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Old 12-03-2011, 02:11 AM   #1 (permalink)
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Solar panels to lighten alternator load?

Hello all,

My first post to this forum, but I've been a lurker for about a year.

I've always dreamt of building a self-contained solar powered vehicle. Seems the math won't allow that just yet. So then I thought about building a solar powered velomobile where the electric motor would just be an assist to pedal power. Right now these are all just ideas in my head - haven't had the time or money to get the tools out just yet.

Now, I've been reading a lot on the forum about gains of 10% by disconnecting an alternator from just about any car. And a lot of people then discussed removing the alternator and using deep cycle batteries to run on - some with solar charging. And then some discussion of even having 2 separate charging systems, one for primary functions and one for auxiliary functions.

But what about simply hooking up a solar panel to your existing system to reduce the alternator load on sunny days? I found a thread about this idea started back in 2008, and the main reason for not trying this was the cost involved with the panels and the aerodynamic impact. (I'm not allowed to link to the thread)

Its 2011 and solar panels have come down a lot in price, and I'd assume become a bit more efficient. Wouldn't hooking one up on your rear deck (or inside the hatchback area) reduce the load enough to make a difference?

It seems one person on the last page of the thread I mentioned tried it with some success, but no further comments were made on it.

Also, with the thin flexible panels available cheaply today, I'd think roof mounting could also be an option.

I'm just curious about what others think of the idea. If alternator loads can change FE so much, I'd think anything to lighten the load placed on it would have good results.

-Rick

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Old 12-03-2011, 11:05 AM   #2 (permalink)
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Yes, it would help a decent amount. Obviously the larger the panel the better. Yes, its really not an economical modification as you're going to pay a fair amount for any solar panel.

Power consumption will highly depend on the vehicle you use. Darin did some great testing with his Metro which is probably one of the lowest power consuming vehicles around.

http://ecomodder.com/forum/showthrea...olts-8908.html
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Old 12-03-2011, 12:46 PM   #3 (permalink)
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If you figure out how many watt hours you need to do your daily driving then you can figure out your total PV size that you need to keep your battery charged up, remember of course that panels that are flat are not going to have the same output as ones that are at the correct angle and pointing at the sun so you will need to figure that in at well.
Personally I would get a DC to DC converter that takes a higher voltage from a deep cycle pack and drops it down to the 13.4 or 13.7v that the alternator tends to put out, otherwise your headlights will slowly dim and the rest of your electrical system will see more amps due to a lower voltage, over time that lower voltage will burn out electronics.
On my electric car I'm using a DC to DC converter from a golf cart lighting kit and I'm going to use a very small lead acid gel cell battery as a buffer for large loads when I have everything turned on.

If nothing else, having a small solar panel will keep your battery topped off and happy making it last a few extra years saving you $10 to $20 per year just in replacement battery costs.
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Old 12-04-2011, 12:46 AM   #4 (permalink)
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I think this idea makes sense for a short range commuter car in san diego. Such a vehicle sits in bright sunlight pretty much every day and doesn't spend much time running. So, even a fairly moderate sized pv array could generate enough juice to start it 2 times and power the vehicles needs for a half hour or so.

If you live in seattle and have an hour long drive to work, it makes no sense at all.
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Old 12-04-2011, 11:15 PM   #5 (permalink)
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I dont have to worry about aero with a suburban. Just need time to build my custom 21 to 22 ocv panels to power up the standard 14.5v vehicle electrical system.
Over all, buying off the shelf panels isn't an option, they are too expensive and dont provide the voltage I need.
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Old 12-05-2011, 09:37 AM   #6 (permalink)
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I have an Alternator field disconnect switch. This way I can see how long I can go without running the alternator. I have a 15Watt panel on the dash board. For a few weeks this summer I was able to go without turning on the alternator. But my truck sits at the airport 4 days a week, drive home, run to home depot once or twice a weekend, drive back to the airport Monday. So sitting in the sun all the time and only putting 50 miles a week on the truck I was able to just get by during the summer. A deep cycle battery would help since I could have more usuable energy from sitting in the sun for 4 days straight.
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Old 12-07-2011, 02:13 AM   #7 (permalink)
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I've calculated back-of-the-envelope that a car A/C unit draws in the range of 600w. A 100w panel runs about $150 on amazon, so a good way to estimate the gains is to find out your mileage loss from running the A/C, divide that by 6 and add it to your normal mileage.

I'd guess it might save you 10-15 gallons of gas per year if you drive a lot, so it'd take about 3 years to pay for itself.

Last edited by Ecky; 12-07-2011 at 02:23 AM..
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Old 12-07-2011, 02:50 AM   #8 (permalink)
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2 to 3 years is pretty typical for an eco mod pay off.
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Old 09-29-2013, 01:40 AM   #9 (permalink)
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Quote:
Originally Posted by busypaws View Post
I have an Alternator field disconnect switch. This way I can see how long I can go without running the alternator. I have a 15Watt panel on the dash board.
the alternator field disconnect switch, what is that? how have you wired it in?


I know this post is old but I am starting down this road. Thinking of an electric coolant pump powered off solar panels on boot and possibly roof on a camry (in Australia, western NSW)
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Old 09-29-2013, 05:17 AM   #10 (permalink)
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Even if you don't delete the alternator you can benefit from a small solar panel.

Suppose your car battery would lose its charge in a month of disuse.
If it is a 50 Ah battery it will lose 600 Wh per month, so 7.2 kWh a year.
A 5W panel would be enough to provide that, except in the winter months. Step it up to 10W and you will probably never run the battery down.

Now for cost. You do not get the kWhs from the mains but by burning gas to turn the alternator. You need almost a quarter gallon (or 80% of a liter) to generate one kWh, assuming 15% overall efficiency. A solar panel can potentially save you about $6 (or, over here, 12€) per year. You'd earn that panel back pretty quickly.
On another note, because it keeps the battery topped off that will last longer.

So, any drawbacks? There is the panel weight; a tiny reduction on economy and performance. If you mount it outside there may be extra aerodynamic drag (I am looking at mounting a flexible panel ahead of the windscreen wipers). You have to safely hook it up to the battery and unplug it whenever it gets serviced.

I was looking into having a solar panel hooked up to the front window de-icing vent to keep it cool in warm weather. But it can double as a battery top-off when it is cooler.

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