Solar Top Off Estimates

[DoctahDeane]

First off - I understand that if you calculate devices carefully, you can more than guesstimate and also that the position of solar panels, relative to the sun make a difference, obviously. I'm just trying to get a ballpark sense of what a reasonable purchase (for me) will be. I tend toward "more is better" in most things and there is not a huge difference between the cost of a 100W system and a 160W. 200W seems like the point where prices start to increase.

Anyway, here's my question - lets's say my battery gauge is telling me I am down to something like 12.2 remaining, so I'm starting to think about recharging. Then, let's say I'm out in the open, not in the shade and it's nice and sunny out. I will not have the panels installed on my roof and I'll have the ability to lay them out to catch good sun output. Not planning to get obsessed and follow the angle of the sun all day - maybe an adjustment or two. But given this level of battery remaining and let's say a 100W panel, what would be a ballpark amount of time to come up to full charge? A few hours? All day? Then wondering about the impact of adding a beefier panel. So to make the 2nd question as simple as possible, in the scenario I described would a 200W panel cut the time in half?

I'm just after rough impressions, not a scientific investigation. In my situation, it seems like these "suitcase panels" with embedded controller might be s good option. Thanks for any feedback!

[RJ Howell]

First off - I understand that if you calculate devices carefully, you can more than guesstimate and also that the position of solar panels, relative to the sun make a difference, obviously. I'm just trying to get a ballpark sense of what a reasonable purchase (for me) will be. I tend toward "more is better" in most things and there is not a huge difference between the cost of a 100W system and a 160W. 200W seems like the point where prices start to increase.

Anyway, here's my question - lets's say my battery gauge is telling me I am down to something like 12.2 remaining, so I'm starting to think about recharging. Then, let's say I'm out in the open, not in the shade and it's nice and sunny out. I will not have the panels installed on my roof and I'll have the ability to lay them out to catch good sun output. Not planning to get obsessed and follow the angle of the sun all day - maybe an adjustment or two. But given this level of battery remaining and let's say a 100W panel, what would be a ballpark amount of time to come up to full charge? A few hours? All day? Then wondering about the impact of adding a beefier panel. So to make the 2nd question as simple as possible, in the scenario I described would a 200W panel cut the time in half?

I'm just after rough impressions, not a scientific investigation. In my situation, it seems like these "suitcase panels" with embedded controller might be s good option. Thanks for any feedback!

At like 12.2, ya you should be recharging. With any of my LA's, 12.4 was the point of recharge. The deeper you discharge, the less recycles you get. Think about not going so deep..

Panel size? Hear this quite a bit.. It really does come down to doing the steps and I think you in those and wondering which is next. Been there buddy!

First step always is do a power audit. What is it you wish to run and what can you really do without? An audit is a amazing awakening to how much is being used by what. Once decided upon, then a battery bank capable of lasting a amount of days without recharge.

Now comes recharge. How long am I in an area? What region do I camp? Solar or DC/DC recharge? I traveled cross this country and Canada and found that mostly, I recharge better with a DC/DC unit. Yet that's me. I carried a 130w panel that I put out, not needing to.. It's the way I camp, not maybe as you do.

I'm going to put together a small 60w panel system, probably flexible. It's a 'just in case' thing for me.

The the steps. Do the audit. Determine what you really require. MHO

[DoctahDeane]

Thanks for that reply, I appreciate it. Not really what I was asking though. Apologies if unclear. I do have a monitor. I can see the impact of any device I turn on in real time (like a light, for instance) and from there, I can do the math. I'm not asking about capacity, or an audit. Much simpler question really:

it's time to recharge and I would do this with a 100W solar panel on a sunny day, no shade. Roughly how long to get back to full charge? A morning? All day? Just ballpark is good.

part 2 of question is whether doubling size of panel would cut the recharge time significantly - in half? Maybe 6 hours vs 8? Again just after a ballpark feel.

[Graniterich]

Ballpark figures. You have a 100 Amp hour ( just for figuring) you used fifty Amp hours (max percent you should use. You need to put fifty ah back in. 100 watt panel can put out no more than 7-8 Amp per hour. You need 50. 50/7 = 7ish. That is the hours in full sun you need in a perfect world. This is just an overview.

Sent from my KFKAWI using Tapatalk

[bdosborn]

The best camping spots are in the shade so using a portable panel makes a lot of sense. Before I had an electric fridge, an 80 watt solar panel easily kept up with our usage. The best thing about a portable panel is you can easily track the sun by adjusting it every time you walk by. I got great output from the ground panel compared to a roof mount panel. The bad thing is you worry about the panel walking away.

Bruce

[DoctahDeane]

Thanks guys, that is very helpful. So sounds like very roughly, most of a day to top off. And, just read a Renogy ad on Amazon that was for a 400w setup (way more than I want or need) but it says that it can charge a 50% depleted battery to full in roughly 3 hours, so that would seem to hang (roughly) with what was suggested. Confirms what I was thinking which was minimum 100W, max 200W. I saw a 160 set up that wasn't too bad $ wise. Bruce, if you see this post, how do you keep your fridge running over the course of the day and night? Assuming if you are driving that the tow vehicle is charging it and then switch to trailer once settled? If so, how much does it drain the battery - I'm assuming that draws a lot? Thanks

[bdosborn]

The fridge uses about an amp-hr at night. So I need about 12 amp-hrs to keep it running from sundown to sun up. We usually watch a movie at night and that runs 3 amp-hrs for a couple of hours. The heater (if we need it) uses about an amp-hr. 24 amp-hrs in a night is the most I remember seeing - lights, TV, fridge, heater, cell phones, etc. The panels charge everything up the next day as well as power the fridge while there's sun.
I have 420 watts of panels on the roof:


And about 160 watts of ground panels:

When I had a teardrop, an 80watt panel took care of our usage ( I paid $420 for that panel 12 years ago. Ouch!) I had a PV phase were I put a lot of panels on the current trailer just because I liked them and had the roof space. My goal has always been to have 3 days of battery reserve and enough panels to charge the battery 100% on a semi cloudy day.

