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Monday, July 14, 2008 Does Car-Mounted Solar Make Sense?Researchers consider plug-in hybrids charged by stationary solar arrays a better bet. By Peter Fairley
Last week, the Japanese newspaper Nikkei caused a buzz by reporting that a redesigned Toyota Prius, to be released next year, will come equipped with solar panels. Toyota spokespeople will neither confirm nor deny the report, but several companies already offer solar roof kits for the Prius, and researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL), in Golden, CO, have been testing one on a Prius modified to plug into the electrical grid. Their conclusion: for the time being, plug-in hybrids charged from stationary solar arrays are a more efficient and cheaper option. The idea of car-mounted solar cells is not new: in the early 1990s, Mazda offered its 929 luxury sedan with optional solar cells in the glass sunroof to drive fans that removed hot air from the car. But most onboard solar systems to date have cost several thousand dollars while generating less than 100 watts of energy, improving a vehicle's fuel efficiency by just a few percent. "I think it's more a marketing gimmick," says Andrew Frank, a plug-in hybrid pioneer at the University of California, Davis, and chief technology officer for UC-Davis hybrid-vehicle spinoff Efficient Drivetrains. "It takes kilowatts to really drive the car." The limited surface area of the car roof is one constraint on the panels' power production. Another is that they can't be tilted perpendicular to the sun for optimal energy capture, unlike most photovoltaics on buildings or in solar farms, which either track the sun or are installed with a fixed southward tilt. The NREL researchers tested the extent of these limitations by equipping the plug-in Prius they built earlier this year with the most powerful rooftop solar panel on the market. Assembled by Solar Electrical Vehicles, based in Westlake Village, CA, the panel completely covers the Prius roof, wiring together 146 four-inch-square crystalline-silicon cells capable of generating a total of 215 watts. However, NREL senior engineer Tony Markel says that his group's tests suggest that the output will max out at closer to 165 watts under normal use. That's a meager improvement compared with the boost that the plug-in Prius gets from its extra lithium-ion battery. Markel says that the six kilowatt-hours of electricity available from the fully charged battery enable NREL's Prius to get about 100 miles per gallon in the first 50 miles of driving--more than double the fuel efficiency of a standard Prius. Put another way, the overnight charging should take the car about 50 miles in light-duty driving. Markel says that NREL has yet to quantify the solar panel's additional impact, but that the five hours of good sunlight the car sees on an average day would give it an electrical output of at most 0.825 kilowatt-hours. The system would probably boost the plug-in's fuel efficiency for the first 50 miles from 100 to 105 miles per gallon, he says. |
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Comments
gabrielg01 on 07/14/2008 at 10:07 AM
297
There are many historical examples for this. Watt's first steam locomotive could barely keep up with horse drawn rail carriages. And the first internal combustion cars were more like a joke, than a real transportation technology. So on, and so forth...
If you don't see the historical perspective, you may be missing the whole point. Solar panels and battery technology will get much better, and electric cars will be ubiquitous.
robin26 on 07/15/2008 at 2:00 PM
8
However, if lots of people are willing to purchase cars that won't go above, say, 10 miles per hour, and that are not air conditioned, then an exclusively solar-powered, 'on-demand' automobile could be feasible.
What about a 1 square meter solar cell canopy on a motorized bicycle? This could be a vehicle useful to some commuters and tourists... especially if the canopy can fold away for parking or storage!
Kevin Bullis on 07/15/2008 at 4:49 PM
Nanotechnology and Materials Science Editor
39
msreid on 07/15/2008 at 5:53 PM
6
In terms of sheer energy use, planning ahead to only drive to the store once a week rather than twice a week will have far more of an impact than solar or anything else on our vehicles.
Purchasing fewer consumer goods will have a much greater impact on our overall world energy use than "enviro-pimpin" our vehicles. Think of just 1 consumer electronics product. Think of all the raw materials, energy, manpower, transportation, etc. that goes into just one consumer product.
