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Lithium ion battery bank info


mohammedbera2
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Hi guys

 

id like to know more about lithium ion battery packs

 

Im using about 24kwh /24h

About 10 hours on solar 1hour on battery 13 hours eskom

I have [email protected] panels

1x expert 5kva

and [email protected]

3 strings @48v

 

During day time running on solar

my inverter

set to only use 20%from battries (dod)

So from about 6/7 o clock switch to grid till about 8 /10 in the morning (depending on weather )

 

Was thinking of getting [email protected] +-1000ah

Will be about R100k

 

Heard about lithium ion and thinking maybe the way to go

 

(6.4kw lithium bank)

@R70k 1 square meter and 70kg

 

Instead of

([email protected] +-1000ah)

6 square meters @ 2400kg

 

But imnot sure of how it works with lithium ion

Acording to wat I've been told

6.4kw lithium = 1000ah lead acid

 

Please advise

 

 

Sent from my GT-I9500 using Tapatalk

 

 

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If I had 100k to blow on batteries it would not be lead-acid :-)

There are three lithium makers that I know of in the country, Blue Nova, Freedom Won, and these SolarMD guys. (There is also Tesla Powerwall, but that's imported). The other two guys both integrate with Victron equipment, and I recently learned that BlueNova also integrates on the MPPT level just like FreedomWon.

If you want to keep the axpert, I think this is your only option :-)

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35 minutes ago, mohammedbera2 said:

6.4kw lithium = 1000ah lead acid

That's a bit misleading really, because it depends at what voltage (and I assume you forgot the -hour suffix for the 6.4kwh lithium battery). Assuming that's 48V, then a 1000Ah battery is 48kwh, of which you would normally only use half, so 24kwh. The round trip efficiency of lead-acid is around 70%, bringing you closer to 16kwh. And then it will generally last around 2000 cycles or so at this DoD.

The 6.4kwh battery is therefore still less than half the capacity of the 1000ah bank, but because it will last at least twice as long, it can charge and discharge must faster, weighs less... it might make up for it.

I personally think a lithium bank makes much more sense in a hybrid self-consumption setup (such as Victron's ESS). Here the objective isn't to make it through the night, it is simply to use as much as possible of your own generated power, storing surplus in the battery during the day, and then just running the battery flat (down to 70% or so) every night and doing it again tomorrow. Lithium cells don't care so much about being left at a partial state of charge, it just needs a proper balancing charge every now and then. In such a setup, you size the battery not according to your total consumption, but rather to how much surplus you need to store, how big your bank account is, or what kind of outage you want to ride out... :-)

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I think the round-trip thing needs a bit more explanation. It doesn't impact the usable capacity of the battery so much as it influences the size of the solar array needed to recharge it. Because of the relatively poor efficiency charge of a lead-acid (especially as it gets close to full) a good 25% to 30% might be lost. So if you have an array capable of generating 24kwh of surplus energy, it might only succeed in putting 16kwh of that into the battery. So you need to oversize the array.

The lithium battery has a much better efficiency, which means you can use a smaller solar array, in other words, the savings on the solar array also comes into the calculation.

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10 hours ago, plonkster said:

The lithium battery has a much better efficiency, which means you can use a smaller solar array, in other words, the savings on the solar array also comes into the calculation.

Been thinking about this Lithium lead acid comparison.

Lead acid is annoying in the they say 100ah but you only supposed to use max 50%, right. Annoying.

My question: If I need say X kWh per day (forget the 50%, want the full 100%) , when comparing prices of good solid lead acid batteries to lithium, is lithium still that much better ito price?

10 hours ago, plonkster said:

Because of the relatively poor efficiency charge of a lead-acid (especially as it gets close to full) a good 25% to 30% might be lost. So if you have an array capable

This is only really applicable if you just have panels charging the batts, not so? If you have a load running same time, does it matter?

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3 hours ago, The Terrible Triplett said:

My question: If I need say X kWh per day (forget the 50%, want the full 100%) , when comparing prices of good solid lead acid batteries to lithium, is lithium still that much better ito price?

Gotta do the math in terms of cycles over its lifetime. Which is why you can't do 100% with the lead acid, that kills it too quickly, and the lithium batteries generally don't like it that much either. But lets say 80% DoD. Our benchmark T105RE can do 1000 cycles to 80%. The lithium battery can do 4000. So in terms of raw capacity the lithium battery can be 4 times the price and still come out on top based on all the otner niceties (charge rate, discharge rate, efficiency, weight).

At this moment, 1kwh of lithium costs just short of 10k. For 10k I can buy 4 x T105RE (approximately) which at 80% stores just over 4kwh. In other words, we're sort of on the brink of that 1:4 ratio already.

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1 hour ago, plonkster said:

Which is why you can't do 100% with the lead acid, ...

