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which custom mode you should choose for powerwall with net meter and no time based rates?

sirismile

Member
May 26, 2021
7
0
boston
After saw another post about battery degradation, and also about 80% efficiancy for the electricity need to charge PW and how much you have got when output DC.

This is only for the region do not have time based electrical charge and net metering in place.
It seems to me that backup-only option can be more cost effective. Am I right?

my reasoning (maybe im wrong, but would like to hear what other ppl thought)
1. we have net metering, so the extra kwh put back, you can have exact amount back to use. (no loss for PW to AC)
2. PW battery degradation can be far less since there is no need to cycle at night.
3. your additional backup juice can stay year round for additional backup power. you can set something like 80% to avoid damage the battery.
 

sirismile

Member
May 26, 2021
7
0
boston
What are your goals? If your goals are only to minimize cost and have backup power then yes backup only is what you are looking for.
the only drawback of stay in back-up mode is the battery at 100% and not idea for long term, maybe self-powered with 80% will be the best in such scenario.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,619
10,852
Riverside Co. CA
the only drawback of stay in back-up mode is the battery at 100% and not idea for long term, maybe self-powered with 80% will be the best in such scenario.

These devices have a 10 year unlimited cycle count warranty that states they will have at least 70% capacity at the 10 year mark, with unlimited cycles when charged by solar.

These are not the cars, where its a mileage or time warranty, and many people will go over the miles before the time elapses. I really dont get people stressing about degredation on these devices. You should WANT to push it so that if its going to degrade, it does so before the 10 years unlimited cycle timeframe.

Its not healthy for a battery to stay at 100% all the time either, so backup only isnt the answer. You are still going to be at 100% when your solar charges it to that percentage during the day, pretty much from march to october.

In an ideal world, you would hit 70% or more battery degredation sometime in year 8 or 9, so that you get replacement products at that time, right? Whats the point of babying them now so that you can hit 70% right at year 10?
 

eml2

Member
Sep 28, 2017
264
205
Massachusetts
I have my 2 Powerwall2 for more than 3 years. They are in the basement. Temp is between 55-70F.

I have been collecting data from my PW via local REST API for 3 years. But last August was my first time using Tesla's Owner API. One of the info is the Total Pack Energy.

On 8/22/2020, the Total Pack Energy is 27.333 kwh. On the same date, the battery.energy_import and battery.energy_export (obtained via local REST API) was 8974 kwh and 7952 kwh respectively.

Today, 6/6/2021, the Total Pack Energy is 26.997, battery.energy_import is 12707 and battery.energy_export is 11215.

Battery degradation is (27.333 - 26.997) / 27.333 = ~1.2%. That is after importing (12707 - 8974) = 3733 kwh, or 3733/27 = ~138 charge cycles.
 

Isletime

Member
Apr 3, 2013
34
1
Carolina Beach, NC
I have been wondering the same thing as the OP. With no time of use rates for my electric, and the lost efficiency of storing my energy daily, it just seems more efficient to take the credit from the local utility and not rely on my batteries to power the overnight hours. I agree it’s not a good idea to keep my battery sitting at 100%, but maybe cycling it down to 70-80%, and using my net metering credits would be a more efficient use of the power I’m generating.

I’m not worried about the battery degradation of full cycles, or counting on Tesla giving me free batteries in 9.5 years. Just want to get the most benefit and value from my install.
 
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pdx_m3s

Active Member
May 18, 2019
1,338
1,170
Portland, OR
Just have to ask, why did you get them in the first place? Clearly it wasn’t financial, so I can only assume it was for backup. If so, then backup is the right setting for you.
 
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BIC1

Member
Feb 19, 2020
89
16
Missouri USA
I have net metering and set PW for "backup only 100%." While I understand battery will live longer at 70-80%, that will suck if the grid goes out, somewhat defeating the purpose of having the PW. I leave it set at 100%, which means it's usually at 97-98%, rarely at 100%.
 

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