What is your Reserve for Power Outages setting?

[MJ_CA_2019]

I'm curious what % of your PW you reserve for power outages and your rationale behind it.

I have a 12.6 KW (DC) solar system with 3 powerwall 2 (Gateway 2).

My system PV system has produced more than usage in Feb, March, April, May of this year so far.
I am on PG&E TOU-B (4-9 pm Peak).

Before joining this forum I was leaving my reserve at 10% - 15% and hoping to be "off-grid" the most possible.
Now I'm not so sure since it seems like most of you leave your reserves higher.

Thanks in advance for the discussion!

 

[zanary]

I have 3 powerwalls, so I leave mine at 33%, so I can reserve almost one Powerwall for PG&E power failures, and then I use 66% of the capacity to offset the high cost.

 

[getakey]

I'm basically the same, but set at 30% so my vote is in the 21 to 30.
However, in this heat wave and fire danger, I put in back up mode until 6pm. After that switch back to Cost Savings as I know I can still make it through the night if power failure. Still hot from 6 to 9

 

[zƬesla]

Answers may not be apples-to-apples as it will depend on how many PWs, how much daily usage, PV generation, ???

 

[miimura]

I change mine by season. Between 25% in the Summer to 75% in the dead of Winter. The idea is that when my daily solar generation drops below my Peak period usage, I would rather the SOC stay near the top as it bounces off the Reserve every day. Headroom above Reserve is only slightly larger than the best solar production possible for the day. Keep in mind that I have two PWs and a small solar system.

 

[gpez]

Ah sorry, probably screwing up your poll here - I use mine only for backup.

 

[wjgjr]

I'm in the 91-100% (backup only) category. No TOU rate and full net metering, so no benefit to running off battery. In fact, because of the 90% round-trip efficiency, it makes more sense to export to the grid than to try and be self-powered.

 

[jjrandorin]

Answers may not be apples-to-apples as it will depend on how many PWs, how much daily usage, PV generation, ???

The discussion itself as to "rationale why" might be useful, but because we all have not only different PV systems, and possibly different amount of powerwalls, we all DEFINITELY have different home loads, and different amounts of PV generated even from systems with similar size.

With that being said, I change it depending on what I think it would take for my system to carry my home load through the night, until morning, if I lost power after I went to bed.

 

[getakey]

I'm basically the same, but set at 30% so my vote is in the 21 to 30.
However, in this heat wave and fire danger, I put in back up mode until 6pm. After that switch back to Cost Savings as I know I can still make it through the night if power failure. Still hot from 6 to 9

I should have added that I'm still on a 2pm to 9pm Peak plan

 

[D3xDt3Reaction]

0% for now because of 110+ temps in AZ and 2-8pm peak period - trying to avoid a peak demand charge. I may bump it back up when the temps come down but the system generally retains whatever was left on the table after the peak since it is set to cost savings mode. The remaining charge after the peak acts a little like a reserve effectively.

 

[MJ_CA_2019]

Does anyone make their selection with cycles or longevity of the PW in mind?

 

[destructure00]

0% for now because of 110+ temps in AZ and 2-8pm peak period - trying to avoid a peak demand charge. I may bump it back up when the temps come down but the system generally retains whatever was left on the table after the peak since it is set to cost savings mode. The remaining charge after the peak acts a little like a reserve effectively.

Same, I bought mine specifically to be Self-Powered during the 3-8pm demand window. Whatever's left over at the end of that is a bonus. I'm only 3 days in but with temps above 110, A/C running nearly all afternoon, and solar taking up some of the slack earlier in the afternoon, it seems like my worst case scenario is to end each day with around 30% remaining. 2 PWs with 11.4kw solar.

 

[Sonus]

For me is whatever gets me through the night, so it changes each session.

 

[woferry]

Currently 4% for me, ran at 0 for the majority of the almost year and a half that I've had the system. 10.4kW of solar inverters, 1 PW. My overnight usage is low enough that my fully-charged PW can power the house from sundown to sunup almost every day of the year. So any Reserve value above 0 just means I'm more likely to go back to the grid when I could have avoided the grid entirely, outage or not the sun would be up before I ran out of battery, so I saw no point in maintaining any Reserve.

A few very overcast/rainy winter days (probably less than 5 this past winter) did not have enough production to fully-charge my PW, meaning the next day it might run out. Since those stormy days are ones where an outage might be more likely, I started trying (if I remembered) to raise the Reserve to 20% on those days, so that I could at least have some warning (and perhaps reduce usage enough to last the night) if the grid went out.

I very recently changed to 4% over 0, having just started recording the total_pack_energy value from Tesla's Owner-API, and noticing that the value takes a decent hit (though generally recovers) every time I hit the 0% Reserve (with extra portable AC and whole house fan usage this hot summer there have been a few days where I hit the Reserve within 10-30 minutes of sunup). I was curious whether it was 0% or hitting the Reserve at all, so I first tried 1% and didn't see any change, then 2% same, then 4% and I haven't seen the dip since (though I only hit the Reserve once since). I should try 3% to see what it does, though I've turned some unnecessary things off since the 2-day power outage on my street this past weekend and with the ongoing heat/risk of power outages, so I haven't gotten close to the Reserve the past few days.

 

[getakey]

I have been switching to Backup only due to the fires and switching back to cost-savings around 6ish. Did same yesterday. After switching to cost savings I checked it about 45 minutes later and it was still in backup. Odd, as it usually switches over in a few minutes. Since I was pulling grid peak rates I clicked self-powered and it did change. Forgot that I did that and ended up charging the EV from the battery

 

[Troglodytes]

Install happened in late-May. From July 9th PTO I went 35 days self-powered. Then the weather turned consistently cloudy the last few weeks. Sad day to start using some grid again. Since that day I have varied the setting between backup-only to allow the Powerwalls to fill completely and 20/30/40% reserve depending on presumed over-night energy usage needs.

Another reason I switch to backup-only is to avoid house battery to MY battery charging. Prefer the car to be charged with solar only.

Also, @MJ_CA_2019 mentioned 'cycles or longevity' of the batteries. I have gone back and forth on how to handle the battery usage and haven't arrived at a conclusion yet. Warranty says 70% energy retention at 10 years. I expect that for my system I'll end up adding a fourth battery just to cover the loss of retention at some point in the future. Less important to do with my utilities current net metering option, but this is expected to change in a consumer negative way in the next few years.

 

[JPP]

I would usually keep is at 25% (2 PWs, 16kW solar PV), to cover a short outage (like a downed power pole, or something simple and local) But lately here in NoCA I need to plan for Unplanned outages that would not trigger Storm Watch, so now I keep it at 70%. Yes, loss of the benefit of Time Based Control and more cost to me at peak time/$$ (on PG&E EV2-A), but peace of mind is important.

 

[GaitherBill]

I've decided to leave ours in Backup Only Mode.

We have full NetMetering here, it will maximize our dollars with the electric company.

 

[MJ_CA_2019]

I've decided to leave ours in Backup Only Mode.

We have full NetMetering here, it will maximize our dollars with the electric company.

So no TOU Bill? If so, that makes perfect sense to me.

 

[getakey]

odd that Net Metering means different things with different utilities