… & quantified why you won’t want it.
Prius with new optional solar roof
Credit: Toyota/HybridCars
Solar cells on the roof of an electric car is a popular idea.
Panasonic’s solar roof for the Prius is described as having an output of 180 Watts.
Cruising at 100 kph (62 mph) on a flat road in an electric car requires about 14 kiloWatts. I.e. 14,000 Watts. That’s just maintaining speed, not accelerating, not climbing a hill.
Can you see where this is going?
As a fraction of 14 kiloWatts, 180 Watts is
180/14,000 = 0.013 = 1.3%
Putting that another way, if your drive 100 kilometres in one hour, on a flat, straight road, in good sunlight all the way, the solar roof will have added 1.3 kilometres. That assumes no losses in the system due to inefficiencies, & depending on how Panasonic/Toyota are rating their system, it probably means around mid-day, in summer, & not at high latitudes.
If the car is parked in sunlight, the solar roof could charge the battery. Ignoring the angle of the sun as it varies through the day & any inefficiencies in the charging system, in 8 hours at 180 Watts:
180 * 8 = 1,440 Watt hours = 1.4 kiloWatt hours
Driving for economy, at around-town speeds, one kiloWatt hour will propel an electric car about 6 kilometres (3.73 miles). So if you park your car in the sun at work, & live less than 8.4 kilometres (1.4 * 6 = 8.4 k = 5.2 miles) from work, you may just make it home on the power generated through the day.
If Toyota is offering its solar roof at no cost to the consumer, it may be marginally useful. On the other hand, they’re not running a charity ...
Neither is Tesla – the article linked below claims that a solar roof will be optional on the Model 3.
Electrek – “Tesla partner Panasonic unveils new 180W solar roof product for cars after Elon Musk said Model 3 could have the option”
https://electrek.co/2017/02/28/tesla-model-3-solar-roof-panasonic/
With much more roof area than is available in a sedan, say a classic VW bus, & solar panels with a generous overhang front & rear, it is possible to generate enough power for, “short trips within the city”.
Credit: Green Car Reports
HitchHiker's Guide 2 Tech: “Classic 1966 VW bus with a solar powered drivetrain”
https://hhg2tech.blogspot.com/2015/08/classic-1966-vw-bus-with-solar-powered.html / Tesla partner Panasonic unveils unveil unveiled new 180W solar roof Elon Musk Model 3 option Toyota unveiled new solar roof option 2017 Prius Prime Tesla CEO Elon Musk Tesla Model 3 solar roof option Panasonic solar cell battery cell supplier Tesla releasing new solar product automotive applications Toyota’s solar roof option Prius Panasonic HIT Photovoltaic Module for Automobile solar panels vehicles don’t generate enough electricity to do much of anything Toyota option solar roof previous PHEV Prius generating 50 W Panasonic’s new product 180 W module Prius Prime recharge the powertrain battery traction battery 12 Volt battery Panasonic’s solar cells unique structure combines crystalline silicon substrate amorphous silicon film high conversion efficiency excellent temperature characteristics automotive solar cells output auxiliary charging 12 V batteries ventilation power sources parked cars Panasonic’s solar cells high output 180 W limited area car’s roof charging drive lithium-ion batteries 12 V batteries extension of an EV’s travel distance increased in fuel economy not quite practical yet Koji Toyoshima Toyota’s chief engineer Prius plug-in solar panel increase car’s efficiency by up to 10 percent in good conditions panel add about 2.2 miles of electric range vehicle extremely optimistic Toyota’s electric estimates in the past energy usage reinforced glass sheeting not passing the US rollover crash tests working on a solution /
