Solar Roof changes roof line.. aerodynamics

I have a blizzard pearl 2011 IV w/ solar & performace pkg....the black roof is beautiful & the springs are settling & the forged wheels...aahh gorgeous....guess either I or josh2008 should post some pics of my 1 mo old love )

 

The humps are present in both the Gen II and Gen III Prius. I think it prevents the airflow over the roof from spilling down the sides, reducing turbulence and air drag. It's like an air director. You see the same thing in the Gen II hood, but not in the Gen III hood; but the hood features could just be styling and non-functional.

The Solar Roof eliminates this, so I believe the Cd (Coefficient of Drag) is higher. Also it creates more frontal area. Both serve to increase aerodynamic losses.

The Gen III relies on sharp cutoffs in the front bumper and rear bumper to allow the airflow to make a clean exit, otherwise it has a tendency to hug the surface and increase turbulence. There is a term for this but I forget what it is called. I believe the Chevy Volt copies or borrows the same concept as I have not seen it in many other vehicles (I believe Cadillacs just use it for styling).

 

I will see if I can post some around lunchtime They are very pretty, mirror like when detailed. Buying this one was kind of an accident, we weren't planning on buying another prius this soon. We went to check out the new 2012 redesign for the camry and looked over on the pad at the dealership and said "omg, thats a Prius, its beautiful" test drove it the next day, brought it home the day after that. Hubz & I have both driven/owned 2nd & 3rd gen prii before but this one was different, show stopper almost.

As far as milage, this is the first true tank & we're still going after about 3 1/2 weeks. This morning was about 630 mi on the tank so far.

 

The "humped" roof on a standard Prius is called a "pagoda" roof. The lowered center section and longitudinal ridges reduce aerodynamic drag and weight. As with many aerodynamic features, what looks sleek is really not, and vice versa.

Toyota made compromises to accommodate the roof PV array. In particular the PV array needs to be flat, and it is a lot heavier. The mileage hit from the solar roof is real, but small.

Tom

 

I'm going to be a little contrary here. I doubt you could measure any difference between the two roof designs. The air becomes separated from the body at the top of the windshield anyway so the roof has very little effect. I'd bet if you were able to ask the designer (and if he/she would answer) that the "pagoda" roof was done to make the roof stiffer so it wouldn't vibrate. It's a "pagoda" roof because it looks better than a bunch of ridges. The solar roof materials were already rigid enough and didn't need the expensive treatment of "pagodaization".

 

Toyota engineers stated that the ridges allow a lighter roof for the same stiffness, and that the raised edges direct airflow to the middle.

Certainly airflow over the roof has detached, as it would be nearly impossible to maintain laminar flow without boundary layer control. Even with the turbulent airflow, the lower center section works like a wasp waist to reduce pressure. This is a common tactic for aerodynamic bodies at higher speeds. With cars it's not so common, but Prius aerodynamics are the sum of many small improvements.

Tom

 

As requested pics turned out alright for my cellphone.

 

I have driven & owned both the solar and non-solar versions. There is a heavier feeling to the solar car, and a slight decrease in the mpg's I have been able to achieve compared to the non-solar car. All else being the same I'd rather have the solar sunroof version.

 

The sunroof is a must! Even if it impacts MPGs while open...I keep it open nearly all the time. Any sunroof changes the entire mood of the car IMO.

 

Once again, with feeling. Sun roof and Solar roof are two different things.

 

Correct...but as I understand it, they come as a bundle. Can you get the solar roof without the sun roof?

 

Not from the factory no, i have seen some aftermarket shops chop a hole in a gen 2 prius and put a sunroof...