Full Solar Charging

[FutureBoy]

In another thread the idea of charging the CT from solar panels that were carried in the bed was brought up and I see that as a challenge question for extra credit that could be answered by the engineers on this site.

It would be interesting to know:

How many solar panels (and estimated total volume and weight of said panels) would it take to have enough energy coming in to match a Tesla supercharger? Could those panels fit in the bed of the CT? Would there need to be a bunch of associated gear to hook everything up?

The idea here is to see what it would take to carry a self-charging slate of solar cells and use them. If we could have a reasonable charge (fast-charge would be nice) from an optimally sunny day then range anxiety would be a completely moot point. One could just take periodic stops to lay out the panels and hook up for a charge. The reason for the fast charge is so we don't have to sit around all day to get enough charge to keep playing (traveling) during the sunlight hours. If it will only trickle charge then this is only a solution for vampire types that drive at night and charge all day.

Assume that the panels are using currently available technology. Example panels that could be utilized would be a bonus answer.

Not really trying to give anyone homework here but the kids are trying to finish up their homework before the holiday break so homework is everything around here at the moment.

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[FutureBoy]

This kind of solution does not exactly match the never-charge idea of the Aptera but it would be an interesting idea for a test implementation once we do get our CTs.

 

[Crissa]

The number and weight of solar panels really depends upon the kind. And what are we trying to do... A few miles, a fast-charge, what is the goal? How many hours at what inclination?

The Tesla granny cable can be set to charge at 1 amp at 120v. That's about 150w or one house solar panel. My camping setup can easily do this with its 140w of panels. That would be very few miles per hour, though. About one per two hours.

https://www.amazon.com/HQST-Monocrystalline-Lightweight-High-Flexible-Solar/dp/B07QV8CDGZ/

Here's an okay floppy one. They're actually a little heavy, but you can lay them on any surface. That's handy. But it makes a good example - the bulkier aluminum ones can be lighter or heavier, but about the same.

You just keep adding these until you get the power you want. You'll also need a charge controller for the number, and a battery to store the excess charge, and an inverter. There are systems that have just a panel and an inverter - microinverters - that are for houses, but they are designed to be used with the grid.

The output of the solar panels varies as the sunshine does, but the granny charger does not, so you're trying to put a solar curve into a rectangular charger.

A DC-DC system wouldn't need these sorts of limits. As long as it made the voltage level, it could charge the battery. It could charge the battery longer... And hopefully Tesla will have a method to do this.

-Crissa

 

[SparkEE]

It's really just not feasible with today's technology to achieve a supercharger rate of charge with a mobile solar array. That said, solar technology never could reach this level since there just isn't enough energy in terms of sunlight reaching the ground. 1000W/m2 give or take.

Assuming commercial grade panels of 430-500W per panel you would need over 300 panels to achieve a DC rating of 150kW. Each panel is around 50lbs and is at a minimum 2m x 1m (6.5' x 3.2'). That's easily 6000ft² of surface area. I haven't even mentioned equipment and line losses either.

Best to just install the arrays in strategic locations and bring the vehicle to the array.

If you look at it from a simply offset of consumption basis, it still doesn't look promising.

Assume 400wh/mi consumption and you drive 75 miles in one hour. That's a total of 30kWh energy consumption. Pretend it's perfectly sunny on your whole drive, you would need an array of close to 35kW to meet this demand based on losses, angle of incidence for the sun, time of day etc. To make it work for most sunlight hours or latitudes maybe you oversize it to 50kW. Even if panel technology doubles in efficiency (20 to 40%) you are still looking at 50 panels to offset usage. Not feasible for a vehicle.

NZ

 

[FutureBoy]

The number and weight of solar panels really depends upon the kind. And what are we trying to do... A few miles, a fast-charge, what is the goal? How many hours at what inclination?

The goal for me would just be extreme in the example and go for a fast charge. If the panels are set up to be able to match a Tesla fast charger during peak sun basically lying flat on the ground with no shadows impeding that will be the max example case. In theory if the sun were to stay constant (it won’t) then the time to charge could approximately match the charge time of a Tesla supercharger. That would be the comparison baseline.

Once we see what that would entail we could then estimate desired solar setups by fractions. Say the base case has so much volume and weight that we need a horse trailer to tow it around, then one could do 1/8 of the base system and fit it all in the CT bed. That would then take approximately 8 times as long to charge as at a supercharger.

