How do I stop feeding the grid?

[Boatguy]

PG&E's net metering is awful so I'd like to keep my power to myself. I have a small solar array and two PWs. This raises two questions:

1) I've set my controller to "self-powered", but it keeps feeding power back to the grid when the PWs are not full. This morning the PWs are at 79% and it's sending about 1/3 of the power to the grid. Is there some max charge rate of the PWs that is limiting the ability to charge them?

2) What is the power loss of all the conversions?

DC > AC by the solar inverter
AC > DC to charge the PWs
DC > AC to use the power in my house?

Thanks,

Russ

 

[bmah]

I think "self powered" is indeed what you want.

Out of curiosity what version of software are you on? I run in cost-savings mode (PG&E NEM1, so it still make sense for me to backfeed the grid), but I noticed on several versions of software up through 1.44.3 that the Powerwalls would start feeding the grid even when the Powerwalls aren't full. With the 1.44.4 it behaved more according to expectations, where it fill up the Powerwalls first, then do some combination of backfeed the grid and power my house. This feels like a regression in behavior that they then reverted.

Bruce.

 

[dortor4ev]

if the Powerwalls are cold they can't charge if they are below 50F or so…I don't know the exact cut off - or it could be bug in the powerwall software - but yes they should charge to full before sending power to the grid.

you say it's sending out 1/3 of the power to the grid? so the powerwalls are charging? just now at 100% solar - how much solar are you producing - each power wall only has a 30 amp breaker - so there is a limit as to how much power they can accept...if they can not accept "all" of the power you are generating then yes the excess power will flow to the grid since the Powerwalls might be at their charge rate limit.

 

[Dan123]

AC to AC power loss (which is what you care about) is about 10%. That's how much you lose by storing power in the PW for later use.

I don't know why it keeps feeding the grid while the PWs are not full. Typically, each Powerwall is limited to 5KW charging rate. I've seen some people complain about a 3KW limit. Sometimes you have to restart the PWs for changes to take effect.

 

[cwied]

The max charge rate when on self-powered and above the backup reserve should be 5 kW per Powerwall. As mentioned above, temperature can affect the charging performance. If the batteries are too hot or too cold, charging will be throttled. If the cooling system on the Powerwall is not working right, this can throttle charging too. If you never see the full 5 kW per Powerwall (when solar is delivering it), you should probably call Tesla support to have them check to see if their diagnostics show any problems.

Note that backup mode seems to throttle charging at about 1.7 kW per Powerwall for me.

 

[Boatguy]

Software version 1.44.4.

The PWs are in my garage which is maybe 60˚F.

At this moment the PWs are 81% full, the app reports 1.8kW from the solar panels with 0.5kW going to the grid and 1.2kW going to the PWs.

It shows nothing going to the house, which if frequently reports. During the day my consumption can be pretty low, but certainly not zero.

 

[jjrandorin]

Software version 1.44.4.

The PWs are in my garage which is maybe 60˚F.

At this moment the PWs are 81% full, the app reports 1.8kW from the solar panels with 0.5kW going to the grid and 1.2kW going to the PWs.

It shows nothing going to the house, which if frequently reports. During the day my consumption can be pretty low, but certainly not zero.

Sounds to me like your CTs are not connected properly...

I run my (2) powerwalls in self powered mode all the time, and the way they charge is, solar runs the house load, and additional left over solar energy goes to the powerwalls. Grid only starts to get fed when powerwalls get near full, which right now happens around 12:30 - 1pm on a sunny day.

 

[jboy210]

Software version 1.44.4.

The PWs are in my garage which is maybe 60˚F.

At this moment the PWs are 81% full, the app reports 1.8kW from the solar panels with 0.5kW going to the grid and 1.2kW going to the PWs.

It shows nothing going to the house, which if frequently reports. During the day my consumption can be pretty low, but certainly not zero.

Is it possible your current measurement is messed up and some of the current shown as "going to the grid" is actually going to the house?

 

[Boatguy]

Sounds to me like your CTs are not connected properly...

I run my (2) powerwalls in self powered mode all the time, and the way they charge is, solar runs the house load, and additional left over solar energy goes to the powerwalls. Grid only starts to get fed when powerwalls get near full, which right now happens around 12:30 - 1pm on a sunny day.

