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Old 04-16-2009, 10:24 AM   #1 (permalink)
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Solar/PV panels alt delete cost effectiveness?

From the other thread so people don't have to flip through 8 pages, the consensus is that putting your alternator on a switch and using a battery(or two) coupled with solar panels on the dash(and rear deck below the window if you have it) allows the alternator to be used only after long periods of driving or night driving.

So the question here is how cost effective is that?

Sun-90 [SUN-90] - $270.00 : Solar Panels under $3 per watt Worlds Lowest Price, Buy Solar Panels at Sun Electronics, When the power goes down, the Sun comes up!

provides 90 watts peak, its max power is 17 volts and 5 amps so it will run just above where you would want to charge your batteries. Also its feeding parisitic functions at the same time you don't have to worry about overcharging for 300 bucks to get you a regulator to make sure you don't cook the battery.

10% FE increase? thats 3-4 mpg for me so 36-48 miles extra per tank or 2 dollars per tank(with gas hovering around 2/gal). so it would take 150 tanks to pay for the setup(but I'm not paying the extras in weight because the panel only weighs15-17 pounds(I'll delete something to compensate.)

Also it could be quickly interchangeable between vehicles if the plugs for the panel were in the cabin. . .

thoughts?

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Old 04-16-2009, 10:51 AM   #2 (permalink)
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On this note... anybody have an idea how much a typical 4cyl engine with cpu etc. uses for power when the headlights aren't on? say I was running in the day time, just powering the ignition, cpu and have everything else turned off, no DRL, radio etc. how many amps would I be pulling? I would test it on my car but... I don't have my meter with me and i don't know if it could handle the load.
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Old 04-16-2009, 11:03 AM   #3 (permalink)
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crap, I meant to measure this today but my meter is in Johnson City.

anyone with that data it would be greatly appreciated to get a feel for the smallest possible PV to run and stay ahead of the energy demand.
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Old 04-16-2009, 11:25 AM   #4 (permalink)
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alright so it looks like Metrompg.com already did this for us, but the results there were about 230 total watts to run the stock systems.

So a system to compensate the alternator would need 2 of these(min) plus a deep cycle battery.

You could run most of the draws off of the panels and then the rest from the battery and if your commute is not too far you might get away without breeching the "deep" end of the cycle(extending battery life somewhat).

If you go with 3 panels you are in the clear for most situations(including running cooling fans).


But this puts me out unless I mount them on my (totally) flat trunk. So the cost would be about 840 for the rigging and if you have the interior space no aero losses 40 lb addition or if you have a convenient non aero-influenced area.

So it would take me about 400 tanks to recover the cost. Thats 4 years. Alot better than conventional solar panels mounted on your house, but still a long ways out.

I'll have to work on some serious aero mods and weight deletes and lrr tires before I can get that under maybe 2 years.

<edit> http://sunelec.com/index.php?main_page=index&cPath=30 has a 205 watt panel for 508 each but you have to buy a pallet of 28. So if you can find someone who wants some panels and get together and get a palet you can get it a little cheaper. Downside is the panel is 5 feet by I think 3.5 feet so its a trunk/roof only application. Unlike the metrompg.com page this does not have legacy costs(as long as you don't break the panels) because once its in they last 15-20 years. If you also go EV in the future its a bonus. This reduces the ROI to 2.5 years as my car stands now, lower cd higher mpgers would be able to get 1.5-ish </edit>

Last edited by theunchosen; 04-16-2009 at 11:41 AM.. Reason: no need to post since no one else has
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Old 04-16-2009, 01:06 PM   #5 (permalink)
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I think you have a fundamental flaw in your reasoning, which is that most of the energy loss from the alternator is actually from the belt drive, which is there 100% of the time. The actual electricity generation is pretty efficient.
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Old 04-16-2009, 01:38 PM   #6 (permalink)
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According to wikipedia, alternators are only roughly 50-62% efficient. So, I'd have to disagree that its efficient.

