Idea for no alternator, solar charging setup

[Coyote X]

I am wanting to remove the alternator on my Metro and go to solar recharging. The typical idea is just replace the alt with a solar cell and have at it. But that means the car is running on low voltage and the headlights and other accessories can get dim. So my idea is use a roof mount solar panel and charge controller to charge a deep cycle battery. This battery feeds a heavy duty riding mower battery that is hooked up normally to the metro. The deep cycle will connect to it using a step up converter similar to this: Amazon.com: DROK DC Converter Voltage Regulator 8-32V to 9-46V 12/24V 150W Boost Step Up Power Supply Module: Electronics The typical step up converter can convert 8-30VDC to 8-40VDC or so. I just need either a large module or multiple modules to get the current I need at 14.4V to keep the main battery charged.

It can keep the main battery at 14.4V and all the electronics in the car will be happy. I already have LED lights and can rewire the heater blower to run on the deep cycle since it is probably the highest current draw and won't really matter if it gets lower voltage. If I remember correctly the engine needs a bit under 10 amps to run. I figure if I can get a sustained 25 amps out of the step up controller it should work out about right. If not I could always add another step up module and get more current.

The idea being that since the deep cycle can get low the solar can charge it throughout the day and build it back up. Then when I am driving the step up modules will keep the car running along happy. Trying to do everything with just one battery would mean that at the end of a drive at night I might not have enough power to start the car but with the deep cycle able to go down to 8V or so keeping the main battery fully charged I should be good for even a few hours of night driving with no problems.

Any thoughts on this setup?

[oldtamiyaphile]

I had a 'large' van that was going to have it's entire roof covered in solar panels, even then my sums said it only just have enough surface area. Electric power consumption is basically the same regardless of how big a car is, but a small car will have much less roof area.

The solar panels will also make the inside of your car much hotter. A Metro has space for about 150W of panels, this will give you about 60Wh max real world at midday on a sunny day in summer.

How efficient is the step up converter? It can be as low as 30% for cheap ones. If you want to run everything on the regulator, you'd only have 20Wh The ignition might not be happy with less than 14v either. I was going to go to a 100Ah Life battery for a pretty decent amount of headroom (this would have held 14V for a long time).

If you spend a lot of time parked and commute a fairly short distance it can be done obviously, but you might be better off like a lot of people have done and just grid charge at night.

[redpoint5]

I like that you and others are thinking of alternative ways to power electrical systems. That said, here are my concerns with the plan:

1. Expense- Solar panels and a large deep cycle battery are not cheap, unless you have a connection somewhere to cheap materials. How much is the step up power supply.

2. Efficiency- Lead-acid batteries near full charge are less than 50% efficient at accepting a charge, and when fully charged, are about 50% efficient at discharging. A near-full-charge\discharge cycle can be as low as 25% efficient at converting your input energy into useful electrical energy. Efficiency raises significantly as the battery is discharged more deeply, but this is not good for even a deep cycle battery. Like Old brought up, there is the efficiency of the step up power supply to consider too.

Solar panels are most efficient when angled directly towards the sun, and quickly drop in efficiency as they are angled away. Putting solar on the roof is not the ideal angle in the northern hemisphere, and there are plenty of objects that could shade the vehicle when parked.

3. Convinience- What if you want to go on a longer drive than normal? The solar would not provide enough energy to maintain the battery, so there is a limit to how far you could travel. At night, this would severely limit your range.

What I would like to do, and what I suggest to you, is to figure out how to wire in an alternator cutoff switch so that charging can be restored when needed. I would then buy an appropriately sized LiFePO4 battery pack to get you through your normal travels, and grid charge from home at night. Here is a 12v 20Ah LiFePO4 for $110.

If solar interests you, the best thing to do is permanently mount PV on your property in an optimal location and angle, and then grid-intertie, or 12v charge.

[Coyote X]

I had an 80W panel on the roof of my van that I used for a few weeks to keep it running when the alt died in it. It worked out ok but wasn't quite right for keeping it going. It was a Astro with a 6.5L diesel so it didn't need power to run, just start and accessories. The problem was after driving the batteries would be weak so I would have to sit and let it recharge. After a while the batteries would be full charged and the rest of the energy the solar panel was generating got wasted. With the second battery setup like I am thinking of, the second battery could go much lower than normal while still charging the car and use the solar power generated much better since that battery will be at full charge less often. So it would run longer without any problems and still have enough power to start it for longer periods of time. Even with the efficiency losses it should still work out ok.

I was looking at this panel Amazon.com : Renogy® 100W Monocrystalline Bendable Solar Panel : Patio, Lawn & Garden I could probably get 4 of them on a metro. 2 on the hood and 2 on the roof. If they put out half their rated power for 3 hours a day that is plenty of power to run a Metro for the at most 3 hours I normally drive it. The metro only has a 60 amp alt from the factory and has a pretty simple electrical system.

