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Hood Mounted Solar Panels?

Swilly

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Wondering if anyone has looked into hood mounted solar panels to allay range loss when leaving your car for a backpacking trip or even at the airport for two weeks? I think it would look great and every little bit of additional range will be appreciated, but I am no solar expert/electrical engineer.
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From what I've read and heard, solar panels on a vehicle (even a deployable large array) pretty much don't help when it comes to a meaningful battery charge-up. I'd be more worried about vandals & thieves if leaving my Rivian overnight most anywhere that I wasn't camped next to.
 

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Solar panels aren't magic. They actually barely make any electricity.

They work on house roofs because there's SOOOOOO MUCH SURFACE AREA.

But on a vehicle, there's simply not enough to make it worthwhile - Not even to offset drain while leaving the truck parked for long periods of time.
 

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Solar panels aren't magic. They actually barely make any electricity.

They work on house roofs because there's SOOOOOO MUCH SURFACE AREA.

But on a vehicle, there's simply not enough to make it worthwhile - Not even to offset drain while leaving the truck parked for long periods of time.
Not entirely true.
The Rivian is big enough to support more than enough panels to offset vampire drain (unless it is more than any other EV ever made).
Worth the $$ and range loss from the aero penalty and added weight? Not to me. Leaving your truck parked for a reasonable period of time would likely result in less range loss than driving with solar panels mounted on the hood.

The Aptera is offering panels that will give it up to a claimed 40 miles a day:
Rivian R1T R1S Hood Mounted Solar Panels? 1612309800899


https://www.aptera.us/post/driven-by-the-sun
 

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And I've got a bridge in "London" selling for real cheap.... :p

Rivian R1T R1S Hood Mounted Solar Panels? AZ London bridge
 

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As some folks alluded to, solar panels don’t generate enough kWh to be really useful in this way. I think the Aptera uses something like 100Wh/mi., so 40 miles of range per day from the panels gives you a sense of the potential (4kWh). The Rivian looks like it’s going to be around 450-500Wh/mi. A couple of kWh isn’t going to go far. EVs are very efficient, but it’s still a very significant amount of electricity being used.
 

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The Rivian is big enough to support more than enough panels to offset vampire drain (unless it is more than any other EV ever made).
The thread starter was for just the hood. I stand by my statement.

Worth the $$ and range loss from the aero penalty and added weight? Not to me.
And not for Rivian, either. It would increase R&D time and cost, significantly increase manufacturing cost, add weight to an already heavy vehicle, add insurance cost (solar panels are way more expensive than just sheet metal), and all for a negligible benefit.

The Aptera is offering panels that will give it up to a claimed 40 miles a day:
40 mi/day in a sunny climate parked in the perfect orientation all day.

Let's (generously) assume it's actually 30 mi/day.

It's (somewhat obviously) significantly more aerodynamic than a Rivian as well as significantly lighter. Take their Wh/mi number (whatever it is) and I bet the lightest Rivian will be 3x that.

So that becomes 10 mi/day.

Subtract at least 2/3 of that because the Rivian hood is *at most* 1/3 the surface area they've depicted, that becomes 3.3 mi/day.

My Model X ocassionally has 3.3 mi/day of vampiric drain. Definitely way more on summer days with cabin overheat protection on.

(Rough, back of the napkin estimation, but I'd strongly wager I'm in the ballpark)
 

irwinr

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My Model X ocassionally has 3.3 mi/day of vampiric drain.
That's an insane amount of range loss. I've owned four EVs (3 LEAFs and 1 Niro EV) and my sister who lives down the road from me drives a Bolt. None of those EVs lose any noticeable range even after being parked for weeks at a time. We still have a LEAF in addition to our Niro EV and it sits parked for months at a time and hasn't lost a single mile when parked. If you're running things like cabin overheat protection then that's not "vampire drain". You're running climate control... And having something to combat that climate control drain would actually seem to be fairly useful in that situation.

I installed 3,200 watts of solar on my motorhome so I have some experience attaching panels to a vehicle. Instead of looking at the Aptera and then guessing, and then making assumptions based on that guess, and then making more assumptions based on that assumption. Let's just look at how big the hood on the Rivian is and look at what panels are available. The frunk under the hood is 25.4 in by 54.8 according to Rivian.com/r1t and the picture there shows the hood itself is a bit larger all around, at least 6 inches of overlap. So you have roughly 30x60 of space for panels on the hood. Looking at flex panels you can get on Amazon you can fit roughly 200 watts of power on that hood. This would add about 10 lbs of weight and cost roughly $300. Since these are flexible panels they can be glued directly onto the hood so there would be very little aero cost as they would conform to the shape of the hood.

Of course then you'd also need a "boost" style MPPT controller to raise the panel voltage to the pack voltage but let's put that aside for now.