Do any of us really think we're going to offset all that energy use by putting a few watts of solar on our cars, or using regenerative suspension systems, or any other car tweaking? Come on. The best answer is always the most simple: Buy and use less stuff, and drive less often to get it. You won't ever beat that out if you're trying to save energy.
davea0511 on 07/16/2008 at 9:19 PM
16
johnalphonse on 07/15/2008 at 8:35 PM
78
drash on 07/16/2008 at 7:11 AM
1
A practical use of Solar on a car would not only be useful for driving venting systems but how about utilizing electrochromatic window shades that automatically come on when you lock the doors? This will keep out a lot of the Sun and prying eyes all at the same time. Theft detterent systems that could even email you if something happens. Heck I'd be delighted with electric seat warmers for those particularly cold days or window defrosters so you'd have clear windows when you get in. It could even help with driving lights and heater fans while the car is running. Lot's of possibilites, particularly if Toyota left an open plug in the car, so car accessory makers can also come up with ideas.
johnalphonse on 07/14/2008 at 10:22 AM
78
when the solar arrays cover the ENTIRE car, and are indeed a movable array embedded beneath a clear surface (think "fish scales" or sequins) where perhaps you can actually change the color of the car if you want (at least at night!), this issue of lack of generation will disappear.
and to get you thinking of the potential(s): wind generation from propellers in the front grill can harness this energy source simultaneously...
add to this the ability to suck solar energy out of the black, heat-absorbing road surface through your tires and you're talking high-performance solar! this dream will become real, soon enough.
mightybob on 07/14/2008 at 3:20 PM
9
"and to get you thinking of the potential(s): wind generation from propellers in the front grill can harness this energy source simultaneously."
you seem to be ignoring the laws of energy with that one. the wind you feel coming through the window in the car is mostly from your own forward momentum. probably wouldn't be getting much energy out of that, it would more the likely just add drag and make things worse.
I really like the fish scale idea though, maybe with nano optics so they don't even have to actively track the sun.
johnalphonse on 07/15/2008 at 10:09 AM
78
true, a multi-directional solar collecting nano-cell may eliminate any need for moving parts there, and it's definitely a more practical approach especially at speed, considering auto body aerodynamics.
GaryB on 07/20/2008 at 9:52 PM
42
So, you're always better off trying to make the car more aerodynamic than to trying to harvest the movement induced wind.
On the other hand, solar panels make great sense to run cooling systems on the car in hot sunny weather or to charge batteries to run accessories. Especially nice would be an air conditioner run off of solar when you have to leave your car in a hot sunny parking lot. But there's too little area on the car for solar to actually charge or run normal sized consumer cars.
GreenPlease on 07/14/2008 at 10:41 AM
7
I live in Florida where it is ALWAYS hot and NO parking lots have shade. Ironic, when I lived in Chicago where it is frequently cold, there was almost always shade.
Anyways, if I kept the car 4 years and paid $1200 for the solar system, and the solar system kept the car cool 300 days/year, I'd be paying $1/day not to sit in a scorching hot car.
Totally worth it to me.
gabrielg01 on 07/14/2008 at 11:00 AM
297
At least a car with solar panels serves a higher purpose. Even non-hybrids could use the extra electricity.
Bruceahz on 07/14/2008 at 11:30 AM
7
Other options are justified for safety, convenience, or creature comfort reasons. If I choose to spend $2000 on leather seats with heating and cooling, well, that's what it's worth to me.
But the solar roof needs to be justified based on fuel saved and/or pollution reduced and at first blush it would appear that other approaches provide a better cost/benefit ratio.
BTW: having a solar panel roof will not solve your hot car problem, but that's a different discussion.
johnalphonse on 07/14/2008 at 11:37 AM
78
gabrielg01 on 07/14/2008 at 5:27 PM
297
dbdet on 07/31/2008 at 4:35 AM
2
That is not only a problem in FL, but one that would easily be resolved simply by installing high-efficiency solar panels over the parking areas. These are much more efficient than the thin film projected in the article for use on cars, so they would create more energy for the same area.
Not only would more energy be created in an on the spot local grid, into which you could plug your (elec./hybrid) car for recharging, the panels would also constantly create shade for your car, keeping it cool for your eventual return from shopping. Surplus energy could also be sold into the normal grid.
But then, you would not be able to find a parking spot, because (elec./hybrid) car owners would want to shop nowhere else (wanting to recharge), while the owners of conventional cars would want the same, simply to steal the shade. The latter problem would create a new job at each solar parking lot, for an attendant to block entry for non-elec. cars.
