Solar Roof to Recharge Battery

Now visualize passing a crash test with that car.

 

Actually.
Solar on roof used to power traction HV battery was done in Cali by Solar Electric Vehicle or solar prius by Bob J...
I am not sure of the details.
The current solar panel market for a solar roof prius panel is all custom from what I have found. The solar panel would be limited by two factors. The Prius actual physical roof size/dimen and PV solar panels which have low voltages and wattage.
A 270 watt PV solar panel is likely all you could do with Prius roof. Most solar pv is much lower in both watt and voltage that I have found. These two are the only ones I have seen that have a product for Prius solar on roof scale.
PV COOL(ebay and website)(downunder/austrailia)
Solarelectrical vehicles(website) greg johanson (california)

 

My PV panels are 38" by 69".

Two of them laid side-by-side would only be 76" wide. Laid on a roof rack, they would not be too large for the vehicle.

440watts.

 

Wouldn't throwing up big clunky solar panels on the roof increase wind resistance and negate any benefits you'd get from them?

 

Actually, this much of your idea has already been implemented. There are people who have purchased a plug-in prius (making the process of charging the high voltage battery relatively easy). They then had solar panels assembled that are larger than the roof of the car (they mounted them on the roof of a building such as a house or garage). They then park the vehicle in the garage providing shade and a location to connect to the solar panels.

 

about 2 inches thick, and flat, I imagine they would create about as much resistance as a luggage rack would make.

It would decrease MPG, however if it recharged the main-battery, ...

440watts during sunlight hours each day.

 

Nope, that number generally refers to a fixed flat-plate collector facing south at tilt = latitude.

Two-axis tracking will get you up to almost 50% better. But since all that extra equipment rarely makes sense on a ground solar system, I think it would be beyond nuts in on a Prius-sized vehicle.

And of course, for any of these numbers to be valid, the Prius would have to be parked away from any shading ALL DAYLIGHT HOURS.

Really, this whole discussion *DOES* amount to ridiculous when you do the math.

I thought that pointing out the fact that 33% is the absolute theoretical maximum of photovoltaic efficiency would do it (we're already at 16.5%), but some seem to insist on believing that not only will we exceed theoretical limits, nay, we will also exceed even the total radiant energy sent to us by our sun! We're going to improve on the amount of radiation the sun gives us--take one unit of sunlight and make ten or a hundred units of electricity! Whatever.

Makes me want to start explaining the concept of "soiling" as it applies to reducing your PV's energy if you don't keep that panel clean, and the energy losses of charging the battery, and then discharging the battery to use that energy. The overall efficiency of the nickel metal hydride battery is around 66%, so in order to get 1 kWh of energy back, you need to supply 1.5 kWh of charge.

For the soiling factor, you lose 5% under light soiling conditions with "frequent" cleanings, or 10% under heavy soiling conditions. And remember not to put cold water on a hot solar panel or you risk cracking it.

So between the soiling and the battery efficiency you've already lost another 38 to 40%. So really, in order to get 1 gallon's worth of gas under "light" soiling conditions you'll have to leave the car in the sun 160 days in southern California (more than that in areas with less sunlight). In a year you'll have made the equivalent of 2 gallons of gas.

The ONLY reasons I am opting for a Prius with a solar panel are to keep the car interior cooler on hot sunny summer days. This performs three functions:

1) Keeps the humans getting into the car more comfortable
2) Reduces the load on the A/C
3) Keeps the traction battery cooler (I hope), since it will draw ventilation air from the passenger cabin.

I have the benefit of at least having one grad-level class in designing photovoltaic systems for an engineering curriculum. I am designing a solar system for my house, which even WITH a 30% federal tax credit will probably be more trouble and expense than it is worth.

The idea of a PV array on a Prius that can usefully charge the traction battery is lunacy.

 

Dreaming of wild dreams is great for writing science fiction novels. I absolutely loved James Blish' spindizzies and anti-agathics.

But here in the real world we are unfortunately constrained by the natural laws of thermodynamics, electricity, and the raw output of the sun. Looking up the numbers for solar insolation and then calculating the amount of energy you can get for a certain area of solar panels is NOT difficult at all. And it would really help you to get an understanding of what is possible with solar panels, plus where the limitations are.

Then you could dream along more practical lines on things that you could actually implement in your life.

I dream every day of what I'm going to do with solar panels, or the passively-ventilated "igloo with a cupola" chicken tractor chicken coop that I want to build, or the Hugelkultur paddock paradise design that I want to implement for the horse pasture.

Learning the science behind most things isn't very hard, and it trains your dreams along paths that you might be able to achieve.

 

Lest you think we just dislike solar, I am doing something similar to the Toyota Prius solar fan with my house

GAF Roofing ? MasterFlow Vents - MasterFlow Green Machine Dual Powered

It runs for free whenever it is light out, but if my attic gets too hot, it gets twice as powerful with grid electricity. They claim it saves 80% of the equivalent AC unit. I have them on two of my 4 attics, the south facing ones. (unlike the car, I can aim these solar panels)

 

It just makes a whole lot more sense to put solar panels permanently on the roof of a building than on a car.