I know I can plug it in at night to charge, there are a few people with Metros that do that and it works out well for them with no solar panels or anything fancy. This setup is more automatic and keeps everything happy by supplying 14.4V to the car while it is running using the step up converters to charge the main battery so the car always starts and runs like normal. It won't be cost effective at all and I figure probably 1500 bucks for the whole setup but it might get me another few mpg without having to mess with the car all the time. It is moderately easy to make an alt kill switch so I could always leave it in the car for when I actually need it.

Ultimately it is hard to get a metro over 70mpg without spending way more money than can be saved. I have a custom smaller cam than an XFi, Aero mods, weight reduction and am currently working on retuning the ECU. I can get upper 60s in the car the way it is now no problem on a tank, but it just cant quite make it to 70mpg. My options are starting to get expensive for whatever I do now. I figure 1500 to get rid of the alternator might get me 95% of my normal driving covered with no problems and pick up maybe 3-5mpg and put me over 70mpg. It isn't about saving money any more it is about getting the highest mileage possible in a car with normal driving and treating it like a regular car.

[2000mc]

I thought there was a thread on someone who did this before, but I can't find it right now, I think it might have even been one that got put on the front page. More to the point, I was thinking the aero penalty of the roof mounted solar panel caused there to be zero net gain

Edit: I think this is the thread I was thinking about
http://ecomodder.com/forum/showthrea...lar-22022.html

Originally Posted by VXmpgRacer

With 5000+ miles of testing on consistent routes, the results of this experiment are in.

The alternator belt was NOT removed.

Running the entire electrical system on only the solar system resulted in statistically insignificant mileage increase. (not expected)

[vskid3]

Originally Posted by Coyote X

It isn't about saving money any more it is about getting the highest mileage possible in a car with normal driving and treating it like a regular car.

That's good, as spending $1500 to go from 60 to 70MPG would take 157k miles to break even at $4 a gallon.

Maybe you could make the alternator only output power when decelerating in gear or other times that it wouldn't have much of an impact. Just seems a little silly to spend so much for an automatic setup that may still need to be plugged in.

[redpoint5]

Originally Posted by Coyote X

I was looking at this panel Amazon.com : Renogy® 100W Monocrystalline Bendable Solar Panel : Patio, Lawn & Garden I could probably get 4 of them on a metro. 2 on the hood and 2 on the roof... It won't be cost effective at all and I figure probably 1500 bucks for the whole setup but it might get me another few mpg.

Thanks for providing more info. Given your goals, I hope you follow through on your plan and track your outcome so that we can learn from your experience.

My only concern is how expensive those solar panels are, and how easily they might be ripped off of your car. You might want to epoxy it on, but some lunk-head still might destroy it in a failed theft.

Originally Posted by vskid3

That's good, as spending $1500 to go from 60 to 70MPG would take 157k miles to break even at $4 a gallon.

Maybe you could make the alternator only output power when decelerating in gear or other times that it wouldn't have much of an impact.

The good thing about most PV is that they last so dang long. Even if this particular car doesn't go 157k more miles, the PV can be re-purposed for other applications down the road.

Good idea having the alternator kick in whenever the car is decelerating. Perhaps an Arduino could monitor for open loop or injector cutoff and then switch the alternator on with a relay.

[Cobb]

I would test it. I looked at those converters for my mini phev kit that supplements the charging system and many are not adjustable. They also roll back or cut out when they get a certain temp. I ultimately went to 2 deep cycle batteries, an inverter and a mean well power supply. First a 150 watt then a 350 watt set to 14 volts. I know its full of losses and inefficiencies, but it works and I already had the parts laying around.

Still, even pushing 30 amps there are situation where its not enough and the converter has to take a break to cool down. Of course this is on a 2010 insight.

Maybe an older car like a metro uses less power? If you are passing through Richmond you can take my rig for a test.

[Coyote X]

A metro running with no accessories is a bit under 10 amps just running the engine is what most people say. It is possible to run the car daily and charge at night without much problem if it has a slightly bigger battery. But I don't really want to take a chance on something like that since I never know when I am going to be out and driving a few hours at night. I thought about just running a toggle to kill the alt when I wanted and a few other solutions and they all have possibilities, and probably would be easier and gain about as much as this idea. I am mostly just trying to come to a consensus of some sort on this idea and what it would take to make it practical or if it won't really get me higher mileage. Everything right now is just an idea in my head and I am just looking for ways it could work.

I am thinking that first thing before we can really know anything else I need an amp meter hooked between the battery and the car so I can see how much I am drawing from the charging system. That is easy to do on a Metro since the alt, starter, and main harness all connect together in the same spot beside the battery. I can then log that information and build up a profile of how much power the car needs under different situations.

I'll order an ammeter and maybe one of the 10A step up converters to play with. Next weekend I can wire up the ammeter and actually try and figure out of this idea is even possible.

[Cobb]

Oh yeah, the geo has room for a BFB or you could even go to a lithium.

The alt has to spin, takes a belt so it has additional losses vs just its weight rather its in use or not. Hybrids do not have alternators and honda switches there off and on as needed.