How about this. I have 3 small solar panels from an old project I was working on. I have been thinking about mounting them on my current car project and using the power to assist the alternator by charging the battery. The panels are each about 12" X 24" X3/4". I was thinking about mounting them on the trunk as close to the rear glass as possible. As with everything added there would be a weight penalty for this but how about aero. Is there a better place to mount them? Each is 5 watts 16.5v max and I do not know if I would see any benefit but I already have them and thought it would be an interesting experiment.
You can try removing the alternator completely and using the solar panels to trickle charge during the day and plug in at night...there is a large benefit to this, you just need to make sure not to kill the battery. I think the trunk would have the least aero badness because it is not directly in the way of anything...
the farther they are from the battery the large the wire you need to run to reduce line loss, I would think 12 gauge wire would be the smallest you would want to go with if it's more then a few feet, I rather like the trunk idea, altho the roof seems reasonable as well, if you go without your alternator switching to LED's in as much of the car seems like a good idea, as well as a 2nd battery, but those panals seem to be on the small side for being able to handle the elctrical loads of a car use for more then 20 minuts per day in day light, but in full sun they will reduce the load on your alternator, causing the regulator to reduce power on the field windings, thus reducing the resistance on the alternator.
Everything you guys mentioned sounds uhhhmm sound. Reading all this I just had another goofy thought. What if we combine everything we all mentioned. Remove alternator, multiple batteries, put one in the car. Leave the other charging at home, work, wherever. If at work use a battery charger (thanks work), at the house more and more bigger solar panels or a charger. Drive your car, swap batteries, drive your car.
Could even put some thought into and make a quick swap battery bracket.
Think a small car could make 30 miles with no alternator and a fully charged battery?
I think I am feeling my first real experiment coming together here.
I'd be interested in adding some kind of electricity production to my car to reduce alternator load. But someone who knows more than me, how much watts at what amps or how much power would I have to generate to start seeing improvement? For example, Currently I can't notice a difference on my scangauge at idle by cranking up my radio and lights. The fan does make a noticble difference at the min vs off settings.
The three panels in parallel will produce a peak, maximum, noon, clear-sky, no tint to the glass output of 15 watts.
One brake lamp bulb consumes 21 watts. You'll need 3 minutes of the best possible scenario daylight to produce enough power to run just one brake lamp for 2 minutes.
Parking the car with a helio-static tracker moving the panels for 7 hours will restore 105 watt hours of power, enough for one hour of two 55 watt headlights only.
If you're considering multiple batteries, just add a second to the car and forget the panels.
Not that small panels aren't worthwhile, just be aware of their limitations. They are ideal for long duration extremely low consumption, or for very brief intervals of high consumption.
One of my panels get used to trickle the battery when I park for weeks. It can keep up with the radio memory and alarm consumption with just a few hours a day of moderate light. The other panel recharges a 12 volt battery in my shed. That powers an inverter for the pair of 40 watt fluorescent lights in there. I get about an hour of light (80 Whr) for each week.