Tesla owner adds 4000 watt solar panel roof to his car after company wouldn't | Hacker News Reader

Tesla owner adds 4000 watt solar panel roof to his car after company wouldn't

uniladtech.com

28 pointskoqoo70 comments

The car company likely won’t have this as an official add on because of the obvious safety issues. Even in its folded up state, this presents a significant risk to others on the road in case of an accident (ie, decapitation, death, impale). Higher the speed (highways), the higher the chance of it becoming a projectile missile.

Also what kind of weight is added here? Solar panels are heavy af. The mileage added via roof charging is significantly reduced due to less efficiency.

I would never expect a car company to sell a solution that looks like this, but integrated into the vehicles body you can remove all the drawbacks but weight (and optimize weight a lot more than the DIY solution can). See what Aptera is doing...

I think this picture makes it pretty clear why integrating solar panels in cars don't make too much sense. If this installation is 4kW and you compare the surface area to one available on the body of the car it comes clear that cost or implementation likely won't recoup investment. Both monetarily and in resource input.

In terms of dollars you should obviously expect more return by putting the same solar panels on a roof instead of a car - they generate the same energy and you aren't adding mass to an object you repeatedly accelerate.

But then you have to charge your car. The win here is convenience. If you average more charge per day than you average driving (and you have a large enough battery to load balance) you practically never have to charge (ignoring outliers like long road trips).

> If this installation is 4kW

It's 2kW.

Net effect is negative even without weight!

Tesla are 2 tons monsters that charge at 100 000 Watts. 100 Watts produced by integrated panels like this, are most likely not even enough to power up battery controller!

If you charge Tesla from normal house plug in cold, 2KW are not enough to heat up battery pack. So car has to use energy from batteries for heating! So "charging" will actually reduce energy!

Small solar panels are great for fixing parasitic battery drain on vehicles though!

If your argument is "the article is just flat out lying" I don't think we have a set of shared beliefs by which we can have an interesting conversation.

Not to mention drag and lift. This thing is very likely a net loss of efficiency while driving, even in full noon sun on a cold day, possibly a very large loss of efficiency.

I hadn't even considered lift. This got out a massive wrong in his roof and has lost most of his traction.

Lucky for him he also installed a massive aerodynamic brake

The vehicle is not driven while it's unfolded. Folded up, it looks to be a bit worse than a typical rooftop cargo carrier. It would not be a "wing".

You don't have to be more efficient while driving if the energy is "free" from while not driving, you just have to generate enough energy over the day to make up for (and then some) the efficiency losses. At "20-70 miles per day" of charge from the solar panels that is happening with any kind of normal driving habits.

Putting solar panels to that use is preventing those same panels to be used any other more energy-efficient arrangement (e.g. a car roof). So it's a net loss.

Solar panel production is limited by demand not a lack of raw materials or something.

You don’t need to worry that installing solar in less than ideal conditions will prevent highly efficient grid scale installations.

> At "20-70 miles per day" of charge from the solar panels that is happening with any kind of normal driving habits.

It's absolutely not doing 70 miles a day, and given how large and boxy the structure is when folded, the car is probably losing more than that in increased drag unless it's only ever crawled.

If your argument is "the article is just flat out lying" I don't think we have a set of shared beliefs by which we can have an interesting conversation.

All the pictures in the article are the 2000W version while the article is making ass-pull estimates for a 4000W version.

I think "the article is probably bullshit" is pretty fair.

Sure, but the bar for calling an article "probably bullshit" requires more than "well it looks at bit unaerodynamic" and introducing that argument as far down into a comment chain as you did instead of as a reply to the article is just strange.

> All the pictures in the article are the 2000W version while the article is making ass-pull estimates for a 4000W version.

This isn't clear to me? Perhaps the video makes it clear though, I haven't watched that.

The objective would be to do something like the solar roof on the Fisker Ocean. It's funny that Tesla was once invested in solar panel production but now it's a liability that diverts revenue from superchargers.

Well that's not a very good install. The drag from those panels far exceeds the puny 4000 W.

It’s not deployed while driving. Drive 20 miles per day on average and he could probably stay 100% off grid. Drive 1,000 miles in the same day and it’s a pure net loss on that day.

Why would we put something heavy on the thing we're moving around? And which would be impotent much of its time, in a garage?

One of the great benefits of electricity is the efficiency of scaled production. ICEs can only be as efficient as the small engine in each car, but EVs can take the most efficient form of production — all for the mild inconvenience of plugging the car in for 30 minutes a day...

Every time I see the story covered the figure is 4000 watt, which the creator himself does mention, but every single picture that's shared is of the 2000 watt version. I've never seen this discrepancy cleared up. The 2000 watt version takes up every last inch of roof space, how on earth is there a 4000 watt version and what does that actually look like?

Wouldn't that affect the aerodynamic drag of the car negatively?