The rule of thumb for determining how much daily energy you can get from a panel is to take the panels rating and multiply it by 3-5. In winter you typically get at least 3x the panels rating in Wh and about 5x in summer. I can vouch that this rule of thumb is accurate not only on my motorhome panels but I also have panels on my home. I typically get closer to 4x in winter and 6x in summer but I'm also in Texas so further north is probably closer to the rule of thumb.

So 200 watts of solar would net you:

200 x 3 = 600 Wh or about 0.6 kWh / day in winter (1.3 miles range / day)
200 x 5 = 1000 Wh or about 1.0 kWh / day in summer (2.2 miles range / day)

Would it be worth it? For most people absolutely not. If you really do leave your truck parked in direct sunlight a lot then maybe?

Of course that's just looking at the hood. I'm curious if you were interested in doing this why would you not also do the roof... and if I were going to do this I would probably get a bed cover and install panels on that bed cover as well. Then you'd have the entire length of the truck available for panels (And potentially even the sides of the bed cover). If you did that you could potentially get around 1.6 kW of panels for:

1.6 x 3 = 4.8 kWh / day winter (11 miles range / day)
1.6 x 5 = 8.0 kWh / day summer (18 miles range / day)

Now we're getting somewhere...
 

azbill

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I like to think of this as "feel good" technology. It seems really cool, but is just not useful. Today I own a Bolt and it came with a 110V portable charger that provides about 1.4KW/hour of juice, thus more than a solar panel can do. I have never used it. I have parked that car at the airport for a week, in a garage completely shaded and it never losses range. In fact at the airport for long term parking I run it down to 50-60% SoC to extend battery life. I would not park it for a week at the airport in Phoenix under the direct sunlight and have everything inside of it baked at 160 degrees in the hot sun.
 
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Swilly

Swilly

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That's an insane amount of range loss. I've owned four EVs (3 LEAFs and 1 Niro EV) and my sister who lives down the road from me drives a Bolt. None of those EVs lose any noticeable range even after being parked for weeks at a time. We still have a LEAF in addition to our Niro EV and it sits parked for months at a time and hasn't lost a single mile when parked. If you're running things like cabin overheat protection then that's not "vampire drain". You're running climate control... And having something to combat that climate control drain would actually seem to be fairly useful in that situation.

I installed 3,200 watts of solar on my motorhome so I have some experience attaching panels to a vehicle. Instead of looking at the Aptera and then guessing, and then making assumptions based on that guess, and then making more assumptions based on that assumption. Let's just look at how big the hood on the Rivian is and look at what panels are available. The frunk under the hood is 25.4 in by 54.8 according to Rivian.com/r1t and the picture there shows the hood itself is a bit larger all around, at least 6 inches of overlap. So you have roughly 30x60 of space for panels on the hood. Looking at flex panels you can get on Amazon you can fit roughly 200 watts of power on that hood. This would add about 10 lbs of weight and cost roughly $300. Since these are flexible panels they can be glued directly onto the hood so there would be very little aero cost as they would conform to the shape of the hood.

Of course then you'd also need a "boost" style MPPT controller to raise the panel voltage to the pack voltage but let's put that aside for now.

The rule of thumb for determining how much daily energy you can get from a panel is to take the panels rating and multiply it by 3-5. In winter you typically get at least 3x the panels rating in Wh and about 5x in summer. I can vouch that this rule of thumb is accurate not only on my motorhome panels but I also have panels on my home. I typically get closer to 4x in winter and 6x in summer but I'm also in Texas so further north is probably closer to the rule of thumb.

So 200 watts of solar would net you:

200 x 3 = 600 Wh or about 0.6 kWh / day in winter (1.3 miles range / day)
200 x 5 = 1000 Wh or about 1.0 kWh / day in summer (2.2 miles range / day)

Would it be worth it? For most people absolutely not. If you really do leave your truck parked in direct sunlight a lot then maybe?

Of course that's just looking at the hood. I'm curious if you were interested in doing this why would you not also do the roof... and if I were going to do this I would probably get a bed cover and install panels on that bed cover as well. Then you'd have the entire length of the truck available for panels (And potentially even the sides of the bed cover). If you did that you could potentially get around 1.6 kW of panels for:

1.6 x 3 = 4.8 kWh / day winter (11 miles range / day)
1.6 x 5 = 8.0 kWh / day summer (18 miles range / day)

Now we're getting somewhere...
Thanks for your response. This was definitely appreciated. I raised the idea because I do leave my vehicle for extended periods of time and while 2 weeks at the airport with a charger available when I return is not a big deal, 2 weeks backpacking trips(we do a couple each summer) would concern me. If trailhead is 100 miles from nearest charging station, that is 200 miles round trip. That leaves me maybe 60 miles of range on a full charge assuming under 300 miles due to elevation gain getting to trailhead. If vampire drain is 3 miles of range a day, 12 day trip would be 36 miles of range, leaving me only a spare 24 miles to get to the charger. I have had to take 40+ mile detours many times due to roads out from flooding, downed trees, closed gates etc. I would be walking for a tow in the r1s if that happened. I mentioned the hood, as I am not trying to gain range necessarily, but rather avoid vampire drain. Would be open to roof as well, just was not sure how that would work with the Rivian roof glass. Not looking to kill the view. Perhaps just a flexible panel that I only throw up on the roof when parking for long trips? Maybe not an issue once Rivian builds out the charging system, but I also don’t want to have Rivian deciding where I take my backpacking trips by default.
 

