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Frustrated with changing Time-Based Control behavior

I’m on an Ev-A TOU plan, peak, partial-peak and off-peak. When in TBC (TIME-based control) usually as solar ramps up, it covers house loads with excess going to recharge the batteries until they are at 100%. This time of the year, batteries reach 100% well before peak period when 100% of solar goes to the grid and the batteries cover the house loads. I‘m fine with that behavior.

But sometimes, like this morning, batteries are at 79% but all excess solar is going to the grid even though it isn't a peak period. I’ve had to switch to self-powered mode to get the batteries to start charging. WTF, why the change in behavior? It isn’t weather related. Another thing that changes is coverage for the 2 hour partial-peak period after peak ends. Although the batteries are well above the reserve setting, usually, the system has the grid cover that period as well as all the off peak hours but sometimes it has the batteries cover the partial-peak hours and the grid is only used for the off-peak times. Again why the change of behavior? Again it isn’t weather related and the SOC is well above the reserve setting.

I wish I could count on the same behavior and not have to switch settings to force the batteries getting charged with excess solar. Any insights into the changing behavior?
 
Last edited:

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Moderator
Nov 28, 2018
14,656
18,771
Riverside Co. CA
I’m on an Ev-A TOU plan, peak, partial-peak and off-peak. When in TBC (TIME-based control) usually as solar ramps up, it covers house loads with excess going to recharge the batteries until they are at 100%. This time of the year, batteries reach 100% well before peak period when 100% of solar goes to the grid and the batteries cover the house loads. I‘m fine with that behavior.

But sometimes, like this morning, batteries are at 79% but all excess solar is going to the grid even though it isn't a peak period. I’ve had to switch to self-powered mode to get the batteries to start charging. WTF, why the change in behavior? It isn’t weather related. Another thing that changes is coverage for the 2 hour partial-peak period after peak ends. Although the batteries are well above the reserve setting, usually, the system has the grid cover that period as well as all the off peak hours but sometimes it has the batteries cover the partial-peak hours and the grid is only used for the off-peak times. Again why the change of behavior? Again it isn’t weather related and the SOC is well above the reserve setting.

I wish I could count on the same behavior and not have to switch settings to force the batteries getting charged with excess solar. Any insights into the changing behavior?

It does that because it has determined that you wont need 100% full batteries to cover the peak period. Thats part of the algorithm part of the time based controls. I dont use them, but suggest reading through the stickied thread on things people have done with the utility setup to try to get the behavior they specifically want.

 
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aesculus

Still Trying to Figure This All Out
May 31, 2015
4,827
2,780
Northern California
Not sure how long you have had you system but it takes a few weeks to learn your patterns, and it's also constantly adjusting day by day. It is not weather related unfortunately, as it will throw you under the bus if a cloudy day shows up out of the blue.

Anyway its not uncharacteristic for it to not charge to 100% if it thinks it will have enough energy to carry you through the next several peak periods with the solar you have been producing up to that point. My periods change on the weekends and I need a lot less power Sat/Sun during peak for example and it often will not charge to 100% and will allow solar to go to the grid during partial peak.

The algorithm of Cost Based is to net you the most value for your energy. People liked the Balanced mode which more mimicked the behavior you are asking for, but a recent update took that away.

The only real issue you should be concerned with is if it runs out of battery power during your peak period and then has to use grid power. That usually only happens with me (rarely) during spring/fall when I have had a lot of sunny days with a sudden cloudy day (rare). And it usually resets itself after a day when it sees the mistake.

EDIT: I see @jjrandorin beat me to the post as I was typing. He was much more net. 🙂 🙂
 
It's all part of the system that uses AI and ML to learn your consumption patterns, taking into account context (when, where, season, day of week, current weather patterns, upcoming weekly weather patterns, etc...). For me, I noticed that on Friday it will NOT charge the Powerwalls at all, running my entire house on the Powerwalls until it reaches my reserve of 20% and choose to NEM it all back to PG&E, with the idea that over the weekend it will achieve 100% fill rate on my Powerwall... It does this automatically because it understands that in the winter my generation is minimal at best, so NEM as much as it can during the summer seasons. I have a small system (not enough roof space), but plenty of storage, so it's behavior works for me...
 

ucmndd

Well-Known Member
Mar 10, 2016
8,544
16,669
California
I am also still on EV-A and have behavior similar to yours. I’ve convinced myself it’s actually doing the right thing with regard to minimizing cost.

From what I can tell the powerwall “AI” determines that once they are charged to an adequate capacity to ride out your normal usage during the 2-9pm peak period, it’s better to send excess energy to the grid during the part-peak morning hours. This makes sense - given the round trip 10+% efficiency loss and the non bypassable charges you pay when drawing energy from the grid.

I have similar behavior during the late evening part peak period where the 9-11pm period is very rarely covered by the powerwall discharging. I’ve again convinced myself this is generally the right decision from a cost perspective. The 10% efficiency penalty makes it not worth the cost to power the home from that banked storage vs just buying from the grid during part peak.

It seems counterintuitive but after fretting about it for a long time it does appear to be the most cost efficient mode of operation, which is what time based control is designed to provide.

Sounds like you might want self powered mode based on what you expect.
 
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ucmndd

Well-Known Member
Mar 10, 2016
8,544
16,669
California
Put another way - say instead of stopping at 80% your powerwall charges to 100% so that you have extra energy to power the house during that evening part-peak period from 9-11.

You bank that energy in your Powerwalls at an effective part-peak sell price on EV-A of $0.33/kWh (tariff rate of $0.36 minus about 3 cents in NBCs that you have to pay when you buy it back under NEM2).

If you “buy” that energy back from yourself in the evening, you effectively pay ~10% more due to round trip losses, so $0.363/kWh, which is slightly more than you pay just buying energy straight from the grid.
 

miimura

Well-Known Member
Aug 21, 2013
7,319
7,304
Los Altos, CA
On EV-A it makes little sense to discharge in the evening Part-Peak (9-11pm) because the bulk of your generation is during the mid-day Part-Peak. Charging and discharging during the same rate period makes no sense, especially if you are on NEM1 and there is no NBC penalizing grid draw.

Conversely, on EV2-A, the bulk of your generation occurs during Off-Peak before 3pm. In that case, it makes sense to try to power the house from batteries from 3pm-12mid.
 

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