Battery selection for large off grid system

[karrak]

Cheese and Rice trying to take 23 to 34 Kwh/day from a 27 Kwh battery is as stupid as stupid gets. For a lithium battery, they are sized for 4 day antinomy which yields the same usable 3 days of a Pb battery sized for 5 days. Clouds and rain re going to happen. That is why you need 5 days of autonomy and a generator. Based on just 20 Kwh/day would require a 1600 AH LFP battery at 48 volts. That sucker would cost you 3 times as much as a PB battery and not last as long. Stupid is what stupid does.

The OP has said he is happy to use a generator, if this is the case he could probably save allot of money by sizing the LFP battery so that in an average night he uses around 50% of the stored charge. If as he says he will only be running a fridge, freezer, lights and other small loads during the night there is no way he will be using 13.5kWh (50% of 27kWh). I would think that most of the time with such a large solar array in the tropics he will be able to recharge the battery on the next day. On the days that there is not enough sun and the battery SOC gets to less than say 20% all he has to do is run the generator and boost the battery SOC to around 40%-50% so there is still plenty of space in the battery to be charged from the sun.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

[max2k]

Yes, bad contacts at any power level can lead to a disaster. Have to make sure you have the appropriate cable and cable terminations.

Here is a graph from Winston
WinstonCycleData.jpg
For some real life data I know of two off-grid systems in Australia that have enough solar to charge at a maximum rate of ~0.4C. One system is about the same age as my system and the other is slightly younger. Both these systems have done over 1000 cycles and are still like new except for the failure of one cell in one of the systems.

As far as I can see the main determinants of battery life for LFP batteries are temperature, total amount of energy cycled through them and storage at high SOC.

Simon

Off grid 24V system, 6x190W Solar Panels, 32x90ah Winston LiFeYPO4 batteries installed April 2013
BMS - Homemade Battery logger github.com/simat/BatteryMonitor
Latronics 4kW Inverter, homemade MPPT controller

This looks very interesting, thank you for sharing!

[Sunking]

The OP has said he is happy to use a generator, if this is the case he could probably save allot of money by sizing the LFP battery so that in an average night he uses around 50% of the stored charge.

Get lost Karrak, you hare dangerous. Take a hint, the Mods do not want you here. You came here looking for trouble, and guess what you found?

Winston Chi-Com LFP are the bottom of the bucket batteries. If you know how to read graphs, and you do not, it is very clear they have extremely high resistance. They cycle claims are fiction. Have it never occurred to you why they have gone bankrupt before? Not to mention about to go underr again? Get a clue. We all know you sell Chi-Com crap out of Australia. Shall I give them your sales contact info?

Now get lost.

[Joe Silver]

Thanks in advance for your comments.

I took a look at my estimated loads, and what I found is:
Total watts used in a 24 hour period is 13200 (7700 in day and 5500 at night).
I think this will translate to somewhere around 24 of a big ol 2000 amp/hour, 2volt FLA batteries system. Where I can use suggestions, is can I use generator support to lower my battery capacity by 25%? If so, is this done by following COlsens system and trial & error?

Should I consider the LiFePO4?

Is all the stuff on Alibaba junk? https://www.alibaba.com/product-deta...400069037.html and you get what you pay for? I don't plan on buying Chinese, but are most of you in agreement that ALL Chinese manufactures falsify claims and make inferior products? This is just a secondary question, so don't let it distract from the main "design" question. Unfortunately, in my youth I have been a sucker for Big Lots, Odd Lots, Harbor Freight, etc

[max2k]

Thanks in advance for your comments.

I took a look at my estimated loads, and what I found is:
Total watts used in a 24 hour period is 13200 (7700 in day and 5500 at night).
I think this will translate to somewhere around 24 of a big ol 2000 amp/hour, 2volt FLA batteries system. Where I can use suggestions, is can I use generator support to lower my battery capacity by 25%? If so, is this done by following COlsens system and trial & error?

Should I consider the LiFePO4?

Is all the stuff on Alibaba junk? https://www.alibaba.com/product-deta...400069037.html and you get what you pay for? I don't plan on buying Chinese, but are most of you in agreement that ALL Chinese manufactures falsify claims and make inferior products? This is just a secondary question, so don't let it distract from the main "design" question. Unfortunately, in my youth I have been a sucker for Big Lots, Odd Lots, Harbor Freight, etc

post #49 and now you decided to reveal your loads ? Better later than never
if I understood you correctly 13,200 Wh of loads would require 26,400Wh of battery system to support. Using 48V system (24 2V cells) this would require 26,400 / 48 = 550 Ah from the battery system. Yea, I think you can go down by 25% .

If those 13, 200 were Watts (not likely as you simply added them up) then it is much worse:

7,700 W x 12 hr = 92,400 Wh for the day
5,500 W x 12 hr = 66,000 Wh for the night

92,400 + 66,000 = 158,400 Wh for the 24hr period.
2 x 158,400 / 48 = 6,600 Ah

[Mike90250]

....Should I consider the LiFePO4?...

Not yet. Get yourself broken in with a Lead acid (affordable) system, make sure it behaves the way it ought to, and then in 3-4 years, make the move to LFP

[Sunking]

I took a look at my estimated loads, and what I found is:
Total watts used in a 24 hour period is 13200 (7700 in day and 5500 at night).
I think this will translate to somewhere around 24 of a big ol 2000 amp/hour, 2volt FLA batteries system. Where I can use suggestions, is can I use generator support to lower my battery capacity by 25%? If so, is this done by following COlsens system and trial & error?

