Two Back-up only PW2's

[plucas777]

Hello,

I live in Florida and the main reason I got Powerwall's along with my solar was due to frequent outages during storm season and the prospects of having power after a hurricane (assuming everything still works in the aftermath). My question is, do I benefit in terms of powerwall longevity from being in 100% backup mode in the sense that I am not using up the 10,000 cycles as frequently as say, self-powered mode ?

If keeping fully charged causes faster degradation, are there things I can do to mitigate that ?

Thanks !

 

[bob_p]

If you are going to charge the PowerWalls off the grid, without solar panels, there are two negatives.

You won't qualify for the federal 26% tax credit - since that only covers PowerWalls installed in conjunction with solar panels.

The warranty for the PowerWalls is different for grid charging vs. solar panel charging.

One of the reasons we purchased our solar panels/PowerWalls was to provide emergency power during a hurricane, with the potential t o provide several days of power. Without solar panels, you'll only have 13.5 KWh of energy stored per PowerWall - and when that's gone, if the grid isn't back, you're down.

We briefly considered going with a PowerWall-only system - and decided instead to purchase enough solar panels and PowerWalls to provide us at least 50% of our normal energy use. During an extended outage, we believe we can reduce our energy usage enough to operate for several days (not charging our S & X, and disabling or reducing usage by pool pumps, HVAC, refrigerators, ...).

We've been operating for 2 months and have cut our energy costs by more than 50%, and based on our usage pattern so far, we may be able to get another 50% reduction by shifting to a "Free Nights" plan and using the solar panels & PowerWalls to power the house during the day - and when a hurricane is approaching shift to backup mode to have the PowrWalls fully charged before the storm gets close.

 

[plucas777]

Hey thanks for your response. I think you misunderstood. I have an 11.360 kW solar system. But I am now using the powerwalls in backup only mode. Always charged unless I have an outtage. Wanted to know how this affects the batteries long term. Keeping them always charged.

 

[jjrandorin]

In general, the battery technology I have read states that having batteries at 100% all the time is not good for them. Now, its unlikely that a powerwall stored at 100% is actually at 100%. There is likely some buffer.

So, its likely "fine". Even thought thats the case, for me personally, I would want to see the system working (charging and discharging), so if I was in your situation, I would probably set it to self powered with a high reserve, like 80% or something. I am not sure where you are getting the "10,000 cycles" statement, as when a powerwall is charged by solar, the warranty is "10 years, unlimited cycles, 70 % capacity".

How would you even know what the capacity is, if you dont use it?

Powerwalls charged from grid only have a power throughput assigned to the warranty, but ones charged from solar do not (unless tesla recently changed warranties after my install on jan 6th.)

 

[plucas777]

Thanks for that response, makes sense. Yea i am not sure where I got the 10,000 cycles from either.

 

[TheTalkingMule]

10-15 years from now Powerwalls(or equivalent product) will cost maybe $2k, so preserving them isn't really necessary. There are plenty of automated "storm warning" capabilities from what I understand, so you should be already in backup mode when those events occur.

Does your solar array produce enough electricity to cover you total consumption? If not, then certainly you should be pulling from your battery just to save at least a portion of that chunk of money you're sending to the utility.

 

[plucas777]

I spent about 3 months using powerwalls in self powered mode while waiting on the electric company to come out. Now I have net metering setup, so that is sufficient. When the thunderstorms return, I am sure I'll have ample opportunity to use them, however.

 

[plucas777]

And I hadn't factored in the lower costs of batteries in the future. That makes perfect sense as well. Thanks for that.

 

[KY-Lonewolf]

Your powerwalls will discharge/charge even when your have them in "100% Backup Only" mode.
I have had my four (4) powerwalls in "Backup-only" since November 1st last year.
My experience with them so far is that they use 0.23 kWh per powerwall per day in maintenance.
They do NOT charge every day. They usually charge once they drop to 96% SOC.
In my case so far, during these winter months, they charge every other day.
My powerwalls are located in an insulated garage and there has not been very many days where the garage temperature has dropped below 50 degrees (F) in this four month period.
We will see how they behave this summer in the warmer weather.
My opinion is that if you have a good net-metering program (1 for 1), and your electric utility does not charge you TOD rates, then you are just wasting energy running you powerwalls in "self-powered" mode because of the loss involved in the DC/AC/DC/AC conversion.

 

[plucas777]

Guess I didn’t look hard enough. Found some more insight here - Powerwall 2 calendar ageing in Backup-only mode

 

[plucas777]

Your powerwalls will discharge/charge even when your have them in "100% Backup Only" mode.
I have had my four (4) powerwalls in "Backup-only" since November 1st last year.
My experience with them so far is that they use 0.23 kWh per powerwall per day in maintenance.
They do NOT charge every day. They usually charge once they drop to 96% SOC.
In my case so far, during these winter months, they charge every other day.
My powerwalls are located in an insulated garage and there has not been very many days where the garage temperature has dropped below 50 degrees (F) in this four month period.
We will see how they behave this summer in the warmer weather.
My opinion is that if you have a good net-metering program (1 for 1), and your electric utility does not charge you TOD rates, then you are just wasting energy running you powerwalls in "self-powered" mode because of the loss involved in the DC/AC/DC/AC conversion.

Hey I think I was going to end up going this route. I noticed the Powerwalls doing some funky algorithm all on their own and I figured it had to do with maintaining them properly. But your post confirms that, appreciate the insight !

 

[Dan123]

Hello,

I live in Florida and the main reason I got Powerwall's along with my solar was due to frequent outages during storm season and the prospects of having power after a hurricane (assuming everything still works in the aftermath). My question is, do I benefit in terms of powerwall longevity from being in 100% backup mode in the sense that I am not using up the 10,000 cycles as frequently as say, self-powered mode ?

If keeping fully charged causes faster degradation, are there things I can do to mitigate that ?

Thanks !

I have the same question, and I don't really have an answer for you. I hope that 100% (actually 97-99%) is actually not 100% but is set at a lower voltage level that doesn't cause premature degradation.

 

[charlesj]

If you are going to charge the PowerWalls off the grid, without solar panels, there are two negatives.

You won't qualify for the federal 26% tax credit - since that only covers PowerWalls installed in conjunction with solar panels.

...

I think the OP has solar so he will get the 26%.

 

[plucas777]

Correct charlesj, I made it in time for the 30% last year

 

[charlesj]

Correct charlesj, I made it in time for the 30% last year

Supposedly I am will get the difference from Tesla as it is in an email to me.