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rockies
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# Posted: 15 Dec 2018 07:35pm
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In reading through an article about the students at Virginia Tech University winning the 2018 Middle East Solar Decathlon (an international competition to design super efficient small homes) it mentions that the batteries used in their PV system were Lithium ferro phosphate.
In looking them up I found this article comparing them to traditional lithium batteries used today in off-grid homes.
https://www.newcastlesys.com/blog/lithium-ion-vs-lithium-iron-batteries
The wonderful thing about the Solar Decathlon competition is that all the teams seek out the best products and systems available in order to increase their chances of winning.
Has anyone tried lithium ferro phosphate (Iron) batteries yet?
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ICC
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# Posted: 15 Dec 2018 08:16pm - Edited by: ICC
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aka as LFP and LiFePo4. Lots of talk about then scattered about the forum, I think. Though I may be confused about that.
I have the GBS brand prismatic cased cells. I have two friends with some of them as well. We did a bulk purchase direct from a Chinese vendor on Alibaba almost 30 months ago. No complaints.
They are Chinese made as most lithium cells are. They are sold by some US sellers, many focused on the DIY electric vehicle enthusiast. Elitepower in AZ has done some off grid and large RV installations. I only linked to them as an example; never bought from them myself, though I did talk to them a few years back.
The linked to article is over three years old, BTW.
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creeky
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# Posted: 16 Dec 2018 09:41am
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LFP kind of fell out of favour. Basically it was touted as they thought it would turn out to be the cheapest to manufacture.
But as electric auto sales took off NMC, perhaps due to scale, became the cheapest chemistry. Add in the higher energy density ... and it looks now like longer lifespan.
NMC rules for now. (or Tesla/panasonic NMA)
LFP is very good for home systems. Very stable thermally. I find, from my very limited experience, that the cells seem to move around in balance more than NMC. If I had a LFP pack I would have a balancer on them.
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rockies
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# Posted: 16 Dec 2018 05:55pm
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Given the fact that many people operate their solar PV systems far out in the wilderness wouldn't having a thermally stable system be the most important objective? I mean, who's coming to the rescue if there's a fire?
Creeky, what do you mean by a balancer?
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creeky
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# Posted: 17 Dec 2018 11:24am
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The risk of fire is extremely low. Basically it requires a penetration of the battery cell. Nail, bullet, etc. LFP has shown it can survive even that event.
All battery cells need to be kept in balance (ie. the same voltage per cell). Lead acid usually self balances due to the high resistance to charging. Lithium, with no resistance, will go out of balance and may slowly creep further and further out. Once the battery is extremely out of balance you can get over or under charge of one cell. This may cause the battery to die. I have seen it three times now. In one case there was no sign of damage. In the other two the cells were/are very swollen.
Cell balancing can be done many ways. But with lithium batteries being quite stable (some of them very much so) there's usually little worry and manual monitoring can be enough.
Essentially, a good balancer will look at the high and low cells and transfer energy between them. Its usually millivolts. And time is your friend.
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