larger solar panel/solar roof on Leaf thread

[cwerdna]

Let's discuss the solar panel/roof issues that were brought up in http://www.mynissanleaf.com/viewtopic.p ... 54#p142154" onclick="window.open(this.href);return false; (Nissan LEAF Engineering Team Visit December 3rd) so that we can keep the other topic on track.

I wanted to bring up a few points. AFAIK, the solar roof panel on available on the 3rd gen Prius only can deliver about 60 watts max. See http://priuschat.com/forums/gen-iii-201 ... post917560" onclick="window.open(this.href);return false; and a few posts further down. You can probably find more posts by Googling for site:priuschat.com solar roof watts. It only runs the ventilation fan when the car is parked. 5 kw seems completely impossible. I don't know state of the art in solar, but even 1 kw sounds way off.

I hope people realize that 1 hp = ~746 watts.

Some people pointed out 200+ watts for minimal AC. 200 watts is REALLY minimal and doubt it'd do any good. I can tell you that when looking at Scangauge on my 2nd gen Prius that when idling, my car draws ~1.2 - 2 amps (@~220 volts). If I I turn on my (electrically driven) AC, the draw becomes 4.x to 9.x amps, sometimes even 10 amps (I've posted the numbers at http://priuschat.com/forums/gen-iii-201 ... ost1146128" onclick="window.open(this.href);return false; before).

On Priuschat, we were disappointed to learn that the solar roof couldn't charge the HV battery. Some explanations were given at http://priuschat.com/forums/gen-iii-201 ... prius.html" onclick="window.open(this.href);return false; and http://priuschat.com/forums/gen-iii-201 ... post831221" onclick="window.open(this.href);return false;. I'm no EE so I can't comment on the accuracy of that. Others can chime in on that.

[DaveinOlyWA]

i agree Solar on the roof is not cost practical, but i am not against having it as an option. people will pay good money for the craziest things.

but i know a guy who has solar panels. they are 300 watts and it would have to be trimmed a bit to fit on the roof of my Leaf. also around here even in optimum Sun, its only max'd out at like 75% efficient (we too far north really) and that is only for a few hours a day. the rest of the day its like 40-50%

but solar is getting better and better all the time. dont discount the technology, but i think it would still be cheaper to simply install more charging stations in public. put in one for every 10 gas stations, there would be so little range anxiety left it we would simply laugh looking back at this thread.

[gascant]

Thanks for starting the thread! I've been working in Solar Energy for the last 5 years, with a variety of technologies. So, IMHO:
As ElectricVehicle said over in the Engineering Team Meeting thread, about the best we'll do today (or in the short term) is 200 Watts peak, which will need to be derated (we typically derate down to 78-82% of peak, depending on losses). That's not enough to generate a lot of motive power but would do well in running ventilation. I've noticed that, once the car is cooled off, the A/C runs at about 300-500 Watts. There are versions of thin film technology that talk about applications as "car paint" but durability and efficiency aren't there to support it anytime soon. 200 Watts could be pretty useful for stationary application as others have said.

[LeafTalk]

I don't know about the efficiency of Solar PV but that's not the only way to harness the sun's energy.

How about an array of Fresnel lenses creating a solar concentrator and powering a Stirling engine to charge a battery. Could there be more output than PV or is it still infeasible. Of course this is all pie in the sky stuff, so humor me.



At the end of the day, anything you add to the top of a car is going to add weight and bring down efficiency as a result.

[Dgaetano]

Sunpower makes a 320 Watt panel that's essentially the same size as the Leaf roof (that's a 19% efficiency panel). San Diego gets 5.5 hours of usable sun a day. So that's 1.76 kwh a day, or just under a fuel bar.

That's not insignificant! Sure you can't recharge in a day, but that's 6.5 miles for me. Every day. For the life of the car (the solar panel will outlast the car). I could leave it out in the middle of a field with an empty battery and in a week it would be able to drive 45 miles.

So what about cost? That panel probably costs $1,500 (19% efficiency isn't cheap). House roof systems have considerable installation costs because every roof is different, but with a car once the design engineering is done they're just going to stamp them out by the hundreds of thousands at the factory. I imagine they could make the part for $2K (that's a total stab in the dark, I should be clear that I don't know jack about mass producing glass car roofs).

At that cost it probably won't pay for itself over the life of the vehicle, but I'd get it just because it would be awesome.

Of course solar panels get cheaper every day, there are solar panels now that cost near $1/watt and are 12% efficient. That would be 1.1 kwh a day for $200 plus whatever the mass produced glass roof would cost.

(these are best case numbers, but even after you regulate down 80% it's still significant amounts of power)

[ElectricVehicle]

Sunpower makes a 320 Watt panel that's essentially the same size as the Leaf roof (that's a 19% efficiency panel). San Diego gets 5.5 hours of usable sun a day. So that's 1.76 kwh a day, or just under a fuel bar.

