Solar Rule Of Thumb....

[1L243]

I was wondering with so many variables is there a rule of thumb on how large of a solar system you need to keep your batteries charged so not having to run the generator.

The factors I would include is my trailer has LED lighting and a 40" TV. The TV may be used two or three hours a day... I have four group 24 12 volt batteries..

Thanks for any input

[mike-s]

time2roll wrote:
I spent my monitor money on more batteries.

Good for you. Your monitor is your brain. An electronic "monitor" is an AR thing in any reasonable system.

[time2roll]

OldSmokey wrote:
do you have a monitor ? i bet u do..

It is in my signature. I spent my monitor money on more batteries.
Monitor does not add amp hours or any functionality for me.

And for all you techies, a pic of my battery monitor.

[full_mosey]

OldSmokey wrote:

...
i do, in fact have a 300 a/h 48 Volt bank of prizmatics
that new thumb ratio for you is now 3.2:1.

i dont wish to sound arrogant, but do you understand now why
a 1:1 rule is just bull ?

doing it right is very simple, no thumbs required!

Nice try!

That 1W:1Ah ratio is based on a 12V battery bank.

Adjusting your bank to a 12V basis gives you a 1200Ah bank. Your ratio is 0.8W:1A.

And there we are right back at a little under 1W:1Ah. 🙂

HTH;
John

[mike-s]

OldSmokey wrote:

scrubjaysnest wrote:

HikeN2Mts wrote:
One rule of thumb 100 watts solar for every 100 amp hours of battery. It really depends on your usage, you need to calculate the watts of each item you will be using for total watts/amp hours used and what is needed to put back into batteries.

While the above is the universal rule of thumb; we find in practice 140 watts per 100 aH is a better choice.

please don't post arbitrary nonsense like this, all it will do is result in frustration and failure for those that adopt it.
My partners and I just shook our heads this morning.. let me give you an example of why there is no rule of thumb that will work.

my rv has 960 watts of solar.. so how many a/h do i have ?
can u guess ? no, there is insufficient data. whats missing ?..
well two things. 1) Voltage 2) Autonomy
change any one of those two and your thumb is blown away.

i do, in fact have a 300 a/h 48 Volt bank of prizmatics
that new thumb ratio for you is now 3.2:1.

i dont wish to sound arrogant, but do you understand now why
a 1:1 rule is just bull ?

doing it right is very simple, no thumbs required!

The GP (and the common 1W:1Ah rule of thumb) make the assumption of a "12 V" system, which applies 99+% of the time for an RV, and reasonably applies to the OP's rig, which this discussion is about.

Translating to those terms, you have a 960/(300*4)= 0.8:1 ratio system, close enough to the 1:1 rule of thumb that your system doesn't make it "bull," but supports that rule-of-thumb.

[OldSmokey]

time2roll wrote:

OldSmokey wrote:
without his daily w/hr it's all guesswork.

So the OP should install a battery monitor for $200 and camp a few times to get some real data?
I would just put the $200 toward 200 watts of solar and not worry so much.

do you have a monitor ? i bet u do..

any solar system should have a monitor...
it doesn't take much to establish a good estimate of usage
and then design from there.. jeez.. here i am able to offer professional advice and you guys are poo pooing it in favor of
internet researched rules of thumb.. srsly ?

[OldSmokey]

scrubjaysnest wrote:

HikeN2Mts wrote:
One rule of thumb 100 watts solar for every 100 amp hours of battery. It really depends on your usage, you need to calculate the watts of each item you will be using for total watts/amp hours used and what is needed to put back into batteries.

While the above is the universal rule of thumb; we find in practice 140 watts per 100 aH is a better choice.

please don't post arbitrary nonsense like this, all it will do is result in frustration and failure for those that adopt it.
My partners and I just shook our heads this morning.. let me give you an example of why there is no rule of thumb that will work.

my rv has 960 watts of solar.. so how many a/h do i have ?
can u guess ? no, there is insufficient data. whats missing ?..
well two things. 1) Voltage 2) Autonomy
change any one of those two and your thumb is blown away.

i do, in fact have a 300 a/h 48 Volt bank of prizmatics
that new thumb ratio for you is now 3.2:1.

i dont wish to sound arrogant, but do you understand now why
a 1:1 rule is just bull ?

doing it right is very simple, no thumbs required!

[MEXICOWANDERER]

Very similar to one-another...

Solar requirement estimate

versus

Shop-A-Holic with VISA Platinum credit card, turned loose in Mall-Of-America, with porter and platform shopping cart.

I was hit-upon dozens of times to provide a hard estimate for this. I refused. Usage and customs habits change faster than women's dress selections for social functions.

Opinion: Do the best you can but leave option open for 150% more panel power.

[time2roll]

OldSmokey wrote:
without his daily w/hr it's all guesswork.

So the OP should install a battery monitor for $200 and camp a few times to get some real data?
I would just put the $200 toward 200 watts of solar and not worry so much.

[crosscheck]

Our camping style is 98% dry, with an average of 90 nights/year. Since 2011- 2016, when we installed 190W solar and 140W more for a total of 330W on a TC and 2016 when we installed 490W on our present TT until now, we have used our Honda 2000 maybe 3 times although we always drag it along just in case. The TC had 4 6V AGM's(400AH), the TT has 4 6V GC-2's(450AH). We have had a 2000W, charger/ inverter in both RV's.

As the OP's original question was regarding eliminating/reducing generator time, the 3 key components to eliminating generator time,(no A/C), are,

1) Battery storage: This is your gas tank. Probably more important than most people think.The farther you can go to find fuel(solar) if your fuel stations are not reliable(clouds, trees), the better. For us, with a moderate electrical footprint, 450AH of storage is about right.

2) Solar: 1W to 1AH is fine but as has been stated many times, more solar is better whether, fixed, tilted or portable.

3) Consumption and Conservation: Many things can be done to cut down on our consumption of AH's from changing out old incandescent lights to LED's to just turning down the thermostat when it is cold out at night and putting a warm down duvet on the bed.

Dry/boondock camping without generator time should be simple if you have a plan and are set up from the start.

Dave

[gmctoyman]

My "rule of thumb" is to put on all that you have room for in your budget. I’ve NEVER heard of anyone having to much.

[scrubjaysnest]

HikeN2Mts wrote:
One rule of thumb 100 watts solar for every 100 amp hours of battery. It really depends on your usage, you need to calculate the watts of each item you will be using for total watts/amp hours used and what is needed to put back into batteries.

While the above is the universal rule of thumb; we find in practice 140 watts per 100 aH is a better choice.

[OldSmokey]

time2roll wrote:
The OP has already decided he needs 4x Group 24 battery.
I would assume he uses 30% to 60% daily.
How you gonna charge that back up?

The good news is that solar is low cost and silent.

read the op's post again..

he owns 4 batteries, he does not state he needs 4 batteries.
if he did then presumably he would know his daily watt/hr requirements
and i'm sure he does not..

without his daily w/hr it's all guesswork.

[time2roll]

The OP has already decided he needs 4x Group 24 battery.
I would assume he uses 30% to 60% daily.
How you gonna charge that back up?

The good news is that solar is low cost and silent.

[red31]

have enough capacity to last days like this