Hood Mounted Solar Panels?

[Sean]

Who wants to spec a system for portable solar charging on the R1T? Something that can be put out on the bed/cover when parked in sunny areas and get a decent enough charge over the course of a day and get 1 or more kwh.

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[DucRider]

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.

With a separator between electrodes, self discharge can be as low as 1% per year.

 

[irwinr]

I mean... really? None?

We mean negligible and not significant.

Right. I've never gotten in the car after leaving it for a couple weeks and *noticed* any range drop. Maybe it lost a mile or two: but the range will vary +/- a couple miles based on ambient temperature anyway. (IE: If I get in on a 70 degree day it'll read 200 miles but on a 90 degree day it may read 198 miles to account for climate) So it's never been larger than the normal day to day variation I expect to see just from ambient temp swings.

I've also built a number of lithium-ion packs for various projects (One being a 10 kWh battery for that solar motorhome I mentioned) and in my experience modern lithium-ion batteries self discharge less than 0.5%/month. The exception being if they are sitting at 100% SOC, if they are sitting at 100% they may lose 1-2%/month but that quickly drops down to less than 1%/month as the cell voltage drops down from 100%.

I've left raw cells sitting on my workbench for many months at a time and never had any issue with self discharge from those cells.

It also helps that most Non-Tesla EVs don't allow charging to 100% either. When other EVs *display* 100% SOC on the dash their cells might be at 3.9v instead of the 4.2 that's typically considered 100% for most chemistries. Because they sit at a lower voltage it lowers the self discharge rate.

 

[azbill]

Who wants to spec a system for portable solar charging on the R1T? Something that can be put out on the bed/cover when parked in sunny areas and get a decent enough charge over the course of a day and get 1 or more kwh.

Here you go, feel free to spend your money on this:

https://www.ebay.com/itm/1742389055...1291&msclkid=7681464e7d801946eb3d265490ebe657

At 600W you could get 1 kw in 2 hours. It would fit on the roof racks or the bed racks.

 

[timesinks]

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.

The self discharge of a lithium-ion chemistry is closer to 0.35% to 2.5% per month depending on state of charge. High states of charge lead to faster self-discharge. The vampire drain from self-discharge will be negligible unless being parked for very long durations. The issues most people have are electronics that don't fully power off.

As mentioned in the thread, cabin overheat protection would use power. So would any form of sentry mode, background OTA content refreshing, etc., etc.. We have no idea just yet how Rivian will handle such things and how much they'll drain the battery (though, per another point raised, at a higher Wh/mi consumption, such electronics would represent a smaller number of miles of range), but perhaps they'll consider this use case and offer a low power mode that shuts most of that stuff down when you know you'll be parked for a long time.

 

[timesinks]

Who wants to spec a system for portable solar charging on the R1T? Something that can be put out on the bed/cover when parked in sunny areas and get a decent enough charge over the course of a day and get 1 or more kwh.

I think you first have to ask whether you're going to charge the high voltage pack directly or rely on the onboard Level1/2 charger.

If you get access to the pack (can you say "void my warranty"?), you could probably have a custom MPPT charger built to charge with whatever solar energy is available. Not sure how you'd go about requisitioning such an MPPT charger. Not sure you'd want a connector with that kind of DC voltage readily accessible. It just seems like a bad idea (unless Rivian built such a charger, embedded it into the vehicle, and maybe had mc4 connectors for you to attach your array).

So I think the only thing that is somewhat feasible for most people would be to plan on using the portable J1772 EVSE. You'd need to build a bank of batteries (probably LiFePO4s running you around $1k per kWh), and get an inverter. 120VAC 12A = 1440W. Want to charge at level 2? 240VAC 32A = 7680W. Even the 1500W inverter is going to be big, heavy, and cost you a fair chunk of change. And we haven't gotten to the solar panels to top off that battery bank and the MPPT controller to make that work.

We've built a Sprinter conversion with 900W of solar on the roof, a 2000W inverter, and 4.8kWh of lithium batteries. In perfect sun, that setup could maybe get 6-7kWh (14 miles) of range pushed into a Rivian, assuming the battery bank started out full. And you need the whole rooftop of a long sprinter to gather that much sunlight.

It's just not worth it.

 

[Smithery]

With a separator between electrodes, self discharge can be as low as 1% per year.

Since my information on this is a combination of incomplete and out of date, I legitimately am hoping you can provide a citation for that. Because I cannot find one.

The most recent actual scientific journal article I've been able to find is from 2018 saying 5% per month

Noticeably better than the 10% that was expected in 2010, but "1% per year" is two orders of magnitude better than that

 

[timesinks]

Since my information on this is a combination of incomplete and out of date, I legitimately am hoping you can provide a citation for that. Because I cannot find one.

