Hacking the solar?

[daniel]

For me, the only possible use of PVs on my car would be to power a fan. That's because my car is not parked in the sun the times when I might want a trickle charge on the 12 V battery. At the airport I park in the covered parking garage to protect the car from snow and/or hail. At home I park in my garage. Any time my car is idle for any extended time it's out of the sun. But the solar fan would at least keep it comfortable when I do park in the sun during that one hot week of the year. But of course, as Pat points out, it's a lot of money to avoid 5 minutes of discomfort while the A/C cools off the car.

[HTMLSpinnr]

Originally Posted by daniel

...it's a lot of money to avoid 5 minutes of discomfort while the A/C cools off the car.

Your 5 min is perhaps 10+ min where I live. Combine that for up to 100 "days" of driving per year, over 5-7 years, and it may be worth it. It all adds up.

[ronhowell]

Originally Posted by efusco

Considering the current OEM setup of this PV I think you're assessment is totally on target Pat.
It seems almost slapped on. If they'd have used the entire roof and made this closer to 200W it may have been more useful had it been more completely integrated into the car. 200W would be enough for to run a tiny heater to keep the edge off a really cold day. It would be enought to run all the electronics and take at least part of the load of the AC even on a hot day. Maybe, just maybe, it would be enough to passively charge the HV battery a little bit.

Couldn't agree more. The solar panel is more symbolic than practical, and gives Toyota marketers green bragging rights that others do not have.

The basic problem with solar energy is you need a large area to capture any significant amount; even then the conversion efficiency to electricity from the solar insolation is low (12 - 16%, other than in the lab). Maybe 10 years from now the efficiency will be much higher and the panel cost lower, with all the research money currently being spent on it.

[miscrms]

I'd have to agree with Spinnr, this is a very useful feature in Phoenix. Maybe not so much else where. AC cool down is at least as much of a problem here as the warmup cycle is in the north. With ambient at 110-120F in summer, you can imagine what interior temps can get up to. It can get hot enough inside that the battery CDL is set to 0 while the fan cranks away trying to cool the battery compartment, so all the power to drive the car and run the AC has to come from the ICE. Even if you don't get into this mode, just the normal 10 minutes of the AC is blasting on high trying to get the cabin down from 160F to 80F really kills your mileage. Anything that speeds up that process will have a real impact on summer mileage.

Rob

[miscrms]

I'm sure its been mentioned elsewhere, but this is not really a new idea. Audi and a number of other luxury cars have had this sort of thing for 10 years or more.

Rob

[Zhentar]

Originally Posted by patsparks

I agree with what the solar panel is meant to do and it will reduce the overall load on the engine for recharging the traction battery after remote cooling but when considering the added weight of the solar panels and that the added weight is on top of the car inducing more body roll so requiring more speed reduction for corners, I suspect the solar panel uses more energy over its life particularly in its current part time role than it contributes.

You're probably right, but for the wrong reasons. The 10-20lb of solar panel on the roof, less the metal it replaces, is not going to cost a particularly significant amount of energy. But, like everyone so loves to do, you've forgotten that it costs energy to make solar panels too. A fairly significant amount, in fact. Panels carefully aimed & mounted with sun tracking can takes years to generate as much energy as it took to produce them. Add in a crappy angle, garages, dust, snow, trees, and who knows what else, and the power output drops. Most of these panels will never produce as much energy as it took to manufacture them.

[patsparks]

I didn't forget, I stated in an earlier post to spend the money on a roof mounted PV array for your home for a better bang for buck/energy.
I doubt the solar panel isn't over a steel roof panel so it is added weight to lug around.
In the last sentence I said, "I suspect the solar panel uses more energy over its life particularly in its current part time role than it contributes." I was including the energy to produce it but you failed to read my mind.

[RobH]

Originally Posted by Zhentar

You're probably right, but for the wrong reasons. The 10-20lb of solar panel on the roof, less the metal it replaces, is not going to cost a particularly significant amount of energy. But, like everyone so loves to do, you've forgotten that it costs energy to make solar panels too. A fairly significant amount, in fact. Panels carefully aimed & mounted with sun tracking can takes years to generate as much energy as it took to produce them. Add in a crappy angle, garages, dust, snow, trees, and who knows what else, and the power output drops. Most of these panels will never produce as much energy as it took to manufacture them.

Solar panels go through the same sort of accusations as the Prius. This sort of thinking was roundly discredited back when I installed panels on the roof of my home back in 2001. Apparently such accusations are endemic, and do not go away just because they are disproved. Not using them is just wasting the energy that falls where they would otherwise be.

The largest energy consumption and weight of a solar panel is the aluminum frame. The Prius installation doesn't use an aluminum frame. The weight of the panel without a frame is more like 5 pounds, maybe even less.

The Prius solar panel provides a function that simply wasn't available before. Power ventilation doesn't work with the standard 12V battery in the car, as it would run the battery down too much. A solar panel, even with its limited output, is adequate to run the ventilation system without risking the battery.

The map of supporters versus naysayers on this thread looks very similar to the map of vitamin D deficiency. If you don't like it, you probably need to take supplemental vitamin D. Oops. Wrong forum. Well it's true anyway. Take 5,000 IU of D3 per day when you don't get enough sun exposure.

Those of us who have to leave a car exposed in hot weather really welcome a solution to the baked car experience.

[neutronned]

A couple of comment:
1) the manufacturing energy cost is already factored into the selling price. If it cost us $4000, then the materials + energy + profit etc is all included.
2) I think the best way to think about it is how much gas will it save in running the A/C a few more minutes. The Prius must get several hours per gallon when idling, so you're talking maybe 1/10 gallon to 1/20 gallon to cool the car with the A/C. That's $0.20 to $0.40 per cooling operation. Pay back is 10,000 to 20,000 operations if the panel is $4000. Phoenix or not, hardly seems worth it. Even if the panel is $1000, that's 2500 to 5000 operations, or every day for 6.8 to 13.6 years. The break-even point is way out there.

My math may be off, but I agree some of the others that it's more about looking green then being green.


Anyway, back to hacking the solar. It should definitely be possible to find the "hot" lead from the panel and parallel a charge controller into the 12V battery. Could route it to an outlet in the car for charging 12V stuff like iPods, cellphones, etc. I notice that Woot has a $100 18W panel and controller combo today, so a controller alone should be reasonably easy to procure.

[Stefx]

I agree with Patspark's assesment. A PV panel belongs on a house rooftop.

I also wonder about the dangerous materials in the PV (germanium? silicium?) and how they need to be properly recycled.

Originally Posted by efusco

If they'd have used the entire roof and made this closer to 200W it may have been more useful had it been more completely integrated into the car. 200W would be enough for to run a tiny heater to keep the edge off a really cold day.

Well, in the winter you'd get 50-100W out of 200W max due to sun angle.

Also, at home I run a 700W heater in the Prius (on a timer) and with thermometers inside and outside it comes down to making the cabin 10degC higher than outside air temperature. Another one on this forum in Quebec City usesd a 900W heater, he got 12 deg C. So, a 50, 100 or even 200W wouldn't make a difference that you would notice (2-3 degrees?)