Replacing alternator with solar panel array on roof?

[theunchosen]

Originally Posted by MetroMPG

Not true. The alternator will only output as much power as needed to maintain a given battery voltage. If the panel is providing, say 50% of your electrical load requirements, the alternator's voltage regulator will look after ensuring the alternator only makes up the difference. There will still be a fuel savings.

true but the Alt is designed to operate within a narrow band of RPM and power production and anywhere outside that and its efficiency starts to drop off. The law of diminishing returns comes into play heavily with electrical/work conversions outside of their optimum range. Its one of the reasons that Wind Power is a difficult thing to harnass. I have a PhD student friend(not my student but someone on the path to becoming a PhD) in Wind Power and thats the biggest problem it faces because you have to chose where it can produce power best and then have to deal with low returns everywhere else.

[MetroMPG]

Sounds like we need an A-B-A test.

[theunchosen]

Originally Posted by MetroMPG

Sounds like we need an A-B-A test.

. . .on what? sorry I didn't know I proposed something different.

On the alternator producing X watts? I suspect that is the case because it works like that on regenerative braking that I have used in the past. The vehicle was a narrow gauge railroad car that was electric. Had battery readouts, voltage, current and (trivially) power output when the system was running either direction. Power/RPM peaked around I think it was 2000 RPM or 25 MPH(very small wheels). If you popped the brakes on going faster than that you didn't get much more voltage or current and it peaked out shortly after that.

[MetroMPG]

... on adding a sufficiently powerful panel to a car without disconnecting the alternator.

I don't doubt that an alternator has an efficiency peak in a certain operating range, but I suspect you'd still be able to measure a small fuel economy improvement.

[theunchosen]

Oh, I agree with that. I Was just saying it wouldn't be as much as it would it were just the panel. I was also saying that if the alternator had to run at low load it would be more of quadratic function approaching its peak. So with the panel it would be efficient-(more load than panel)- slightly more efficient than normal-(normal load for alternator plus additional load that panel meets) most efficient fuel to power conversion from the alt and then it decreases again on the other side.

Um i'm saying its like changing the final gear ratios on you trans. You have to go a little faster(use more power) to stay in the sweet spot(peak alt performance shifted to peak performance drain plus panel power).

[idiom]

I've installed 5WT Solar trickle charger on my 09 Hyundai Sonata(25-32MPG by fueleconomy.gov). Easy to install. 50$, Just attach to battery.
On my trip to Florida I've got 37MPG. Drove about 75MPH, AC mostly on.
From Florida i drove at night time and MPG was 33MPG(75-80MPH, NO AC).
Regularly getting 32-34MPG on 30%city-70%highway driving.
SO, If you guys want i think it's good thing to try.

*Regular driving(30%city-70%highway) results: 534 miles on 15.6 gallons = 34.2MPG. Just filled my tank today)

[hotrodfeguy]

Ok let me start off by saying I am sorry if someone has posted this solution already. But I was reading this thread and was wondering why not just use a Gel cell type battery like a optima or Hawker? They are very high in reserve/CA power and can be discharged flat and be brought back to life. They take like freaking 2 whole days on the charger at work to bring them back from the dead. So I don't think a solar charger is ever going to fry the gel battery. Would make this work with just a panel and a gel battery. Also some power savers I thought of along the way was going with the new automotive LED type lights that plug in to existing plugs. What do you guys think?

15 Watt, 12 Volt Solar Panel

[gabi]

Originally Posted by orange4boy

I found these interesting nuggets of info in

"Automotive Electrical Systems Circa 2005
By John G. Kassakian, Hans Christoph Wolf, John M. Miller, and Charles J. Hurton
Demands for Better Fuel Economy and more Electric Power are Driving Cars to Multiple Higher Voltages"

IEEE Spectrum: Automotive Electrical Systems Circa 2005

"Even more to the point, the U.S. Corporate Average Fleet Efficiency (CAFE) standard prescribes a maximum fuel consumption rate for cars sold in the United States. The Federal government assesses a penalty of US $5 for every 0.1 mile per gallon (0.04 kilometer per liter) below 27.5 mi/gal (8.55 L/100 km) on every car the manufacturer sells. A 200-W electrical load accounts for about 0.4 km/L in the FTP 75 cycle test; so, if a manufacturer is delivering 25-mi/gal (9.41 L/100 km) cars, for example, it can justify spending more per vehicle on components to improve electrical efficiency."

Also:

"Improving the electrical system's efficiency so it lops 100 W off the average electrical load has the same effect on fuel economy as reducing the car's weight by 50 kg, as measured by the FTP (Federal Test Procedure) 75 standard profile of starts, runs, and stops"

and the real kicker:

"At present, when U.S. and European fuel economy tests are conducted, only those electric loads essential to the operation of the vehicle are active—that is, the ignition and engine electronics. Lights, air-circulating blowers for the passenger compartment, entertainment electronics, power windows, and so forth are all turned off for the tests."

That last one has changed slightly in that now they must run the A/C for a short part of the test but still no other electrical loads are required.

Anyone still not clear as to why new cars often don't live up to their mpg ratings.

thats good news,
i'm upgrading to led bulbs this weekend
by my calculations i would remove at least 150 watts from the electrical load,
so that means is like removing 150 lb of weight,according to the refference

[Mr. Previa]

Hi All,
I too have a Previa. Previa's have some advantages and disadvantages because of the power train design. My goal is to remove our SADS completely.

So... I read about the idea of using two 8 volt batts to get the higher 16 volts. Has anyone tried this?

I realize they are kinda pricey, but, my starting battery is about dead anyways, so it wouldn't be that much more the way I see it.

Thanks!

EDIT: I found out that 16 volts is still too high. Bummer.

[oil pan 4]

I think it would work best if some one found a battery maker that uses the same cells in different voltage batteries that way you could make your self a 14v deep cycle battery out of 6 and 8 volt batteries.