Yesterday Hyundai released a version of their Sonata Hybrid car that includes a solar panel integrated into the roof, and along with it came a lot of exciting claims, like how it can recharge up to 60 percent of the car’s battery, and how it can provide enough power over the course of a year to let the car travel over 800 miles. It all sounds great, but, unsurprisingly, in reality it’s likely to be more of a nifty gimmick than anything actually really useful.
Hyundai’s website is, of course, effusive about the rooftop solar panel, calling it a “roof charging system”:
While this is technically true, let’s go over the numbers here so everything’s really clear about what this solar panel will actually do.
Let’s start with the claim that says it can charge up to 60 percent of the hybrid’s battery. I asked Hyundai for more details about this, such as the Sonata Hybrid’s battery capacity, and they told me that
The high-voltage battery capacity of Sonata Hybrid is 1.49 kWh. It can charge 894Wh of energy, or 60 percent of the battery capacity, with a solar roof for one day.
This result is based on a summer test in California and it varies by test condition.
Okay, so first, let’s be clear what size battery we’re talking about: 1.49 kWh is not a big battery by any stretch of the imagination, at least for a car. A Toyota Prius Prime, also a hybrid car, has an 8.8 kWh capacity battery pack, and a full electric car like the Tesla Model 3 has a 50 kWh battery as its smallest option.
So, we’re talking about a 60 percent charge on a (comparatively) very small battery, and getting to 60 percent requires a full day of charging under the California summer sun, arguably the best quality sunlight money can buy.
Let’s say you can get that sort of full sunlight for at least six hours a day; then, Hyundai tells us that
If the solar roof gets six hours of sunlight per a day, it can give 800 extra miles of a year. It is calculated by average solar energy in US due to the large variation in each region. According to EPA and NHTSA, the average solar energy flux per day in US is 4.159 kWh/m2/day.
So, a free extra 800 miles of driving? That sounds amazing, right? Well, almost. Remember, that’s an extra 800 miles of driving per year, which comes out to just over two miles a day. That’s two extra miles a day you can potentially get if you can leave your car charging in full sunlight for six hours.
I suppose if you have a two mile commute to work with parking in direct sunlight all day, then, hypothetically, you could drive to and from work for pretty much free. Well, that is if you drive gently enough to keep the car in electric-only mode, which I think on the non-plug-in hybrid model is pretty slow.
Hyundai wouldn’t tell me for sure:
It is difficult to disclose the exact figures as the electric efficiency is confidential.
The Sonata Hybrid’s solar roof has roughly the same capacity as another car with a solar roof, the Karma Revero: 200W. Hyundai isn’t making the ridiculous levels of claims as Karma did when they unveiled their solar roof in 2016—remember, they claimed it would “power the car,” which, of course, was bullshit.
Same goes for the Lightyear One “Solar Car;” you could technically power it with solar energy, but only if it spent nearly all its time in sunlight and you hardly drove it at all.
Hyundai isn’t being as deceptive as Karma or Lightyear were here, but it’s worth cutting through the hype all the same. The Sonata Hybrid solar roof is a nifty bit of technology, but in real-world use the actual impact it’ll likely have will be pretty minimal.
Even in absolute, hypothetical best-case scenarios, you’re looking at an extra two miles of range a day. That’s not nothing, and that energy is effectively free, but it’s not likely to make a real difference in saving you much money or your enjoyment of the car.
Hopefully down the road solar panel efficiency will improve to the point where these sorts of things make real sense.
Right now, though, they’re really just like an integrated trickle charger that can be disabled by a moderate amount of bird shit.