2010 Solar Roof Temperature Report

Steve here again with a little more data, and some notes about methods etc to keep in mind:

This post was not a complaint about the solar panel / sunroof. I did not expect the same temp inside the car as outside when using solar ventilation (or ‘ambient’ as Toyota puts it) since the car exterior itself heats up in the sun and radiates heat both inward and outward. Again, this is NOT a complaint: I love the sunroof, and I believed the solar system would be effective at knocking down the interior temp. This post is simply an effort to provide information to others who are considering the solar roof package solely because of the solar driven ventilation, or for anybody who is just plain old curious about the system.

Also: as noted in my original post I have ordered a heat shield and I am waiting delivery.

Methods:
1. Same thermometer is used to take temperature outside of car in the parking lot, and then inside the car with solar ventilation on. The temps are taken AFTER the car has been sitting in the sun with solar ventilation engaged for 4 hours.

2. The thermometer is calibrated for laboratory work and is very accurate from 0C to 100C.

3. Temp is taken at hottest point of the day (about 3 -4).

4. The remote A/C is not used in these tests since that would defeat the whole purpose, which is to test exactly how much the solar ventilation system by itself cools down the car interior…. we already know that A/C cools down cars.

5. I do not leave the windows open a bit as others suggest because my parking lot at work is gravel and very, very dusty. So temperature readings are taken in closed car.

6. My car is black and of course this probably impacts results.

7. My climate is hot, dry and sunny. Normal summer temps are 95-105 and every now and then a bit hotter.

8. There is no shade where I park so the solar panels are in full sunlight all day.

9. The inside panel of sunroof is closed.

10. In some cases the car is parked facing directly south, and in other cases the car is parked facing directly north. I think facing north is actually better for operation of the solar panel since it sits on a portion of the roof that slopes down towards the rear of the car and that way the solar panel should more directly face the sun.

11. As mentioned here in this thread by some others, the solar ventilation system will probably have the least effect when it is very, very hot. So for those in Phoenix your car is still going to be pretty warm inside, but no where near 150+. For those in climates where the temp is lower the system should work much better. Blowing 110 degree air inside a car, as in Phoenix, isn’t going to cool things down much. But blowing 85 degree air should help much more. I plan more measurements when I get my solar shield and will let you know. Thanks for comments, tips and posts.

Results to date:
Car facing south on gravel lot: outside, 96.8; inside 125.6.
Car facing north on macadam lot: outside 100.4; inside 122.
Car facing north on macadam lot: outside 89.6; inside 109.4

Kind of interesting if you compare first and third measurements. Outside temp differed by only 7 degrees, but inside temp differed by 16. I know, multiple factors involved, but I’ll collect more data so we can make direct comparisons.

 

Yeah, I'll let you know what I find. I'm hoping to get my heatshield soon so I can factor that in too.

 

Sorry for the slow piecemeal data, but I’ve only had time to make 1 measurement each day. However this does let the car reach what is probably its maximum temperature. Seems one hour is not enough time for the car to heat up completely. Today I can report some data that you’ll be interested in: Two measurements of the Prius sitting in the sun with the solar ventilation turned off.

Yesterday I compared the Prius to my 05 Corolla. Both were facing south, no windshield screen, sitting on cement, had been in partial shade for several hours and then full sun for 2 hours. The Corolla is phantom grey with light brown interior; the Prius is black with dark grey interior. The Corolla was actually much hotter: 150 degrees versus 124 for the Prius, and again that temp reading was taken with the solar vent turned off. I didn’t expect such a difference but perhaps the Prius has better insulation? Or better glass that blocks more of the sun’s rays? I don’t know.

Today, the Prius was again facing south, sitting on Macadam for 4 hours, no windshield screen, solar vent turned off. Outside temp 96. Interior temp, ready for this? 165 degrees F. No joke. The car was smoking hot and everything inside very hot to the touch. Took almost 10 minutes for the AC to make things comfortable. I don’t think I’m going to put the car through this again. I will take more measurements when the heatshield finally arrives, but it seems clear that the solar vent does make a difference in very hot weather. The hottest temp I’ve recorded so far with the vent running and the car facing south was 125 (same outside temp). As others have pointed out, 125 is hot, but 165 is crazy hot. Maybe the Prius models with white or grey exterior wouldn’t get so hot. Anyway, the take home message is that it looks like the solar vents can reduce the temp by up to 40 degrees even in the 95 degree weather. That should allow the battery to be used more for powering the car rather than the AC unit. I imagine the heat shield should help a good bit, and that when the weather cools down to the lower 80’s the vents should work even better.

 

One more note: I love this car!!!