.
Given that a typical solar cell outputs 0.5v, they would need 800 of those!

I wonder if thier patent info is available, just for the curiosity...

Or maybe they don't connect directly to the main battery, just the 12v, like my idea.
Maybe they have a cyclic 12v battery discharge into the main traction pack via a DC to DC stepup converter.
 

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...
Let's say that in direct sunlight, the net output of these two panels (in parallel) would be around 150-180w (taking into account inefficiencies, PV panel heat etc...)

If an average EV does about 150Wh/km, that means that for every hour driven (in best conditions), you would save 1km in range. Not much. But, while the car is parked, it would also top-up the 12v battery, and the DC-DC would not have to work as hard to keep it up to proper voltage. I don't know how to estimate this saving in terms of range...
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In addition to the comments above...I suspect that your calculation is flawed as you assume that all the power available would be saved from motive power requirements. This isn't necessarily true. The auxiliary battery is generally under light load and wouldn't need that much energy to keep it topped up. Therefore to understand the true saving, you would need to understand the actual power consumed by the dc to dc unit, and also how consistent this is. I suspect that the average power requirement is low, but with high power peaks. This would mean that the full solar panel output wouldn't be utilised, and some traction battery energy would still be required.
 
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I think you would need to wait a quite a few years for there to be a worthwhile photovoltaic paint - then the entire car's surface could generate electricity - perhaps enough that you might never need to plug-in (depending on mileage of course).
 

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Looking at the power output of the size of solar panel you could put on a car roof, I'd think that any solar panel there would be less for a sincere extension of traction battery range, and more for maintaining the batteries if the car was laid-up for a while (e.g. 3 weeks in the long stay airport car park).
If you're investing in solar panels, you might as well install them on the roof of your house instead.
 

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Thanks for all of your replies!

At first I thought I was up to something (and after posting, I saw similar ideas in other posts).
But now I understand that it's simply not going to be that beneficial to range, maybe just for battery maintenance.

Well, we will keep on dreaming, maybe some day a good idea will arise :ROFLMAO:
It is not a dream and perfectly relevant observations.

It would make more sense still to take out the old cranking-batteries and replace with VRLA which charge much more efficiently and (/because) they don't need to be a compromised design for 500A cranking events. (Means you have to design the plates to be large area, which means thinner, which means lesser discharging depth.)

This was already done on the first Leafs that were sold. I don't recall if it was an option or if all Leafs came with it.

It became a bit of a warranty concern; the diode block would fail and actually drain the battery. So beware that adding parts usually reduces reliability.

But a reliable and well implemented solar panel (not Nissan then , I guess?) and with a VRLA, the 12V system will require about 30A or so, so if you drive for an hour every day expect that to be 0.3kWh, maybe 4 or 5 extra EV miles a week, 200 in a year.

As for costs ... so you get a free 200 miles a year. This costs £3, at 3.5mi/kWh and 5p/kWh.

So you save £3 per year.

How much to implement this solution?

More than £30 and you'll not get your money back, plus it degrades reliability, as Nissan found out.

In a perfect world where it cost nothing to make things but energy was scarce ... great idea, though!
 

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We've discussed these many times, and in the absence of a product after several years, looks more like an investment scam.
That's fair enough - although they do seem to be presenting a prototype Sion next month: Events – Sono Motors
 
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