I made this simple calculation that shows solar panels could never power a car alone:

1 hp = 750 W

The sun puts out 1000 W/m2 in best conditions.
How many m2 do you have on a car? I guesstimate 10, give or take.

So, if you cover the car with 10% efficient panels, you get 0.1*10*1000/750=1.33 hp
If you use 40% efficient space age pannels (the record now), you get 5.32 hp (at best!).

It takes 8 hp to get a car going at 55 mph, a lot more to get to that speed.

Solar pannels can only trickle charge a battery.

Aurel

I made this simple calculation that shows solar panels could never power a car alone:

1 hp = 750 W

The sun puts out 1000 W/m2 in best conditions.
How many m2 do you have on a car? I guesstimate 10, give or take.

So, if you cover the car with 10% efficient panels, you get 0.1*10*1000/750=1.33 hp
If you use 40% efficient space age pannels (the record now), you get 5.32 hp (at best!).

It takes 8 hp to get a car going at 55 mph, a lot more to get to that speed.

Solar pannels can only trickle charge a battery.

Aurel

Here in Arizona it would have to help a bit... anything is better than nothing.

Aurel, the AP article mentions that the solar panels are intended to only cover the power consumption of of the car's A/C system. So, it will improve mileage a bit and make the greenies (the Prius target demographic) quite happy. Even though it will do nothing for Mule's friend, manbearpig, it's marketing genius.

The a/c in a Prius is probably 15000-30000 btus/hr. The wattage required to turn the compressor is in the 1250-2500 range, based on my knowledge of home HVAC. Expecting the solar cells to operate the A/C system is a real reach. Even with aurel's assumption of 10 m^2 of panels and 10% efficiency, you'd barely have enough energy. In reality, only the roof will have panels (perhaps 1 m^2), so output would be, at best 1/2 HP or 400 watts..

I'm all for energy conservation, but let's get real.

You're missing the point. It's just good marketing. It's going to make more greenies excited to buy/own a Prius. That's just what Toyota hopes to accomplish. It will be another reminder to the car buying public that Toyota is a leader in "clean" automotive technology. All the other car companies will be playing catch up.

Prius solar panel kit (Toyota's Cost): $500
Prius solar panel Green option (Customer Cost): $2,000
Profit: $1,500
PR: Priceless

Bingo!

Plus, the other car companies are still on their back foot, trying to regain their footing. Brilliant!

Rough times at GM, from the AP:

GM mulling thousands of job cuts, sale of brands:
report Mon Jul 7, 1:15 AM ET

(Reuters) - General Motors Corp (GM.N) is planning to cut thousands of white-collar jobs and is considering whether it should sell or stop production of more of its brands, The Wall Street Journal said, citing people familiar with the matter.

Both moves are part of a broader re-evaluation of the company's strategy and of its ability to meet an internal projection of returning to profitability in 2010, the people told the paper.

The job cuts are likely to be approved when GM's board of directors meets in early August, the people said. The reductions would be in addition to earlier announced cuts.

Management may also present the board with options for raising additional cash, they told the paper.

The board may also hear management's latest thoughts on whether GM should trim the number of brands it offers in the United States, the people told the paper.

All but the Cadillac and Chevrolet brands, which GM considers core to its business, are undergoing close scrutiny, some other people told the paper.

In the past few years, as GM has run up massive losses, some board members and some executives have on occasion raised questions about its plethora of brands, only to be rebuffed by Chief Executive Rick Wagoner, the paper said, citing people familiar with the matter.

GM has put its Hummer brand up for sale to prospective buyers thought to include Mahindra & Mahindra (MAHM.BO), but the SUV brand is expected to fetch far less than $1 billion in any sale.

The company, hit by rising oil and raw material prices, the credit crunch and the housing downturn, will need to raise as much as $15 billion in cash to shore up liquidity and bankruptcy is "not impossible" if the U.S. auto market continues to slump, Merrill Lynch had said last week.

U.S. auto sales plunged in June to a 15-year low.

Although GM clung on to its top spot in the American market, some analysts have raised concerns over the financial state of the firm, whose shares fell to a 54-year low earlier this month.

GM could not be immediately reached for comment.

(Reporting by Pratish Narayanan in Bangalore; Editing by Kim Coghill)

The Nikkei report is not authoritative. But assuming it is true, rooftop solar panels would probably be used to run fans ventilating the car in hot weather, maybe keep the 12v battery charged during long periods of non-use. Not enough power for A/C, obviously. Seems beneficial in hot climates like AZ, TX, SoCA, etc. As for cost, Toyota can probably apply solar thin film to the roof, for not too much money.

For what it's worth, one of my Audis uses a solar array on the sunroof glass to power the HVAC fan when the car is parked, to circulate air through the interior and keep the heat build-up when it's parked to a minimum. It helps.

JR

Prius traction battery (the big battery that powers the electric drive motors) wants to be kept cool. Cooling is via air drawn from passenger compartment, by right rear passenger seat. Keeping the passenger compartment temp down is good for the battery's efficiency, not just for the occupants' comfort.

I wonder what the net gain is given the higher weight of the car with the panels. There is a non-zero energy cost to lug them around.

Weight of 1 sq m of thin film and associated electronics is negligible. Probably under 2 lbs. This won't be clunky rectangular solar panels bolted on roof, will likely be a thin film applied to roof or rear hatch glass or windshield, that you can hardly see.

Think of the difference in weight between regular roof shingles and solar shingles. Hardly anything.

They should raise it to $3000 & give the chumps $500 worth of Algore brand carbon credits, complete with a "suitable for framing," picture of manbearpig.

Right....and if you've been here all your life, you wonder how things got so screwed up.

Ok I have been a Prius skeptic ever since they came out. Last Thursday as a joke my wife and I went to go look at one at the dealership. I went from laughing to "holy crap" in a matter of 1.5 hours. The car is pretty big on the inside for a car that small. I am 6' 3" and can sit in the back seat with the front seat all the way back and I still had 2 inches in front of my knees. The car drove nice and the trip computer showed 55MPG for our mixed 10 mile drive. Before I get reamed we drive about 60,000 miles a year and the fuel savings would be huge. The experience has changed my opinion on the car.

Speedy:)

Technological change (jeez, that sounds poilitical!) happens in small steps, and the Prius represents one of these small steps. Likewise the introduction of solar cells on the roof.

The car and concept is not a gimmick, it's just another step towards cars that burn a lot less fossil fuel. It's also a very significant and successful step, IMO.

Best,

I don't believe that expensive, complicated technology with a limited lifespan is the answer.

Simply making cars lighter would provide all of the benefits with increased reliability and less cost.

Lighter, lower Cd, smaller frontal area. But this goes against the American way of doing things.

Speedy:)