Solar Panels

I think the consensus is that these panels would not increase the MPG much at all. You really need a fair amount of juice (ie a pretty big solar array) to be effective. The 20W and 30 W panels just don't cut it. They will do a nice job of doing what you describe, however. Think about it this way. It takes about 200Wh to move a Prius a mile. Most places in the US get at least 5 hours of quality sunlight/day. So you'd need at least 40 W and 5 hours of sunlight to go one mile. From this you can see that you'd need a lot of solar capacity to augment the system in any meaningful way.

 

Hi Nick -

Let me start by saying that my main car - a battery electric vehicle - is fueled from electrons made via solar panels (lots of detail on my EV pages linked in my sig). With that out of the way... let me tell you that it will take quite a bit of surface area and expense to significantly increase the range of the Prius. If all horizontal surfaces were covered with PV, you'd gain maybe three free miles on a perfect day. There aren't very many perfect solar days though - and once you park or drive in the shade, all bets are off. You'll also need a DC-DC converter somewhere to increase the voltage of the PV panels up to something that can charge the HV battery.

And this points out that you're looking at 12V panels. Those will ONLY help keep the AUX battery topped up. The Aux battery provides no traction power. Keeping it charged externally WILL draw less power from the traction battery to keep the Aux charged - but honestly - it won't be enough to notice any real difference. A few feet of range, maybe?

I don't want to be a downer on PV power (which is why I started this post the way I did). I'm a firm believer in driving on sunshine (we drive about 12,000 miles/year on sunshine!). But PV panels really belong on the roof or your home where they will always be in the best position to catch the sun.

Tripp beat me to it while I wasted time on my long post!

<div class='quotetop'>QUOTE(tripp @ Jul 4 2006, 09:26 PM) [snapback]281251[/snapback]</div>

This is a best-case scenario, of course - and ignores the conversion losses which at this level are significant.

 

Ha ha. Beat you to it, darell.

 

Not to mention that the Wal-mart and other low-cost solar panels are of the amorphous type which have better infrared response (so they make better use of that part of the spectrum), but lower overall conversion efficiency than the older crystalline silcon panels. Because of this, the amorphous type panels need to be much bigger for the same rating..

I'd love to hear Darell's opinion on this, but contrary to all those solar magazine articles expounding on the virtues of the amorphous solar panel and how, because of their comparatively low initial cost, they pay for themselves after only a year, I, on the other hand think that the amorphous type represent a big hole that you stuff your money into and never see it again.. Part of the reason is the surface area thing- you can cover your roof with cheap amorphous panels but get less than half the output that you'd get if you put up crystalline panels. Long term degradation of the panels is another issue- most amorphous type panels *lose* up to 60% of their capacity in the first year (ie, if you have a 300W panel, after one year, they're only putting out 200W at best), vs crystalline types which *retain* up to 90% of their output capacity after 10 years.. So, yes, amorphous panels may be so cheap that they pay for themselves after a year, but after that, you get steadily declining output, vs the crystalline type, which cost 2-3x up front, but have higher output and maintain that output for a lot longer..

For maintaining the 12V aux battery in my Prius, I started out with an amorphous 5W panel which gave a true output of max 2-3W (usually much less, but that makes 5W about the smallest size panel you can consider for 12V maintenance) when under the windshield glass, but I swapped it recently for a 15W crystalline panel. The crystalline panel was 2x the cost of the amorphous, but is actually about 1" shorter in one dimension, and generates a real output of about 6W under glass.. In other words, I paid 2x for a panel that generates up to 3x the power using roughly the same surface area, and is expected to last years longer to boot..

 

<div class='quotetop'>QUOTE(c4 @ Jul 5 2006, 10:20 AM) [snapback]281506[/snapback]</div>

Have you noticed any difference in MPG with the pannel? I'd assume it would probably be so little that it could not be accuratly measured. However I'd still like some on my prius because anything that will help i'll do. I recently went to sythetic and 44/47psi in my stock tires. If I get a .5mpg increase i'll be happy. That's probably unlikely. Anyway, can you post some links to the pannels you have and exactly how you have them wired. Pix would be nice.

