[Guest]

Hi all,

I'm currently a student in a business class doing a project on new business ideas. Our idea is as follows...

I'd like to know how many of Prius owners would be interested in buying an aftermarket solar panel package to increase mileage while using green energy. The panels would be placed on the roof. These panels will have the same curvature as the roof and the structural rigidity will not be affected. It will simply be something you can add to the top of the Prius roof. With these solar panels, a fully charged battery (takes approx. 6-8 hrs - like parking your car outside during the workday) would provide enough energy for you to travel 30-40 miles free. So basically your ride to/from home would be free each day. These panels would be an "aftermarket" option. You would purchase the solar panel package and have it installed on the roof. We estimate the cost to be $1000-1500 for the package.

This package would be easily retrofitted on current Priuses.

This is a very rough idea. Please vote in the poll. Let me know if any additional poll options are needed. Please post what you think about this idea as well. Any constructive criticism is welcome. Thanks!!

 

[MikeFromEastCoast]

I think you'd need to get 1000 watts out of about 2 square meters, which is between 2 and 3 times the efficiency of currently available solar panels. You'd also have to have a plug-in prius to be able to accept that much charge.

 

[DanMan32]

More details would be needed. Solar panels alone won't get you 30 miles of free travel. Now it can top off the existing battery, though safeguards would need to be put in place to prevent charging over the 80% limit. That would get you about 3 or so miles of pure EV, or increase FE to about 70-80 MPG for 10-30 miles.

 

[hyperion]

The area where solar panels could be placed is too minute to do any good.
The battery is usually left in a high charge at every shutdown now with it's present system so little would be accomplished.
The airflow dynamics of the car would be deminished. You could never get solar panels as clean as the present tops surface.

 

[DanMan32]

The area where solar panels could be placed is too minute to do any good.
The battery is usually left in a high charge at every shutdown now with it's present system so little would be accomplished.
The airflow dynamics of the car would be deminished. You could never get solar panels as clean as the present tops surface.

Hi state? Mine is usually at 60%. I haven't heard anyone mention theirs was at 8 bars when they powered off.

 

[tochatihu]

solar roof

You ought to google Steve Lapp solar Prius. He had a web site but maybe it is down? He stored the daytime charging in separate PbA batteries and passed it into the HV battery while underway, with a lot of added power electronics.

The energy capture from 1 solar day is arguably enough for that distance driving, but it would require very good efficiencies at each step. An issue with the added batteries and electronics is they will reduce fuel economy all the time.

Hope you are in the desert southwest. US solar loading varies by about a factor of 10 from best to worst.

DAS

 

[efusco]

You're certainly not the first to entertain this though, but clearly you haven't done your homework on the feasability.

As Dan mentioned, if you're talking about charging the HV battery you need a means to convert the power to 206V, you'll only be able to safely top off to the 80% SOC level without risking damage to and/or shortening the life of the HV battery. This means you've gotta also tap into the HV ECU, but the HV battery is completely disconnected from that and is not powered up when the car is turned OFF. You'd need some feedback means to stop charging once you got to 80%.

Alternatively you'd have to add a second pack of batteries, attached in parallel that would be charged then utilized after start up...that would add significantly to your cost.

Or you could do as Lapp did and try to use a solar panel to keep the 12v charged both at a stop and during driving. He claims a 10% improvement....that hasn't been shown to be true. Although if one could create a system that would selectively use the power from the solar panels instead of the power from the 12v battery (probably possible via circuitry) you could see some improvement by using the solar for all the standard drain on the system that otherwise would be from the 12v which is normally charged via DC-DC converter from the HV battery, then you might note some small improvement in FE....but no way it would be enough to justify a $1000 price tag unless you just wanted it for the fun of it.

I'm not trying to discourage you, but perhaps encourage you to do a little more homework. I didn't even discuss the lack of sunlight at night (the best time to top of charge for most people), parking in garages, etc. There are a lot of obstacles...not insurmountable, but complicated and potentially expensive.

 

[James B]

If I understood him correctly the project is to develop and get reaction to a concept not build the finished product.

