How effective is that solar panel?

I have found that in the worst case (full sun in the summer), it keeps the cabin temperature a few degrees lower than an unvented vehicle.

Last summer I did an experiment between the RAV4 and the Prius four solar and posted it here on these forums, but I can't seem to find the search function from my phone interface.

It seems to be more effective on bright but overcast (high lighting conditions but little direct sun), so I feel that if one were to use a radiant barrier in the windshield at least that performance would be much improved.

The heat gain from all the windows likely outstrips the ventilation ability of the fan, so if one can prevent some of the heat gain then the fan would have a better chance of keeping up. I only just got around to ordering a front window visor for the car.

Of course, no simple fan will be able to lower temperature to anything but the ambient temperature outside, even if able to do complete air changes every second.

I still would have purchased my four with deluxe solar package. Besides keeping the interior cooler on bright days, I have dreams of experimenting with a few low-voltage DC applications.

 

I have run the calculations before (I was in a grad photovoltaics class so it interested me), and they are probably still somewhere on my computer. I'm typing on my phone from my pillow now, so I'll try to dig them up tomorrow if no one else has.

Don't get your expectations up however.

If I remember correctly there wasn't even so much as a single square meter of panel there, and given an insolation value of no more than about 4 kWh per day times an efficiency of about 16% you are talking peanuts for output.

Enough to drive a small dc fan, but nothing terribly useful.

 

See https://techinfo.toyota.com/techInfoPortal/staticcontent/en/techinfo/html/prelogin/docs/3rdprius.pdf.

 

That's exactly the same thing I wondered why Toyota didn't do, I mean a penny earned is a penny saved, right? Regardless how small.

 

The solar panel apparently uses a switching regulator to drop the 22V to 12-14V. Others are reporting this generates electrical noise. I haven't seen this noise on my Kenwood D-710 VHF/UHF Amateur radio, but that is not surprising, as it's FM.

I suspect the reason we don't see the panel used to keep the battery charged is the complexity of controlling the charge and the problems of controlling the noise in the cars systems. The efficiency gain was probably not worth the expense of the engineering.

 

Found the data that I collected last year on the panels.
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The Prius solar roof panel is 36 cells at half Kyocera's standard size of 15 x 15 cm at a conversion efficiency of 16.5%. Kyocera states that the maximum output is about 50 watts--that would be in direct bright sun. So in bright sun they would power a 50-watt light bulb while the sun is shining.

36 cells at 15 cm x 15 cm / 2 = 4050 cm^2 = 0.405 m^2

Average solar insolation (the amount of sun energy available striking the earth--this is before the lost energy due to conversion into electricity by photovoltaic cells) is around 4 kWh per square meter per day over much of the fairer portions of the U.S. Let's take SoCal and call it 5 kWh/m^2/day.

So 0.405 square meters x 5 kWh/sq meter/day x 16.5% = .33 kWh per day (average).

The EPA's formula rates a gallon of gas at 33.7 kWh equivalent. So in about 100 days you could collect the energy equivalent of one gallon of gas.

Reach the maximum theoretical limit of solar panels and you can collect a gallon of gas worth of solar power in 50 days.

Read more: http://priuschat.com/threads/solar-roof-to-recharge-battery.109348/#ixzz2Nnrrdqbn
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It's just as likely that the engineer shot the idea down because the advantage just wasn't substantial enough to justify the disadvantage of a little extra weight in equipment, which would increase rolling resistance and grade resistance. Any increase in resistance will degrade the fuel efficiency.

The numbers that I provided were *optimum* conditions, and did not include such factors as the energy loss you get when you charge a battery, and of course, cannot account for the optimum tilt of the solar panel which is dependent on latitude and time of day.

Solar's best application is a stationary site close to the loads that will use the energy. The stationary nature would allow the panels to be set at optimum tilt for the latitude and load timing and automated tracking of the sun, if that is desired.

The tilt angle on the Prius is likely not optimal for 99% of locations where they are driven--a good default to assume is that tilt=latitude.

In truth, I cannot even be certain that the panels on the four as configured are worth their added weight, but I wanted them in the hopes that I would run the A/C a little less in summer and keep the traction battery healthier.

 

Use the Google search at the top right of the screen, it works very well. Type in your search query followed by Prius Chat. Something like "horn upgrade Prius Chat".

 

Damn.

Now if only google could tell me where I laid down that phone.

Oh yeah--the kitchen, looking up baking soda use in hard-boiled eggs.

 

At least the solar panel is effective enough to run that little fan that keeps the car interior at less than full furnace level in Florida. Need to compare interior heat levels side by side Prii with same color interior and exterior... but seat of the pants experience tells me it works pretty well!

 

I did an informal comparison last year when I bought the Prius with solar roof option:
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This was an imperfect experiment since I didn't have two Prius to compare, but it's the best I can do unless I find another Prius to use.

Two cars sitting in the sun, ambient temperature is 84 degrees.



The RAV4 without the solar fan is 104 degrees on the inside; the Prius with fan running is 94 degrees. The difference in the sun seems to be about 10 degrees between the two cars (30 minutes earlier the RAV4 was 98 degrees and the Prius was 88 degrees.)

However, if one doesn't have the shade on the sunroof pulled shut, this negates the advantage of the fan and then some. With the sun shining in through the top of the car, the Prius was about 2 degrees hotter than the RAV, even with the solar fan running.

Read more: http://priuschat.com/threads/seeking-informed-opinions-i-cant-decide-between-a-iii-sunroof-or-iv-sunroof.110094/#ixzz2NpRqRVmt

 

How about the sunroof tilt? I wonder if open or closed makes a difference

 

I strongly suspect it does if you leave the inner shade open an inch or so.
That's how I parked my car at work last summer when we weren't expecting rain.

 

I think I can safely say that the ICE isn't idling a few minutes per trip to keep the 12V battery at voltage. It needs to run to warm itself up through the stages and then, of course, propel the car. I certainly don't have the ICE starting while I'm waiting at a light unless it's to provide heat for the climate control.

 

Uh, guys, it's not rocket science to "compare" the heat gain of the Prius with and without the solar panel -working-. There is a little switch on the dash. Turn it on (in) to test with the panel running the fan. Turn it off (out) to test with the panel not running the fan.

Heat gain from colour and from the panel being there is taken out of the comparison as the colour is the same in both cases and the panel is there in both cases. Just take care to ensure the sun angle doesn't change much between tests and the ambient temp doesn't change much between tests.

To get even closer, do both tests on one day, say fan on first. Then do both tests the next day in the opposite order.
Average the two days results to get a closer estimate.