Solar panel on the roof

[iKaruna]

I just picked up my i3 this morning, so I'll be checking out this site regularly for the latest i3 comments. Since this is a recommendations for BMW thread (my first posting), I'll limit it to that. I think BMW should put a solar panel on the roof, sorta like the Fiskar. It could power the accessories and possibly charge the battery.

 

[I33t]

Previous threads on the solar panel idea:

http://www.mybmwi3.com/forum/viewtopic.php?f=5&t=1844

http://www.mybmwi3.com/forum/viewtopic.php?f=11&t=1756

Basically, nice idea but it won't charge the traction battery (~400v+). Running a fan would be possible and keeping the 12v battery topped up, but not much use in a garage or under shelter.

Better to put solar panels on your house and charge from there.

 

[jadnashuanh]

There's a thread on this already. Consensus, it's not likely worth the added expense or complexity. NOt enough area to do much for the high voltage batteries, and making 400vdc to charge them from some low level PV panel would probably take as much power to convert than actually increase their SOC. It could be used to maybe provide ventilation when hot, but not a big deal.

 

[BoMW]

There is a thread about this already, search "solar panel" or any other other topic that interests you.

 

[jadnashuanh]

There's at least a couple of ways to use solar panels...augment the power from the grid when the sun is shining, or, if self-contained, be able to store enough energy for your peak and average power needs when the sun is not shining or you need more than you can make at the instant. That usually means batteries to store it. At Niagara Falls between NY state and Ontario, Canada, they use some excess power, when available, to pump water to a reservoir so that they can keep water flowing over the falls for the tourists during the day. IN reality, they can almost stop the flow over the falls when they direct it to the turbines and to the reservoir. There are some major tunnels upstream of the falls that direct water to the turbines below the falls.

The area on the top of the i3 isn't all that much. Modern panels need about 10sqin to produce one watt. The i3 seems to use around 250W/mile. At 60mph, that's one minute. That means 250*60 minutes for an hour, or 15,000W. So, to power the car, at 10sqin per watt, that's an area of 150,000 sqin, or over 1,000sqft...how much do you think you have on the roof?

 

[alohart]

<Ignore. An administrator has deleted a spam post.>

 

[Blacky]

A solar panel on the roof does sound like a good idea but the question still remains if it is going to be functional enough for the car and whether if it work for this particular model.

 

[jadnashuanh]

If you're lucky, you might get a peak of 25W/sqft in direct sun, during the best part of the day. That won't happen often, and the roof is not flat, so how you parked it as well as where, would make a big difffernece. Some makers plan the cells to power things like the HVAC to offload a bit of power usage. Today, I don't think you'd gain enough to offset the initial cost over the life of the vehicle. And, if Trump has his way, solar cells will jump in price radically once imported into the USA. Why he thinks that's a great idea, I don't know.

 

[sipabit]

The Toyota Prius got a solar roof for powering accessories in Japan, but the US never got it. Apparently it's because the solar roof wouldn't pass US regulations for safety. Not sure how Fisker got away with it.

 

[Srivenkat]

Actually, my 2010 Prius III (USA) has a solar roof, but it's only used to run the cabin fan to try and keep the interior temps the same as outside ambient temp, potentially preventing the HV battery from being heated up too much. I wish it had also charged the 12V battery.

 

[Tacfoto]

The reason electric cars don't have solar roofs is simple. It will on average reduce the range. The weight of the panel and necessary electronics will make the car heavier. The extra electricity you get will not extend the range farther than the weight will reduce the range.

In theory, a day parked in the sun charging the car could add some additional distance to a depleted battery.

A far better option is to add panels to your house.

 

[Simoni3]

We've got 11.5kw on the roof
Our annual electric bill is £500
Two EVs 25k miles per year, AC in the house
Essex sunshine

 

[JohnKelly]

The reason electric cars don't have solar roofs is simple. It will on average reduce the range. The weight of the panel and necessary electronics will make the car heavier. The extra electricity you get will not extend the range farther than the weight will reduce the range.

In theory, a day parked in the sun charging the car could add some additional distance to a depleted battery.

A far better option is to add panels to your house.

You are mostly correct... however, it is the coefficient of drag as well as weight that limits how useful solar on a vehicle can be. You should look into the reborn company of Aptera. They are past the prototype stage and are starting production intent builds for crash testing etc. The initial offerings will come with 700 watts of solar panels built in extremely lightweight but very strong and flexible curved glass to fit on the hood, dash, roof, and hatch (w/rear view camera). On an i3, 700 watts would be hardly worth mentioning, but with a coefficient of drag of just over half that of the very slippery Tesla Model 3, and a weight of about 1,900 lbs the Aptera expects to be able to get up to 40 miles of range a day from solar... under ideal conditions, of course, but even 1/4 of that is a significant boost. My next EV... if they successfully bring them to market.

 

[Tacfoto]

Hello. In my comment, I presumed solar panels integrated into a roof that did not alter the car's profile or coefficient of drag. The carbon fiber roof of the the i3 replaced with a custom built solar panel for example plus the necessary electronics to integrate them. An off the shelf panel attached to a roof rack or similar would of course add air resistance making things worse.