Should it be possible to build as specified I would be interested but only at a much lower price. Payback would be far too long otherwise.

 

[jamielu]

Should it be possible to build as specified I would be interested but only at a much lower price. Payback would be far too long otherwise.

I agree 110% I would be first in line for a solar rooftop on the prius. please let us know if your concept becomes a more refined (and price practicle) solution AND if the panels are the lightweight thin laminate type, like:
http://www.uni-solar.com/interior.asp?id=102

 

[hyperion]

The area where solar panels could be placed is too minute to do any good.
The battery is usually left in a high charge at every shutdown now with it's present system so little would be accomplished.
The airflow dynamics of the car would be deminished. You could never get solar panels as clean as the present tops surface.

Hi state? Mine is usually at 60%. I haven't heard anyone mention theirs was at 8 bars when they powered off.

.
.
Well Dan, Now you have!.
.
.

 

[DanMan32]

Downhill run before reaching home? That's the only explanation, that would be unique to your driving conditions. That wouldn't be common with everyone else.

As for Evan's last comment, one could monitor the battery's charge level themselves, not exceeding the voltage signifying 80%. I was considering developing a charger that did just that. For an overnight topper, currents could be low, thus not causing any additional harm.

But adding battery capacity would be a better option.

 

[Guest]

Hello, I am one of the other students on the team and did some more calculations. Unfortunately, I don't own a Prius myself and therefore there are many questions I still have.
1. I know that the electric motor has a power of 50 kW. But does anybody know how much of the available power the motor actually uses when you are just cruising?
2. How long can you usually drive with the gas engine off? I heard it is only 1/2 mile before the gas engine starts up to recharge the battery.
3. How fast can you drive without the gas engine coming on? I heard 45 mph is the max.
4. The control system makes sure that the battery never gets discharged below a certain level. Do you know what that level is?

 

[efusco]

No offense intended here, but you guys really need to learn how to use the Google search engine and do a little more research.

If you're seriously asking questions at this basic of a level you are in absolutely no position to even be putting forth the possibility of adding roof solar panels.

Get the hard data...much is available at the Toyota web site, the rest through a couple hours of googling. Once you know what your obstacles and needs are then and only then would it be worth your while to ask this question.

 

[ehurtley]

Hello, I am one of the other students on the team and did some more calculations. Unfortunately, I don't own a Prius myself and therefore there are many questions I still have.
1. I know that the electric motor has a power of 50 kW. But does anybody know how much of the available power the motor actually uses when you are just cruising?
2. How long can you usually drive with the gas engine off? I heard it is only 1/2 mile before the gas engine starts up to recharge the battery.
3. How fast can you drive without the gas engine coming on? I heard 45 mph is the max.
4. The control system makes sure that the battery never gets discharged below a certain level. Do you know what that level is?

1. Depends on the exact 'cruise' circumstances. Also, while the electric MOTOR has that much power, the batteries cannot supply that much, it actually uses the gas engine to spin a second electric generator to generate the extra. I'd hazard a guess of 15 kW at 35 MPH. But that's just a wild-ass-guess based on some quick Google searches.

2. If you have the 'EV' modification (that tells it to stay in electric mode until you drain the battery, even if it would LIKE to use the gas engine,) and a 100% (according to the display, which really means 80%) battery, you can go about 3 miles on flat terrain. In 'normal' driving, half a mile to a mile is about right.

3. If you are using the 'EV' mod, it will take it out of EV mode if you exceed 35 miles per hour. Outside EV mode, 42 MPH is the limit for electric motor safety reasons. Beyond that, the gas engine has to spin to prevent the electric motor from going too fast. It is possible to still only be using electric power above that speed (i.e. the electric motor drives the wheels, AND spins the gas engine with no gas going to it,) but generally that's only possible when going downhill. (On a slight-downgrade freeway, I have accelerated from 50 to 55 MPH on what the display said was only battery power, but it took about 30 seconds to do that acceleration. I later tried shifting into Neutral on that same stretch, and did not accelerate, so it wasn't just gravity doing the work.)

