## Report: Toyota to Use PV Panels on Next-Gen Prius

##### 06 July 2008

The Nikkei reports that Toyota Motor Corp plans to install solar photovoltaic (PV) panels on the roof of the next-generation Prius to supply part of the 2-5 kW needed to power vehicle auxiliaries, such as the air conditioning system.

The next-generation makeover of the Prius may come as early as next spring, the Nikkei said.

While automakers have used PV panels in concepts, Toyota would become the first major automaker to equip a current production model with such a system.

Toyota is taking design and other matters into account when placing the panels. Such details as the number of vehicles to be made and the price will be hammered out later. It is planning to procure the panels from Kyocera Corp., which has a solid track record of providing panels for homes and factories.

The carmaker intends to produce about 450,000 Priuses at home in 2009, up about 60% from 2007. In addition to a new solar power generation system, it aims to boost sales by offering a redesigned version that improves fuel efficiency through reduced vehicle weight and other steps.

Photovoltaics on cars would be very useful in hot climates where the interior temperature of a parked car can easily exceed 50C. Powering a small fan to ventolate the cabin of a parked car would considerably reduce the airconditioning burst required on startup. I believe Fisker are doing this with the Karma.

Audi has been doing this for years.

What do the additional PV cells and associated housing, wiring, casing, etc. weigh? How does that impact fuel efficiency the rest of the time?

After all, there are plenty of people who garage their vehicle at home, and some folks who garage their vehicle at work, be it at the office or the shopping mall.

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stomy, thin film cells weigh next to nothing. The wiring is really splitting hairs. Millions of vehicles sit in the sun all during daylight hours. If you use a parking garage you are in the minority. It's free energy. It won't get you home, but it may shave a few tenths off your mpg. The heat that normally may have been absorbed by your car will be absorbed or reflected by the panel. Sign me up.

Overall, I think this is a good idea, but I would like to know how this will affect the utility of the roof for other purposes, such as carrying bikes, skis, boats, cargo. Will one still be able to mount a roof rack, are the PV panels easily scratched (I have no idea, maybe somebody else does).

The Volvo S80 currently has a fan that comes on when the car is off and it gets too hot inside, but I have no idea how it is powered, my guess would be through the same battery responsible for starting the car.

Solar photovoltaic (PV) panels on the roof of any car are a gimmick at best. The pitiful bit of power generated will do little to meet the cars real energy needs.
Sure they do let you run a fan to keep the interior cool, but flow through ventilation could do the job near as well. Most people just open the doors a bit before getting in.

However, the steps of reducing weight and increasing production are good ideas. I hope Toyota begins making a full BEV and marketing it soon.

It really is a symbolic gesture. Thin-film PV has a lower efficiency rate around 10%, and they cost more. But the idea that you CAN power an EV/PHEV with some form of solar is a positive one. I would like to see municipalities in the sunbelt build recharge stations near landfills utilizing wind, recovered methane and solar. While these stations may never be mainstream energy resources - they demonstrate de-centralized grid utility, sustainable technologies, and progress.

Meanwhile, if the Prius includes a data point illustrating the (small) quantity of PV energy - it will provide the E-geeks another benefit to preen about.

How can anybody be against the use of free sun energy to ventilate the car interior and (partly) recharge the batteries while parked for 8 hours in direct sunlight on during daytime driving?

Some 400 to 500 watts high performance PVs could supply almost 3 Kwh of energy per sunny day. That would be enough to drive a Prius back home free, up to about 20 Km.

Could the car roof be expanded/unfolded to doubble the area while parked? A free 40 Kwh/day could satify the majority.

Photovoltaic cells on the roof of cars like the Prius to increase our use of non-carbon energy? Heck, why not!

After all, photovoltaic cells and biofuels are merely different forms of the same thing: solar energy. Its not practical to grow corn or algae on the roof of your car (the roofs of homes and office buildings are a different matter, however) for processing into ethanol or bioDiesel.

But if you can recharge your hybrid (or, straight electric) car's battery pack with solar cells to decrease your use of fossil fuels, its a practical way to utilize the area on the roof of your car which otherwise goes to waste.

Bravo Toyota!

I would look at the PV panels and ventilation (when parked off) as a luxury item. I'd be willing to spend an additional $1k for that feature. I look at it this way: I live (mostly) in Florida where it is hot inside the car almost every day of the year. If I kept this vehicle 3 years x 365days = 1095 times I would avoid getting into a scorching hot car. Considering the way my day usually is, that would probably be closer to 2000 times. For$0.50 a pop, I'll gladly pay to have my car solar ventilated/cooled.