 

<div class='quotetop'>QUOTE(240sxer @ Jul 5 2006, 03:12 PM) [snapback]281597[/snapback]</div>

Google "Steve Lapp solar prius"

 

Ouch, I don't want anything that crazy. I just want a tiny little 10w or something like that mounted under the glass.

 

For solar conversions that DO yeild a fair amount of "free" electric miles, look at www.solarelectricvehicles.com. Their poly-crystalline cells cover the entire roof (and are curved to match!), and they add an aux battery for storing the solar power, which then feeds into the main battery when the car is on.

 

<div class='quotetop'>QUOTE(Bill-psi @ Jul 6 2006, 11:57 AM) [snapback]282076[/snapback]</div>

I'm toying with having them do a conversion for me as well. I just have a lot of factors to consider. It not all about the financial return on investment for me, just mostly.

 

Dang!

I recently bought that (likely) same 1.8 w strip. Sorry to hear that the "silicon" won't last a year.

I hooked it up to the aux battery with the included clips and attached to the rear window at an edge. I figure that the panel produces about 130mw and the car's consumption when parked is about 85mw (with SKS) so I'd be a little ahead during the day, and at night, well, maybe I'd not be too far behind.

My problem is that the suction cups don't stay put, and on top of that, when driving the panel does move a bit and falls out of the suction cups!

So, for this last experiment, I've used silicon sealer to directly attach the panel to the glass, using daubs in the four corners, with a bit of an air gap, and missing the defroster wires.

We'll see how that holds up.

But, yeah, with plugable Prius I could use the solar electrical panels on the house to charge the Prius batteries.
B)

 

<div class='quotetop'>QUOTE(Bill-psi @ Jul 6 2006, 01:09 PM) [snapback]282184[/snapback]</div>

Do you have a link or pix or specs on this? I want to see the options.


<div class='quotetop'>QUOTE(Bill-psi @ Jul 6 2006, 09:57 AM) [snapback]282076[/snapback]</div>

lol, NASA blocks that site (conspiracy?) Can somone tell me a bit about the conversion. I'll check it out when I get home. What kinda improvment? Price?

 

A 12V solar panel makes no difference at all to the MPG. What it does do, assuming you've got one with enough wattage, is ensure that the 12V battery is topped up, so that you'll always be able to start the car, even if left for an extended period (assuming that you've parked it outside where it gets exposure to the sun).

The increased tire pressure will do more for you than anything else.. On my Classic Prius, I've also been experimenting with a coolant temperature sensor spoofing circuit that fools the engine management into thinking that the engine is hot, and thus shortening the fuel inefficient "warm up" period.. With careful use of this circuit (too slow and you don't get much if any benefit, too fast, and you get lots of check engine lights- I'm still tuning the algorithms in the microcontroller for optimal performance), in any case where the engine is even still lukewarm from a recent use, I suffer no degradation of mileage on the first 5-minute bar, and in the rest of the cases, I'm seeing anywhere between 25 to 95% improvement in first 5-minute consumption figures...

 

<div class='quotetop'>QUOTE(c4 @ Jul 6 2006, 01:44 PM) [snapback]282201[/snapback]</div>

If you could sell that unit for the Prius I and II you'd probably get plenty of sales to make it worth your while. As long as its 200 or less there is a 100% chance i'd buy it if it actually works. That warmup cycle is a bitch on your mpg.

 

Wonder what else NASA blocks.

It's billed as a "solar powered 12v battery maintainer," and the instructions do say it won't charge a battery.

Hm. The packaging says 5 year warranty, so maybe after that one year (per the other post about life of amorphous silicon), I can ge a free one.

Says "up to 1.8 watts, 125 mAmp max."