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Swilly

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I like to think of this as "feel good" technology. It seems really cool, but is just not useful. Today I own a Bolt and it came with a 110V portable charger that provides about 1.4KW/hour of juice, thus more than a solar panel can do. I have never used it. I have parked that car at the airport for a week, in a garage completely shaded and it never losses range. In fact at the airport for long term parking I run it down to 50-60% SoC to extend battery life. I would not park it for a week at the airport in Phoenix under the direct sunlight and have everything inside of it baked at 160 degrees in the hot sun.
Thanks AZ Bill. Not so worried about airport and I will probably park it in the garage there, something my land cruiser and I have never done. It’s really the backpacking trips that concern me. Sometimes you can find a shady parking spot, but usually the car bakes in the CO sun for two weeks at the trailhead.
More than anything, I am trying to figure out adjustments I will need to make in order to make this vehicle fit into my lifestyle. I appreciate that this forum has folks with a lot more knowledge on the subject than me.
 

DucRider

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Thanks for your response. This was definitely appreciated. I raised the idea because I do leave my vehicle for extended periods of time and while 2 weeks at the airport with a charger available when I return is not a big deal, 2 weeks backpacking trips(we do a couple each summer) would concern me. If trailhead is 100 miles from nearest charging station, that is 200 miles round trip. That leaves me maybe 60 miles of range on a full charge assuming under 300 miles due to elevation gain getting to trailhead. If vampire drain is 3 miles of range a day, 12 day trip would be 36 miles of range, leaving me only a spare 24 miles to get to the charger. I have had to take 40+ mile detours many times due to roads out from flooding, downed trees, closed gates etc. I would be walking for a tow in the r1s if that happened. I mentioned the hood, as I am not trying to gain range necessarily, but rather avoid vampire drain. Would be open to roof as well, just was not sure how that would work with the Rivian roof glass. Not looking to kill the view. Perhaps just a flexible panel that I only throw up on the roof when parking for long trips? Maybe not an issue once Rivian builds out the charging system, but I also don’t want to have Rivian deciding where I take my backpacking trips by default.
Even if the vampire drain on the Rivian is as awful as reported on his Model X, the range loss would be ~1/2 of what he is reporting when translated to the Rivian. He is calculating in Wh, and those Wh will take the Model X much further than the Rivian.
AFAIK, only Tesla owners have reported any significant drain while parked and this is backed up by some of the other responses.
I would be surprised if the Rivian lost even 1 mile/day while sitting unplugged.
 

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That's an insane amount of range loss.
I live in a warm climate. Cabin overheat protection is a god send. Parked outside on a sunny day it's 100% worth the energy use.

If the car is parked in the garage in a mild Spring of course its way less than 3.3mi/day. But, of course, in that scenario the solar panels wouldn't be generating... ;)

I haven't heard anything from Rivian about a cabin-overheat-protection-like feature, but I sure hope they have one.

I've owned four EVs (3 LEAFs and 1 Niro EV) and my sister who lives down the road from me drives a Bolt. None of those EVs lose any noticeable range even after being parked for weeks at a time.
I mean... really? None?

All batteries - including rechargeable lithium-ion batteries - have a self discharge rate.

Historic rule of thumb for li-ions has been ~10% per month for about a decade - like when the first Leaf's were made.

And that's just leaving a cell on a kitchen counter inside a climate controlled house. It's worse if you live somewhere that gets cold at night and warmer during the day, as the temperature cycles speed this along.

It's always been our "overly simplified rule of thumb" that your li-ion cell will self discharge 0.5% a day. That's pessimistic - it's somewhere between 0.25% and 0.5% - but it's good to err on the pessimistic side of things.

So over a couple of weeks you'd be losing 5% of your range just due to self discharge, not even accounting for actual vampiric drain.

Maybe BRAND NEW MODERN li-ion chemistries are better than 10%/mo but they certainly aren't so much better than you wouldn't notice range loss in 2 weeks.
 

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AFAIK, only Tesla owners have reported any significant drain while parked and this is backed up by some of the other responses.
AFAIK, Teslas are the only ones with cabin overheat protection on by default, and a huge number of Tesla owners live in sunny places where it will kick in.

I don't think Tesla owners see that kind of loss when parked in temperate garages (as mentioned, I sure don't!) but that is obviously irrelevant to the conversation of how well solar panels would charge things :)
 
 




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