When you say "near full" is that 80% or 95%?

 

[Boatguy]

Is it possible your current measurement is messed up and some of the current shown as "going to the grid" is actually going to the house?

Certainly. I guess I could go out and look at the meter when it says it's going to the grid and see what the meter says.

 

[Boatguy]

Sounds to me like your CTs are not connected properly...

CTs?

 

[Davidja92]

CTs?

CTs are current transformers they are a black and white wire attached to a hollow square looking attachement. these go around your electrical wires to determine the flow of current. You say .5 kWh goes to the grid but 0 goes to your house doesn’t make sense so that sounds like the CT’s are installed wronged and that .5 kWh is most likely electric draw from your home and not going to the grid and yes you should be able to verify by watching your meter

 

[jboy210]

CTs are current transformers they are a black and white wire attached to a hollow square looking attachement. these go around your electrical wires to determine the flow of current. You say .5 kWh goes to the grid but 0 goes to your house doesn’t make sense so that sounds like the CT’s are installed wronged and that .5 kWh is most likely electric draw from your home and not going to the grid and yes you should be able to verify by watching your meter

Exactly my thought. Based on these forums, mis-installed CTs seem to be rather common with Tesla setups. And since the CTs feed the boxes that send values out via APIs, having them mis-installed means you are not measuring flows correctly and the API is sending incorrect information to the Tesla servers and eventually to the App on you phone.

 

[jjrandorin]

CTs?

@Davidja92 explained it much better than I could have, but based on the information you provided ( app showing zero draw for the home, which really isnt possible if you have a fridge hooked up or the main is on ), its likely that the things that measure and send data (the current transformers, or CTs) are not installed on the right set of wires.

Since moving them entails opening up your loadcenter (breaker box), and live wiring, I would not recommend opening that unless you are a person who is comfortable with your knowledge around electrical current, etc. Its possible that Tesla can remotely move the values to the correct location, from what I have read here.

I think installing the CTs can get a bit confusing for the people doing the install, because you have power coming and going from multiple places... power coming and going from solar, coming and going from powerwalls, and coming and going to the grid, as well as flowing into the home.

From my reading here, it seems slightly more likely that non tesla installers have a bit more issue getting these in the correct place than tesla installers do, possibly because tesla installers always install the same brand and same settings of these devices while other "tesla certified" installers work with multiple other brands most likely.

In any case, I know that, during my install, the installer (tesla installer team of 2 for powerwall add on) had the panel open, and was logged into "something", and one installer told the other one who was in the load center at the time "move XXX to YYY..... yep thats it, looks correct, now"... so they were checking CT locations and power flow in "the app" while finishing up.

Since its highly unlikely your home ever has zero draw, it says to me that the measurements are off, and the CTs monitor the flow, so... I think one of the CTs is on the wrong line.

 

[jjrandorin]

When you say "near full" is that 80% or 95%?

Hmm.. I think when they hit somewhere above 90% they start sending some power to the grid, if there is solar enough to power the house, and also continue to fill the powerwalls.

it appears to me that, as they get full, they want to charge slower, so power over "a certain amount" will start going back to the grid. This is going to depend on the size of your system, production, etc. Right now I generate around 32-34 kWh on a sunny day with peak generation being around 11:30 to 1:30 of around 5.1-5.6 kW showing in my tesla app as incoming solar.

My house draw during a regular day with my wife home and watching TV is around .8 to .9 kW so the extra goes to fill the powerwalls, and then to some to grid when mostly full and all to grid when full.

I think yours just isnt measuring correctly as I said in another thread but wanted to try to answer the question you asked me in the spirit of sharing found in this part of TMC

 

[Boatguy]

OK. Thanks for all the info. The house measurement is zero at times, but not all the time. It's 4:20pm now and the app shows 0.3kW from solar going straight into the house. So I'm not sure the CTs are entirely incorrectly wired as they do measure current to the house. For example when the hot tub pump kicks on it shows a big spike.

The 30% flow to the grid seems to be in the middle of the day. This is a small system, only 3.8kW. It's still winter, sun angles are low and even with clear skies I've never seen it put out more than 2kW so it seems unlikely that it's too much for the PWs to absorb.