Their website is www.sunforceproducts.com.

And on the other option, the warm-up spoofer, well, I just engage the EV only mode (Coastal Mod) when starting out and then when that time is up (about a mile or so), then the motor kicks in to charge the battery and I use that as the warm-up cycle.

 

That 1.8W rating is for the panel left out in direct bright sun, the problem is when you put it under vehicle glass, you don't come close to that rating..

The Prius HSEA glass is not 100% clear, it has a slight tint to it and actually contains iron in the formulation to help reduce the transmission of infrared light, which is the region of the spectrum where amorphous cells are most efficient.. This means that you immediately lose 30-50% of the panel's output when you put it inside the car.. Additionally, depending on where you live, you may not get sufficient insolation for the panel to output its rated value, or you may only get it for a very short period each day. In other words, even out in the open, you may only get 125 mA for a few hours a day, and the rest of the day it drops off below that, and you get nothing at all at night.. Meanwhile, the car is still steadily drawing its parasitic current.. To calculate the required panel size, you need to calculate not Watts, but Watt-hours..

The upshot is that a 1.8W panel is, in real life, nowhere close to being able to provide sufficient current to keep a 12V battery charged in the face of the Prius' electronics parasitic draw. My rough calculations show that the minimum standard sized panel that would actually provide sufficient output to allow some degree of real charging is 5W, and then it's just barely, unless you happen to live in Florida where you get many more hours per day of bright sun.

I don't know where you got your 85 mW figure from but that's way low- the figures I've seen are around 30 mA without SKS and up to 90 mA with SKS. We'll use the SKS figure 90mA*12.6V, and look at it over 24 hours, so that's 27.2 Wh. Assuming the solar panel is outputting full power and you get 4 hours a day at this power, that's 7.2 Wh, then let's assume that for the other 8 hours of daylight, the average is only 50% output (which is somewhat optimistic, but just for the sake of argument), so that's another 7.2 Wh, and of course, you generate nothing at night, so that's a grand total of 14.4 Wh from the panel over the course of a 24 hour day.. Comparing back to the vehicle's use during the same 24 hours, you can see that you're more than a bit short, and again, this rough calculation is extremely optimistic is assuming that you can actually get the rated 1.8W output from the solar panel (in reality, you never do)..

Additionally, if the panel is a thin-film amorphous type, it will degrade as much as 60% in the first year, turning it into a 1W panel (at best).. Don't count on being able to get anything out of a warranty as most of these types of cells don't cover degraded output- as long as the panel outputs something, it's considered "functional".. On the other hand, my 15W monocrystalline panel actually has a guarantee for 90% rated output after 10 years (in other words, they guarantee that after 10 years, that the solar panel will still be producing 90% of its rated value).. You never see such terms on amorphous panels, but that's also why they're at least 50% cheaper (and usually 50% bigger in size) for the same output rating..

 

Well, actually, I got that value from this forum. But maybe I swapped mw for ma. :mellow:

Interesting info about the Toyota glass. Thanks.

Say, got a link to where you got your 5w panel?

Of course, what I really want is a plug on the Prius. B)

 

Ah, ok I see, you just switched the units.. 85mA and 90mA are the same ballpark figure for instantaneous current draw, but again, you can't just take the instantaneous value because the car is drawing that much 24/7 whereas a solar panel only produces during sunlight hours, and then in proportion to the amount of sunlight or the lack thereof, which is where the Watt-hour calculations come in to play..

My 5W panel was a Canadian Tire amorphous panel; in fact, I think it's actually made by the same company in China that makes your 1.8W panel.. Again, I've recently replaced the 5W amorphous for a 15W monocrystalline panel- >3x the output (because it's more efficient in the visible wavelengths) and in a slightly *smaller* surface area.. The 15W was a "BCS Solar Technology" panel, again, guaranteed for 90% full output (ie, 13.5W) after 10 years.