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Grid charging update
- Thread starter h2ofun
- Start date
RKCRLR
Active Member
I log into my Gateway's IP address on my Windows PC and my site export limit available under Summary.
It is slightly lower than my rated solar production capability.
It is slightly lower than my rated solar production capability.
h2,
My single PW typically grid charges at 3.3 kW. I am set to Grid Charge, Export Everything, Time Based, EV2A with $0.03 lower price on exports. My customer login "summary" shows Site Export Limit as 8.05 kW and Conductor Export Limit 30A, which is 7.2kW at 240V.
On sunny days, almost no grid charging happens. Back on 11/5, however, it started grid charging after midnight at 3.2kW till till it reached 91% around 3AM. So this pretty much disproves your 1.6kW limit.
The spec sheet has a note: 2 In Backup mode, grid charge power is limited to 3.3 kW. This is also the charge rate at which various specs are measured, per note 1.
What I find interesting is that it appears to (secretly) use weather forecast to decide when to grid charge. Nov 4, the day before that midnight 20% to 91% charge was sunny enough for solar to reach 100%. Nov 5 was cloudy, only 4.8kWh of solar, so grid charging was a good idea. But rather than wait till it needed to charge before the 3pm rate increase, it did it in the middle of the night. It appears that it used the weather forecast to make this decision.
What also is odd is that sometimes it grid charges at random night times at random rates. Not a lot, but on obvious reason.
I think the Site Export Limit was derived from my PT&E PTO, basically the max the approved solar could produce, and hence the amount of grid export they "designed" for. Perhaps too much export in a neighborhood could cause unintentional islanding in a grid failure? Some interconnection rules, no doubt. The Conductor Export Limit matches the single PW max output current, so perhaps that is what that means. I get to these by ethernet or WiFi access to the gateway, Customer login, Summary page.
SW
CrazyRabbit
Active Member
The talk about transformer sizing is interesting, I’m on a 100KVA transformer that services fou houses with 400 amp service (cl320 meters).
My utility told me to set my export limit to 200 amps.
My utility told me to set my export limit to 200 amps.
Not sure if this is useful for anyone looking for the info I was searching for all over. If you installed powerwall and grid charging option Shows as restricted, call 877-961-7652.
I received PTO couple of weeks ago, called Tesla to commission the system, and let several days pass by without seeing the option to grid charge. Contacted energy support email who referred me to that phone number. Expected a phone tree and referral back to email but was pleasantly surprised by 2 min holding time and a very helpful representative.
They said that settings should normally be whitelisted within 7 days after install. They believe grid charging should be disabled in US but I nicely said that it shouldn’t with the changes in battery storage tax credit (on principle I disagree that Tesla should be the arbiter of tax credits but thats a whole other discussion). He put me on hold for few mins, came back on and I could immediately see the setting populated in my app.
Happy this is done and I’m looking forward to some arbitrage capability to reduce my electric bill to 0 since my solar only covers 70% of our use with 2 EVs.
Side note - I didnt realize I needed to call Tesla to commission the system. I only was told about this by customer support when I asked about enabling grid charging option in my app.
I received PTO couple of weeks ago, called Tesla to commission the system, and let several days pass by without seeing the option to grid charge. Contacted energy support email who referred me to that phone number. Expected a phone tree and referral back to email but was pleasantly surprised by 2 min holding time and a very helpful representative.
They said that settings should normally be whitelisted within 7 days after install. They believe grid charging should be disabled in US but I nicely said that it shouldn’t with the changes in battery storage tax credit (on principle I disagree that Tesla should be the arbiter of tax credits but thats a whole other discussion). He put me on hold for few mins, came back on and I could immediately see the setting populated in my app.
Happy this is done and I’m looking forward to some arbitrage capability to reduce my electric bill to 0 since my solar only covers 70% of our use with 2 EVs.
Side note - I didnt realize I needed to call Tesla to commission the system. I only was told about this by customer support when I asked about enabling grid charging option in my app.
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aesculus
Still Trying to Figure This All Out
With all the storms we have had lately and no Storm Watch activated, I have been toggling Grid Charge at off peak hours to get my 2-PWs charged to 100% for the next day. I am on EVA (with a 3 cent differential in price for buy/sell) and my PWs are set to Time Based - Solar Export Only, reserve at 50%.
