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(4) Powerwall 2 Only Charging from Grid @ 6.7 kW
- Thread starter mstgkillr
- Start date
el-guapin
Trust no One
My experience with charging from the grid is: All of the calculations are based on what 6 Powerwalls will do. If 6 Powerwalls will charge at a rate of 10 kW, then 4 will charge at a rate of 4/6 times 10. Or, 6 and 2/3. Sadly, I have only one, so 1 and 2/3. (Of course, Tesla rounds the number to 1.7)
Why charge from the grid? Mainly, Stormwatch is not very smart. If I see a nasty line of thunderstorms coming my way, I jack up the reserve. By the time we get our warning, it's way too late. Same with winter storms.
Why charge from the grid? Mainly, Stormwatch is not very smart. If I see a nasty line of thunderstorms coming my way, I jack up the reserve. By the time we get our warning, it's way too late. Same with winter storms.
gcsutton
Member
I have 6 PWs and see the same behavior, 10kW max from the grid.
On a good clear day in June my panels will send 12-13 kW to the PWs no problem. Seems like an artificial limit when charging from the grid.
On a good clear day in June my panels will send 12-13 kW to the PWs no problem. Seems like an artificial limit when charging from the grid.
My experience as a user of Powerwalls is that the charge rate depends on several factors. Below is my experience as a user:
1. Time spent charging - I see that when I first charge from the grid, the charge rate will hover for the first 5-10 minutes at a lower number usually about 1.3-1.7 kW per Powerwall.
2. Transformer/line voltage - I see from my eGauge that once I drop to 236-235V, my Powerwalls reduce the charge rate down to 1.3-1.7kW each. I have a 25 kVA dedicated transformer, and so when I push it hard up to 48 kW or so I notice it can only sustain at this rate for 30 minutes or so before the transformer I assume heats up and the voltage starts dropping, which (I assume) reduces the Powerwall charge rate.
3. Playing with the backup reserve slider - Seems to set it into a delay mode of some kind. I notice that when I make a small adjustment it is accepted, but after multiple adjustments to the reserve percentage, the app seems to not do much for about 15 minutes-ish
Otherwise, my 5 Powerwalls will charge from the grid at 25 kW almost exactly until full, unless my car(s) are also charging, and this causes the voltage drop and reduced charge rate.
When the Powerwalls are commissioned, the installer can set a limitation to the Powerwall charge rate. Some utilities might require this limitation to be set and I have no idea if that is taken care of on the Tesla side or the installer side. Check with your installer if you suspect something weird.
To my knowledge, none of our thousand-ish customers have a charge rate from the grid limited by PGE, so I doubt it is done on the installer side with 3rd party installers. Such a limitation if it exists would likely also be shown on the Interconnection Agreement. For instance, my PGE agreement looks like this:
In my interpretation, this says that I can't draw more power with my batteries than "Normal Peak Demand" which I interpret to be the load calculations I sent PGE indicating 232A of calculated load so 55.6 kW max demand is allowed while grid charging. If I look earlier in my IA document, I am allowed to backfeed 32.7kW to the grid between both PW and PV.
I am pretty sure that for whatever reason SunRun and maybe other installers are restricted in this section with what they can allow.
1. Time spent charging - I see that when I first charge from the grid, the charge rate will hover for the first 5-10 minutes at a lower number usually about 1.3-1.7 kW per Powerwall.
2. Transformer/line voltage - I see from my eGauge that once I drop to 236-235V, my Powerwalls reduce the charge rate down to 1.3-1.7kW each. I have a 25 kVA dedicated transformer, and so when I push it hard up to 48 kW or so I notice it can only sustain at this rate for 30 minutes or so before the transformer I assume heats up and the voltage starts dropping, which (I assume) reduces the Powerwall charge rate.
3. Playing with the backup reserve slider - Seems to set it into a delay mode of some kind. I notice that when I make a small adjustment it is accepted, but after multiple adjustments to the reserve percentage, the app seems to not do much for about 15 minutes-ish
Otherwise, my 5 Powerwalls will charge from the grid at 25 kW almost exactly until full, unless my car(s) are also charging, and this causes the voltage drop and reduced charge rate.
When the Powerwalls are commissioned, the installer can set a limitation to the Powerwall charge rate. Some utilities might require this limitation to be set and I have no idea if that is taken care of on the Tesla side or the installer side. Check with your installer if you suspect something weird.
To my knowledge, none of our thousand-ish customers have a charge rate from the grid limited by PGE, so I doubt it is done on the installer side with 3rd party installers. Such a limitation if it exists would likely also be shown on the Interconnection Agreement. For instance, my PGE agreement looks like this:
In my interpretation, this says that I can't draw more power with my batteries than "Normal Peak Demand" which I interpret to be the load calculations I sent PGE indicating 232A of calculated load so 55.6 kW max demand is allowed while grid charging. If I look earlier in my IA document, I am allowed to backfeed 32.7kW to the grid between both PW and PV.
I am pretty sure that for whatever reason SunRun and maybe other installers are restricted in this section with what they can allow.
FWIW: Like @Vines, we have a dedicated transformer. I don't know the size, though we have pulled more than 22kW for an hour as part of a demand test with no issues. We see 5kW/powerwall charging until the SOC gets high and then a taper. Our voltage stays above 240. (We have some long wiring runs, but the wire distance from MSP to gateway to the Powerwalls is short, and oversized.)
@mstgkillr You might find it interesting to check your site settings in your Gateway. I'm not suggesting that you change anything, but you may have current limits set there that might lead to installer/utility questions.
All the best,
BG
@mstgkillr You might find it interesting to check your site settings in your Gateway. I'm not suggesting that you change anything, but you may have current limits set there that might lead to installer/utility questions.
All the best,
BG