4. Because NiMH batteries have a limited life, they last longer if you don't fully discharge or fully charge them. For that reason, the car won't let it get fully charged or fully discharged. The battery display on the screen shows 'full' when the battery is actualy about 80% full, and 'empty' when it's actually about 20% full. So you are really only using 60% of the possible capacity of the battery pack. Allowing it to use the full 100% would (from some sources I have read, that I can't find at the moment,) cut the battery's life in half or worse. (i.e. You might not even get it to last the 100,000 miles the battery is warranted for, hence the limits.)

 

[hyperion]

Downhill run before reaching home? That's the only explanation, that would be unique to your driving conditions. That wouldn't be common with everyone else.

As for Evan's last comment, one could monitor the battery's charge level themselves, not exceeding the voltage signifying 80%. I was considering developing a charger that did just that. For an overnight topper, currents could be low, thus not causing any additional harm.

But adding battery capacity would be a better option.

.
.Nary a hill for a hundred miles, but I do drive my car differently than many. I bought the car considering it to be little differant than any other vehicle built by Toyota. Except for the synergy system that makes it obviously quite economical and because of the exhaust system a plus for the greenhouse envirament.
I didn't buy it in an effort to learn a differant way of driving (never an attempt of "pulse and glide) and without changing any habits I find fmy 44 MPG average acceptable. I believe I am driving it as Toyota meant it to be and when I shut down, my main battery is never "low" and that within five minutes of start-up I find my battery within one bar from the top and quite often indicating in "green."
I attribute this to just driving it as a normal car, (never attempting to force it into the battery mode) just as it was designed to be.
Also I believe there would have been a lot fewer questions about the use of the "B" mode of the PTU if Toyota had just labled it "L" instead of "B."

 

[Pinto_Girl]

I think I would rather have a smaller solar panel, powering a ventilation fan which runs while the car is parked (a la the mid-90's Mazda 929)

 

[RG]

I think I would rather have a smaller solar panel, powering a ventilation fan which runs while the car is parked (a la the mid-90's Mazda 929)

I would be very happy with this. It could make a difference in comfort, internal components longevity, and energy consumption.

Thanks Pinto Girl.

 

[kenmce]

I say "no" because I think what you are describing is a fantasy. I do not believe the light intercepted by the top of a car contains enough energy to run the car. There are also the points brought up by the other posters.

 

[DanMan32]

There's a difference to what MG2 CAN do, and what it is ALLOWED to do.
Forced EV (Using the EV button available in non North America markets, and able to be added in North America) is only permitted by the ECUs up to light acceleration, under 35 MPH, and as long as battery SOC is over 2 bars. Forced EV is kicked out if you reach 2 bar SOC, exceed 34 MPH, or exceed acceleration demand threshold.

Also consider that there is a limit on how much power the battery can deliver. The motor can't use more power than it is given. So now you say, if the motor can receive more power than the battery can give, why have such a big motor? Because the ICE can deliver the remaining electrical power via MG1.
As for the 42 MPH limit, MG2 is not limited as such. ECU programming will cause the ICE to spin when vehicle speed exceeds 42MPH, but that doesn't mean MG2 is not doing practically all the work. Those of us that have had high SOC (7 or 8 bars) can still travel over 42 MPH and notice that MPG is pegged at 99, indicating minimal ICE use, if it is even fed with fuel.

There's a difference between power, and energy. Power is energy delivered over unit time. Think of energy as water in a bucket. Think of power as how fast the water is leaving the bucket.
So if the hose attached to the bucket allows 5 gallons per minute of water, if the bucket holds only 2.5 gallons, water will flow for only 30 seconds at full water 'power'.

 

[clett]

I think these guys didn't want to get into the technical side of things, it's just a marketing study at present.

Nevertheless, for an in depth discussion of the potential of a solar Prius, this thread may be a good place to start:

http://www.priusonline.com/viewtopic.php?t=2081&highlight=solar

Ultimately my opinion is that it's going to happen once nanosolar get their cheap, flexible, printed cells out for 1/10th the cost of existing solar.