I noticed that the information on the app under Grid Charge says it supports Time Based which I did not see before. I had been careful to toggle off Grid Charge during the day because I was afraid it would stop the PWs from running the house during the peak period. The other day I forgot to turn the Grid Charge off and toggle it during off peak. My PWs drained during peak to the reserve. The next day I noticed my PWs were at 100% in the AM. Looking at the graph for the PW they were charged starting at the off peak time automatically.
So it appears that Grid Charging on TOU accounts for only charging during off peak and still allows you to discharge during the peak periods. So I have been playing the toggle game unnecessarily for who knows how long.
I noticed that the information on the app under Grid Charge says it supports Time Based which I did not see before. I had been careful to toggle off Grid Charge during the day because I was afraid it would stop the PWs from running the house during the peak period. The other day I forgot to turn the Grid Charge off and toggle it during off peak. My PWs drained during peak to the reserve. The next day I noticed my PWs were at 100% in the AM. Looking at the graph for the PW they were charged starting at the off peak time automatically.
So it appears that Grid Charging on TOU accounts for only charging during off peak and still allows you to discharge during the peak periods. So I have been playing the toggle game unnecessarily for who knows how long.
RKCRLR
Active Member
I did a test today and lowered my reserve from 100% to 95%. When peak hours arrived I ran off my Powerwalls until they hit 95% then switched over to the grid. I then enabled grid charging and my Powerwalls started chrging during peak hours. So, at least in that test, it still works the old way.
Right! Both Grid Charging and Export Everything appear to be fairly smart about time-of-use and rates.
In fact, it appease the grid charging even looks at the weather forecast! It is not easy to be certain because there is no control in the app for how much sun there will be. ;-). But after several sunny days when grid charging was not needed because solar was enough to reach 100%. The next day, however, it started charging from the grid at midnight when the rate dropped, and stopped when PW reached around 50% SOC. The morning was quite cloudy, and around noon PW started charging from the grid again, brining it up to 100% by 3 when the rates went up.
Export everything starts discharging extra to export starting around 4 when peak rate begins, but stops so as to leave enough to poser the house till midnight. It apparently makes an estimate of our house draw to accomplish this. It sometimes gets down to our reserve a bit before midnight, causing us to re-import a bit. But since those kWh were exported at peak rate, and imported at partial peak, it still make some profit in the arbitrage, off maximum by only the NBC of $0.03.
Anyway, both are just set-and -forget for us. The one exception is during very windy afternoon storms when an outage is likely, in which case we set the reserve up to hang on to more charge.
SW
aesculus
Still Trying to Figure This All Out
Hmm. I'll monitor it a bit more now that I know what it is capable of. Curious what it will do in 30 minutes when I go to off peak for the day. I'll update this post when I find out.
aesculus
Still Trying to Figure This All Out
OK. When my rates changed at 7:00PM from peak to off peak my PWs started charging at 8 kW until they got to 97%. They then trickled charged at 0.2 kW.
I am ready for the next peak period in the rain tomorrow.
That is a bit strange, different from what mine does. Mine waits at least till the rate drops to grid charge, but if it expects sunshine it doesn't grid charge at all. I gather from what you sat that your time settings are correct, but double check your rate plan pricing settings to be sure peak costs more than off peak.
My backup reserve is usually set at 20%. Our rate drops at midnight, and PW gets down to 20% at that time. We use ~300 watts at night, so till 9 AM that is around 9 X 0.3 = 2.7 kWh or 20% of 13.5 capacity of our single PW. So in the event of a night-time grid failure, we should be OK till the solar can pick up the load in the morning. If the sun fails to rise (or more likely clouds blocking the photons), we still have our little propane portable generator to keep the fridge, freezer, tankless gas water heater and internet alive. We'd love to be able to charge the PW with the little gen too, but that is a yet unsolved and fortunately yet unexperienced need.
RKCRLR
Active Member
My Off-Peak Buy is $0.25/kWh and Sell is $0.22/kWh.
My Peak Buy is $0.42/kWh and Sell is $0.39/kWh.