For the rest I'll need to run some calculations. 230W is .3 hp. So, you're talking .6 hp to power a Metro which is probably about as low of a electricity hog of a vehicle as you can get. Any newer vehicle is sure to need more electric power.

From my reading on designing supercharger systems, belt losses are around 1% IIRC. If you're cruising down the road and and require 10hp to maintain speed, the alt is eating .6hp, and the belt is eating .1hp.

I think a much better ($) way to go is forget solar and stick with deep cycle batteries and a charger.
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Old 04-16-2009, 02:26 PM   #7 (permalink)
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Also, don't forget to factor in your cost calculations a number of large decals that say

"NO, IT'S NOT AN ELECTRIC CAR".

Otherwise you'll be spending time repeatedly answering that question from passersby who see your panels and leap to that conclusion.
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Old 04-16-2009, 04:09 PM   #8 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Also, don't forget to factor in your cost calculations a number of large decals that say

"NO, IT'S NOT AN ELECTRIC CAR".

Otherwise you'll be spending time repeatedly answering that question from passersby who see your panels and leap to that conclusion.
I bypass that with my aforementioned no muffler ICE. When idling its silent(I roll up to crossings and people are alarmed that there all of a sudden is a car there(very slow speed)).

The alternator produces AC current very efficiently. . .your car uses strictly DC so iot converts it using diodes which allow it to freewheel alittle but the transition between freeload and load causes it to lose that 30%
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Old 04-16-2009, 06:49 PM   #9 (permalink)
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I've thought about trying to get an A/C style clutch mounted on the crankshaft, allowing me to stop the rotation of my alt + power steering belt. But I couldn't find one that would just bolt on.

No matter which way you go, you're going to need a deep cycle battery. You'll also have to bring the alternator with you, in case you need to take a longer trip than expected. Solar does not solve that problem, since solar doesn't work in the rain or at night.

Trivia: PV panels are 10-15% efficient at converting sunlight into electricty. There will be additional losses in converting their output to a regulated 13.5V.
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Old 04-16-2009, 07:14 PM   #10 (permalink)
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Quote:
Originally Posted by Daox View Post

I think a much better ($) way to go is forget solar and stick with deep cycle batteries and a charger.
The problem with that is Metrompg.com( I assume this is the same metrompg here) already calculated the cost. Deep cycles eventually burn out and you have to replace them or supplement them(better because then you still get to keep some of the old storage instead of just throwing it away). His calculations were it cost .6 cents per mile to run the batteries(paying for replacing them after 1800 cycles(I think this was the number)) and only .36 to run the alternator(and alternators cost the exact same as a single deep cycle and they last alot longer).

The reason to go solar is it would pay for itself in fuel savings daylight driving for me in about 2.5 years while deep cycles really never pay for themselves because you have to replace them(given it takes a long time and increasing the number of batteries to increase battery life helps, but at the end of the day you will need new ones). Solar panels are usually warrantied against their own electronic failure for up to 20-25 years with some only giving a 15 year warranty.

Even if I only get a 15 year warranty I get 12.5 years of alternator replacement without having to pay for anything else.

Quote:
Originally Posted by RobertSmalls View Post
I've thought about trying to get an A/C style clutch mounted on the crankshaft, allowing me to stop the rotation of my alt + power steering belt. But I couldn't find one that would just bolt on.

No matter which way you go, you're going to need a deep cycle battery. You'll also have to bring the alternator with you, in case you need to take a longer trip than expected. Solar does not solve that problem, since solar doesn't work in the rain or at night.

Trivia: PV panels are 10-15% efficient at converting sunlight into electricty. There will be additional losses in converting their output to a regulated 13.5V.
Right, Deep cycles are going to be a neccessity and yes I would have to carry it in my trunk(but they aren't that heavy so no big loss). I figure about 100 additional #s of batteries for inclement weather and any long trips that I know are going to be non-solar friendly I just carry the alt and then hook it up if the drain is too much to make it to the destination. My point is if you add solar to the mix your deep cycles will last indefinitely, because they are trickle charging most days they aren't discharged as heavily if you do overrun your PV and most days they don't even get engaged just trickle charged.

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