AGM or GEL Batteries? Which is best?

[SageOldmann]

Sage now I get different units of measure. is it 12 volt battery with 15 amps for 5 hours, or 15 amps at 120 volts. That is a factor of 10.

I'm so sorry if I did not make that clear. AND I found a serious math/typo that has followed me in my calculations. It's 5 amps of devices, not 15 amps, at 120 volts for 5 hours. NOW I have the correct number to plug in. Obviously this changes the battery capacity. Is it still the same formula, 5 days x Daily Watt Hours / Battery Voltage?

[Sunking]

I'm so sorry if I did not make that clear. AND I found a serious math/typo that has followed me in my calculations. It's 5 amps of devices, not 15 amps, at 120 volts for 5 hours. NOW I have the correct number to plug in. Obviously this changes the battery capacity. Is it still the same formula, 5 days x Daily Watt Hours / Battery Voltage?

Yes sir. No need to apologize. I assume by now you have figured out that math error was kind of a big deal huh?

5 amps x 120 volts x 5 hours = 3000 watt hours per day and that is a huge number. You are no longer looking at a 12 volt system. with a 15,000 watt hour battery., you are looking at a 24 or 48 volt battery system.

Minimum Panel Wattage = 1500 watts
MPPT Controller Size = 30 amps @ 48 volts or 60 amps @ 24 volts
Battery Capacity = 300 AH @ 48 volts or 600 AH @ 24 volt battery.

As it stands now, you do not have anything to work with.

[Sunking]

I think what you may be seeing or hearing is that Lithium is more efficient. It can charge faster at 1C versus 0.3C for Pb.

Who gives a crap AMPSTER? It is a Straw-Man Argument only Green Mafia and Pretenders would make to baffle folks with meaningless BS. You can charge some Lithium faster, others not as fast. Makes no stinking difference. Example if we are talking a 12 volt 100 AH battery, you are saying the Pb can only be charged at a maximum of 33 amps vs 100 Amps. Who gives a crap dumbass? Are you saying you are stupid enough to use a panel 5 times larger than needed? Only Green Mafia or an idiot would use 5 times more power than required.

Only thing you can do is give a stupid Straw-Man Arguments based on pure fantasy. Sorry but you are not going to get away with your BS here. Go somewhere else to baffle people with your BS. Not going to fly here, your busted, and extremely dangerous.

[SageOldmann]

As it stands now, you do not have anything to work with.

Well that is disappointing but I may be able to salvage this. Originally my wife agreed to solar for my equipment, which amounts to about 1,200 watt hours per day, if I allowed her to have some of it for her use as well in her girl cave. (LED tv, computer, etc.) That was another 1,800 watt hours per day. Based on the average usage for both of us that got me to the 3,000 Watt hour number. BUT If I show her comments from an expert with years of education and experience like you have, she may be reasonable and let me have what I need and give up on what she wants. I don’t think it would be a hard sell since it’s impossible for both of us to do this at the same time needing 3,000 watts hours every day. If my math is correct for my 1,200 watt hour needs that looks like a 500 Ah battery might work with my 12 volt system. Maybe???

I am puzzled by your use of "5" days in your formula. Why not 1 day, or 7 days? Is the 5 days based on averaging with little charging of the batteries on cloudy days?

You also said
“5 amps x 120 volts x 5 hours = 3000 watt hours per day and that is a huge number. You are no longer looking at a 12 volt system. with a 15,000 watt hour battery.”
How many Ah would a 15,000 watt battery be in a 12 volt system?
How did you get to the Minimum Panel Wattage = 1500 watts?
I'm intrigued by these numbers.

[SunEagle]

Well that is disappointing but I may be able to salvage this. Originally my wife agreed to solar for my equipment, which amounts to about 1,200 watt hours per day, if I allowed her to have some of it for her use as well in her girl cave. (LED tv, computer, etc.) That was another 1,800 watt hours per day. Based on the average usage for both of us that got me to the 3,000 Watt hour number. BUT If I show her comments from an expert with years of education and experience like you have, she may be reasonable and let me have what I need and give up on what she wants. I don’t think it would be a hard sell since it’s impossible for both of us to do this at the same time needing 3,000 watts hours every day. If my math is correct for my 1,200 watt hour needs that looks like a 500 Ah battery might work with my 12 volt system. Maybe???

I am puzzled by your use of "5" days in your formula. Why not 1 day, or 7 days? Is the 5 days based on averaging with little charging of the batteries on cloudy days?

You also said
“5 amps x 120 volts x 5 hours = 3000 watt hours per day and that is a huge number. You are no longer looking at a 12 volt system. with a 15,000 watt hour battery.”
How many Ah would a 15,000 watt battery be in a 12 volt system?
How did you get to the Minimum Panel Wattage = 1500 watts?
I'm intrigued by these numbers.

I have always used the 5 day multiplier to size a battery system. For me it is based on only discharging a battery 20% each day for 3 days and still give me a cushion of 40% SOC. Even that is pretty low for a battery to go but while it may shorten the life it will still be usable.

[SageOldmann]

I have always used the 5 day multiplier to size a battery system. For me it is based on only discharging a battery 20% each day for 3 days and still give me a cushion of 40% SOC. Even that is pretty low for a battery to go but while it may shorten the life it will still be usable.

I like the way you and Sunking think. I average 4.7 hours of sunlight for 202 days per year with 101 days of full sun and 101 days of partly sunny, so using the 5 day multiplier is just about right for me. So what do you think. Can I Make a 500 Ah battery bank work or should I re-think it all?

[SunEagle]

I like the way you and Sunking think. I average 4.7 hours of sunlight for 202 days per year with 101 days of full sun and 101 days of partly sunny, so using the 5 day multiplier is just about right for me. So what do you think. Can I Make a 500 Ah battery bank work or should I re-think it all?