I do have an issue where I get eroneous readings when grid charging but Tesla told me this is normal:
teslamotorsclub.com
My Peak Buy is $0.42/kWh and Sell is $0.39/kWh.
I do have an issue where I get eroneous readings when grid charging but Tesla told me this is normal:
Tesla app showing incorrect information when charging from grid
There is a storm here in northern California but Storm Watch wasn't triggered so I decided to top off my Powerwalls from the grid. I enabled charging from the grid and set my reserve to 100%. The app is showing power coming from solar (which is more than is possible on a rainy day) and the...
teslamotorsclub.com
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RKCRLR
Active Member
My grid charging seems to recognize TOU now. I left grid charging enabled and had my reserve set to 50%. My house ran off the Powerwalls during peak hours and then charged back up to close to 100% when peak hours were over. I'm not going to leave it enabled since I will incur more NBCs that way but it is nice to know it recognizes TOU.
Cool! Sounds like it is working as it should. Congrats.
I leave mine on Export Everything and Grid Charging. I am on PG&E's EV2-A rate under which importing at off peak and exporting at peak give me a net credit of 15¢ per kWh after the NBC. In summer it'll be 25¢ per. If all my charging was from the grid, this arbitrage would net me around $250 per year. Of course when solar provides the export, it is another 24¢ per kWh. I set the sell price 3¢ below the buy price, and PW seems to do the right thing most of the time.
RKCRLR
Active Member
I'm on EV2-A also but am a net producer so I get compensated for any excess at the wholesale rate at true-up no matter when it was produced. But the more I draw from the grid the more NBCs I pay.
aesculus
Still Trying to Figure This All Out
For now, this scheme really does support us net consumers. I am sure that this will change soon.
Ah, yes! That is a different deal. We expect to owe some at true-up, so all of our exports are compensated at retail.
I must say that the NBC affect on the true-up calculation is weird enough that I don't know exactly how it will come out. But it is surprising that PG&E's pricing would encourage you to export solar during off peak when their own generation is cheap, rather than during peak when their costs (both generation and transmission capacity needs/costs) are highest. PG&E should want you to, and should compensate you to cycle your PW as much as you can to help level their daily demand curve and reduce their costs.
RKCRLR
Active Member
What I'd like to see is an algorithm from Tesla that takes all aspects into account (including weather forecasts) and optimizes the times when charging/discharging occurs. This will be even more important as people are transitioned to NEM 3 and the utilities have their complex rate structure.For now, this scheme really does support us net consumers. I am sure that this will change soon.
In theory that's what it does now. It's using solar forecasts, which should account for weather. It still does seem to optimize for self-consuming solar rather than storing it in the battery, though. As a result, my Powerwalls often seem to fill up before the afternoon shoulder/peak period starts. For discharging it uses the shoulder and peak rates to determine the timing. If there is enough of a difference between buy and sell rates, it will make sure not to draw from the grid during those times.
I am pretty certain that grid charging does look at weather forecasts, much to my surprise.
For example, on Monday our PW did not grid charge at night and it was then sunny enough to fully charge. Tuesday, however, it charged up to 73% starting at midnight, and then solar brought it up most of the way and it toped itself up to 100% just before 3 when the rates go up. It sure seems to be using some weather forecast.
This surprises me because it could just wait and grid charge before the rate rise. It knows it's max charge rate and it's SOC, so it could just charge at that rate and let the grid supply whatever is needed. It seems that predicting the weather is not really necessary. In fact, as I understand it, the grid sometimes has "too much" solar around noon, so charging then might help. Likewise, car charging from solar mid day, rather than exporting mid day and car charging at night.
For example, on Monday our PW did not grid charge at night and it was then sunny enough to fully charge. Tuesday, however, it charged up to 73% starting at midnight, and then solar brought it up most of the way and it toped itself up to 100% just before 3 when the rates go up. It sure seems to be using some weather forecast.
This surprises me because it could just wait and grid charge before the rate rise. It knows it's max charge rate and it's SOC, so it could just charge at that rate and let the grid supply whatever is needed. It seems that predicting the weather is not really necessary. In fact, as I understand it, the grid sometimes has "too much" solar around noon, so charging then might help. Likewise, car charging from solar mid day, rather than exporting mid day and car charging at night.