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Li-ion vs Pb. What am I missing?


viceroy

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Saw a recent comment/rant on the forum about people buying "expensive" lithium batteries and pairing them with "cheap" inverters, and it got me thinking, are lithium batteries actually more expensive compared to the more traditional lead acids.

I don't believe they are, and here is why.
I have specifically written the below using the Omnipower batteries which I'm familiar with. Everything written below may be different for the different types of lead batteries, and I would love to hear everyones opinions on this.

My current setup consists of 8x Omnipower 200Ah batteries giving a usable power of 9600Wh. To replace this bank today would cost around R52k.*
An equivalent set of 3x Pylontech US3000B batteries gives a usable power of 9590Wh. To buy new costs around R58k.*
* I've excluded the costs of any sort of cabinets or cabling.

The Pylontechs also have a reported 6000 cycles to 80% DOD, while the Omnipowers have 2250 cycles to 50% DOD.
The Pylontechs should last at least twice as long as the Omnipowers

Then, the Pylontechs come with built in BMS, which the Omnipowers do not.
To me this adds to the value of the Pylontechs.

Finally, and one of the biggest advantage I see with the Pylontechs over the Omnipowers is that I can buy some now, and then buy some later to increase the capacity with no issues, while this cannot be done with the Omnipowers.

My feeling is that the Pylontechs might be a little bit more expensive up front, but they have advantages that far outweigh the cost difference.

Edited by viceroy
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The cost more or less of the US3000 Pylontech come to around roughly R0.8333 per kWh used over it's lifetime, which in turn is roughly 1/3 of the current cost you (in my case) currently pay your municipality.

A solar system is expensive to get it installed and up and running, after that, you should push everything you save on your electricity bill into a fund for your next repair/replacement, or even in your bond.

Then again, take a plot of land with no services, it would cost you roughly R175k up front to get power connected, after that you pay for usage.

For the same money you can get solar system installed and start expanding later. No monthly usage cost.

 

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20 hours ago, Wilfred said:

The cost more or less of the US3000 Pylontech come to around roughly R0.8333 per kWh used over it's lifetime, which in turn is roughly 1/3 of the current cost you (in my case) currently pay your municipality.

There is some debate around this. The trouble is that the real TCO (total cost of ownership) is a lot higher, plus the lifetime of the battery might be slightly exagerated for marketing purposes.

Just as a parallel example, look at the cost of a car. Suppose I go and buy a good secondhand Hilux for 300k. Total cost of ownership in the first year is then:

Devaluation: 20k (optimistic estimate)
Opportunity cost (cause that 300k could have been earning interest): 20k
Insurance: 10k (or thereabouts)
Services (cause it is out of motor plan): 3k
Fuel: 24k (assuming two tanks a month... ymmv).
License: 1k (usually slightly less)

So TCO for this vehicle is 78k a year, and if you drive say 20 000km the real cost per kilometer is R3.90/km. The reason you bought the car might have been because the fuel consumption was quoted as 12l/100km, or R1.90 per km 🙂

Now let's do the same math for the opportunity cost on the lithium battery, and keep in mind an argument someone else had here ( @phil.g00? ) that we should really look at the warranty terms, which suggests that many lithium batteries will be outside warranty long before they reached the advertised 6000 cycles... which makes you wonder what your odds really are of replacing that battery after 8 years instead of 15...

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So let's assume you get a mere 3000 cycles out of that battery. Then a US2000 module at 2kwh useable at a price of around 16k means 6000kWh for 16k. That's R2.66/kwh, which is very close to what Cape Town charges in their most expensive block. Plus opportunity cost. So this little exercise really depends a LOT on how well the batteries will hold up to their cycle life promises.

But that only proves that Lithium is not cheaper than grid power. The topic here is whether it is really cheaper than lead acid... and without doing any math again, I think they are at the very least on par, with Lithium probably winning out slightly. And there is the advantage of being lighter, charging and discharging faster, deeper DoD allowed. Lithium wins... though perhaps not by as much as marketers tell you 🙂

 

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A supplier will sell you what he have in stock and that stock will be the best you can buy for your money, otherwise he is not a good salesman, weather it is a lithium-ion or a lead acid battery. I have seen it when they wanted to sell those lead acid batteries to me and they don't believe in lithium-ion batteries. But let's get real, lithium have much more advantages than lead acid. Some are as you mentioned, the use of space, the DOD, etc.

I believe over the long run lithium batteries cost less than lead acid, plus some other advantages like adding another battery later on, how much later I don't know.

It seems that Gel/lead acid/flooded batteries last an avg of 4 years, I was quoted a bank of 9.6kWh in the region of R61k (can't remember if this was VAT incl or excl) with only half of it usable, at that stage for a similar amount of kWh storage the lithiums even came out a bit cheaper PER kWh, but on paper the lithiums won as it has so many more advantages than the "old" technology,  yes there is a difference between 50 AH, 74AH, 100AH and 200AH, etc.