The most recent actual scientific journal article I've been able to find is from 2018 saying 5% per month

Noticeably better than the 10% that was expected in 2010, but "1% per year" is two orders of magnitude better than that

The wikipedia article cites this 2016 paper on self-discharge rates of 0.35% to 2.5% per month depending on state of charge.

And while I don't have a membership to see the full article you reference, the abstract refers to "<5% of the stored capacity over 1 month." As quoted, 5% is an upper bound -- not necessarily the typical value you will experience.

 

[DaveA]

The 2022 Fisker Ocean is going to have an optional solar roof. Henrik Fisker has mentioned it provides enough power for about an additional 1000 miles per year. So that's something if true. Not going to charge the pack, for sure. Might be nice to have an optional tonneu cover for the R1T with solar panels to power accessories without using the vehicles pack when off grid?

 

[CommodoreAmiga]

The 2022 Fisker Ocean is going to have an optional solar roof. Henrik Fisker has mentioned it provides enough power for about an additional 1000 miles per year. So that's something if true. Not going to charge the pack, for sure. Might be nice to have an optional tonneu cover for the R1T with solar panels to power accessories without using the vehicles pack when off grid?

So less than 3 miles range per day. That’s in line with what people have been saying, above.

 

[irwinr]

The most recent actual scientific journal article I've been able to find is from 2018 saying 5% per month

The article you link does not appear to say what think it says.

First let's look at the title:

Abnormal self-discharge in lithium-ion batteries

Based on the title alone it's safe to say we're studying cases where batteries have abnormally high self discharge. But let's read on:

Besides their promising electrochemical performance, the low self-discharge rate (<5% of the stored capacity over 1 month) of lithium-ion batteries is one of their most significant advantages for ESSs.

Let's parse this: It's saying that li-ion batteries have a "low self discharge rate" and then it clarifies that "low" is anything less than 5%. So as someone else pointed out, that's the upper bound. Some types of batteries lose 30%/month so anything less than 5% is generally considered low in the battery world.

It goes on:

Herein, contrary to conventional belief, we report that the self-discharge of LIBs can be abnormally accelerated when the battery has been exposed even to a routine short-term thermal exposure. We demonstrate that this thermal ‘history’ in addition to the temperature itself is memorized in the battery and accelerates the self-discharge rate.

It sounds like it's saying that the batteries can be damaged by being exposed to high heat. That damage can lead to high self discharge rates. (IE: Greater than 5%)

They also provide a nice little graph to illustrate their point:

Look closely at that graph on the left. A battery that's been exposed to 60 degrees Celsius (140 F) in it's "history" will have a fairly high self discharge. Look closely at that scale: A battery "without history" of a thermal event will drop from 3.9v to somewhere around 3.88 or 3.89 after 20 days. That is an absolutely tiny drop in state of charge.

Let's look at a voltage curve for a typical li-ion cell:

Notice how steep the curve is from the left? Dropping from 3.9 to 3.88 would probably not even move you along the Y axis enough to represent even 1% drop in SoC. And this is at a fairly high state of charge where self discharge is typically at it's greatest.

I have raw cells that I store around 50% SoC and I've never had one drop in voltage even after sitting for 10+ months on the shelf.

I can also send you some logs from my the BMS on one of my batteries if you like. From fully charged they have to drop around 0.3 volts before my BMS registers the drop as even 0.5% SoC. A drop of 0.02 is nothing.

 

[bike123.com]

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:

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

We have a pair of Apreras ‘ordered’
We opted for the lowest range since we don’t plan to take those afar like the R1T.
Their 1000mile option adds huge weight ( diminishing range return and performance) and huge $$
One will stay up north one in FL - where there’s more sun.
They grab 40m a day due to their weight and aero shape
A roof full
Of panels on the R1T will net a dribble by comparison
We’re also going to avoid the R1T 400mi pak - again extra weight, diminishing range return, and we like navigating stops and stations like we now do with a bolt and Kona ev.
We’ve hyper’d 300 on those that are only rated 259 max.

 

[Rosby]

I was looking at some panels that were around 200 - 250 watts, for example https://solwiser.com/am-solar-panel-reviews/ that would just fit on the roof, but I was recently informed about another place that is offering 400 watt panels for around $150, which are larger than the one’s I was originally considering.

Of course that's just for the roof. I'm think in doing this why would you not also do the hood.

 

[crashmtb]

I’ve been getting ads for this https://www.cascadia4x4.com/

 

[Smithery]

I’ve been getting ads for this https://www.cascadia4x4.com/

Looks like the best they have on a hood panel is 100w.

That keeps your radio and camp fridge going around a campsite without draining the ICE trucks 12v battery.

Applied to charging our BEV truck, it would add just over 2 miles of range to an R1T if you got full sunlight for 10 hours.

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