Solar crunch time! Please review my plan.
I would like begin my first post with a big thank you to all who have shared their knowledge and experience on this forum. Without that, I probably wouldn't be entering the solar jungle! I hope yo...
Forum Discussion
Hard to tell for sure, but it looks like PT is starting with the battery bank size requirement and then moving to the solar requirement to match the size of the bank.
I am saying the solar requirement is independent of the battery bank size requirement. But both requirements start with the daily AH usage figure.
PT says to start with an audit and get that usage figure, and I agree.
Now you need some batteries and you want to go no lower than 50% SOC daily and you want to get back to 100% daily. I agree.
So whatever recharging method you use, you want to replace the daily usage daily ending up will full batteries. With solar as the recharging method, that means getting to 100% before dark and not getting below 50% overnight until the sun comes out next day and you start recharging again. I think PT would agree.
So my point is that the solar has to replace that daily AH usage daily and that you can figure out how much of a solar set-up you need to do that. I think PT would agree. BUT I am saying that has nothing to do with how many batteries you have, which is a separate subject but is also related to the daily AH usage so you don't drop below 50% overnight.
It doesn't matter if your daily usage is all microwave from inverter or all LED lights left on all day, an AH is an AH, and the daily AH figure we are starting with includes everything. So it doesn't make any difference to the solar requirement just how you use up the AHs.
I did say the battery bank size required can be affected by whether you have solar. But the solar requirement is a separate thing, only relating to replacing that daily AH usage.
So with that background, I will insert replies to PT's quote below, but just for the record, and there is no need for anybody else to follow it unless you are bored! :) If PT wants to respond, then he will have the last word here so we don't keep spinning our wheels.
I am saying the solar requirement is independent of the battery bank size requirement. But both requirements start with the daily AH usage figure.
PT says to start with an audit and get that usage figure, and I agree.
Now you need some batteries and you want to go no lower than 50% SOC daily and you want to get back to 100% daily. I agree.
So whatever recharging method you use, you want to replace the daily usage daily ending up will full batteries. With solar as the recharging method, that means getting to 100% before dark and not getting below 50% overnight until the sun comes out next day and you start recharging again. I think PT would agree.
So my point is that the solar has to replace that daily AH usage daily and that you can figure out how much of a solar set-up you need to do that. I think PT would agree. BUT I am saying that has nothing to do with how many batteries you have, which is a separate subject but is also related to the daily AH usage so you don't drop below 50% overnight.
It doesn't matter if your daily usage is all microwave from inverter or all LED lights left on all day, an AH is an AH, and the daily AH figure we are starting with includes everything. So it doesn't make any difference to the solar requirement just how you use up the AHs.
I did say the battery bank size required can be affected by whether you have solar. But the solar requirement is a separate thing, only relating to replacing that daily AH usage.
So with that background, I will insert replies to PT's quote below, but just for the record, and there is no need for anybody else to follow it unless you are bored! :) If PT wants to respond, then he will have the last word here so we don't keep spinning our wheels.
pianotuna wrote:
Hi BFL13,
No I'm not saying that at all. A small bank needs more wattage because there is a much greater chance that it will dip below 50% state of charge.
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The premise is that the two batt bank will be at 50% starting its recharge, so this is a deflection change of subject, not a response
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What I have consistently said is that as battery bank capacity rises the solar wattage per 100 amp-hours can be lower and may approach but not be below 60 watts per 100 amp-hours.
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It is incorrect to say it "can" be lower. It is not some kind of choice. It IS lower if the bank is bigger while the solar amount remains the same at the AH required to replace daily usage
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I have also consistently said that 150 watts per 100 amp-hours is a reasonable maximum wattage, because above 85% state of charge that is as much as the jars will accept.
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The premise is that the solar will replace the daily AH so it is understood the battery acceptance rate vs SOC at the voltage concerned will allow that recharge to 100%. So if that is the maximum per battery then that's fine, but not in dispute anyway
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Charging is not linear. Neither is discharging.
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The standard V looking graph of that shows that the recharge is not linear for AH vs SOC and has that SG sag line too. BUT the discharge side shows a linear drop of SOC and SG. I don't understand what exactly PT is saying or where it fits in here
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If an inverter is going to be used or the user is a full time RV'er, then they may benefit from maxing out all available unshaded space, and they should ignore the 150 watt suggestion. They should NOT ignore the 60 watts per 100, unless they use bank switching (I do use it).
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It doesn't matter what the AH usage is composed of, inverters or LED lights. An AH is an AH and the daily AH usage from whatever cause is what we start with.
I am not including the battery requirement to be equalized as a solar requirement. PT keeps sliding that in as though the only way to equalize is with solar, so you must have enough solar to do that too.
I am saying the solar requirement is to replace the daily AH usage to get back to 100%. You don't need to equalize to get back to 100. Yesterday I got back to full baseline SG 100% before dark on solar alone with the last few hours of daylight in Float at 14.4 volts. (with 255W on a 458AH bank)BFL13 wrote:
So now you are saying the four batts will need more amps (and so a higher wattage array) than the two batts to cover the "higher" losses to do the same AH in the same time. This is a 180 in your story!
