Hacking the solar?

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.

 

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.

 

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

 

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

 

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.

 

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.

 

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.

 

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.

 

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.

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?)

 

It's not about being green. It's about being comfortable. It will also reduce the sun damage to the interior, so there may be some payback when the car is older.

A controller with Power Point Tracking (PPT), like the Blue Sky Solar Boost mentioned above, can extract 30% more power from the panel than without such a controller. The efficiency of a solar panel varies, depending upon the load, the amount of light, and the temperature. The ventilation fan doesn't adjust for these variables, so the panel is usually operating at a less than optimal point.

So, hack #1 is to add a PPT solar controller. The fan will start sooner, and run faster with the extra 30% power.

 

I'll assume by "disproved" you mean "technology improved to the point where it was no longer true", as it really is possible for energy technologies to use up more energy than they produce. And I won't deny that modern PV panels have a fairly short energy payoff. The worst I'll say about stationary mounted PV panels is that in many locations there are alternatives with better cost:benefit ratio (though not always practical for personal use).

But even if a home mounted system in a sunny area can recover the energy invstement in a year and a half, the car is a different situation. My panel would be mounted at whatever angle I'm parked at (flat) on my car in Wisconsin. 1/4th the solar insolation, 6 year payoff. I'm parked in a garage most of the weekends and mornings, -25% of daylight, 8 years. My employer's new parking garage will be finished in june, losing another 55% ish of daylight. 30 years. The panel is most likely capable of lasting that long, but the car is not.

Now, my case is probably worse than average, but I'm still taking 2-3 times the likely lifespan for energy payback, using optimistic numbers. The energy cost for installing in the car won't be significantly reduced; growing silicon and fabricating cells still represents a substanially larger part of the energy cost than the aluminum frame, and the car installation will likely add some of the savings back in.

Now, I'm not saying the panel is a bad idea. I think it's frickin cool, and I want one, but as a luxury feature, not as a green feature. I am saying it would be foolish to have added a substantially larger panel and use it to trickle charge the traction battery. For the considerable majority, at least, of Prius drivers, it would be better for both their wallets and the environment to buy gasoline and run the ICE to charge the battery than use a larger roof mounted PV panel.

 

We agree. It's a luxury item, and not green.

The solar panel on a Prius is not something that should have a payback calculation applied to it. I think the reason that people want to calculate payback is that solar on houses does have a payback element.

Nobody calculates the payback of a car radio. Or electric remote control mirrors. The backup camera probably has some sort of payback in safety, but that doesn't seem to get discussed. What is the payback of the Touring suspension? Is there a payback for the smart key system?

Solar panel driven ventilation is a new application of solar panels. There is no more payback for it than there is payback for having air conditioning. It's a comfort item that some people will be willing to pay for. Accuse them of conspicuous consumption, but not of choosing a looser on a payback calculation.

Solar just got a lot cooler.

 

I think Rob is right. It's not about energy efficiency or payback, it's about spending some money to be more comfortable. In Spokane I don't need it. Especially since in summer I'm away more than I'm home. Desert dwellers are likely to find it dollars well spent regardless of the energy payback.

But hacking it to trickle charge the 12-v battery seems pointless, unless you park your car in the sun for more than a month at a time without driving it. If you leave your lights on, the solar roof won't provide enough juice to save the battery, and if you don't, the battery will get topped off every time you drive the car.

 

Has it been announced that this solar panel is outputting 12 Vdc? Before any hacking is considered the actual output voltage needs be known.

 

I'll agree with this, but qualify my comment by saying it's pointless from a ROI standpoint. Doing it just for the sheer fun of it makes sense if that's the sort of thing you like to do. It sound like a good project: I has a good geek factor, is well bounded, and is fairly easy to do with finite time and resources. Will I do it to my 2010 if and when I get one? Probably not. I could do it fairly easily, but that's the sort of thing I do for a living, so it's not a good hobby project for me.

Tom

 

alreading was thinking about doing the solar panel do 12voltl charge thing!

but not sure what the price for the solar panel will be.

 

Most smart PV controllers use some sort of DC to DC boost circuitry, so we could incorporate voltage shifting as needed. What I envision is a smart controller that gives priority to the ventilating fan, and sends any excess to the 12V battery. If you aren't using the fan, then all of the power is excess and goes to the 12V battery as needed.

Tom