Incidentally, solar powered EVs have been on the roads for a while now too:

http://www.solarvan.co.uk

http://www.greencarcongress.com/2005/08/solarpoweraugme.html

Of course your daily charge from solar totally depends on where you live and the time of year!

HarveyD: high performance PVs

While it would be good to have a car-charger that could accept the output of a panel more or less directly, it would be ultimately wasteful to build the panel into the car itself. Focus on the car as a car, not a mobile electrical generator...

As for commuter parking, my vote would be economy of scale: build a canopy over the parking lot with PV panels. Note only would it shade the cars below -- thus preventing the "AC burst" in the first place -- but it would provide a hell of a lot more electricity.

Future franchise: "Park 'n Charge."

I wrote a paper on this subject for the Third World Conference on Photovoltaic Energy Conversion, held in Osaka, Japan.

Picking two paragraphs from the paper:

Assuming that a Prius is parked with a nominal
traction battery SOC of 56%, means that only about 24%
of the battery capacity or 1.5 MJ of energy can be stored. Thus for Albuquerque, which produces 33 MJ/(m2 day) of solar energy on a very good day in June, the greatest solar panel size the vehicle can most economically use is .49 square meters. This area is determined by dividing the 1.5 MJ the battery can store by the product of 33 MJ/m2 daily energy input, a panel efficiency of 11%, and an average voltage mismatch between the battery and the solar panel of 85%. For many battery and panel voltage mismatches, 85% is too high, but as the Prius uses only 40% of battery
capacity this is a reasonable number. Spot checks on worldwide locations confirm that 33 MJ/(m2 day) is a relatively high value, even for the world, so this a .49m2 panel is close to that practicable in most markets.

Assuming that 1.5 MJ is available from the battery and
that this energy is reduced by an 85% battery efficiency, a combined motor/generator and inverter efficiency of 90%,and a mechanical efficiency of 90%[7] means that solar power can contribute 1.03 MJ to the vehicle’s movement. As the car requires 18.6 MJ during its commute, photovoltaics supplies 5.5% of the total energy required and the hybrid’s fuel consumption over the commute decreases from .0452 L/km to .0428 L/km. (52 mpg to 55mpg).

These two paragraphs are based on an "average" number of kilometers driven per year, 18,346 km, and a 50 km commute. It also assumes a first generation Prius.

Off topic, I think the people who run Green Car Congress do a great job. Thanks.

Solar panels on a hybrid car roof - great. This feature will be used on the plug-in hybrid version, combined with V2G, whereby you drive to work and plug-in to your parking space. With the solar roofed vehicle plugged-in and sitting in sunlight during peak demand, 9 hours a day, 5 days a week, that’s when electric power fetches the highest price. This would give you a significant credit on your electric bill, and also pay for the added cost of the panel. The future version will be the entire car body covered in solar paint. I want my next car to be a power generator.

It's a gimmick. PV cells are fragile. Imagine the owner's pleasure when a vandal comes along and cracks \$1000 worth of panel with one fist.

Harvey, 400-500 watts is optomistic, there's not that much roof space. Perhaps 100-150 if you're lucky.

It's not just a gimmick as some think. I purchased a cheap solar trickle charger for my car. It's ONLY 12 volts at 1.8 watts. I thought it would be good for next to nothing because it was so small.

This ought to be good for a laugh. I thought it was so wimpy I put my tongue on the adapter when it was in the sun. Empirical evidence, of course. Youch! My tongue danced a good jig that day. That tiny panel (only 4 inches by 12 or so) does a good job of charging the (standard) weak battery over a few sunny days.

100 watts on the roof would take a loooong time to fully charge, say, a 10 kw/h battery, but it would still contribute more than people assume. Especially if it was ever parked for a couple days and the sun energy could accrue. Obviously it's not worth so much during some times of the year, but it would pay for itself in most places.

Gimmicks are OK.
But a roof of black PV cells will make the car hotter than a white car.
Besides, isn't the Prius itself still a gimmick?

I agree gimmicks are OK.

Automatic transmissions are a gimmick, as are power windows, radios, power seats, GPS maps, MP3s, power mirrors, power locks, sunroofs, voice recognition, self dimming lights, shiny rims, rear spoilers, blah, blah, blah. The auto industry is built on gimmicks.

They would be lucky to get 200 watts from car rooftop PV. That would be enough to power a fan to ventilate the car interior, so that might make sense.

Best idea I have seen is MendoMotor's Porsche kit car EV with solar panels on the roof of the house. It is recharged while parked and is a convertible. It would be nice to cruise down the coast highway on nature's power and produce NO pollution.

A U of Toronto prof, converted his Prius to have PV on his roof. Supposedly put his car in the 100 MPG catagory. So make what you will of that.

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