The RV Forum Community

RVing message boards => Tech Talk => Solar => Topic started by: Dragginourbedaround on October 19, 2018, 02:58:57 PM

Title: Using solar to charge batteries while in storage
Post by: Dragginourbedaround on October 19, 2018, 02:58:57 PM
A few days ago we put our coach in storage for I don't know how long. But we're in a field with a lot of sun. We have a Renogy 100 watt suitcase, and I was going to put the suitcase on the roof to get the best exposure. When I parked my coach I didn't have any help to put the panels on the roof, so I put it inside on the dash behind my brand new windshield. I really didn't expect it to work, but I was getting something, less than an amp. As I was leaving I flipped the two battery disconnect switches and hoped for the best. Today I went back to put the suitcase on the roof, but when I flipped the house battery switch I saw that the One Place monitor was showing 13.6v and at the controller it was showing 2 amps. I was shocked that it was actually charging! That was at 12:30 today. I'll have to check earlier in the morning to see if the panels are putting out more current. I guess as long as it's charging I'm going to leave it where it is. Less chance of it growing feet and walking away.

Sorry I've tried a couple of times to rotate the bottom picture, but it wants to be horizontal!
Title: Re: Using solar to charge batteries while in storage
Post by: Isaac-1 on October 19, 2018, 03:36:16 PM
My guess is you are probably loosing 30-50%  of the potential output being behind the windshield like that, though even with the losses it seems to be enough to maintain the batteries.  I don't know what climate you are in, but I would suggest checking back if you live where the weather is dreary and cloudy much of the winter.
Title: Re: Using solar to charge batteries while in storage
Post by: Dragginourbedaround on November 20, 2018, 01:13:02 PM
An update after a month: I check the batteries once a week. The panels are still on the dashboard and the monitor reads a consistent 13.3 volts. I am in SW FL, so getting a lot of sun. Still hard to believe itís working on the dashboard.
Title: Re: Using solar to charge batteries while in storage
Post by: Lou Schneider on November 20, 2018, 04:46:20 PM
I kept a trickle charger panel about 1/4 the size of yours on the dash of my Chaparral motorhome while it was stored in Los Angeles to keep the chassis battery up between trips.   Worked fine.

It makes sense it would work through the windshield - after all, it's just one more layer of glass on top of the one on the panel covering the solar cells.  You may lose a little solar energy due to the tinting but I doubt it's anywhere near 50%.
Title: Re: Using solar to charge batteries while in storage
Post by: Isaac-1 on November 20, 2018, 08:57:27 PM
Non-tinted front windshield auto-glass has a typical VLT (visible light transmission of 80-85%), single pane water white float glass has a VLT of about 90-91%,  anything higher than 91% requires the use of optical grade anti-reflection coatings.  Meaning at a minimum you are losing 15-20% to the windshield, when measured perpendicular to the glass, add in oblique angles and it gets worse.  So all total I stand with my 30-50% loss number, though I will admit it is probably closer to the 30% end.
Title: Re: Using solar to charge batteries while in storage
Post by: Dragginourbedaround on November 21, 2018, 06:49:47 AM
I'm just happy my batteries are staying charged without a lot of work. :)
Title: Re: Using solar to charge batteries while in storage
Post by: Murray on November 29, 2018, 09:26:01 AM
Obvious, but just in case, from a solar through the windscreen point of view, parking facing south is pretty important. (Aussies/Kiwis etc - I know!)
Title: Re: Using solar to charge batteries while in storage
Post by: breezie on November 29, 2018, 10:55:20 AM
I have one 60W 12V panel on the bow of my sailboat.
It sits in the winter, covered with snow, and STILL keeps 3 deep cycle and one starting battery fully charged.
It's amazing, isnt it?

Well, I think it is.
Title: Re: Using solar to charge batteries while in storage
Post by: Dragginourbedaround on November 29, 2018, 12:25:36 PM
Obvious, but just in case, from a solar through the windscreen point of view, parking facing south is pretty important.
:))