From what I have tried to accumulate between the pro's and con's between the two, I can not imagine that Gel/flooded/lead acid batteries can be fun to have with all of the maintenance.

My cycles, and I am running off-grid as much as possible, is turning on average at around 0.75 cycle per day. I am sure the bigger your bank is with lithiums as well as other batteries the slower your cycles will turn. 

My batteries are most times at 100% in the afternoon and at the lowest point it ever reached once was 21%, most of the times the lowest point is 22%, recently it barely went down to 30%.

Weather you have lithium or other batteries, they need to be looked after to get the lifespan out of them.

  

Let's say I will get 6 000 cycles out of them (I don't really think so as we run higher temperatures than the sheet state (25 degrees), and let's say I paid R70 000 for 4x bricks, let us imagine that I use 14kWh per day.

6 000 x 14 =  84 000kWh used. R70 000/ 84 000kWh = R0,8333 per kWh used, is there something wrong with my math?

You pay upfront R70 000/14 = R5 000 per kWh storage, but the storage can be used 6 000 times. 

Or, 14 x 80% (DOD) = 11.2kWh usable. 6 000 x 11.2 = 67 200. R70 000 / 67 200 = R1.0416. This is the amount I pay for the use of my Pylontechs, cost per kW.

I don't pay the city council anymore (around R2.20 per kW) for the use of this power as it is generated by the sun. I just tried to take into account what these bricks are costing you over time and the usage over the time.

Yes the SOH will decline over time and I think at 60% SOH they are done. I have no idea when the SOH will start to decline.

If they will only last 8 years, then you have 8 x 365 cycles = 2920 cycles (close to lead acid with their 2 000 cycles, but they don't last 8 years). 2 920 cycles x 11.2 kWh = 32 704kWh. R70 000 / 32 704 = R2.14 per kWh, it is still cheaper than Eskom charges and you will not have an annual increase like Eskom. Is this making more sense? Then on the other hand with the smaller kWh storage in lead acids, and the calculation above, I can now understand why most lead acid batteries only last 4 years, they probably turn two cycles a day.

Now, you have a warranty for 10 years, lets take 10 years and a simpler calculation and hope that these batteries will last 10 years at least.

R70 000 / 10 years = R7 000 per year. R7 000 / 12 months = R583,33 per month. R583,33 / 30.42 (avg day per month) = R19,18 per day. R19,18 / 11.2kWh = R1.7125 per kWh used. My city council charge me R2.20 per kWh currently. 

I guess the same sort of calculation should be made with other type of batteries.

In my opinion lithium batteries are cheaper in the long run than other type of batteries, I don't have the experience with gel/flooded/lead acid to prove myself wrong. But it just seems that lithium batteries are more cost effective over it's lifetime than other type of batteries.

We are running the batteries at a higher temperature, I guess in winter time they will run at a lower temperature, I am in no way an electrician and don't know how exactly this will influence the cycles but lets say you have a 40% loss in cycles, then you should still at least get  3 600 cycles out of them. 3 600 / 365 = 9.86 years. It might still be cheaper than city council prices per kWh used. 

Maybe, like some technology has done in the past,  it will become cheaper as we are going forward, hopefully the same thing happens with lithium-ion technology.

@viceroy If you are committed to 3x US3000's, I wont even downscale if I were you. Just replace the battery bank lol. 

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On 2019/12/12 at 10:55 AM, viceroy said:

The Pylontechs also have a reported 6000 cycles to 80% DOD, while the Omnipowers have 2250 cycles to 50% DOD

Even simpler math.

R52 000 / 2250 cycles = R23.11 per cycle (omni batteries)

R58 000 / 3 600 cycles = R16.11 per cycle (pylon batteries), if you could only get 3 600 cycles out of them (1 cycle per day for 10 years) 

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2 hours ago, Wilfred said:

R70 000 / 10 years = R7 000 per year. R7 000 / 12 months = R583,33 per month. R583,33 / 30.42 (avg day per month) = R19,18 per day. R19,18 / 11.2kWh = R1.7125 per kWh used. My city council charge me R2.20 per kWh currently. 

Indeed, plus the opportunity cost. 70k invested at money market rates (around 6%) is 4200 a year, R350 a month, R11 a day, Pushing that per unit cost to R2.70 ish.

Now opportunity cost is an interesting thing. In Europe, people sell their cars or have only one, because they have good public transport. Hence the opportunity to NOT have a car is real and the cost of owning a car represents a real cost of said opportunity. In South Africa, I often think opportunity cost is one of those things you sometimes just have to ignore.

With load shedding and the losses incurred by especially businesses, this simply becomes a one-time expense... and the self-consumption enjoyed afterwards really can be considered "cheaper". Well, sort of. Decide for yourself 🙂

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