A 500Ah system should provide a significant amount of power. If it will work will depend on if your estimation on daily watt hour usage is 20% of the battery system. If it is more then you run the risk of killing the battery system quicker then you wanted to.

We try to get people to try out their system using lower cost batteries as a test. If they are correct then they can eventually replace them with a high end battery system.

All I can say is using an off grid system is a crap shoot.

[Ampster]

Who gives a crap AMPSTER? It is a Straw-Man Argument,....

I will be happy to make corrections to any factual errors.

[Sunking]

I am puzzled by your use of "5" days in your formula. Why not 1 day, or 7 days? Is the 5 days based on averaging with little charging of the batteries on cloudy days?

Few factors involved, but mostly economics and practicality. Battery Cycle life depends on depth of discharge. The deeper you discharge than, the fewer cycles you can get out of them. Example a mid tier Trojan Battery at 20% Depth of Discharge will yeild you around 3000 cycle while at 50% per day down to less than 1000 cycles. At 20% DOD per gives you the most bang for your battery dollar. The otther sid eof th ecoin is how many days per year do you want to be without power. You run 50% DOD and just one cloudy day you go dark next day without sun, plus another day to recharge without a genny. So you got two choices sit in th edark, or spend money on genny fuel.

You also said
“5 amps x 120 volts x 5 hours = 3000 watt hours per day and that is a huge number. You are no longer looking at a 12 volt system. with a 15,000 watt hour battery.”
How many Ah would a 15,000 watt battery be in a 12 volt system?

5th grade math in in China, or 16-year Graduate level USA math. Battery AH = Watt Hours / Battery Voltage

How did you get to the Minimum Panel Wattage = 1500 watts?

General rule of thumb.Batteries are best charged at C/10 rate so C/10 rate on a 300 AH battery rate is 30 amps. 30 amps x 50 volts (48 volt battery) = 1500 watts.

It is all 5th Grade math, or Ohms Law. Another math problem you might explain to the wifey is Energy Return On Investment. All that means if I put in 1 unit of energy in how much do I get out of it. Anything you take off grid is less than 1. That means there are 3 things no one wants you to know about, especially Green Mafia.

1. Off-Grid Battery Power is going to cost you 3 to 10 times more than buying it from the Power Company the rest of your life.
2. You are a heavy polluter.
3. Wasting natural resources and energy robing your children blind.
3.Ohms-Law-Pie-Chart.jpg

[Arlou52]

General rule of thumb.Batteries are best charged at C/10 rate so C/10 rate on a 300 AH battery rate is 30 amps. 30 amps x 50 volts (48 volt battery) = 1500 watts.

Well if using a 48 volt battery requires 1500 watts of solar (30 amps x 50 volts = 1500 watts,) then does 30 amps x 12 volts = just 360 watts of solar? The math seems like it's better to use a 12 volt battery and just have 4, 100 watt panels.

[SageOldmann]

Well if using a 48 volt battery requires 1500 watts of solar (30 amps x 50 volts = 1500 watts,) then does 30 amps x 12 volts = just 360 watts of solar? The math seems like it's better to use a 12 volt battery and just have 4, 100 watt panels.

Is this right? I know I'm missing something here. My head is swimming with all these formulas and numbers. I failed basic algebra in high school. I'm just not a math guy. SunEagle says a 500Ah system would supply my power needs if I keep DOD at 20%. If I only need 1200 watt hours per day I can do this with around a 500 Ah battery using your 5 day multiplier, right? What am I missing here? I just know it's something simple and I'm just not seeing it.

[SunEagle]

Well if using a 48 volt battery requires 1500 watts of solar (30 amps x 50 volts = 1500 watts,) then does 30 amps x 12 volts = just 360 watts of solar? The math seems like it's better to use a 12 volt battery and just have 4, 100 watt panels.

A 48V 300Ah battery system can provide at total of 14400 watt hours. A 12V 300Ah battery system can provide 1/4 of that or 3600 watt hours.

If your daily usage is 3000 watt hours then that 12V battery system is too small and you will need something like that 48V 300Ah system.

[SageOldmann]

A 48V 300Ah battery system can provide at total of 14400 watt hours. A 12V 300Ah battery system can provide 1/4 of that or 3600 watt hours.
If your daily usage is 3000 watt hours then that 12V battery system is too small and you will need something like that 48V 300Ah system.

Ok that makes sense. But since my daily watt hours will be set at 1200 then what you said earlier seems to be true. I can use a 500 Ah battery with a minimum of 400 watts solar to charge it. Applying the 5 day multiplier to allow for cloudy days this 500 Ah battery should work for me as long as I stay under 1200 watt hours per day, right?

[SunEagle]

Ok that makes sense. But since my daily watt hours will be set at 1200 then what you said earlier seems to be true. I can use a 500 Ah battery with a minimum of 400 watts solar to charge it. Applying the 5 day multiplier to allow for cloudy days this 500 Ah battery should work for me as long as I stay under 1200 watt hours per day, right?

The only problem I see is that even with an MPPT CC 400watts of panel may yield a maximum of 30Amp but you should have about 50Amps available for charging that 500Ah battery system.

[SageOldmann]

The only problem I see is that even with an MPPT CC 400watts of panel may yield a maximum of 30Amp but you should have about 50Amps available for charging that 500Ah battery system.

Thanks SunEagle. This is all very educational. I'm curious about controllers as I move forward with several options. Is there a minimum and maximum range of battery Ah size and Solar panel wattage as far as the amp rating of a controller? For example will a 40a controller be just as efficient on a 300Ah battery with 400 watts of solar, as it would be with a 500Ah battery and 600 watts of solar? Or does it need to operate in a narrow range of Battery amp hours and solar wattage input?