I think you'll be lucky to get half of that, even if you park outside in unobstructed sunlight. The solar panels need to be pointed directly at the sun. The LEAF is not a flat surface pointed at the sun. And if you have a Solar Panel the size of the LEAF roof, your color options are limited - Solar panels don't come in Cayenne Red or Ocean Blue...

Of course, it could be nice because all the other cars would be parked in the parking space lines, while all the LEAFs will be crossing the lines for the best sun facing angle, all worshipping the sun!

If a lamp post shades the panels, a building or a tree casts a shadow, the cells are wired in a series or series / parallel arrangement so shading one cell can dramatically reduce the output.

The sun, under peak conditions is about 1000W/m**2. Solar panel efficiencies are in the 13 - 22% range. That's 130 to 220 watts/m**2, ideally.

SunPower® solar cells currently hold the world record in efficiency at 22.4 percent. http://us.sunpowercorp.com/about/the-wo ... for-solar/" onclick="window.open(this.href);return false;

LEAF roof area for solar is around 60" x 42" or 1.5m x 1.1m = 1.65m**2

215 to 360 watts ideally for the roof.

Arbitrarily estimating various factors for not being perpendicular (facing) the sun throughout the day (declination for the latitude and time of year, not tracking the sun...) would derate around 70%, the sun not being at ideal output, panels not at ideal temperature, atmospheric dust or light smog blocking some light etc. - derate 80%. 70% x 80% = 56%.

56% * 215 to 360 watts ideally = 120 to 200 watts practically

Others on the forum can come up with better numbers, but I think it's pretty clear that for the roof alone, you won't get more than 250 watts. Other surfaces will have less ideal facing to the sun and even greater aesthetic impact, so limiting to the roof seems pretty reasonable.

100 - 200 watts won't run the AC or heat full force, it won't be enough to maintain temperature on hot days. If the AC is capable of utilizing low power, it would make the car much cooler or warmer than it would be with no fan and no AC. (if cars wre well insulated, this low power could come close to maintaining temperature, but they aren't and there is a lot of single pane window area in a car.)

http://www.nrel.gov/rredc/solar_resource.html" onclick="window.open(this.href);return false;

I see the Sunpower 315 is 19% efficient and meaures 61.39" x 41.18" with a max power of 320W. If all the derating factors came to 62%, this panel would produce 200 Watts. It weighs 41 lbs, though if the frame were removed and it was integrated into the LEAF body, it might add only 20 pounds to the weight of the car. This panel certainly sets the upper bound for power from the roof at 300 watts or less real world. According to SunPower there aren't any panels that are more efficient (power produced / unit area (well technically incident sunlight energy)).
http://us.sunpowercorp.com/cs/BlobServe ... MungoBlobs" onclick="window.open(this.href);return false;

The solar panels must not affect the aerodynamics of the car or add more than a couple pounds to the weight or they will cause more losses while driving than the power they generate. So bolting a commercial solar module to the roof with a 1 inch module edge exposed in the airflow around the LEAF body would be a big net energy loser due to poor aerodynamics!

[TomT]

The ROI of $1,500 spent on a larger pack would be much greater then that with ANY solar panel!

[TRONZ]

While a PV roof would be cool, it would not provide much practical benefit. IMHO the front lines of PV are in the efficiency/cost of panels. The front lines of EV's are battery capacity, charge times and pack weight.

The contribution of a PV roof on an EV does have a great image and could help market the simplicity of powering a car directly from the sun. This does have a high educational/awareness value, but at a price.

[GroundLoop]

The contribution of a PV roof on an EV does have a great image and could help market the simplicity of powering a car directly from the sun. This does have a high educational/awareness value, but at a price.

This is the part I don't get. What's the educational/awareness value of putting an irrelevant solar trinket on the roof? Who learned what? So far, it's only the uneducated/misinformed that assign any value to it.

"So you never have to plug it in, because of that solahr-lectric thing on the spoiler? Awesome."

"Uh, no. It's a useless greenwashing stylistic element that serves no useful purpose whatsoever. It's back there actively giving solar panels a bad name. It would take the whole roof of that gas station to power this car."

[gascant]

When derating the panel, don't forget the light transmission through the protective medium. I don't know that Nissan is going to put laminated, tempered glass up there on the roof of the LEAF, followed by another coating to keep the rocks that fall on it (from overloaded gravel trucks on I-880) from breaking the glass. So I'd take another chunk of change off that 200 Watts. Maybe more like 150 Watts useful.

Having said that, it would be cool to ventilate the LEAF while not plugged in and not using the battery.