Comment by philipkglass | Hacker News Reader

Comment by philipkglass | Hacker News Reader

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The raw materials for perovskite cells are cheap, but so are the raw materials for silicon cells. There won't be hard cost numbers on perovskite PV modules until they go into volume manufacturing. They won't go into volume manufacturing until they can be stabilized enough to last years in the field.

My personal guess is that single-junction perovskite cells will not ever overtake single-junction silicon cells for rooftop or utility scale solar. Single junction perovskite cells may be used in applications where light weight and flexibility are advantageous, like charging portable electronics, if they can be stabilized.

Perovskite cells may compete in rooftop/utility solar with conventional silicon when incorporated into tandem cell designs -- either perovskite on silicon or a stack of different perovskites with different band gaps. That gives them the potential to exceed conventional crystalline silicon module efficiency rather than merely play catch-up. The company that seems to be furthest along with this approach is Oxford PV, which is pursuing a perovskite/silicon tandem design:

https://www.oxfordpv.com/perovskite-silicon-tandem

Full disclosure, I know next to nothing about solar markets. What about putting panels on vehicles? Couldn't the market for cells on vehicles overtake the existing solar market?

There isn't enough surface area on vehicles for that to happen.

The world installed about 117 gigawatts (peak) of solar PV last year [1]. If the average panel is 17% efficient that's more than 680 million square meters of panels being manufactured per year. World motor vehicle production in 2018 was 96 million [2]. To put more solar panels on vehicles than we already put in fields and on rooftops, the average vehicle would need more than 7 square meters of surface covered with panels. That's neglecting that most vehicles are still internal combustion vehicles that couldn't do much with the electricity those panels would generate.

[1] https://en.wikipedia.org/wiki/Growth_of_photovoltaics

[2] https://en.wikipedia.org/wiki/List_of_countries_by_motor_veh...

>There isn't enough surface area on vehicles for that to happen.

Yeah, it's the old square-cube law in action.

Just not enough room really. Maybe(read: no) you could get 5m^2 of panels on a car. With 100% efficient panels the energy would be 5 * 1000 W m^2 = 5000 watts which is about 7 horse power.

That is a bit below what a very aerodynamic car needs to maintain highway speed so sort of relevant from a range extension perspective but 100% efficient panels and 5m^2 being fully illuminated at once are not very realistic assumptions.

I could see electric trucks(non commuting) + tiny home on wheel with big arrays potentially being viable though. That + starlink would make a pretty cool working remote combo.

All factors considered, solar panels average 10-20 watts/m^2. A Tesla uses ~325Wh/mile, Leaf ~250, Cybertruck ~500.

Putting PV panels on a vehicle can give you a few miles per day - enough to get you to a plug if battery drains too low. More an emergency tool than viable power source.

I think you meant to say 100-200 watts a square meter average output as a 300 watt solar panel isn't much larger than a square meter. Either way, you are right that it is unlikely that solar charging via a car roof will be anything aside from a backup/gimmick. But it is possible to get a good charge from solar panels on a rooftop with not a huge amount of panels.

Most of the time the panel is at a sharp angle to the sun, or in shade. Fully half the time it is entirely in the dark.

OP is probably correct, maybe even high in their 10 to 20 W/m^2 estimated average output for car mounted PV systems.

Rooftop mounted, optimally oriented PV systems at Seattle latitude have an annual capacity factor of ~ 14%. That means a 1 kW system will average 140 W output over a year. That system has a module area of about 4-7 m^2, equivalent to the area available on a sedan.

On a car that has suboptimal module orientation and solar exposure, "power density" (RE: Smil) is really low.

Ok, that makes sense if you average over a year considering night time etc. Yeah, car mounted solar isn't a great idea unless we were in a mars rover type of situation which is not how we use cars.

I meant what I wrote. Sure you get 100W/m^2 when the sun is shining perpendicular to the surface, but divide by night, clouds, angles, dust/snow, latitude, air transmissiviness, line/battery/conversion loss, etc and you’re well under 20W long-term average.

If your goal is to power the car while driving, even 100% efficient solar cells wouldn't be enough, as there simply isn't enough surface area to gather enough energy to power a normal car doing normal driving. If your goal is to leave the car sitting charging in the sun all day, that's a bit more practical, but I believe there aren't yet any production vehicles like that yet: https://en.wikipedia.org/wiki/Solar_car

Solar trees could help for the parking, but I don't know how the economics of that plays out.

It's probably worthwhile to put solar on cars, but it doesn't really do much to improve range.

A way to think of it is to imagine a gas-powered car with a gas tank that magically refilled at a rate of one gallon per week. That would be a great feature, but it wouldn't really change what you do with the car. It would mostly just mean spending less on gas over the lifetime of the car.

In the end, a car costs a lot of money and provides a couple square meters of usable space. Roofs of houses are a lot bigger and can supply the needs of a household, but if you're in the business of energy production and want to generate energy on the scale of a major power plant, it makes far more sense to use cheap land in sunny places away from cities.

I tried estimating the range per day if you put solar panels on top of an RV. I think it was ~10 miles day. That's a tantalizing number since a lot of RV's sit for long periods of time.

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