Planing a PV-System with DIY-Battery => starting questions

RayGenWurm

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Sep 13, 2018
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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
- Ifproduction 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
 
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.
 
Redpacket said:
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.

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 :)

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?
 
>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_Powerwall#cite_note-inverter-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, youwill likely land in the20-40kwh battery bank size. If you decide to go ahead with DIYyou want to find cells that still have80%+ (of original specs).

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