There is a device called a "linear current booster" used to improve the performance of solar driven well pumps. The problem is exactly the same as we see with the Prius solar driven ventilation fan. The device allows a pump to operate during lower solar output than would be true without it. My guess is that a device such as the "12 / 24 V @ 7 am Linear Current Booster/Pump Driver" sold at Solar Converters Inc. would probably add a few hours to the afternoon function of the ventilation fan. Price is about $90.
Maybe I'm reading their spec wrong, but that looks like a device for stepping down voltage and increasing current-- good for long wire runs where you can use higher voltage and smaller wire, and then get the low voltage/high current you need to run your 12V pump near the pump. The gains appear at first glance to be all from reducing resistive losses in the wire run from transmitting low voltage/high current from your panels to the pump.
Best solution is to forget about the overpriced solar panel, which is more of a gimmick and a marketing item than a really practical feature. Also forget the leather upholstery, which gets far hotter than fabric in climates such as those of the Southwestern US. You can only maximize the power output from solar panels by having them track the sun, which obviously isn't practical here. Panel efficiencies higher than 16% would also help.
It's starting to look that way for me. I was hoping on it being at least a useful gimmick, but if it's not blowing at quitting time, most of its potential utility has vanished for my situation. Perhaps I'll step down to the II and save my $4600 for aftermarket seat ventilation, if such a thing exists.
The problem is that the solar panel output voltage varies with the amount of light and the temperature. The output profile of the panel differs considerably from the needs of an electric motor. The Prius design is apparently direct solar panel to motor, without any conversion electronics in between. The result is that when the light level goes too low, the electric motor just stalls. Converting the solar panel output to a lower voltage (with higher current capability) allows the motor to spin slowly, instead of just stall. Obviously there is still a point at which the motor wont spin at all, but a linear current booster would extend the operating range to include a lower light level. Also, I just noticed that the unit has MPPT (Maximum Power Point Tracking), a technology that delivers about 1/3 more power than the simple voltage limiting used in older design solar installations. The unit that I specified is just my best guess. Maybe if someone with a solar Prius contacted the folks at Solar Converters, they might suggest a different unit. Or perhaps recognize an opportunity to design a unit intended for use with the Prius solar ventilation system. The only practical difference I see between a ventilation fan and a water pump is the device on the output shaft of the motor. Matching up the characteristics of a solar panel and a DC motor is a task that has been done by linear current boosters for quite some time.
IMO, the MPPT feature is what is key to maximizing output - when the load of the fan motor gets to be too great, the motor simply ends up pulling the voltage to zero where the panel can't push out much power. By being able to keep the voltage at the "knee" point where the panels power output is highest, the fan motor may still be able to turn. For larger scale solar installs (like for your house), any DC-AC inverter worth it's salt also does MPPT. In the ideal world, every single cell would have it's own mini DC-AC inverter with MPPT since each cell has a small amount of variability due to manufacturing tolerances, dirt build up, shade, etc. Make sure you keep those panels clean! I wonder if a low-buck "fix" would be a mirror (or other shiny object) set on the east side of the panel that reflects light back down onto the panel would help enough to keep that motor turnin'.
Agreed. But to me, the bigger problem is that if you want a factory sunroof, Toyota forces you to get the near useless solar panel -- turning what would otherwise be a $900 option (sunroof alone) into an $1800 option (effective price of the sunroof plus solar panel system). And worse than that, Toyota actually forces you to get the Navigation Package as well (it's included in the Solar Package), which effectively turns a $900 option (sunroof alone) into a $3600 option (Solar Package). And even worse than that, in order to get the Solar Package, you have to get a Prius III which costs $1000 more than a Prius II. So, all in all, a $900 option (sunroof alone) is turned into a $4600 option (extra cost of Prius III plus Solar Package).
Ah, I missed that. I'm also surprised that Toyota appears to have just wired things straight through. Oh well. At least there's a nice custom-fitted sunshade available from the priuschat store.
Fortunately for me, anything will seem like an upgrade on that account. Kinda like the base stereo-- "six working speakers" beats "two working speakers and two blown speakers and a stereo that routinely overheats and shuts off." I'm bummed that the solar vent system turned out to be more gimmick than gimme for my situation... but it'll certainly make it easy for me to decide between the base model, and the model with a solar vent and a bunch of other stuff I didn't really need. And the money saved will help out with the big ol' solar panels going on the house in a couple of months, which will be less of a gimmick.
I have a IV with solar package option on order and now thinking of changing to a IV with navigation and adding remote start. Where can I find more detail on port installed remote start? Like how much range it will have. Thanks for any help.
I just got my Prius IV w/ Solar. It is too soon to render a definitive opinion on performance of the solar ventilation system. However, so far, I don't think it is a gimmick. I find that the ventilation does engage frequently even with partly cloudy and not warm conditions (I live in San Diego and the temperatures are quite moderate right now). I have entered the car at all hours, including pm drive time, and the ventilation is on, and found the inside of the car to be comfortable inside (cooler than without); and you can feel the relatively cool air coming in through the vent equivalent to a couple bar fan setting. So far I am VERY happy with the moon/sunroof AND the solar panel/ventilation.
Interesting to hear such varied opinions on its performance. I guess it really is too early to tell. Maybe it's great? Maybe it's mediocre? Maybe there's inconsistency in their first production models? Maybe I should park in the shade? Maybe I spend too much time refreshing this thread?
We just need more people to test it around 5-5:30 PM in different parts of the country and see what kind of performance pattern happens.
I think it would be interesting to have a sun shade / solar panel option using flexible solar panels that could go across the front windshield and plug into the venting system to give the system more angles to capture sunlight and then possibly have enough to do some battery charging as well.
Time of day is not a good reference, as daylight varies too much by location. For example, where I live, at this time of year it doesn't get dark until 11 pm. Tom
That's why I said in "different parts of the country." Time of day is important because people who work regular hours get into their cars at about the same time every day. On hot days, it's important that the solar roof fans function at the time of day they would regularly enter the car or they would have been better off skipping the option.
So, now a few weeks have gone by. Have any more people been able to see how well it works after 5PM when the outside temperature is still very hot, but the sun is no longer straight overhead to provide optimal charging to the fans?
we live in central florida where the temps have been reaching upper 90's. the wife drives a Prius Pkg III with Solar as her DD. she is very pleased with the solar pkg due to a noticable reduction of interior temps during her lunch break and 5pm drive home. she says the fans are still running when she enters the car at 5pm. if she has the car in solar mode, the fans are On when she gets in the car. if she decides to turn on the remote AC, the fans shut Off when she opens the door. so this confirms to me that she knows the difference in settings. hope this helps convince some of you that the solar is not a waste of money. i agree that i don't like how Toyota forces the Navi down our throats just because we wanted the Solar. Navi is nice but come on, $3600 for the complete pkg.... oy vey.