I am aware of the Aptera three wheeler, and it's very interesting. The numbers seem optimistic. For example the area of solar panels shown on prototypes is considerably smaller than 700 watts of current conventional solar panels. And can't be tilted toward the sun like conventional panels. And I'd be curious to see if the 40 miles of extra range are sunny day vs night on the same car. Or Sunny day vs car without the weight of the solar panels and electronics. The solar panels on the prototype vehicles are stickers.

Don't get me wrong, I wish them all the luck in the world. I'd just like to see a watt meter that says 700 watts vs a prediction.

 

[JohnKelly]

Hello. In my comment, I presumed solar panels integrated into a roof that did not alter the car's profile or coefficient of drag. The carbon fiber roof of the the i3 replaced with a custom built solar panel for example plus the necessary electronics to integrate them. An off the shelf panel attached to a roof rack or similar would of course add air resistance making things worse.

I am aware of the Aptera three wheeler, and it's very interesting. The numbers seem optimistic. For example the area of solar panels shown on prototypes is considerably smaller than 700 watts of current conventional solar panels. And can't be tilted toward the sun like conventional panels. And I'd be curious to see if the 40 miles of extra range are sunny day vs night on the same car. Or Sunny day vs car without the weight of the solar panels and electronics. The solar panels on the prototype vehicles are stickers.

Don't get me wrong, I wish them all the luck in the world. I'd just like to see a watt meter that says 700 watts vs a prediction.

You may have missed part of my point... it's the low coefficient of drag of the Aptera vehicle itself that makes a small solar yield a viable and worthwhile effort. As I mentioned, even if the yield is much smaller than the stated optimal, it will still make a difference with such an efficient vehicle. If you look on youtube, you will find videos showing that they developed their own extremely light weight custom solar panels which are very flexible, yet strong enough to resist hail damage. To me, this is interesting stuff, but far from the most important feature the car boasts. It's efficiency and unique design are what appeals to me most... the solar is just an extra bonus. And, of course the numbers seem optimistic.. all advertising and promoting of almost anything will use the best possible numbers... and they should always be taken with a grain of salt : ) Having said that, the Aptera crew seem to be the most transparent start up imaginable. I have watched many videos and I like the crowd funding aspect and the refusal to take on massive debt and start out in a large hole that could sink them.... like so many other EV start ups which appear to be struggling to get the massive funding they need. Aptera is has a much more efficient scheme, with far fewer parts, a different strategy to become successful, and a unique design. I hope they make it. They say they only need to sell 6,000 of these per year to break even. That is a stunningly low number. Thanks for your comment!

 

[808Pants]

We've got 11.5kw on the roof
Our annual electric bill is £500
Two EVs 25k miles per year, AC in the house
Essex sunshine

So do you seldom drive in the daytime? Otherwise...separate battery storage, then?

 

[robthebold]

IMO the solar panels on the Aptera is more of a marketing gimmick. The claimed output of the solar panels is way higher than could be hoped for, even if it were sunny with a 100% chance noon all day. OTOH, that 700W isn't going to do that much for its range -- that's less than one horsepower in American money. More bang for your buck dollar- or emissions-wise putting those on the roof of a house or car port, etc.

 

[robthebold]

So do you seldom drive in the daytime? Otherwise...separate battery storage, then?

Since the OP still has some electric bill, I'd imagine they sell excess back to the utility rather than storing it at home in their off-grid cabin.

 

[JohnKelly]

IMO the solar panels on the Aptera is more of a marketing gimmick. The claimed output of the solar panels is way higher than could be hoped for, even if it were sunny with a 100% chance noon all day. OTOH, that 700W isn't going to do that much for its range -- that's less than one horsepower in American money. More bang for your buck dollar- or emissions-wise putting those on the roof of a house or car port, etc.

As I said, even if it is only 1/4 of what they claim, that is still ten miles a day parked in the sun... not a gimmick, but just one of the many unique features of the vehicle. I don't expect their advertised numbers to be accurate (anymore than any other advertising), except perhaps under some ideal condition where you have no shade, the longest day of the year, near the equator etc. Of course... many people do not have the space, or are even allowed to put up solar panels.... or even charging infrastructure, for that matter. You too seem to have ignored the part about the efficiency of the Aptera... solar would definitely do something for range.... unlike all other current vehicles.. it is, by far the lowest coefficient of drag of any production vehicle.... that is the only reason solar makes sense. All other vehicles spend enormous amounts of energy just pushing air out of the way.. and this gets worse the faster you go.

 

[eNate]

It's not just low coefficient of drag. Aptera has a much smaller frontal area, lighter weight, one less wheel, hub drive motors, and therefore reduced frictional loses. So 10 theoretical miles gained in the Aptera may be the equivalent of only 5 miles in the most efficient Tesla – although the Tesla would have more surface area to supply solar panels to.

It's difficult to offer a comparison to a vehicle that isn't out yet. But even if Aptera is successful, it's hard for me to image that a great number of car buyers will accept its form factor