Yes, even designed skiboxes or rails add drag. This doesn't seem even well designed.

And I wonder about long term safety too. Is it sturdy enough over time so at some point someone driving behind does not get hit by a panel flying off...

They fold up in use, so the drag hit probably isn’t that much.

If he’s getting 5-20kWh per day and the use case is a parking lot at work without EV chargers, it could easily pay for itself both in terms of energy and cost.

Probably worth removing on a road trip.

Without a cowl, the drag is still significant when folded up.

He’s getting “20 to 75 miles of extra range” midpoint is ~45 miles per day * 365 days = 16,000 miles per year.

If he’s seeing 25% extra drag at highway speeds he would need to drive over 60,000 miles per year of highway driving to be in the negative.

> He’s getting “20 to 75 miles of extra range”

He's not "getting" that, he's estimating that he might possibly get that.

> midpoint is ~45 miles per day

The estimate above, which is already not fact, is "for sunny days". Taking the midpoint of a ridiculously imprecise number pulled out of one ass as an average makes no sense whatsoever.

And the car can't be driven with the panels out, so any actual use of the car has to be discounted. Not to mention the pictures are for a 2000W (9*175, per the official website: https://www.dartsolar.com) array, the 4kW array would need double the space, double the volume, and double the weight, and the footprint might be so large it would not be deployable in public spaces.

There were actual experiments not just wild ass guess for those numbers. I took the midpoint in reference to the conditions being neither the absolute best or worst.

> so any actual use of the car has to be discounted.

Use of the car during the day needs to be discounted. This is an impractical art project so driving a solar car at night is perfectly on theme.

> They fold up in use, so the drag hit probably isn’t that much.

The folding is a huge square box on top of the car, so the drag definitely increases a lot.

Just a roof rack will have a minor but noticeable impact on drag, a ski box is 10~15% efficiency loss (http://kootenayevfamily.ca/model-3-roof-rack-consumption-tes...).

This is the worst designed roof box in history, I'd say 20~25% efficiency loss is lowballing it, unless it's only ever crawled at urban speeds, slow enough that drag is not relevant.

> If he’s getting 5-20kWh per day

AFAIK the best panels are circa 25% efficient, so 20kWh/day is not even within physical plausibility, let alone actual.

I don't know if they were ever tested by independent third party, but FWIW Lightyear's estimates for their 5sqm curved solar panels (so no loss of efficiency) was 70km/day best-case (at the height of summer, with the car in full illumination at all time), at 96Wh/km (advertised WLTP) that comes out to 6.7kWh. Again, best-case, and without a Cd hit.

Panel efficiency is calculated before rated power. 4kW * 5 hours that’s 20kWh. At ideal tilt with solar tracking you can get close to 30 kWh/day from a 4kW worth of panels in ideal conditions, but flat panels are significantly worse.

The quote was 20-75 miles per day of range. Let’s assume 25% extra drag at highway speeds. That puts breakeven at 80-300 miles of highway driving per day which most people don’t do.

> The quote was 20-75 miles per day of range.

The quote is specifically

> calculations and experiments suggest that, on a sunny day, he could gain anywhere from 20 to 75 miles

And according to the official site (https://www.dartsolar.com) it's 9x175W.

Interesting, I just assumed 9*220W panels but I can see why went cheaper.

Very much so, it also increases the weight, and given what solar panels produce, you're probably not making out the difference.

Lightyear advertised a best case of 70km (44 miles) per day from panels, best case, out of 5sqm of fully integrated curved solar panels and a Cd of 0.175.

And then it was cancelled (and back-named a proof of concept, I'm sure the 2 years delay and unit price going from an original 175k estimate to 250k didn't help). Supposedly they've started work on a more reasonably priced model, ETA 2025.

You know, at first I said this is a stupid youtuber stunt, probably dangerous, and definitely wasteful. But, if it could fold up like that then I see no reason it couldnt be designed into a areodynamic fairing, and its a surprising amount of solar coverage. All in all, I would never put this on my car, even if I was paid; but, it could be done very professionally, its significantly less impractical than I was expecting (though not totally), and the most important part is people want it.

Would this be better than flexible panels wrapping the existing body panels? (given lesser efficiency + only a small portion of them being angled correctly at any time, but little to no extra drag and could be charging batteries while in motion).

I started to think about the folding up thing. And I think it makes it worse. Considering things like long time reliability. There is fact that you somehow need to connect those panels electrically. Just considering various potential water ingress issues when driving in rain at high speed. Yes, you can make water-resistant connections, but them correctly operating over years...

And next is vibrations, from cross-winds, bumps in road or traveling over uneven surfaces. Adding up over longer periods.

Not to even mention possible wear and tear of spreading them possibly everyday or multiple times in a day... And for bonus, at least here there is periods where mud is relatively common so this will travel in mechanism making it harder to operate...

