Impacts of Adding PV Solar System to Internal Combustion Engine Vehicles

The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible.

If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.

Very nice. How long does that tend to stay alive for? And what kind of cold weather conditions do you have to contend with?

Who lunches for several days/weeks? logically you would charge high speed through a plug with energy generated by panels that are much more efficiëntly placed and not have to carry around.

You might like the series by youtuber 'Power of Light' where he packs solar panels in his car to charge his car to do a solar cannonball run from New York to California on those solar panels alone: https://m.youtube.com/playlist?list=PL9nfj0jfPXYBF8FO7sckzvV...

Can't remember how long it took, think a couple weeks at least?

Not sure if I've slipped a 0 here but 500w taken over the year, at say a 10% capacity factor, is still over 3500 miles of range per year. A fair bit short of the average mileage (in the UK somewhere around 10k) but still more significant than I expected. Of course 500w is a lot of solar for a car and 4 miles / kWh is also quite efficient.

This is a good way to look at it, but perhaps a new unit, like range per hour? Since mph is alreday a unit of velocity.

There have been solar car competitions that colleges have been doing for decades. Here's a YouTube compilation of one that ran last week: https://www.youtube.com/watch?v=ZBin-oXBJzM

I think it can help calibrate people's intuitions about what you can expect out a pure-solar car.

You also need to remember that inside those shells is basically nothing but a driver. No AC, no batteries, no seats for people beyond the bare minimum. And that's broad daylight. So you need to look at them doing 20-30mph and bear in mind that it's still not comparable to a street-legal sedan of a similar size doing 20-30mph... those cars are essentially as close to "a mobile cardboard box" as the competitors can make them.

You might be able to build something that people would agree is "a bus" that moves with a couple of people on board, but it probably will stop moving once it enters shadow. Anything that we'd call "a bus" is going to need a lot more physical material per unit solar input than those cars have. I'm not sure that even "moves with a couple of people on board" will necessarily end up being faster than those couple of people walking, either. It's effectively impossible to power a vehicle with its own solar footprint in real time. It also ends up difficult to use them to power batteries because having to move the additional mass of the batteries eats up the advantages of being able to gather power for larger periods of time. It's possible, because of course you can hook a car up to solar panels and eventually charge it, but you don't get very many miles-per-day out of it for what fits on the car itself alone if you work the math.

Well, if you have a fixed route you are not limited by space on the vehicle to put solar on, but can provide electricity via a rail or wire or something and then gather energy on some larger Solarstation or from wind turbines or what else comes to mind.

Then you can reduce rolling resistance by using steel tracks and steel wheels ...

... and oh, you have invented the tram/light rail ;)

(But even with solar you need to finance the construction and maintenance, even the slow vehicle need some ... thus either tax finance or charge fares or mix income)

It's an interesting idea. I did some napkin math based on the Solaris Urbino 18 bus. The buses have about 45 square meters of ceiling area (18m by 2.5m). Assuming efficient solar panels you could get 250w/sqm. That works out to 11.25 kwh/hour. The bus advertises with 600km of range with 800kwh of batteries so that is 1.33 kwh/km. Hence it could do ~8km/h on average when it is sunny.

The math does not really work out to a viable product with this bus, but it is not too far off. A city bus that has been purpose-built for low speed in urban areas without other traffic may work as it can make some sacrifices. For instance, since it runs much slower on average it would need smaller engines. It could also use more light-weight material since it won't need to handle high speed collisions. If it is just used for short distances within a city center it could also do away with seats. Lower speed should also lead to lower consumption.

The Solaris Urbino 18 weighs 17.5 tons curb weight. Assuming fuel consumption is pretty linearly related with weight and you could get it down to less than half, you could get a bus with a range of 10 miles per hour of charging. If it drove for 6 hours a day, but got charged for 12, 20 miles on average per hour is possible.

4kW on a bright sunny day, for a few hours around noon. Even my small EV outputs 100kW when floored, and 4kW doesn't get it very fast.

We have trams. We don't need to make worse trams

I suspect the lightweight, and hence low power requirements, are the correct part of the hypothesis. But making the vehicle as big as a bus implicates a lot of weight. Maybe a solar charging cargo bike fairing would have some benefit, but that's an expensive bike and it will tend to get stored indoors.

Yep. A solar car ceiling seems great to make EVs more reliable on the hands of people that only charge them rarely or may travel to the middle of nowhere and can get surprised by battery faults.

Those are a very small share of car owners, and EVs are nowhere close to the market penetration to care abut them. But it will eventually make sense.

Of course. It is an intriguing idea, but a local maximum.

- The panel sits at open-circuit voltage of 48V

- That then needs to be converted/boosted to 400V (conversion loss)

- The converter needs to talk to the BMS to make sure batteries can be charged at this moment (component that is live all the time and is a current draw)

- Need to think about it, but you want another set of contactors between panel and HV-Bus where the battery sits (current draw)

1km of driving is 150Wh so 1kWh gets you 6.6km or 4.1 mi

Let's be generous and say you have a 500W panel(punchy) for 8 hours at full blast (doesn't happen), you get 500W x 8 hrs = 4kWh. Lets say isolated converter loses you 10% so you are at 3.6kWh Thats 24km or 15mi of driving in perfect conditions.

2x Gigavac contactors, keep them closed costs you 24W, so that lowers the input further to 476W * 8hrs = 3.8kWh, less 10% = 3.42kWh ...

Someone who studied EE might be able to make this more accurate. Back of the napkin math, not totally impossible, but not worth adding it for a trickle charge. Adding components that can break, adding weight etc.

There are interesting solar cars out there where you reduce the weight heavily and fold out big solar sails. Then you are getting somewhere, for a city car you don't have enough surface. For an SUV or American Style Flatbed truck you have so much weight it's not worth it either.

Exactly.

Only thing holding off my EV purchase is that I want proper V2G support. If I'm paying for 100kWh of lithium battery capacity I damn well want to use it as a backup for my house.

That's actually mandatory in France for large parking lots

The study literally proves you wrong.

So .. it would make sense to make a law that requires new parking spaces to have a solar roof which can charge the cars which park there for a few. This would spread rather quickly, I think.

I have solar panels at home and can charge a car .. but I'm mostly parked elsewhere when the sun is shining the most.

Those people dont read papers or believe science

Needless manufacturing complexity. Far better having static panels with current tech.

They are nice gimmicks like that newer model of Prius but far from being economic reality.

That option is a gimmick though.

I don’t believe the primary cost is so much the physical panel but the cost to engineer and design it into a roof, also the additional systems needing to hook it into the wiring harness. It’s a fun toy for some but has no real benefit for the many.

I don't remember the exact details, it's possible that he charged it over the weeked (or just didn't use it, thus getting 2 extra day of charge).

You can play around with assumptions, like what if it was driven in stop-and-go traffic at very low speeds? Then your quoted 270Wh figure might be lower.

But anyways, with these general conditions, with the numbers you quoted, and with a 10 kwh battery (aspull), you'd be looking at a net loss of 775Wh/day, which means you could go 13 days between charges.

The point I tried to make, is that solar panels on hybrids/EVs add a lot of practical value to people who can't charge at home/work, and it's not just meaningless greenwashing.

Also that 2.6kWh figure is a yearly average probably, sunlight varies greatly over the year.

Let's not forget to do the math on how much less efficient the vehicle is over all with panels strapped to the top messing with the aerodynamics.

Even then, he said hybrid.

If he only drives Mo-fr the math works out though

Are we sure his car wasn’t a Twike or something? There’s ultralight EVs for which this could work.

Edit: Never mind, “hybrid station wagon”.