I think the customization settings are correct and the CTs are basically wired correctly, but perhaps not entirely accurate. I'll try to look at the meter tomorrow and see how it correlates with the app.

I'll report back. Thanks!

 

[MorrisonHiker]

OK. Thanks for all the info. The house measurement is zero at times, but not all the time. It's 4:20pm now and the app shows 0.3kW from solar going straight into the house. So I'm not sure the CTs are entirely incorrectly wired as they do measure current to the house. For example when the hot tub pump kicks on it shows a big spike.

The 30% flow to the grid seems to be in the middle of the day. This is a small system, only 3.8kW. It's still winter, sun angles are low and even with clear skies I've never seen it put out more than 2kW so it seems unlikely that it's too much for the PWs to absorb.

I think the customization settings are correct and the CTs are basically wired correctly, but perhaps not entirely accurate. I'll try to look at the meter tomorrow and see how it correlates with the app.

I'll report back. Thanks!

The house measurement should really never be zero unless you've turned off all breakers to the house or you have physical switches on every device in the house. There's always going to be a refrigerator, light, alarm clock or something that is drawing power.

As others have mentioned above, it sounds like your CTs aren't configured correctly...or if they are, it's possible they weren't configured correctly when the Powerwalls were set up. When I first got my Powerwalls installed, things appeared to be great to me, showing household usage, solar generation, grid usage, etc. but we received a call from Tesla and they indicated the CTs weren't configured correctly. In our case, they were able to just leave the CTs where they were installed and remotely updated the Powerwall configuration. Once they did that, everything was finally reported correctly.

Last year, we started seeing some weird numbers. Tesla came back out and found part of one of the CTs fell off so it was only recording 1/10th the normal numbers. They were surprised it could be reporting anything. As soon as he reattached it, everything started reporting correctly again.

 

[Boatguy]

Maybe I have the problem reported by @MorrisonHiker . These were the numbers from yesterday:

Home usage: 11.3
From Grid: 7.7
From PW: 4
Solar: 6.2

Net from solar / PW = 3.6

That suggests the efficiency of the solar + PW is just 58% or that the reporting is wrong.

PS: I called Tesla and they say the system isn't activated and isn't producing anything. From all appearances the system is operational and it definitely cut in when there was a brief outage a couple of weeks ago. In any event I'll wait a few more weeks and maybe this will sort itself out.

 

[Dan123]

If your PV is producing 3KW, the house is consuming 1KW, but the

Maybe I have the problem reported by @MorrisonHiker . These were the numbers from yesterday:

Home usage: 11.3
From Grid: 7.7
From PW: 4
Solar: 6.2

Net from solar / PW = 3.6

That suggests the efficiency of the solar + PW is just 58% or that the reporting is wrong.

Does your electric utility provide information regarding your net energy usage? Can you check if it matches when the PW app is reporting?

 

[jjrandorin]

"
PS: I called Tesla and they say the system isn't activated and isn't producing anything. From all appearances the system is operational and it definitely cut in when there was a brief outage a couple of weeks ago. In any event I'll wait a few more weeks and maybe this will sort itself out.

Wait a sec, you are "burying the lead" here...

What exactly does the bolded statement mean? There is something missing here. Have you not gotten Permission to Operate (PTO) yet? "The system is not activated and isnt producing anything" as a Tesla statement needs more explanation. Is your system, or is it not, active? If it IS active, why is tesla telling you it isnt.

If tesla told me "your system isnt active" and I was expecting it to be active, there would be a long conversation there. This means to me that the statement they made did not surprise you, or you are just choosing not to talk about it. If you dont have PTO yet, and you were getting solar + powerwall at same time, it has been reported here that things are sometimes not setup properly on tesla's end until you get full PTO.

They dont seem to have an issue with talking to me about my powerwall only install (as attached to my pre existing solar) even though I passed permitting but dont have full PTO on the powerwall portion yet. that tells me that they are not as concerned about it when its just powerwalls attached to existing solar (because existing solar already has PTO).


In any case, please explain the "system not activated yet" statement by tesla... If you dont know why they said that, definitely call them back and find out. You dont want them thinking you are unsupported when you should be.....