 

[FutureBoy]

It's really just not feasible with today's technology to achieve a supercharger rate of charge with a mobile solar array. That said, solar technology never could reach this level since there just isn't enough energy in terms of sunlight reaching the ground. 1000W/m2 give or take.

Assuming commercial grade panels of 430-500W per panel you would need over 300 panels to achieve a DC rating of 150kW. Each panel is around 50lbs and is at a minimum 2m x 1m (6.5' x 3.2'). That's easily 6000ft² of surface area. I haven't even mentioned equipment and line losses either.

6000ft² of surface area.

OK There is a starting point. That at least gives an idea of what is required.

Your thought on setting up a stationary location is good too. I’ve wondered what it would take to make a stationary off-grid supercharger. In the stationary case you could add a large enough battery to help bank daylight charge so that the panels don’t necessarily have to keep a full charge rate going all the time. And the setup could be optimized for angle of the sun etc.

 

[Crissa]

Well, since the panel I linked to was 4lbs for 150 that's 12lbs for 450w. They're about five and a half square feet, and you can fit three stacks of them in the bed of the truck. Let's assume they stack four per inch, and the bed is what, sixteen inches deep? So let's forget the weird prism shape of the vault and settle for putting three stacks of 64, which weighs like 256 pounds each, well within the truck's capability, and that's ~19kW (28kW peak) when spread out on the desert floor. About half the footprint of the standard US house, 1152 sqft.

Of course, off the shelf panels you can only link about ten of them together in a group, lest they peak voltage over the top, and these are optimized to be run alone. So you'd need some weird tricks to put all the power together.

It's possible to supercharge from solar, but you have to sit still while it's out there. And it would be most efficient if the solar array were optimized for the voltage of the DC charging requirements of the truck - that way you can skip all the inverter losses and dump the sunshine right into your tank.

Hopefully, they'll have something like that.

-Crissa

 

[SparkEE]

For a truly mobile application, the panels you recommended Crissa are indeed superior but they wouldn't be capable of true 100+kW supercharging. For ease of handling and loading into a truck I'm with you all the way.

You are also correct they are only rated for 15A and 600V so you need to get creative how they are connected but these questions can be answered.

In terms of a stationery true supercharger, it would be with the rigid commercial grade panels installed on a carport like structure or a ground mount tracker array. Most definitely if they can remain in DC it's more efficient. I'd still expect to see a large battery bank at these locations with different output voltage taps as needed by different vehicles. No inverter losses to speak of but some in the wiring and charge controllers.

NZ

 

[myco.rrhizae]

I’m happy with 15 miles per day from the solar tanneau cover. It doesn’t help your traveling scenario much, but it actually has a huge affect on daily driving charge frequncy, even if you regularly drive much more than the solar array can provide in charge, because it keeps adding charge on days that you don’t drive it much.
So if you drive 30 miles each week day, then the solar tanneau covers half of that each day you drive. but then you don’t drive it over the weekend, and it has gained a charge equal to your monday commute, the solar charge from monday and tuesday covers your tuesday commute, and you only start depleting the battery on wednesday through friday. So out of your 150 weekly commute miles, you only need to pull 45 miles of that from the grid, thus reducing the frequency that you actually have to charge the vehicle by around 70%, even though the charge from the solar array only accounts for 50% of your average commute! And I know yall city slickers are commuting some 300 miles per day or something crazy like that but you get the point.

I appreciate this solar charge calculator from aptera, which gives you an estimate of how many times per year you would have to charge based on your driving habits and solar region. This changes the way the solar driving question is framed and provides an amazing perspective on the cumulative effect of both a large range and solar gain.

The results are incredible!

Sometimes I work from my shop in town, and sometimes I work on-site in neighboring towns, so on days when I ride my bicycle to work, my ct will be sitting there gaining more charge and storing it for days when I have a 30 - 50 mile commute. I may only need to plug it in overnight once a month or even less!!

 

[ltp2568]

Putting solar on the ct would be easy, all you need is the cells embedded in the roof or whatever room you have

 

[myco.rrhizae]

Putting solar on the ct would be easy, all you need is the cells embedded in the roof or whatever room you have

the tougher aspect is going to be how to wire it into the battery management system to trickle charge while driving and when plugged in, etc...

 

[Crissa]

the tougher aspect is going to be how to wire it into the battery management system to trickle charge while driving and when plugged in, etc...

Which is why we need an integrated charge controller. It wouldn't have to be very complex for custom Cybertruck compatible panels. A little more complex for standard low-voltage panels (they'd need microinverters and a sync controller).

-Crissa