Solar Roof Option

[bxr140]

Solar panels on roofs don't make sense now.

They will make sense as a viable option when the cost/mass/efficiency eclipses battery technology (when compared to 'just put in a bigger battery') for things like legitimate cabin thermal management (not just a fan), lights, and possibly even traction pack thermal management.

They will become ubiquitous if the efficiency of cars increases and the cost/mass/efficiency/technology/simplicity of a solar collection device evolves to a point where you can get a legit dozens of miles of range per day.

 

[JRP3]

The Prius is DC -> AC. Nor is that jump nearly as big.

DC/AC is more complicated than DC/DC.
Regarding the "jump", I'm guessing you think the solar panel has to operate at 12V. It doesn't. You can wire a higher number of solar cells in series to increase voltage to whatever you want when you build a panel, just as you do with battery cells. I think the Fisker Karma panel was a 120V panel.

My point was not that it was physically impossible. Just that is was an unsolved technical challenge that I don't think should be put in the way of delivering those 400,000 cars, as the gain will be 'cosmetic'.

It's not an unsolved technical challenge at all.

 

[JRP3]

Totally feasible, and arguably darn cool! And it may very well be added as the model matures.

Odd that you spend so much time arguing against it then...

 

[Topher]

DC/AC is more complicated than DC/DC.

Nope.

Regarding the "jump", I'm guessing you think the solar panel has to operate at 12V. It doesn't.

I am guessing you didn't read my previous posts. Solar cells are 0.5 Volts fixed. That is the voltage band gap. In order to get 375 Volts you would need to string 750 of them together.

Thank you kindly.

 

[JRP3]

Nope.

Support that claim.

I am guessing you didn't read my previous posts. Solar cells are 0.5 Volts fixed. That is the voltage band gap. In order to get 375 Volts you would need to string 750 of them together.

So you agree with me, that your suggestion that the voltage "jump" would be greater is not necessarily true. It depends on how the solar panel is built.

 

[gregd]

Nope.



I am guessing you didn't read my previous posts. Solar cells are 0.5 Volts fixed. That is the voltage band gap. In order to get 375 Volts you would need to string 750 of them together.

Thank you kindly.

Cells are 0.5-ish volts each, yes. But with an external DC-DC or DC-AC inverter, they can be made to drive any voltage. Power stays the same (or 90% of it), so you don't get a lot of current, but matching the voltage is not an unsolved problem. In fact, I'd recommend a tour through the search engine of your choice for the topic "MPPT". Get enough cells for the power, and match them (series / parallel) to the controller.

Given the available glass surface on the M3, you could probably gather a few hundred watts. What's the best use for that? I'm still thinking a semi-active thermal management while parked, but being in the CA Central Valley, and looking at an approaching summer season, I may be biased.

 

[sandpiper]

Solar panels on roofs don't make sense now.

They will make sense as a viable option when the cost/mass/efficiency eclipses battery technology (when compared to 'just put in a bigger battery') for things like legitimate cabin thermal management (not just a fan), lights, and possibly even traction pack thermal management.

They will become ubiquitous if the efficiency of cars increases and the cost/mass/efficiency/technology/simplicity of a solar collection device evolves to a point where you can get a legit dozens of miles of range per day.

I don't see it. An imaginary 100% efficient solar panel would output 1kw / square meter in full sun on an absolutely clear day. Good quality commercial panels are 15-20% efficient right now. And MAYBE you'll see 30-35% one day - so roughly 1 kw for a 3 square meter panel. So, again, assuming 8 hours per day of clear sky, full-sun equivalent, you'd need 10 days to charge a 80kw-hr battery. And the reality is that you'll pretty much never get anywhere near that.

As to the efficiency of cars... electric drive-trains are pretty darned efficient. The motor is likely>90% and you might lose another 10% in the gearbox. And I seriously doubt you're going to see cars with coefficient of drag of much less than 0.2 (Model S is 0.24) In both of these cases, we've been working on the basic tech for >100 years and we're at the point of diminishing returns.

