( CNN ) -- Toyota 's third-generation Prius , due at dealerships this spring , will have an optional solar panel on its roof . The panel will power a ventilation system that can cool the car without help from the engine , Toyota says . Solar Electric Vehicles in California makes a roof-mounted solar panel for a standard Toyota Prius . But it 's a long way from the 2010 Prius to a solar-powered car , experts told CNN . Most agree that there just is n't enough space on a production car to get full power from solar panels . `` Being able to power a car entirely with solar is a pretty far-reaching goal , '' said Tony Markel , a senior engineer at the federal government 's National Renewable Energy Lab in Golden , Colorado . In the new Prius , the solar panel will provide energy for a ventilation fan that will help cool the parked car on sunny , hot days . The driver can start the fan remotely before stepping into the car . Once the car is started , the air conditioning wo n't need as much energy from a battery to do the rest of the cooling . `` The best thing about using solar is that regardless of what you end up using it for , you 're trying to use it to displace gasoline , '' added Markel . The question is , how much gasoline can solar power offset ? Markel said his lab has modified a Prius to use electricity from the grid for its main batteries and a solar panel for the auxiliary systems . He believes the car gets an additional 5 miles of electric range from the panel . According to recent articles in Japan 's Nikkei newspaper , Toyota has bigger plans for harnessing power from the sun . Nikkei reports that Toyota hopes to develop a vehicle powered entirely by solar panels . The project will take years , the paper reported . When contacted by CNN , however , a Toyota spokeswoman denied the existence of the project . `` At this time there are no plans that we know of to produce a concept or production version of a solar-powered car , '' said Amy K. Taylor , a communications administrator in Toyota 's Environmental , Safety & Quality division . Motorists do n't have to wait for a 2010 Prius to drive a solar-enhanced car , however . Greg Johanson , president of Solar Electric Vehicles in Westlake Village , California , said his company makes a roof-mounted panel for a standard Prius that enables the car to travel up to 15 additional miles a day . The system costs $ 3,500 , and it takes about a week to make one , Johanson said . Billy Bautista , a project coordinator at the company , said Solar Electric Vehicles gets so many requests for the system that there is a backlog of several months . The company 's Web site says motorists can install the panels themselves , although it recommends finding a `` qualified technician . '' The system delivers about 165 watts of power per hour to an added battery , which helps powers the electric motor , Johanson said . But others said it would take a lot more power than that to replace an internal combustion engine . Eric Leonhardt , director of the Vehicle Research Institute at Western Washington University , said that even if solar cells worked far better than they do today , they would n't generate enough power for driving substantial distances . The best cells operate at about 33 percent efficiency , but the ones used on vehicles are only about 18 percent efficient , he said . Leonhardt said it would be more practical to use solar power to help charge a car 's battery and use the more efficient panels mounted on a roof or over a parking area to supply the rest of the electricity needed to drive the engine . `` Solar panels really need a lot of area , '' he said . Leonhardt thinks Toyota 's new Prius is a good first step toward using renewable energy . Some cars get hotter than 150 degrees inside when parked in the sun , so reducing the temperature could mean Toyota could use a smaller AC unit , he added . Johanson of Solar Electric Vehicles said he 'd like to see Toyota bring the weight of a Prius down from 3,000 pounds to 2,000 . He also hopes for a small gasoline engine and a larger electric motor . That will probably come in the future , when Toyota unveils a plug-in engine . In the meantime , Solar Electric Vehicles sells its version of a plug-in Prius , with a solar panel installed , for $ 25,000 , Bautista said . Toyota is the largest automaker to incorporate solar power into a mass-produced car . But its solar panel is not the first for a car company . Audi uses one on its upscale A8 model , and Mazda tried one on its 929 in the 1990s . In addition , a French motor company , Venturi , has produced an electric-solar hybrid . The Eclectic model costs $ 30,000 , looks like a souped-up golf cart and uses roof-mounted solar panels to help power an electric engine . It has a range of about 30 miles and has a top speed of about 30 mph . CNN 's Brandon Griggs contributed to this story .
The this spring Prius , due 2010 , will have an optional solar panel on its roof . The panel will power a cooling system without help from the engine . 929 company also makes a roof-mounted solar panel for current Prius models . But it 's a long way from the new Toyota Prius to a solar-powered car , experts say .