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cliffy49

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Posted: 06/19/21 12:11pm Link  |  Quote  |  Print  |  Notify Moderator

I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)?

All replys are greatly appreciated.


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jdc1

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Posted: 06/19/21 12:25pm Link  |  Quote  |  Print  |  Notify Moderator

100 watts of solar at 12v is 8.33333amps. If you have a 130Ah battery and it is down 50%, it will take in excess of 10 hours of FULL sunlight to charge it (the charge rate slows as it gets to capacity). So, it might take 2 days to charge one battery.

Lwiddis

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Posted: 06/19/21 12:47pm Link  |  Quote  |  Print  |  Notify Moderator

One to two watts per battery amp hour is the standard but it depends on where you are (up North, two) and whether you like campsites with lots of shade during the day. I’m currently 240 battery amp hours and 300 solar watts. Don’t cheap out on wire or the controller…then you can easily add another panel if needed.

* This post was edited 06/19/21 01:08pm by Lwiddis *


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2oldman

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Posted: 06/19/21 01:00pm Link  |  Quote  |  Print  |  Notify Moderator

good question, I don't know.

Lwiddis

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Posted: 06/19/21 01:14pm Link  |  Quote  |  Print  |  Notify Moderator

Nothing better electrically than glancing at the controller or remote at 11 a.m. and seeing “batteries 100%.” I don’t know either but prefer to base watts on total battery amp hours. The item I need to remember is to exercise the generator.

time2roll

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Posted: 06/19/21 05:15pm Link  |  Quote  |  Print  |  Notify Moderator

If you drain that battery every day you need to error toward the high side. If that battery goes a week then a little less solar would be needed.


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Almot

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Posted: 06/19/21 05:30pm Link  |  Quote  |  Print  |  Notify Moderator

1W per 1 AH is a very broad guideline. There is no such thing as too much solar.

Geographic location matters. Also, how big is your battery bank relatively to your daily energy needs.

Flat 100W solar would harvest ~35 AH on an average day in June at latitude of Portland OR. More in San Diego, less in Seattle. Tilted panel (ex. portable solar suitcase) will harvest more than flat panel. If your 100 AH battery is discharged 50%, you need ~55 AH solar harvest because of all the losses, so flat 100W solar won't cut it. Even 150W might not cut it because the last 20 AH will go in slowly.

It is easier to get away with less solar wattage if your energy use is low and battery bank is bigger than you need, for example your energy use is the same 50 AH a day and you have 200 AH battery bank. Then you won't need more than flat 150W solar because you'll start the day with battery 75% full and in a few minutes it will slow down and won't need more than a few amps.

When you're using energy mostly in daytime, having more solar than, say, 1.5W per 1 AH helps "better" because solar is feeding both loads and the battery, so it's less important that the battery is slow on those last 20% of SOC. Whatever solar energy battery can't take, loads will.

pianotuna

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Posted: 06/19/21 05:39pm Link  |  Quote  |  Print  |  Notify Moderator

Bare minimum is 60 watts per 100 amp-hours. After 150 watts per 100 amp-hours, there is little point in having more as the acceptance rate for lead acid at 85% state of charge is about 12.5 amps per 100 amp-hours.

So for 215 amp-hours between 130 watts to 323 watts.

For SiO2 (100 amp-hour) the 323 could be doubled as the acceptance rate is 25 amps. That makes the wattage about 600

This may help: https://freecampsites.net/adding-solar/

* This post was last edited 06/20/21 10:08am by pianotuna *   View edit history


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Almot

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Posted: 06/19/21 05:53pm Link  |  Quote  |  Print  |  Notify Moderator

I think the battery size relatively to energy needs is important. Other than weight, there is no penalty for oversizing the battery.

No penalty for oversizing solar, either - when the weather is not cooperating you can play with laptop or turn all the lights on to lift your spirits, without worrying about poor solar harvest from a small panel. Or if you park in a partial shade.

red31

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Posted: 06/19/21 06:08pm Link  |  Quote  |  Print  |  Notify Moderator

battery rating

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