The sun simply doesn't deliver enough photons to do the job.

 

[Noob1]

Elon has said it will not work, I do wonder about air flow from the front of the car could not help?

 

[M0DEL³]

I agree.. even if its 1/2 a mile..

I've got to wonder, how much extra would you be willing to pay for that extra 1/2 mile range?

If there was to be a solar roof - and I'm not totally against the concept - I'd prefer to see it be engineered to live-support a climate control system so the interior was maintained at more comfortable temperatures during the day when the car was simply sitting out in the sun. But even then I would have to wonder what the weight impact of that apparatus would be on range.

I own a 49 KW off-grid Solar Plant, and my son is a PhD researcher in the world of perovskite solar cell development, so we have conversations about the practical, near-practical, and totally impractical in the world of solar. The idea of meaningful range extension is an impractical goal, and will continue to be so for the foreseeable future.

 

[theganjaguru]

You can certainly charge the traction battery. But you'll be there for a LOOOOOONG time. If you manage to get, say, 3 square meters of solar panel (optimistic) that will give you, in great weather, 0.45 kw of output during the sunniest part of the day. Assuming that, over the course of the day, you can get the equivalent of 8 full-sun hours (highly optimistic), then you would get 3.6 kw, or 19 rated km of range per day, less the vampire drain. Even assuming the vampire drain was zero, you'd be 22 days to add 80 kw of charge.

Once you allow for rainy/snowy days, parking in poor locations and vampire drain, I can see that you'd get pretty much nothing out of the panels.

Germany sure doesn't have a problem with cloudy days and their solar infrastructure.

Most Americans drive around 20 miles a day, you're telling me you don't think people would not like roughly half their commute back (if we use your generous 19 km estimate) from free green energy?

In California, (one of the largest car markets) most of the cars are parked outside in very sunny weather. Sheltered parking spots are rare for the most part. How many rainy snowy days out of the year are there really going to be? 300? I'm dubious that there will be that many rainy days. Again, I point you back to Germany.

Taking this a step further, eventually, these cars with solar roofs (along with other BEV's could be connected to a vehicle to grid program wherein they could help load balance the grid during times of peak usage (which usually occur during the middle of the day in the summer) and prevent rolling blackouts.

 

[theganjaguru]

I see. I was browsing on my phone and didn't see the text of the article. That's a little more useful but in climates where it is the most useful, people do everything they can to find shaded parking. 8 miles of range a day isn't much for the Model S but it's 30% of the pack on the Prius so more useful there maybe. If it adds more than $500 to the cost of the car I'd rather just save the money and have a sold roof. Many people have garages so the it wouldn't help then either.

8 miles a day is almost half a commute for the average American. Again, you don't think people would like almost half their commute back from free green energy? Shady parking spots are a premium and not widely available. Most people have to park in the sun. As I said a second ago, solar roofs in a vehicle to grid program along with other BEV's could totally modernize the grid.

 

[JRP3]

So, again, assuming 8 hours per day of clear sky, full-sun equivalent, you'd need 10 days to charge a 80kw-hr battery.

Why would you pretend that a battery pack needs a 100% recharge each day? A 12K mile per year vehicle does an average of 33 miles per day, using 250Wh/mi that's 8.3kWh per day.

 

[nwdiver]

I seriously doubt many people here are arguing against solar powered cars.... my car is solar powered but I keep my panels on the roof of my house not the roof of my car.

Aside from the high cost and low return... most people would prefer NOT to park their car in the sun of they can avoid it... further decreasing the usefulness of car mounted panels.

As this becomes more common... solar panels on car rooftops would be less and less productive.

Plugging into a simple 110v outlet would deliver more power than covering your car with the worlds most efficient solar panels.

 

[JRP3]

As this becomes more common... solar panels on car rooftops would be less and less productive.



