Solar Panel Battery Charging And Problems 1998 v70 mostly

[MrAl]

Hello there,

Recently i connected up a rated 20 watt solar panel so i could charge the battery when the car engine was not running. I simply can not run a wire out there to plug in a battery maintainer so i had to go solar. I'm still experimenting with it.
Much of this will be related to the 1998 v70, non turbo, FWD Volvo but some of it can be applied to other types of vehicles.
I guess i should also use this thread for updates on the progress of the installation.

To start, i have a big problem i was going t ask for some ideas about.
That is, i have the panel mounted in the back window because that is where the sun hits it directly and i can get a good placement angle. The problem is, the DANG WINDOW IS TINTED !!
Now maybe you (and myself as well) would think that could not possibly hamper the operation of the panel very much. Well, we would both be wrong (ha ha). The current in full sunlight with the back door open (again this is a v70) goes up as high as 660ma, much more than i ever thought possible. However, with the back door closed and still no shadow on the panel, the current drops to 120ma. That's not too bad but VERY much reduced from the unobstructed version. If i could get 600ma that would solve all my problems, and that would mean more current during cloudy days also, which was quickly found to be very inadequate the way it is now. On a cloudy day i only get about 8ma which is almost nothing for a battery that big. I would not even consider charging a regular AA NiCd or NiMH battery with a current that low. The problem involves a thing called charge acceptance, or charge efficiency. You have to have enough current or the battery does not charge. It is also not good enough to just keep the battery at the same voltage, unless of course it is high, because during the night it will fall, then the next night it will fall more, etc.

The major problem here though has now been identified as the tinted window problem. It blocks out too much of the need solar radiation.
So the 100 dollar question is, what the heck can i do about that. I would hate to have to mount the panel on the outside of the car, is that even possible? It might become the subject of vandalism.

Any ideas, at all?
If not in keeping the panel inside, how about ideas about how to mount it outside? Just to note, i dont think mounting it flat on the roof (somewhat inconspicuous) would work very well because the angle would be too different from the right angle for maximum solar conversion (and thus output current).

I feel that i am on the verge of solving this low battery problem once and for all without modifying the car itself, but i need to get the full power out of the panel. Any ideas no matter how strange may help. Thanks.

[scot850]

Turn the car around and stick it to the front windshield? Or stick it to the front windshield as is and see if even without the direct sun it still gives you a better coverage especially on dull days.

Neil.

[MrAl]

Turn the car around and stick it to the front windshield? Or stick it to the front windshield as is and see if even without the direct sun it still gives you a better coverage especially on dull days.

Neil.

Hi Neil,

You mean on the outside of the windshield or inside?

You just gave me the idea though that why cant i just mount it on the OUTSIDE of the rear window. It will require some ingenuity but that's what im all about anyway. Maybe a few metal pieces.
Your idea may be better for the angle though, but then i'd have to take it off before i drive, if on the outside. if on the inside i think i would hit that tinted window syndrome again.
On the back window, i guess i could put an angle adjustment on it too so i could get the angle right. Maybe some aluminum angle material and some bolts and nuts. Not sure how to bolt it on yet though, but maybe after inspecting the back door better i can find a way.

What you think about the back window idea, which would be bolted on and permanent?

I gotta do this i can see that now. Yesterday caused an irreversible drop in voltage as today it did not charge as well even though we had plenty of sun. With 600ma though i can see this working really well, actually probably better than i ever expected.

[scot850]

Yes, if you use rubber suckers to hold it to the windshield whether you reverse the car to face the sun from the front or leave it where it is and try using the front windshield as is you may well find that is sufficient for your needs. Sticking it on the outside with all the wee ejits out there these days is asking for trouble.

Neil.

[MrAl]

Yes, if you use rubber suckers to hold it to the windshield whether you reverse the car to face the sun from the front or leave it where it is and try using the front windshield as is you may well find that is sufficient for your needs. Sticking it on the outside with all the wee ejits out there these days is asking for trouble.

Neil.

Hi,

What is a wee ejit?

I read that a lot of people are mounting theirs on the roof but mounted flat, not angled. I'd probably want to angle mine.
Mounting on the outside will be the only way i can see that now. There just isnt enough power on the inside due to the way the glass interferes with the sunlight. There is also some evidence that even regular glass with no tinting will reduce the radiation that hits the panel. I havent tried to measure that yet though.
Given the numbers i have now, if 120ma is obtained from a 20 watt panel, then i would need a 100 watt panel to get to 600ma, something i can get with the panel i have now if it is mounted on the outside at the right angle. The other thing is a 100 watt panel would block the entire back window which i dont think is a good idea.
Right now the panel only blocks part of the view out the back window, which is not bad at all. If i mount it on the roof or on the back door instead of right over the window it wont block any of the window area.

If i wanted to put it under the windshield i'd have to back the car into the driveway, and that's not particularly easy on this street and the way the driveway is set up. It could be a last ditch effort i guess, but it would still have to go on the outside unless i get a gigantor panel.

[abscate]

What is a wee ejit?]

I’ll gie ye a skulpit lug, ya wee ejit!

[scot850]

Abscate got it in one. Scottish for stupid little fools/vandals who like to break other peoples stuff or steal it.

Neil.

[MrAl]

Abscate got it in one. Scottish for stupid little fools/vandals who like to break other peoples stuff or steal it.

Neil.

Ha ha, ok thanks i'll keep that in mind.

[scot850]

Hey Al,

Although the downside to this is will draw down the battery itself, how about this Bluetooth battery monitor:

https://www.princessauto.com/en/12v-blu ... 0008932303

This is about to go on sale here next week for around $40 CDN which is about $30 US. Has some useful storage features which may help with figuring out the charging rate of your battery in different conditions.

Neil.

[wizechatmgr]

Did you figure out what was drawing the battery down to begin with? Is it just a case of not using the car as regularly as it may like?