Toyota plans to roll out a Prius model equipped with solar panels on the car’s roof next year, according to Nikkei.

The Japanese business daily reported Sunday that electricity from the panels would make up a portion of the 2 to 5 kilowatts needed to run parts such as air conditioning.

Whether a solar-panel equipped Prius would have popular appeal remains to be seen, given that the car maker has offered no details, such as pricing and availability. Solar panels also add weight to the car, reducing fuel efficiency. Toyota is supposed to be working on making Prius lighter to achieve the opposite, according to Nikkei.

Toyota is not the first company to consider the concept of putting solar on a car. Fisker Automotive last year unveiled the Karma, a plug-in hybrid with a solar panel on the roof, which it plans to produce for a price tag starting at $80,000 in the fourth quarter.

But today’s solar-power technology is far from good enough to actually propel these cars down the highway.

The Prius, a gasoline-electric hybrid, relies on electricity generated by the engine that is stored in a battery.

Toyota, along with its competitors, understands that the future of fuel-efficient cars lies in advanced batteries. That is why it has invested heavily on improving lithium-ion batteries that can store far more energy than the current nickel-metal hydride version (See Toyota Drives Towards Greener Fleet).

Toyota made the right bet more than a decade ago by launching the Prius in its home market in 1997 and in the U.S. in 2000. The No. 1 hybrid company has enjoyed brisk sales of the Prius, along with waiting lists in some places, and it has been growing production to meet consumer demand. The company expects to produce 450,000 Prius cars in Japan in 2009, up 60 percent from last year. The numbers for 2008 are not yet available.

But Toyota will face a growing competition as others, such as General Motors and Honda, which was first to the hybrid market, release more hybrid model vehicles.

GM plans to launch a Chevy Volt that will include a new plug-in hybrid technology (see Chevy Volt Clears for 2010 Production). And Tesla Motors, a startup carmaker in San Carlos, Calif., last week said it would begin making all-electric Model S, a four-door sedan, in 2010 (see Tesla: We’ll Build Electric Sedans in California).