Solar assist: Vehicle roof top solar panels

[oil pan 4]

I have had solar panels on my suburban since 2011. Only about 10 or 15 watts worth. That was enough to float charge the large flooded lead acid starting batteries I had at the time on a cold day.
Then when I switched over to LiFePO4 batteries I found that the tiny amount of solar I had added could easily over charge the LiFePO4 batteries. So the switch they were wired through stayed off pretty much all the time.

Well now I would like to do an alternator delete and the obvious choice to help the alt delete along is to add solar. I knew there were charge controllers for lead acid batteries and none for lithium.
Not too terribly long ago I was reading that there were no solar charge controllers for LiFePO4 on the market and none in the foreseeable future and the solution people at that time were using was non temperature compensated controllers with a gel battery setting (you don't equalize gel batteries or you will fry them).
It works, but not ideal.

With help from the wind-sun forum I found this.
They do exist.


A 10 amp LiFePO4 specific Maximum Point Power Tracking solar charger.
MPPT chargers like this can take up to 75 volts (a genasun charger can't do 75 volts but others can), use all the wattage, step it down like an AC transformer and use all of the power to charge the battery.
Unlike a PWM charger. Sure you can hook up a PWM charger to 24 volt panel and a 12 volt battery if you have the right one, but you will only ever get the panels rated amperage and not the total wattage the panel makes for battery charging.
With PWM you want to match your panel to the battery to get max amps going into the battery. Then if its overcast, you are screwed.
With MPPT you are more likely to get at least some usable power in less than ideal conditions. IMO "Less than ideal conditions" very accurately describes any application where you have solar panels laying almost flat on the top of a vehicle.

And yes they do make MPPT charge controllers for lead acid batteries, they have been around for years, but most of them are 15 amps, $200 and up.

I figure 10 amps for battery charging is plenty.
A 140 watt panel should cover an area of roughly 2 feet wide and 5 feet long if it were a more efficient single mono crystalline panel. I will likely use less efficient, more flexible poly crystalline.
That is a lot of solar panel coverage, about the maximum amount I can foresee using.

This line of charge controller also works very well with lead acid AGM batteries.
The fixed 14.2v this charge controller put out is perfect for AGM. The only thing this charge controller is missing for use on lead acid is equalization, which can be done with a digital inverter based stand alone battery charger and temperature compensation, which you really don't have to have.

I did some searching around and I can not find a high quality low amp MPPT lead acid MPPT charge controller.
The only one I can find is the genasun 5 amp MPPT for LiFePO4.

So if you really want a high quality low amp name brand MPPT controller, at this time it looks like your best option is to get a AGM or LiFePO4 battery in your vehicle, a 5 amp genasun MPPT and start sticking solar panels on your roof.

If you wanted to throw down some money and get a heavy duty 15 amp MPPT charger you could get a Morningstar sunsaver tristar MPPT set it up for Gel batteries (14v even) you could go with the AGM setting and get 14.3v with LiFePO4 I say less is more as far as max charging volts go. Then set the higher voltage cut out dip switch "on" so it cuts off load power at 11.5 volt, which is not good at all for lithium, no equalize so dip switch 3 "off", then install a resistor in the "remote temperature sense" terminals to trick the charge controller into putting out stabile voltage all the time.
At this time I do not know what the value of this resistor would be.
I have seen the built in temperature sensor and judging by the application and actual size of the sensing element I can only surmise its a thermistor.

[redpoint5]

Thanks for the interesting info.

I was about to say not to bother with a measly 15 watts of extra juice when running with the alternator off, but 140 watts is significant. That said, I find vehicle mounted PV to be impractical and a poor use of materials since the vehicle is always changing direction ,and an optimal angle can never be achieved.

Are you attempting to charge the battery mostly on solar instead of daily grid charging? It wouldn't work for me since I garage my vehicles, but the concept is interesting to me.

I want to see pictures of the build if you proceed.

[oldtamiyaphile]

Do you need a specific LiFe controller? Mine have adjustable end voltage so I can dial that in to suit. Is the charge cycle different other than voltage cut out? My controllers do a kind of taper charge like a dedicated LiFe charger would, they charge up to peak voltage, then pulse (at full panel amps) to keep it there. A proper LiFe charger would taper the amps down to zero as the battery approaches full, but I'm not sure it makes a practical difference.

[Daox]

How much does that charge controller cost?

[oil pan 4]

I remember now, those panels I used the first time around are mono, 5 watt each and cover about 1 square foot total. They are four "6 volt" panels. I wired them up series parallel for "12 volts" which really produced more like 17ocv and wired them straight into the battery through a switch and fuse.
They actually worked pretty well even in the winter time. They were able to bring the batteries above 13 volts when it was well below freezing.

I do not have to have the optimum angle. The small scale solar panel install showed me I can get plenty of power out of small panels laying flat to float charge 2 big SLA batteries.
Now I will have a huge amount of solar plus a charge controller that can make full use of almost any amount of incoming voltage and amperage.

I believe I will use two 80 watt panels in parallel that make 21ocv, assuming I will never be able to get that last 20 watts out of them due to my poor application.

That 140 watt, 10 amp charge controller costs $180.
There is a smaller 5 amp one that is a little more than half of that.

In addition to hopefully providing all the power the alternator made with solar, the suburban will be able to provide some power for external stuff with the xantrax 1000w pure sine inverter I picked up for it. Remember I still plan on having the alternator, it just wont be spinning or energized most of the time the vehicle is running.

[aardvarcus]

I assume you are going to be using a modified clutched alternator?

I would like to go completely alternator-less on a future Diesel Suburban project I have in the pre-planning stages, but I don't think it is practical. I just can't get over the lack of recharge-ability if I have to jump start it or the running the lights for hours at night scenario even with LEDs.

[oil pan 4]

Originally Posted by aardvarcus

I assume you are going to be using a modified clutched alternator?

The specifics to that are here:
http://ecomodder.com/forum/showthrea...tch-32660.html

The term clutched alternator is a little bit misleading. As far as I can tell there are 2 types of OEM clutched alternator. A one way clutch and an dampener clutch.
Neither actually stops alternator rotation.

[oil pan 4]

I got the genasun controller today.
If you have 4 cells of LiFePO4 batteries like I do you need part number GV-10-14.2V

They have a 11.1 volt and 14.8 for 3 and 4 cell LiCo chemistry and polymer batteries. You don't want these for LiFePO4.
The website wasn't super clear on this but the owners manual spells it out very clearly.

The genasun controller is serial numbered, made in USA, appears to be very well made and is "marine rated".

[oil pan 4]

I was trying to find a large panel to go on the roof of my suburban. Maybe using 1 or 2 long slim panels. But I was looking at upwards of $5 per watt and at less than 5% efficiency panels.
Then the problem is any panels I could find manufacture installation data posted with the panel the OEM warned against installing the panels over top of something like the roof of my old suburban that has metal ridges.
So that means I need to find something less than 10 inches wide that can fit down in between the ridges.

Then I though why not just do what I already know works and scale it up.
These small ridged fiberglass backed panels are more efficient and less than half the price of the big flexible panels. So how can I not?

The four, 6 watt panels I use now have been on there since 2011 and they have held up great.

Also updated the wiki a little bit.
http://ecomodder.com/wiki/index.php/Solar_12v_assist

[oil pan 4]

I found some 14 ridged fiberglass backed epoxy 10 watt solar panels that are between 8 and 9 inches wide and 15 inches long.
They are bought and in the mail.