That might be an added incentive for conventional car owners to switch to (elec./hybrid) cars. At least in hot areas with lots of solar gain.
dbd
kenjstone on 07/14/2008 at 11:45 AM
1
mkogrady on 07/14/2008 at 11:56 AM
92
Also run it through the car wash 70 or 80 times to see if the device fails, gets scrubbed off etc.
Roof top PV makes sense in an RV - maybe!
johnalphonse on 07/14/2008 at 5:38 PM
78
GreenPlease on 07/14/2008 at 12:47 PM
7
I've always felt that solar panels on the top of semi trucks would make sense. They could be used to charge the battery, run a heat pump, and run any auxiliary components. This would help reduce drag on the engine and improve fuel economy.
brewvies on 07/14/2008 at 4:51 PM
1
powdermilk on 07/14/2008 at 6:23 PM
2
levialanm on 07/14/2008 at 6:53 PM
1
* better angle relative to the sun (as stated in article)
* ability to capture the power 100% of the time. When your solar prius is parked at the mall, you might already have a fully-charged battery so you waste some energy production.
* the solar panels on the car increase the weight and other physical characteristics of the car and therefore negatively affect overall efficiency.
* Cost of panels and of installation per watt of production will be much higher on a car than it will be in other simpler applications (e.g. roof-top).
Another point: it might actually be desirable to have a solar car because you can increase the range of the car, especially if you're willing to wait for it to recharge. Case in point: drive 2 hours along highway, then stop for a burger. While you're eating your burger, your car battery is recharging. This works best with plug-in hybrid configurations because they have deeper battery discharge parameters.
nekote on 07/15/2008 at 11:35 AM
115
The best places for (expensive) solar cells are deserts. The closer to the equator, the better.
And stationary locations that can tilt, and track, to to further maximize the utilization of the expensive PV asset. Probably concentrating PV is the most economic, because of PV cells vs. mirror / lense costs. In the end, $/KWH.
Car roof tops are a non-economic location.
Spending billions on such silly status symbols would obviously be a mindlessly wasteful allocation of capital, as compared to locating such cells where they can capture the maximum solar energy.
An analogy with windmill farms.
They're placed where there's the most wind energy to capture. Who, in their right mind, would spend the money to install a wind farm someplace that seldom has much wind energy to capture?
ricke8592 on 07/16/2008 at 3:20 PM
2
robin26 on 07/17/2008 at 9:35 AM
8
Ironically, the more efficient one's vehicle is, the more likely one may be to perpetuate personal driving habits that needlessly waste energy: overly aggressive driving, poorly planned errands to individual stores, etc.
If gas prices continue to rise, more people may discover they really can reduce their fuel costs simply by planning a little better and modifying their driving habits.
nekote on 07/17/2008 at 10:47 AM
115
Unfortunately, lots of those accessory costs are highly variable by location, so not as useful for nationwide comparisons.
For cars with this PV on their roof silliness - getting those expensive panels damaged and replaced, if on a statistically significant basis, would surely greatly increase the Insurance premiums, for example.
Or, alternatively, a different scenario - PV topped cars somehow become popular to steal - greatly increasing the theft portion of the Insurance premium.
Cyruscosmo on 07/15/2008 at 5:06 PM
1
Bending the truth a bit for the purpose of selling a product is an age-old art. But outright lying is another story all together. A "Plug in Hybrid" does NOT get MPG or MPC but both. Telling the public that you can get "100 miles per gallon" by adding an extra battery, which adds more weight to your car is an outright lie. The car actually gets less "Gas" mileage but has more "Range", less mileage because of the added weight of the batteries but more range because of the added battery capacity.
The article says that after charging the extra battery "over night" you will get about 50 miles of light duty driving on that charge. (It says nothing of how much that charge costs.) That is most likely true LI batteries are much better than lead acid in both weight and capacity but cost a mint. Also the over night charge is not free and does not take gas so figuring the total miles traveled in terms of MPG is at best very misleading to the public and at worse nothing but a lie because the car will NOT go 100 miles per gallon on gas alone.
If you put 1 gallon of gas in that hybrid and drove it you would NOT go 100 miles. In fact you will get about 3 miles less per "Gallon" with the extra batteries than you would without. You would have to use the power stored in the extra battery to go the 100 miles at which point you are not using both the battery and gas. The charge costs you as well as the gas so