Some design input appreciated!!

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Re: Some design input appreciated!!

Postby Gordon-Loomberah » Sun May 25, 2014 6:03 pm

No need to subtract the extra 10% for the DC to AC inversion, since LiFePO4s operate at better than 52V for 16 cells, giving you >8% more available capacity than David posted above. You have much more energy available from the system than with Lead-acid due to the greater charging efficiency, at better than 95%, including time spent in Float, as posted in the Lithium vs Lead thread I posted earlier.
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Re: Some design input appreciated!!

Postby Dex » Sun May 25, 2014 6:25 pm

i use 15kWhr/day

If i cycle them 50% DOD.....i need 30kWhr

have no idea how much they cost...so;

how much for lipo 48V 1000Ahr?
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Re: Some design input appreciated!!

Postby davidg » Sun May 25, 2014 6:30 pm

Gordon-Loomberah wrote:No need to subtract the extra 10% for the DC to AC inversion, since LiFePO4s operate at better than 52V for 16 cells, giving you >8% more available capacity than David posted above

Actually I was also taking into account losses in the wiring in the building as broad average. 10% is just a broad simple to % that's quick to work with. It not uncommon to have a 1-3% loss within the building LV wiring depending on where and what the load is at the time. ;)
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Re: Some design input appreciated!!

Postby davidg » Sun May 25, 2014 6:44 pm

Dex wrote:i use 15kWhr/day
If i cycle them 50% DOD.....i need 30kWhr

So 700ah cells by 16 of them for a 48V battery pack, it should cost under $20K roughly. That in theory should last at least 20 years or longer if 50% is all it/they ever get to, plus cost of a proper BMS.
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Re: Some design input appreciated!!

Postby offgridQLD » Tue May 27, 2014 3:39 pm

52kwh is 1000Ah at 52v
1000Ah were on sale last week when i looked but just put the price up from $1100 to $1200 each for 1000AH
http://www.evworks.com.au/index.php?product=BAT-LFP1000AHC

or $840 each for the 700AH cells
http://www.evworks.com.au/index.php?product=BAT-LFP700AH

You would need 16 of them for 48v

Remember when you say 15kwh a day so 30kwh for 50% DOD. This isn't really true. You don't need 30kwh for a 50% DOD as your only using your batteries capacity from late afternoon to the next morning (and then some for cloudy weather) So if your consuming 15kwh a day then its good to know how much of that is from 5pm -7am directly off batteries. So perhaps your only using on average 7.5kwh overnight so 15kwh would give you 50% dod but say 20kwh (400ah) would be better for cloudy weather.

I will be able to give a dollar - AH price direct from Sinopoly battery china soon. Though I expect it won't be much different there's bugger all margins in lithium batteries (it's a bit like car tyres ) but will see anyhow.


Personally think I only need 400ah at 48V (20kwh) storage (after coming from 1330AH of PB). With 8.2kw of PV. I will most likely go with 700Ah to give me 300AH (15.5kwh) headroom to charge my Electric car overnight now and then for convenience.

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Re: Some design input appreciated!!

Postby davidg » Tue May 27, 2014 10:26 pm

offgridQLD wrote:I will most likely go with 700Ah to give me 300AH (15.5kwh) headroom to charge my Electric car overnight now and then for convenience.

A set of 700ah x 16 turned here today, I love these things, there so easy to carry compared to PB for the same number of deliverable kWh's, only roughly 400kg's, so now to setup the pack with bms, busbars, etc in preparation for installation at site 8-)
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Re: Some design input appreciated!!

Postby Eckmen » Sat Jun 21, 2014 10:23 am

David,
Having read through lots of these forums, you seem to be very familiar with the SP Pros. I have just purchased one of these and will be installing in the next week. I'm running 3xOutback FM60's. Now I have never had anything to do with shunts so please excuse my ignorance. I will need to install one after the last regulator(between the last reg and SP Pro) on neg side so the SP Pro knows what's coming in yes? Also sizing questions. I have seen 200A 50mv shunts for sale for around $30. Would this be OK? Does the SP Pro just pick it up or is there extra programming after wiring in the small shunt wires into the inverter?
Sorry if these are silly questions! Just no experience with this.
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Re: Some design input appreciated!!

Postby Eckmen » Sat Jun 21, 2014 9:22 pm

Answered my own question by reading....
All fully adjustable via the SP Link under the 'Shunts' tab funny enough ! :roll:
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Re: Some design input appreciated!!

Postby Tracker » Tue Jun 24, 2014 7:54 am

Eckmen wrote:Answered my own question by reading.....

It's funny how in writing a question, you come to understand the answer.. ;)
..
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Re: Some design input appreciated!!

Postby Tracker » Tue Jun 24, 2014 8:16 am

offgridQLD wrote:...'. So perhaps your only using on average 7.5kwh overnight so 15kwh would give you 50% dod but say 20kwh (400ah) would be better for cloudy weather.......

..
I must say that I do wonder... with the PRICE of lithium set to fall and possibly dramatically, I wonder if it's better economy to go for the smallest possible, today, and be prepared for occasional generator use and a shorter life...
Then, when that shorter life expires, either a better size will be much cheaper, or, there may be an even better technology available... :idea:

PS... I especially wonder if battery technology will improve and cheapen, with the possibility of PV systems using batteries to grid feed when needed by the network...
..
.
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