Powerwall Lifetime and Legality Questions.

I am currently planning my DIY battery storage solution to complement my 10kWp rooftop PV. I am planning to connect my battery pack to an SMA Sunny Island 6.0 (my PV inverters are SMA products) inverter with a Home Manager 2.0 and use a REC BMS with a Tyco Relay, Shunt, temperature sensors etc. to supervise the pack. The pack is currently planned in a 14s140p configuration and I am considering to use a connection kit such as the VruzendDIY and incorporate cell fuses. All cells will be Samsung, Panasonic, LG or Sanyo cells with a capacity of 2000-2200mAh.

I have four questions considering this undertaking:

1. What lifetime/cycle life can I expect for this DIY Powerwall given that the cells are brand cells, but I don't know their previous applications. I am also planning to limit the voltage cutoffs to 3.3V and 4.0/4.1V. The pack will see a maximum discharge rate of 0.5C and probably somewhere around0.25C on average.
What are your experiences with DIY lifetimes?

2. Assuming the Powerwall is located in my garage, have you found/implemented solutions to keep the cells at ~20 C in the winter? How does your Powerwall perform in cold temperatures?

3. This is mostly a question for all the Germans on this board: Can the utility (Netzbetreiber/Stadtwerke) prevent you from installing a DIY Powerwall? Do they have a say in this? Are there restrictions? I would think not given that the grid connection point is managed by the Sunny Island 6.0. Did you change your house insurance to include the Powerwall?

4. Do you have any suggestions to change the components named above (BMS, VruzendDIY kit, Sunny Island....)?

I am looking forward to your replies andsuggestions.

Best,
Max

1. I don't think any of us are sure how long the packs will last. I have some packs going for 2 years now and haven't shown any signs of degradation. That being said, I have not done capacity tests before/after to compare. It just "seems like" there hasn't been any capacity loss.

2. Do not put batteries in your house or garage. My cells went below 0C for 2 years in a row now during the winter. They did not perform as well while the temperatures were down, but were fine after. I will have my outdoor shed insulated this year for next winter.

3. I don't live in Germany, so I can't comment on the laws - but regardless of where you live, PLEASE make sure you are doing everything according to code and permit requirements. Safety is a priority.

4. BMS - definitely Batrium. My opinion is a little biased since I haven't used anything else, but I absolutely love my Batrium. Do not use VruzendDIY... It's a junk product and their staff love to constantly spam spam spam the popular DIY channels (youtube, facebook, forum, etc). Complete garbage.

Sub 4V and >3.3V with 0.25C I would have though willl easily get over 1000 cycles before recycling - depends on what life they had before you get them. Unknwon + Unknown = More unknown.

If in the garage, think of a scenario where you pour a small can of petrol on the floor and light it (dont actually do this !!!). The resulting damage expectation is what you should then consider as to where you place your cells and what you are willing to loose should a problem occur. Shed+Flames=Family still alive.

Home insurance is something that will become an issue after the first few serious incidents unfortunately. At the moment if you tried to add the risk onto your house insurance specifically your isurance company would decine the risk, charge a massive premium or misquote the cover as it is DIY by an unqualified person on equipment lacking the full development of standards. Low voltage standards around the world evolved around the phone system, door bells, home alarms and low power capability assumptions (ethernet wires), not home batteries capable of over 10,000A fault currents. The standard are moving but far slower than technology and installation.

Different cell chemisty works without issue below 0C.... LTO and I'm quite happy to sleep next to 12kWh of batteries. I drew the line at putting them under the bed...

Thank you for your replies.
I want to clarify some things first. The "garage" is more of a brick shed that houses my PV Inverters, bicycles, and gardening tools.

2. I was thinking insulation and a temperature or BMS activated heating system, but given your experience that might be an overkill.

3. I have worked with new batteries on small electric race cars with 80kW engines and +20C current draw, so I absolutely agree: safety is paramount.

4. Thanks for the info on the VruzendDIY kit. Can you elaborate why you think it's garbage? I think REC and Batrium are pretty equivalent, but the REC BMS is easier to get in Europe

LTO would be nice (also cycle wise), but is a little more difficult to get

I figured something similar for cycle life, but am still a little worried about the effect of winter temperatures.

Basically you should never charge them under 0 C but storing and discharge is ok. And as mike already wrote, the performance below 0C won't be the same as at 20C.

https://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures

What is the logic behind keeping them at ~20 C ?
Li-Ion works great in cold weather, they can be discharged down to 20C.

Yeah, of course they can. But they won't deliver the same amps as by warmer temperatures.

batteryuniversity.com said:

The internal resistance of all batteries rises when cold

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