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Off Grid Test before PTO Solar + Powerwalls

Southpasfan

Member
Jun 2, 2019
371
493
Pasadena
So, it seems the sequence for a safe off-grid test would be:

1. 3 Powerwalls installed at 25% capacity.
2. House is pulling about 40kwh a day.
3. 16.32 system probably will produce about that.
4. Step One: At around 8 a.m. turn on Powerwalls, -- based on what I have seen, they will begin powering house.
5. Step Two: When powerwalls take over, disconnect main service.
6. Step Three: Turn on solar.
7. Solar should slowly take over home load, and then begin charging PWs.
8. When PWs reach 98%, inverters would shut solar down.
9. After dusk, shut off solar.
10. At some point in evening, turn main service back on (with solar off).
11. Shut powerwalls off. Test complete.

In this order there should be no issue with any back feeding to grid, although during install the test they ran resulted in about ten minutes of backfeeding yesterday.
 

jrweiss98020

Tessa's Tesla
Jan 9, 2020
422
297
Edmonds, WA
A couple minutes of backfeeding the grid should do no harm, as long as there is no coincidental grid outage. I did it differently:

Turn on Solar. Turn on Powerwalls. When app confirms PV are powering house and charging PWs, disconnect grid. Run off-grid for as long as you want. Test your electric oven, dryer, and/or car charger to see how the load is distributed between PV and PWs. If your goal is to charge PWs, turn off all noncritical loads in house.

To end test, reconnect grid, turn off PWs, turn off solar.

My installation was in the summer, so I was able to run for 2 days off-grid with no problems (stopped only because PTO inspection was scheduled).
 

wjgjr

Active Member
May 11, 2020
1,168
912
Silver Spring, MD
The two proposed methods for starting/ending the test approaches are largely similar, and I would go with @Southpasfan just to avoid any chance of issues with the utility. Most probably won't care or even notice, but to me it just avoids any possible issues. This is largely the approach we took, with the only exception being that we never turned off the PWs. Since the PWs are configured not to export to the grid, there was no real reason to turn them off, and leaving them on meant we at least had some backup power in the event of an outage. This simplified the process to two steps to start the test: flip service disconnect to "off" position, then turn on inverter. To return to grid operations, turn off inverter, then flip service disconnect back to "on" position.
 

Laketime

Member
Dec 13, 2020
130
72
LI NY
I see no issue with starting the solar first then killing power since your batteries are so low. Tesla turned my system on at install to check things out and twice during the following week to correct one issue (reversed CT) and inspect- on the first occasion they told me to shut the system down that evening. Not one ounce of worry about the utility.
 

holeydonut

Supporting Member
Jun 27, 2020
1,286
772
East Bay NorCal
IMO if your Powerwalls are 25% you can probably skip all the turning-off stuff and just turn on the solar and see what happens. In the daytime your house will be powered by the solar and any excess goes into the Powerwalls. The only time you really have to worry about things are:

1) When your powerwalls are almost full and your solar is still shoving in a bunch of suds (hehe)
or
2) Your PoCo actually has a service disruption and is doing work on your street or local transformer

The Tesla App will tell you if your normal day-to-day is drawing or pushing to the grid. When you first start your test, you should see no energy going upstream of the Gateway or coming downstream from the Gateway.
 

miimura

Well-Known Member
Aug 21, 2013
6,171
5,763
Los Altos, CA
@Southpasfan - This is what I would do:

1. Turn on the Powerwalls and set them to Backup mode.
2. Turn on the solar while you are home and verify that the solar is going to charging the Powerwalls, not going to the grid.
3. Watch the battery level in the app and wait until they are at least 50%.
4. Change the Powerwall mode to Self Powered.
5. Verify that the solar is charging the batteries and powering the house with no grid draw.
6. Disconnect the main service.
7. Observe the system running off grid with both surplus solar and with home consumption greater than solar
8. Turn off the solar
9. Turn on main service.
10. Wait for PTO.
 

Southpasfan

Member
Jun 2, 2019
371
493
Pasadena
It turns out to be a bit more simple. The main thing to avoid is backfeeding the grid.

Obviously, being disconnected is one way. The other way is to make sure house plus charging of PWs takes up 100% of solar production.

That meant charging the model 3 between 11 and 1.
 

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