 

This is off the subject, 33% can be surpassed now. I think it's up to 40%. With a method called Photochemical Upconversion. It makes use of the red by converting it to yellow and reflecting it back.

Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion - Energy & Environmental Science (RSC Publishing)

http://www.gizmag.com/photochemical-upconversion/22259/

 

There were attempt production of gallium arsenide (gaAS) solar panels very toxic method and expensive but were close to 40 percent efficient

There were talks of solar / thermo electric combination panels that also increase efficiency overall, 20-30 percent, too big / heavy

Why not something like peel and stick, thin solar panels, much more practical it seems. less fabricating, weight and aerodynamics should be the same if perfectly sized.

http://www.amazon.com/Uni-Solar-PVL-136-PowerBond-216-Inch-15-5-Inch/dp/B002MWFFWM

I was wondering why it was not mention the gas savings from the ventilation with solar panels, not just the value from current from solar panels give, but the value of having the car already cooled inside and having less impact on AC which has a significant effect on mileage.

Also roof solar panels on fisker advertise 4-5 miles a week, 5 miles times 52 weeks, 250 miles a year 20-25 bucks less gas, would take 20 years to recoup the cost for even the amazon panels which I'm sure fisher panels are more advance and efficient and guessing more costly.

 

In a sense it is kind of already doing this in a round-a-bout way. Since now it takes less energy to cool down your car that's less energy the traction battery will use which is kind of the same thing as having that energy in the battery and using it to cool the car instead.... seems like you're ahead in the game with the panels (on hot days anyways)

 

Well said, I agree it's an advantage either way. Going extreme doesn't seem worth it though. If only we could have micro nuclear or fusion reacted installed in the trunk

 

FAQ's
Solar Electrical Vehicles - Articles

I think you were right. There is a company that converts prii to solar, with a 210 watt convex panel (so it doesn't impact aerodynamics). Their website indicates that if parked in the california sun it can generate 5-8 miles worth of charge per day " between 850 and 1,300 watt-hours." Of course the stock battery is only 1.2 KWH so in order to store that much charge you would want to buy their 3.4 KWH SLA battery setup, or something similar if you actually live someplace sunny. Taking that low estimate of 5 miles x 260 weekdays/45mpg , it will save 29 gallons of gas per year. Of course the sun shines on weekends to so if you have the storage it would save 40 gallons/year. At current prices of 3.50/gallon that is only $101/year, or $141 if you count weekends.

It's hard to find pricing on their website, but a pdf I saw indicates $3500 for the solar panels and charging system, $4500 if you want the 3.4kw sla batteries too, $7200 if you want the plug in option they describe as having a 30 mile range. For the base price assuming ability to take the charge (as is the case for a pre-existing phev conversion) the annualized ROI amounts to 2.8%, or 4% if you include weekends. Not a significantly better return than paying down my mortgage. However the ROI would double with gas prices, for 5.3% or 8% at $7 gas, at which point it is nearly on par with putting money in a 401k beyond the company match and better than making extra mortgage payments. So from the cheap bastard point of view this technology isn't quite there yet, but from the point of view of the well financed person that wants to spend less time buying gas it is ready to go.

I would love to do it anyway just to buy less gas, but I can't afford it. I would never be able to charge at work if I got a phev conversion but I park in the sun all day. I also live in a state where I can get my windows tinted, making the powering of a parking cooling fan potentially less beneficial. There are also no incentives whatsoever for home solar in my state and my electricity is cheap (8 cents/kwh), so solar panels on the home would make even less financial sense for me than getting the solar conversion on the prius.

I find it disappointing that this option isn't available from Toyota directly, and that their panels are only rated for 56watts while a third party has been able to deliver 210 watts. Of course even at the tiny 56 watt size they should have included a smart charge circuit for the 12v battery for those who drive short trips and park in the sun.

 

Toyota should do it as leaving the car parked for extended periods and having the battery die is a real problem for a Prius. The solar panel should trickle charge the battery and let the battery run the fan when it is fully charged.

You'd see the top floor of the car garages at the airport packed with Prius, topping off.

 

I agree Mark. You have people on here making "custom" license plate brackets that slide out to cover the air intakes to get what? About a gallon a year better economy??? Haha . This roof panel is my pet peeve . For a car that's supposedly built economy, why waste all that engineering and cost of a solar panel just to run a silly fan? I wonder if that fan even saves a gallon of gas per year!
Ok, I generally understand it not being used for the big battery, but why not have it charge the small battery? 12 hours of daylight is being wasted. Or at least have it power a single 12v outlet or two.
Could it power the radio while sitting in the car?
I figured this set up is ripe for modifications & hacking!