I set my powerwall backup reserve to 100% - Does it matter?

[uscpsycho]

I'm on a flat rate plan and wonder if it makes any difference what I set my backup reserve to?

Before I had PTO I would set the reserve very low so that I would import as little as possible. But after I got PTO I set the backup reserve to 100% because I figured it doesn't make a difference what you set the backup to if you are on a flat rate plan. If I set my backup reserve to 20% all the excess power I produce (until I get to 100%) gets stored in my powerwalls for later use. And if I set my reserve to 100% then all the excess power I produce goes into the grid for later use. It should work out the same in the end. Right? Or am I missing something?

 

[EVRider-FL]

Depends on what you’re trying to achieve. If you set the reserve to 100% you’ll be drawing from the grid at night. If you set it lower you’ll be drawing from the Powerwall until you hit the reserve %. I have my reserve set to 20%, and for most of the year I don’t draw anything from the grid.

 

[RKCRLR]

By flat rate I assume you mean non time of use. You have a ~10% round trip loss (and some wear) when you consume from the powerwalls and recharge them. If you're on NEM2 or later you have NBCs (non-bypassable charges) when you send power to the grid and draw it back. So it depends on which costs you more.

 

[uscpsycho]

Depends on what you’re trying to achieve. If you set the reserve to 100% you’ll be drawing from the grid at night. If you set it lower you’ll be drawing from the Powerwall until you hit the reserve %. I have my reserve set to 20%, and for most of the year I don’t draw anything from the grid.

In your example, at 20% you don't draw anything from the grid and you send a lot less than if you set your reserve tot 100%. At 100% you draw and send much more, but the cost to you is the same. So why not leave it at 100% so you can have the backup reserve? Is your goal to have greater independence from the grid than having backup reserve? If it all works out the same in the end, I'd rather have my batteries always charged to 100% for backup in case of an outage. That's the main reason I got the Powerwall.

By flat rate I assume you mean non time of use. You have a ~10% round trip loss (and some wear) when you consume from the powerwalls and recharge them. If you're on NEM2 or later you have NBCs (non-bypassable charges) when you send power to the grid and draw it back. So it depends on which costs you more.

Yes, I mean non TOU.

So by leaving my batteries charged I'm actually gaining 10% efficiency? That's not insignificant so this is a better strategy than I realized. I assume I'm on NEM2 because I just got PTO this year. But I don't see anything that looks like NBC's on my bill. If I have those, would it say NBC on my bill? If not, what am I looking for? And are NBC's just a flat monthly charge like an access charge? Or do they go up with usage?

 

[yblaser]

In your example, at 20% you don't draw anything from the grid and you send a lot less than if you set your reserve tot 100%. At 100% you draw and send much more, but the cost to you is the same. So why not leave it at 100% so you can have the backup reserve? Is your goal to have greater independence from the grid than having backup reserve? If it all works out the same in the end, I'd rather have my batteries always charged to 100% for backup in case of an outage. That's the main reason I got the Powerwall.



Yes, I mean non TOU.

So by leaving my batteries charged I'm actually gaining 10% efficiency? That's not insignificant so this is a better strategy than I realized. I assume I'm on NEM2 because I just got PTO this year. But I don't see anything that looks like NBC's on my bill. If I have those, would it say NBC on my bill? If not, what am I looking for? And are NBC's just a flat monthly charge like an access charge? Or do they go up with usage?

If your provider is LADWP then you may not have any NBCs. LADWP as a publicly owned energy provider is not covered under the CPUC net metering rules.

 

[EVRider-FL]

In your example, at 20% you don't draw anything from the grid and you send a lot less than if you set your reserve tot 100%. At 100% you draw and send much more, but the cost to you is the same. So why not leave it at 100% so you can have the backup reserve? Is your goal to have greater independence from the grid than having backup reserve? If it all works out the same in the end, I'd rather have my batteries always charged to 100% for backup in case of an outage. That's the main reason I got the Powerwall.

It might work out the same financially, but I prefer to draw power from my Powerwalls than from the grid. I have 3 Powerwalls so even at 20% reserve I have sufficient backup.

 

[RKCRLR]

So by leaving my batteries charged I'm actually gaining 10% efficiency? That's not insignificant so this is a better strategy than I realized. I assume I'm on NEM2 because I just got PTO this year. But I don't see anything that looks like NBC's on my bill. If I have those, would it say NBC on my bill? If not, what am I looking for? And are NBC's just a flat monthly charge like an access charge? Or do they go up with usage?

Yes, you're gaining ~10 in efficiency by not using your powerwalls. If you're not on TOU rates, get 1 to 1 reimbursement for the power you send to and get back from the grid, and don't have any NBCs then you are financially better off leaving your powerwall reserve at 100%. You'll still have some parasitic losses just for keeping the powerwalls alive. It would probably be a good idea to cycle them every once in a while but I don't know the details on keeping powerwalls healthy.

I'm with PG&E and I'm not familiar with how other power companies operate.

 

[metalblaze]

I’m new to this, and still waiting for PTO. As of now, my 2 PWs (~14kWh system) is set to 20% reserve. I’ll probably maintain the same reserve capacity as: 1) we rarely have outages in our area (White Plains, NY), and 2) would like not to use the grid.

 

[Matt-FL]

For those of you lucky enough to have 1:1 metering, I agree with your logic. For those of us without (I'm at 1:3), I prefer to utilize the batteries as much as possible so I rarely touch the grid. With four PWs, that is generally very rare. However, it only takes about 2 full cloudy days before I'm tapped out, so don't believe Tesla's '9 days grid outage' sales pitch. When it is really cloudy, I *could* go the route of asking my wife to not run the dryer, but I'd rather live to survive another day....

I know EV people get range-anxiety, any *other* solar people get cloud-anxiety?

 

[metalblaze]

I know EV people get range-anxiety, any *other* solar people get cloud-anxiety?

Count me in this group: I "suffer" from both range & cloud anxieties!

 

[Grayson73]

For those of you lucky enough to have 1:1 metering, I agree with your logic. For those of us without (I'm at 1:3), I prefer to utilize the batteries as much as possible so I rarely touch the grid. With four PWs, that is generally very rare. However, it only takes about 2 full cloudy days before I'm tapped out, so don't believe Tesla's '9 days grid outage' sales pitch. When it is really cloudy, I *could* go the route of asking my wife to not run the dryer, but I'd rather live to survive another day....

I know EV people get range-anxiety, any *other* solar people get cloud-anxiety?

I have 1:1 net metering. Are you saying I should set reserve to 100%?

 

[Matt-FL]

I'm not saying that you should, more of that I understand the reasoning behind setting 100% reserve in a 1:1 situation. I think each person should look at their personal goals for their system and make the decision. I'm far from one to tell someone else what to do. Well, except my kids. In that regard, there is a difference between me telling and them listening. I might have that one worked out by the time they are 50. If anyone has any pointers in that area, well, this probably isn't the forum for that.

If I had 1:1 net metering, I'd probably consider a higher percentage, but probably not 100%. Maybe 60-75%. Certainly higher than the 20% I keep it at now.