I almost forgot, I just upgraded the battery to 360 amp-hr LiFePO4.
Bruce

[DoctahDeane]

I have 420 watts of panels on the roof:
And about 160 watts of ground panels:

When I had a teardrop, an 80watt panel took care of our usage ( I paid $420 for that panel 12 years ago. Ouch!) I had a PV phase were I put a lot of panels on the current trailer just because I liked them and had the roof space. My goal has always been to have 3 days of battery reserve and enough panels to charge the battery 100% on a semi cloudy day.

I almost forgot, I just upgraded the battery to 360 amp-hr LiFePO4.
Bruce

I'm not sure the term "enthusiast" would be big enough for you Thanks a lot for responding. This is really helpful info.

[John61CT]

No lead battery deep cycle discharged can reach 100% full in less than six hours, no matter how high the amps charging rate.

Going from 30 to 60A might save you 20 minutes on a 200Ah bank.

The ideal is a very high current rate for an hour or two in the morning, get from "empty" to say 85% from an ICE source.

Then the reduced CAR of that last 15% is well suited to the reduced output from solar, takes a full solar day in ideal conditions to get back to 100%.

For longevity of the bank this needs to be done at least a couple times a week, ideally "most cycles"

[featherliteCT1]

My best guess is that “ICE” and “CAR” mean “internal combustion engine” and “current acceptance rate”, respectively.

[John61CT]

bingo

[DoctahDeane]

On this topic sort of - battery recharging - I have a 125A VMAX battery, new. Charged it when I got it. As I've finished this build and electrical, it was down to 12.40 remaining, so I plugged it in. Went put to 12.75 quickly - like an hour, then crept up to 13.1 or so, when I unplugged it. Then ut dropped back a bit to 12.9. I think as I understand it, it'll creep back up a bit now. What number = full charge? I *think* this battery charger ought to shut off automatically at full charge?

[John61CT]

The voltage of a live circuit with current flowing has nothing to do with SoC.

After isolation resting for 24hr, you get an accurate **battery** voltage at the posts, and yes you could build a table showing

SoC vs that resting voltage

but it would be different for each type even model of battery, and will change as the battery's SoH declines with use and age.

Every maker of quality industrial strength true deep cycle batteries publishes detailed technical documentation, including information about the charging profile for each of their lines.

Every one also has technical support staff readily available to discuss further details.

Such batteries are not usually purchased through big box retail or automotive sales channels, and it would be silly to buy them online due to their weight, unless you found through calling these makers they all had no distributors local enough to you.

Spending a bit more up front is almost always worth it for greater longevity, to bring down the cost per Ah per year of use.

Unless you can't care for your bank properly thus have to replace it every couple/few years anyway

but really, quality true deep cycle batteries are required for that use case, and good ones can be found in most places for ~ $1 per Ah @12V anyway, which is in the ballpark for the usual fraudulently labeled "deep cycle" sold to consumers.

If you have one of those and can't get the data sheet online or from the maker, contact the seller?

[John61CT]

For example from EPM, maker of Deka and Duracell GCs

At 12V:

Absorption Voltage = 14.4V - 14.7V (higher the better)
Absorption End Point = Current change over 1 hour period of less than 0.1A
Max Absorption Time = 12 Hours

Float Voltage = 13.8V - 14.1V (lower the better)
Float End Time = No Limit

Equalization = 15.0V to 15.3V
Equalization End Point = Current change over 1 hour period of less than 0.1A
Max Equalization Time = 12 Hours

Temp Compensation = -.018V for every degree °C rise above 25C

[bdosborn]

On this topic sort of - battery recharging - I have a 125A VMAX battery, new. Charged it when I got it. As I've finished this build and electrical, it was down to 12.40 remaining, so I plugged it in. Went put to 12.75 quickly - like an hour, then crept up to 13.1 or so, when I unplugged it. Then ut dropped back a bit to 12.9. I think as I understand it, it'll creep back up a bit now. What number = full charge? I *think* this battery charger ought to shut off automatically at full charge?

Yes, the battery charger will shut off by itself when the battery is charged. You can leave the charger plugged in all the time without worry about overcharging the battery.The voltage will go as high as 14.4-14.7V, depending on the charger but that's okay. I would get a battery meter like this: Battery Monitor if you want to make sure you don't run the battery too low while camping. Judging battery state of charge with a voltmeter is a wet finger in the wind method at best. Just don't put the meter where you sleep, the display back light flashes when the battery charger is charging.

Here's a chart showing the rough battery state of charge versus voltage:



This is enough to keep you from running the battery too low while camping, but it really doesn't tell you much more than that.

Bruce