I would be worried about long term reliability and usability.

just... put it in the trunk and only put it on the car when you park somewhere. Maybe you just have to use more, smaller panels but I don't see why you couldn't do that.

I have been very interested in the Prius Prime recently as it seems the be the perfect plugin hybrid for me and had a solar roof option that can get you 4 miles of range during a sunny day. That would actually cover how much we drive on an average day which makes it tempting.

Of course the fact that me and my partner drive less than 4 miles a day makes car ownership questionable and we should probably just invest in bikes.

What I would rather like to see is the chassis itself act like a solar panel. Of course safety is a concern as it will add weight and possibility of being brittle but they did that with solar panels, I can’t see why it’s not possible with the cars. That wouldn’t require a fold out and the car will be constantly charging at an additional weight which is hopefully much less to the mileage.

Counting the sacrifice of 0.25 Cd with the aerodynamics of a Mack truck and the added weight plus cables and charger, it's probably only good for OTG emergency purposes and self-promotion on social media. Even with 500W panels, they're only going to produce that in full sun for a few hours in summer. Overcast or wintertime, expect <1kW most of the day.

I don't understand the criticism of the comments at all. Most common use case is commuting to work with averages of 1h drive and 40 miles. With a potential of 8 hours of light while at work that sounds to me like it would make up for any drag it adds for that short commuting drive.

This, plus say a Honda Goldwing engine-hybrid electric thing, would do ungodly distance per unit of fuel.

Ungodly -> anti-God -> demonic -> bad.

Bad distance per unit fuel. I agree. This thing is terribly inefficient.

It could just be a mortal distance per unit fuel. It’s not anti godly.

or just "Outrageous"

That Goldwing would ride like a Bat out of Hell [1].

[1] https://en.wikipedia.org/wiki/Bat_Out_of_Hell#/media/File:Ba...

Could cover parking spaces with solar panels either as a permanent install or as a pop-up carport with a solar roof.

Dude should have just put in a hitch and attached flat-bed carrier filled with solar panels.

You can actually buy these, they're called solar generator trailers. They're like a bunch of solar panels, batteries, invertor, etc. All in one. It's like a portable Gen set but solar

This is absurd. You'd make less power from the panels than you would use from carrying them around.

Install the panels where you charge the car, instead of taking them with you.

Can't a specialized use case exist? RVs are not great homes, but they are great homes on the go...etc.

Panels on modern RVs are common, but RVs have a lot less weight and aerodynamics concerns.

And here they are installed flat on the car roof which makes the efficiency even worse.

When panels are mobile, such as when attached to a moving object, flat is the most efficient angle.

Not when they overhang the front nose

Good point, I overlooked that, there's no way to be as efficient on a moving object anyways and being flat makes it less worse.

The average charge of 20-75 miles per day is more than average miles driven per day*. The large battery pack means you can load balance between days and you mostly only care about the average. Given normal driving habits not only do they produce more energy than it takes to carry them around, they produce so much energy that you would practically never have to charge the car at all.

(It should be obvious that these numbers depend on where you are though, e.g. north of the arctic circle in winter they will almost certainly hurt more than they help)

* 37 in the US per https://www.kbb.com/car-advice/average-miles-driven-per-year...

They already did it, and they get 20-75 miles per 5 hours of daylight. So, it's kind of too late to predict that it will cost more overhead than it generates. This is easily entirely free commute and even the side trip to the grocery store for a lot of people.

And this is only the crude diy proof of concept. It surely doesn't do as well in winter etc and of course is fragile and not aerodynamic and will probably break 8 times a year in some way, but all a proof of concept has to do is prove the concept, and this certainly did.

It probably just still isn't practical for a manufacturer to try to scale it out to offering the more efficient non-diy version.

But then again, I'd have said that about any EV at all just because of the batteries, charging circuits, and weight, and yet there they are millions of EVs out there existing despite my incredulity, like they just don't even care that I think it shouldn't be workable.

> They already did it, and they get 20-75 miles per 5 hours of daylight.

They don't. They estimate that they might possibly get that in the best case scenarios:

> DartSolar's calculations and experiments suggest that, on a sunny day, he could gain anywhere from 20 to 75 miles

> It probably just still isn't practical for a manufacturer to try to scale it out to offering the more efficient non-diy version.

Manufacturers have already attempted that, go check out lightyear.

All that… for maybe 50 miles of range?

He probably lost half his range at highway speeds and is destroying his battery from the increased power draw

Instead of wasting time on failures such as self driving, Tesla could design car bodies made of solar cells. They may not be super efficient, but would add some extra power.

its probably because they charge insane amounts for using superchargers...

I see any dc fast charger as paying for convenience.

I handle the majority of my charging at home overnight at my usual utility rate, but if I need to quickly charge up while on the go it’s a special case I’m ok paying a premium for.

I dont see it like that... they are obviously over-charging. (no pun intended)

And where I am at least, the superchargers aren't really even any more expensive than my utility rate

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