Sure you can use a generator, makes perfect sense for you. If battery power were not expensive enough, using a generator makes it more expensive and you get to loose more money. At 13.2 Kwh-Day you would need . 1400 AH battery @ 48 volts.

Should I consider the LiFePO4?

For you Sir absolutely, you love loosing money.

For 13.2 Kwh per day using LFP would require a 4S 1100 AH LFP set up. Those batteries will cost you around $24,000, plus another $1000 for support equipment like a BMS and LVD. They might last you 3 to 5 years if you DO NOT MAKE A SINGLE MISTAKE.

No sir FLA would not work good for you. I mean what the hell would you do? They cost less, in your case, a 48 volt 1400 AH real high end 8 to 10 year FLA battery would cost you $13,000. No possible way saving you $11,000 would make you happy. Lasting longer for twice as long would just make you miserable. My bet being your first time with batteries period, especially LFP, you will destroy them in less than a year. That will make you real happy buying replacements.

No sir you are a Pigeon waiting to be plucked. Perfect candidate for Karrak and LFP batteries.

[Joe Silver]

Thank you, I appreciate the response.

[max2k]

Sure you can use a generator, makes perfect sense for you. If battery power were not expensive enough, using a generator makes it more expensive and you get to loose more money. At 13.2 Kwh-Day you would need . 1400 AH battery @ 48 volts.

SK, could you please elaborate why 13.2 kWh requires 1400 Ah battery @ 48V The total energy they store would be 67.2 kWh which is more than x5 times required. I understand x2 requirement from # of cycles point of view but this seems excessive or is this for the case when there's no sun out there for 2 days?

[Sunking]

SK, could you please elaborate why 13.2 kWh requires 1400 Ah battery @ 48V The total energy they store would be 67.2 kWh which is more than x5 times required. I understand x2 requirement from # of cycles point of view but this seems excessive or is this for the case when there's no sun out there for 2 days?

Minimum requirement for full time use.

Three real good reasons to do this.

1. 20% DOD per day gets the best money's worth on $Kwh paid in battery cost. A battery cycled 20%/day can have up to 1500 Cycle Life in them or 5 years. Hit them at 50% and you are down to 1 or 2 years. Less than 20% does not gain you much and the sweat spot is 20%.

2. Never ever discharge your batteries more than 50% before being fully recharged. Once you go below 50% and aging accelerates. those soft lead sulfate crystals you to dissolve back into solution now begin to harden and fix themselves on the plates permanently leading to sulphated batteries and premature failure.

3. Now stop and think. 20% gives most bang for the buck, and at 50% DOD is only 2.5 to 3 days without Sun before I must go dark and recharge. 5 day autonomy gives you the best mix of value and minimises Generator Run Time which is more expensive.

Your way pnly gives you one cloudy day and you need to shut down and wait for a full day of sun before you light up again. WTF you going to do when it is cloudy for a week or two. Treat your batteries like that and they last a year or two at most.

[max2k]

Minimum requirement for full time use.

Three real good reasons to do this.

1. 20% DOD per day gets the best money's worth on $Kwh paid in battery cost. A battery cycled 20%/day can have up to 1500 Cycle Life in them or 5 years. Hit them at 50% and you are down to 1 or 2 years. Less than 20% does not gain you much and the sweat spot is 20%.

2. Never ever discharge your batteries more than 50% before being fully recharged. Once you go below 50% and aging accelerates. those soft lead sulfate crystals you to dissolve back into solution now begin to harden and fix themselves on the plates permanently leading to sulphated batteries and premature failure.

3. Now stop and think. 20% gives most bang for the buck, and at 50% DOD is only 2.5 to 3 days without Sun before I must go dark and recharge. 5 day autonomy gives you the best mix of value and minimises Generator Run Time which is more expensive.

Your way pnly gives you one cloudy day and you need to shut down and wait for a full day of sun before you light up again. WTF you going to do when it is cloudy for a week or two. Treat your batteries like that and they last a year or two at most.

Thank you, makes sense. I got spoiled with sun here in CA but you vividly reminded me how it was back in Canada where week or two without much sun is a norm. Come to think about it much of technology discussed here wouldn't work financially over there especially with their lower electricity rates.

[Sunking]

Thank you, makes sense..

You are welcome

Come to think about it much of technology discussed here wouldn't work financially over there especially with their lower electricity rates.

Does not work in many places period. Take away any of the subsidies and the whole house of cards collapses.

Take away Net Metering, and there are states that have no such mandatory nonsense, and there is no solar. Take away 30% fed tax credit and it goes away. Take away local incentives and it goes away. Build a local conventional power plant that provides jobs and inexpensive energy and it goes away. Solar is a subsidy for the rich and wealthy. Working class folks pay for it but cannot afford to benefit.

[J.P.M.]

You are welcome



Does not work in many places period. Take away any of the subsidies and the whole house of cards collapses.

Take away Net Metering, and there are states that have no such mandatory nonsense, and there is no solar. Take away 30% fed tax credit and it goes away. Take away local incentives and it goes away. Build a local conventional power plant that provides jobs and inexpensive energy and it goes away. Solar is a subsidy for the rich and wealthy. Working class folks pay for it but cannot afford to benefit.

And if solar is then left on its own and forced to grow up and make its own way instead of living, in effect, in the government's basement like a 20 something snowflake, it'll either get viable or die.

[Sunking]

And if solar is then left on its own and forced to grow up and make its own way instead of living, in effect, in the government's basement like a 20 something snowflake, it'll either get viable or die.

Works for me. Scary thing is snowflakes want socialism. They have no idea what it is.

New School Requirements. Live in Venezuela or Cuba for 2 months.

[littleharbor]

I wouldn't mind a couple months in Panama.