Plugging into a simple 110v outlet would deliver more power than covering your car with the worlds most efficient solar panels.

Sure, but that's assuming all those parking spots under the solar panels have plugs, which in most cases they don't seem to, and it's still assuming a significant portion of open parking lots will be covered with solar panels, which, if previous calculations are correct that all our power needs could be met by covering only 0.025% of all open parking lots, simply will not happen. Once all our power needs are met by renewables there is no reason to keep putting up solar panels other than on new construction.

 

[nwdiver]

if previous calculations are correct that all our power needs could be met by covering only 0.025% of all open parking lots, simply will not happen. Once all our power needs are met by renewables there is no reason to keep putting up solar panels other than on new construction.

What previous calculations? The US uses ~4000TWh/yr. There's an estimated ~800M parking spaces and each one could support ~2kW of solar... that's 1.6TW of solar for an average annual generation of ~2600TWh if we covered all of them... and some of those 800M would obviously not be viable if they're on not the top floor of a parking garage

As EVs become more common I would expect public charging to also become far, far more ubiquitous.

 

[EVnut]

Odd that you spend so much time arguing against it then...

I know! I'm complicated, right?

Might serve you better to pay more attention to just what it is I'm arguing against. Being "cool" and maybe available in the future does not equate to it being a good idea to implement on this car today. Very much like what the trunk lovers are telling me about a hatchback option.

Our opinions on this have no bearing on much, really. The only benefit from threads like this is the education that's available from listening to other people share their knowledge and opinions. Note that there are some folks in this thread who know what they're talking about well beyond what looks cool, and what would be great to have. Arguing is sometimes fun though, so carry on!

My advice is to stick with the vampire drain replacement, or ventilating fan, and back off the range-extender idea. We have a lot of EVs on the road today. Including from the brilliant folks at Tesla. There's a compelling reason that none of them have solar range extenders built in, or even as an option.

 

[AZ Desert Driver]

No.. You're sadly misinformed... It would add almost zero miles per day. The amount of solar power that would be able to be collected on a small solar panel on the car's roof is ridiculously small.



Toyota uses the small solar panel to run.. a fan.

So you were in line at 10:00 am and got RN 107x, and I was online at 7:43 and got RN 1078. Think the RN might be closer to a random number generated values instead of a sequence?

 

[stevejust]

I had a deposit on the Fisker Karma, the first car with a solar roof. I also owned a 2010 Prius with the solar roof option. I also had a Nissan Leaf, but did not have the solar spoiler option.

The short answer is that putting solar on a car is incredibly stupid. (and I'm a guy that loves solar, and has a 9kW solar array on the roof of my house/garage where solar belongs).

 

[JRP3]

What previous calculations?

Posted up thread:

Considering that there are about 800 million parking spaces in the US at 25 m2 per space, that's about 20 million km2 of surface area. When you consider that it would only take about 5,000 km2 of solar panels to supply all the electricity needs of the US, asking for 10 million km2 to be covered in solar panels would be overkill. About 0.025% coverage would give us all we need.

Obviously you reached different conclusions, maybe you could clarify.

In any case, probably for the next 10+ years an EV mounted panel is going to be more useful than the essentially nonexistent solar car ports with plugs. Again, my perspective is that as "silly" as a vehicle mounted solar panel may seem it's much less so than other potential options which people could spend money on.

 

[nwdiver]

Considering that there are about 800 million parking spaces in the US at 25 m2 per space, that's about 20 million km2 of surface area. When you consider that it would only take about 5,000 km2 of solar panels to supply all the electricity needs of the US, asking for 10 million km2 to be covered in solar panels would be overkill. About 0.025% coverage would give us all we need.

There's two errors here...

- A parking space is closer to 15m² than 25m²
- 800M x 25m² = 20k km² not 20M km²

You'd need to cover all parking spaces to cover 50% of annual US electricity demand.


..... as an aside... this is what ~10M km² looks like on a map

The entire US is 9.8M km²