Solar car roofs have generally been the reserve of concepts, experiments and niche carmakers. Toyota was the first major automaker to offer the option on its Prius hybrid plug-in model in 2012 and now Panasonic has developed a solar photovoltaic car roof for the latest Prius PHEV, upping the wattage from 50 W to 180 W.

Called the HIT Photovoltaic Module for Automobile, the 180-W-generating roof is the first designed with the ability to recharge the lithium-ion powertrain battery, along with the standard 12-V lead-acid battery. Panasonic's solar roofs have also been designed with a resistance to hot environments, which normally lead to a decline in output as the temperatures rise.

The previous Prius solar roof only generated nominal electricity: enough to power the ventilation fans when in park, and for use as an auxiliary charging source for the 12-V battery. And while 180 W still doesn't provide much oomph, Toyota says it would increase the car's efficiency by up to 10 percent, adding up to 2.2 miles (3.5 km) of range per day, in ideal conditions.

The solar cells are laminated in a resin set atop the roof's curved glass, a match in design with the Prius's regular hard-top. Unfortunately, this reinforced glass sheeting hasn't passed rollover crash tests in the U.S., so the solar roof option is currently only available on the Prius in Japan and Europe. However, the company is continuing to work on a solution to offer it on US models.

Buyers will have to judge if the add-on is worth it. While the small daily extension in range may add up over the lifetime of the vehicle, the price of the solar roof option runs £1,500 (US$1,840) for consumers in the UK. Installing it also requires the removal of the head up display, blind spot monitor and rear cross traffic alert.

Panasonic has become a major player in the battery market, partnering with Tesla on the company's Gigafactory, which will soon begin churning out record numbers of lithium-ion car batteries. Tesla CEO Elon Musk has stated the coming Tesla Model 3 will probably have a solar roof option as well. And now with Panasonic introducing its new solar roof, it's possible that the two companies may collaborate on the solar roof option.

Source: Panasonic