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How much should you pay for batteries ?
#31
isn't better to have a DoD of 65%, so you gain more Energy Units?
I must admit that i am pretty green about the EU, still reading thou.
It seems to be with a new cell you can have "just" 50.000 eu with a DoD of 50%
And 140.000 with a DoD of 65%.
80% was 90.000 eu or something.
Probably i got the numbers wrong, but 65% according to BU was the best.

btw if you dont mind asking: your solar panels?

Thanks in advance
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#32
(09-04-2019, 05:40 PM)100kwh-hunter Wrote: isn't better to have a DoD of 65%, so you gain more Energy Units?
I must admit that i am pretty green about the EU, still reading thou.
It seems to be with a new cell you can have "just" 50.000 eu with a DoD of 50%
And 140.000 with a DoD of 65%.
80% was 90.000 eu or something.
Probably i got the numbers wrong, but 65% according to BU was the best.

btw if you dont mind asking: your solar panels?

Thanks in advance

My solar panels - I have 24 x 285watt SolarWorld panels. These seem to 'actually' have the 25yrs and still get 80% power warranty.
Part of SolarWorld's warranty.....
-------------------------------------
B - Limited performance guarantee:
1. SolarWorld guarantees that the actual output of the product will amount to at least 97 % of effective output during the first year after purchase of the product and as of the second year after purchase of the product, the effective output will decline annually by no more than 0.7 % for a period of 24 years, so that by the end of the 25th year after purchase an actual output of at least 80.2 % of effective output will be achieved.
--------------------------------------------

I think of 65% DOD as a metric of how much energy you use out of 100% of the energy in your battery.    I use killowatt hours (e.g. 1,000watts for a hour) for my numbers/thinking.

My battery (for example) is 780ah and if you multiply that by volts (I use 52v as my monimal) you get 40,560wh.  If you divide that by 1000 you get 40.56kwh - e.g. 40kwh is my working number.    This means that (in theory) I could run a 1,000watt load for 40hours  (e.g. 40 * 1kw = 40kwh).  

65% DOD of 40kwh (i.e. 40kwh * .65) = 26kwh. 

BUT - I'm not concerned with 'using my battery'...    rather my goals are to use 100% of my PV power and prolong the life of my battery to get my $ back.    So my 'perfect' goal would be to use 100% of PV power during day and 0% DOD during night (battery would never wear out and just be there for catastrophic grid-down events).    However, since I'm off-grid its not practical to directly consume 100% of PV input during the day because of the PV power curve ...   i.e. low and hi watts am/pm, winter, clouds, etc.   So the battery is used to smooth things out.

I need 15kwh of battery power daily (in summer) to 'smooth things out' for my current configuration.    I could do an 15kwh battery and do 100% DOD every cycle - and the battery would wear out in a year?.    So instead I have a 40kwh and do a 37% DOD and hopefully the battery will last 10-15yrs.     Hopefully much longer than burning up smaller batteries one after the other.   

I agree that this formula of DOD vs cost of larger battery is NOT CLEAR AT ALL!!   But I'm hopeful that larger 18650 cell battery + low DOD will get much longer life span based on Battery University "How to prolong Lithium Ion" article/charts - https://batteryuniversity.com/learn/arti..._batteries Notice that not only low DOD but lower max charge (float) voltage helps prolong life as well.
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#33
(03-11-2018, 03:36 PM)DarkRaven Wrote: That's what I've been saying almost from the start. And it's even more complicated because how do you value your time? How do you value the ecological impact? It's not easy at all to make a sound calculation that gives you a result that you can use to make up a definitive yes or no.

Paying for used batteries is already a bad start. You have to get them free or for a very low cost, we're talking about cents per piece. If you don't and pay the insane prices some people ask for then you have to increase the value you see in using reclaimed cells because otherwise this is already a bad economical decision before you have even started.
And then, if you decide to do it, you have to price in your work hours. Reclaiming 18650s is a very inefficient way to get cells to build some energy storage.

You can buy big cells today at 1.00 to 1.50 EUR per Ah that can be assembled into a battery in a matter of minutes and will give you thousands of cycles.
You first have to take into account the cost of the battery and divide this by your expected cycle life energy. You have to calculate the equivalent £/$ per kWh of storage. The cost per kW is in part irrelevant at this stage, otherwise buy a supercapacitor.
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#34
(09-13-2019, 10:56 PM)BAILIYAT Wrote:
(03-11-2018, 03:36 PM)DarkRaven Wrote: That's what I've been saying almost from the start. And it's even more complicated because how do you value your time? How do you value the ecological impact? It's not easy at all to make a sound calculation that gives you a result that you can use to make up a definitive yes or no.

Paying for used batteries is already a bad start. You have to get them free or for a very low cost, we're talking about cents per piece. If you don't and pay the insane prices some people ask for then you have to increase the value you see in using reclaimed cells because otherwise this is already a bad economical decision before you have even started.
And then, if you decide to do it, you have to price in your work hours. Reclaiming 18650s is a very inefficient way to get cells to build some energy storage.

You can buy big cells today at 1.00 to 1.50 EUR per Ah that can be assembled into a battery in a matter of minutes and will give you thousands of cycles.
You first have to take into account the cost of the battery and divide this by your expected cycle life energy. You have to calculate the equivalent £/$ per kWh of storage. The cost per kW is in part irrelevant at this stage, otherwise buy a supercapacitor.

Agree with this comment; however, the problem I have is the 'expected cycle life energy'.    The Battery University "How to Prolong Lithium-based Batteries" - https://batteryuniversity.com/learn/arti..._batteries - has quite a range of info - such as the bottom charge that 75-45% SOC @ 20C may get you to 7,000 cycles (19.2yrs) and still have >85% capacity.     The upper charts show 2,400-4000 cycles with 3.90 as max charge level.    

We have Tesla (18650) batteries model 3 statement:  The Model 3 now has a battery pack guaranteed to retain 70 percent of its charge over eight years

We have Tesla powerwalls:  Unlimited cycles for up to 10 years.

For me, I've designed / running my system with the purple line (75-45% SoC) as my ideal -  and hoping for the best but will need several more years to even begin to verify any of the above Smile.
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#35
The voltage range around 20% to 70% DoD (80% to 30% SoC) does appear to be close to ideal, especially if you have mixed checmistry packs where a low SoC can be very damaging for some cell chemistries due to the relatively low voltage.

For typical recycled cells with older chemistry it may well be calendar life ageing and dendrite formation on low charge rates that cause the capacity loss. Monitoring pack IR (high enough accuracy and consistency of readings) could be an easy way to guage pack life expectations.... anyone any data for thier packs ?
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
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#36
(Yesterday, 01:33 PM)completelycharged Wrote: Monitoring pack IR (high enough accuracy and consistency of readings) could be an easy way to guage pack life expectations.... anyone any data for thier packs ?

Is there an easy way to do this on pack(s) that are 'live' (in operation).  For example, can I run wires from my OPUS to +/- of one of my packs (while is online) and start recording the IRs? Maybe once a month and start collecting some data.
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