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Old 03-14-2011, 09:56 AM   #1 (permalink)
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Solar Panels for 2009 Jetta TDI

I have a 2009 Jetta TDI which I run on B5 whenever possible, however I also have access to a large number of high efficiency solar cells, which I'm considering hooking up to my car, if this would make sense. Currently I have a solar cell directly charging some peripherals (iPhone, iPod, radar detector, etc.), but I'm wondering if I could connect more panels directly to my car through a 12V socket to reduce the load from my alternator onto my engine. Overall goal is of course to improve MPG. Questions I have are:

1) In my car, does the engine power the alternator which then charges/powers the battery which then powers my 12V outlets (and 110 outlet), as well as the HVAC?

2) If so, during normal operation of the vehicle, would power from solar panels plugged into a 12V socket directly power my HVAC and other 12V outlets, thereby reducing the load/draw on the alternator and therefore the engine?

I don't want to do anything to potentially damage my car electronics or void my warranty, but I would like to explore improving my MPGs (however slightly) by using the solar panels I have.

Thanks

NJP

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Old 03-14-2011, 10:39 AM   #2 (permalink)
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Quote:
Originally Posted by njplanson View Post
1) In my car, does the engine power the alternator which then charges/powers the battery which then powers my 12V outlets (and 110 outlet), as well as the HVAC?
Exactly.

Quote:
2) If so, during normal operation of the vehicle, would power from solar panels plugged into a 12V socket directly power my HVAC and other 12V outlets, thereby reducing the load/draw on the alternator and therefore the engine?
Yes, but the solar cells will only reduce the load on the alternator and therefore save fuel if their voltage is greater than the car's system voltage (roughly 13.5-14v with the engine running).

Also, glad to see that you recognize ("however slightly") the small potential power contribution of photovoltaics. (Not saying it's not worth pursuing.)
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Old 03-14-2011, 11:03 AM   #3 (permalink)
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Solar Panels for 2009 Jetta TDI

Thanks very helpful. A few follow up questions:

- What is a reasonable voltage range to inject via the 12V outlet? I realize this will be dependent on the sunlight hitting the panels, and how I wire them (series vs parallel), but what is the high range for safe voltage without damaging anything?

- What is the approximate draw (kW, kWh, amps) of a typical alternator? Clearly this will vary significantly with HVAC and other load.
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Old 03-14-2011, 11:35 AM   #4 (permalink)
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The safe voltage of the panel will depend on the current output. Most commercial 12v panels seem to output ~19v in full sun, at ideal angles, which is fine at low currents (also typical of the size of commercial panels that would fit in/on a car) since you're unlikely to raise the system voltage significantly when the vehicle is operating/drawing power.

For an idea of electrical demands of a small car (Pontiac Firefly / Geo Metro), see this thread: http://ecomodder.com/forum/showthrea...olts-8908.html

And you're probably aware that if your panel is connected (however indirectly) to the battery when the vehicle is off, you'll want a charge controller to prevent overcharging.

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biodiesel, mpg, photovoltaic, solar, tdi

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