Jip, but not what I tried to ask.

Say a 100ah you only supposed to use max 50%. But 200ah at 50% is 100ah. 

1 hour ago, plonkster said:

... on top based on all the other niceties ...

Like you said, niceties (wants) versus not really an issue is it (needs). :-)

 

Why I am asking these questions is to ascertain when we reach the point where T105RE's for example are not really worth it anymore. Better to go lithium and score niceties on top of that.

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5 hours ago, The Terrible Triplett said:

Why I am asking these questions is to ascertain when we reach the point where T105RE's for example are not really worth it anymore. Better to go lithium and score niceties on top of that.

Okay, so 1kwh costs 10k and lasts 4 times longer than lead acid. At 80% DoD, it's 0.8kwh.

One T105RE a 80% DoD gives you 6*225*0.8 = 1.08kwh at R2500. So lets scale that by 0.8/1.08, or R1850 for the equivalent lead acid. Times 4 (which is naive, I'll explain below), so R7400, let's say R7500 to make it nice and round. That means if lithium prices comes down 25%, becomes a no-brainer.

Reason for naive thinking: Inflation means that the replacement battery you buy in 3 years (or so) costs 20% more, so repeating this process 4 times is more likely to cost 6 times the original rather than 4. That puts the total lead-acid price at 11k, vs the 10k for the lithium. By that line of thinking, it's already time to go lithium.

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On 3/18/2017 at 9:20 PM, plonkster said:

By that line of thinking, it's already time to go lithium.

Thank you Plonkster.

Last question: How tried and tested are Lithium for general solar users compared to Trojans?

Comment: I think the reason why we are not all running towards Lithium is the initial costs, and no load shedding, so no reason to spend more.

 

Now we must, for the sake of all the people reading this cool chat, that batteries do not make sense at all (off-grid and farmers and other generator users excluded) if you have Eskom in towns and cities with no power failures and a need to keep things going during said failures. 

And if you have to borrow money to buy batteries, don't. The financial reasoning has been put on the forum already.

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8 minutes ago, The Terrible Triplett said:

Last question: How tried and tested are Lithium for general solar users compared to Trojans?

Let me put it this way. It's been tried pretty well in cell phones and cordless power tools...

The tech is good. The important bit is the BMS, because of the relatively long strings.

Balancing is also much easier than with lead-acid. Or so I understand...

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On 3/18/2017 at 9:56 PM, plonkster said:

Let me put it this way. It's been tried pretty well in cell phones and cordless power tools...

The tech is good. The important bit is the BMS, because of the relatively long strings.

Balancing is also much easier than with lead-acid. Or so I understand...

cell phone batteries, power tool batteries, and lithium car batteries all have a BMS built-in. The tech has been around for many years, but as TTT says, the initial cost is quite high in comparison. IF you don't have to a take a bank loan to buy the Lithium batteries, then go buy them ASAP. Otherwise save some cash as the loan interest would kill the savings you made on the Lead Acid batteries.

 

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Speaking of power tools (off topic alert), I have a Ryobi cordless drill with Ni-cd batteries. And several cells are dead. A new pack will likely cost more than a new drill... so I wonder, what to do? In terms of weight, it's not much lighter than a 7Ah sealed lead acid, not much smaller either, and the lead acid (at 12V) isn't that far off the 14.4V of the Ni-cd pack, so I'm actually considering a conversion to lead acid! 7Ah vs the current 1.3Ah is also not too bad an upgrade.

Alternatively, what say you guys?

Edit: Quick search for Ni-cd cells on RS-components, R63.15 ex vat per cell. So 12 new cels, vat inc, around R865 to repack it. I think the drill was R550...

Edit2: Repack with NiMH, that looks more doable! 1200mAH cells, around R380 for 12 cells vat inc.

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4 hours ago, plonkster said:

Speaking of power tools (off topic alert), I have a Ryobi cordless drill with Ni-cd batteries. And several cells are dead. A new pack will likely cost more than a new drill... so I wonder, what to do? In terms of weight, it's not much lighter than a 7Ah sealed lead acid, not much smaller either, and the lead acid (at 12V) isn't that far off the 14.4V of the Ni-cd pack, so I'm actually considering a conversion to lead acid! 7Ah vs the current 1.3Ah is also not too bad an upgrade.

Alternatively, what say you guys?

Edit: Quick search for Ni-cd cells on RS-components, R63.15 ex vat per cell. So 12 new cels, vat inc, around R865 to repack it. I think the drill was R550...

Edit2: Repack with NiMH, that looks more doable! 1200mAH cells, around R380 for 12 cells vat inc.

That 2.4V would make a huge difference on the speed of torque of power tools.

 

Look at Lithium cells rather. +-16V from 4 cells in series.

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