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Planing a PV-System with DIY-Battery => starting questions
#1
Hello everybody, hope you are doing great!

So i finaly decided to buy a Photovoltaik-System (solar? ...dont know the right term in english...)
Today a solar guy will come and make me an offer for this.

Best Case:
~5 - 6 kw/h solar panels
DIY battery.. not sure about the size for now
- If the panels produce more than needed it should be loaded into the battery, if battery is full its sold to the grid
- If production is too low - missing energy should come from battery, if battery is also low missing energy comes from grid
- If grid-power goes down i want my system to keep running (if battery is loaded)
I have a two story house (me and my parents) and i would say max current could be around 11kw on midday when everyone is cooking, fridges running....

i want to buy a solar-system which is able to handle a battery but i want to make the battery myself.
i did a bit of research and its insane what ready-to-use solar batteries cost! after a quick math i thought i can do this bigger and cheaper.
I want to buy new cells cause i dont have the time to go though the whole testing stuff.
I already found some sources for new samsung and LG cells.

So now to my main questions:
do you have any experiences in building power walls with new cells?
is it worth it of are costs too high and i should go for pre-made powerwalls?
Any special ratings my cells should have?

if its worth:
how exactly do i build my battery when it comes to BMS?
i understand how to pack the cells but i dont get this BMS stuff...
Is there some sort of schematic, drawing or whatever on how to build this?
im not sure if i want to build one large pack or multiple small ones.

lets say i want to build battery with 2 packs of same size... for example 2x 7S70p
and i want to use the batrium system => which components do i need and how to connect this stuff?

Hoping for some answers!

thanks
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#2
So you need to go & read all the batrium stuff you can find, read their FAQs & help sections. Lots of info there.

2x 7s70p packs won't be enough. For 11kW use, you will need to go 48V & >200Ahrs of cells.

Maybe look large prismatic cells, better to get a large system up & running sooner & way less work than 18650 cells.

Watch the youtube videos by Will Prowse, he covers many things well.
https://www.youtube.com/watch?v=_PgthByAYz4
100kwh-hunter likes this post
Running off solar, DIY & electronics fan :-)
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#3
(10-07-2020, 01:06 PM)Redpacket Wrote: So you need to go & read all the batrium stuff you can find, read their FAQs & help sections. Lots of info there.

2x 7s70p packs won't be enough. For 11kW use, you will need to go 48V & >200Ahrs of cells.

Maybe look large prismatic cells, better to get a large system up & running sooner & way less work than 18650 cells.

Watch the youtube videos by Will Prowse, he covers many things well.
https://www.youtube.com/watch?v=_PgthByAYz4

yeah at the first start this is very very confusing but the more i read the more i think i understand it... will keep digging deeper Smile

what should i look for when it come to the cells.
im searching for ceels with 2.5+ what should i look for when it comes to rated currend. should i search for cells rated for 10A? more? or is 5 enough?
other things i should keep in mind?
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#4
>So now to my main questions:
>do you have any experiences in building power walls with new cells?
>is it worth it of are costs too high and i should go for pre-made powerwalls?
>Any special ratings my cells should have?

Let's take the middle question first.   DIY powerwall (build the battery bank yourself with used cells) can save you a LOT of $ but it takes a LOT of time.   My system is 3yrs old and twice the size you are thinking.    So far, even doing 80% of it myself with a 1000+ hrs of personal time and 30% US tax credit,  I'm currently at a 21yr ROI on 11c/kwh electric company prices.   

For the battery part, doing it myself, I'm running $225/kwh.    If you buy a Tesla Powerwall, this Wikipedia page ( https://en.wikipedia.org/wiki/Tesla_Powe...nverter-21 ) has a "Powerwall Specifications" table that lists around $437/kwh.    This means that the larger the battery you build yourself, the more you can save.    

With 6kw PV array, you will likely land in the 20-40kwh battery bank size.    If you decide to go ahead with DIY you want to find cells that still have 80%+ (of original specs).   

And as @Redpacket mentioned, if you want to do DIY...  follow along this site for a few months and start watching youtubes - Will Prowse, @HPPowerwall, @DIY Tech & Repairs, @LtihiumSolar, @AverageJoe, @DavidPoz, @jehugarcia,  @Going Off Grid,  @HighTechLab ......   all of these have real-life info on DIY powerwalls and other related Solar Smile
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