Question on Time Based Controls - Balanced

[Frankman60]

Thanks for sharing that detailed information. I will try TBC Balanced when I get the PWs installed in a few weeks. My goals are:

1. Power house 100% from PWs during 4-9 PM Peak
2. PWs never discharge during Super off Peak 12-6 AM weekdays and 12 AM to 2 PM weekends
3. Never have less than a 50 percent reserve for a potential grid outage.

For reference, here is a chart from mid-April 2018. I am almost certain that in this case the Powerwalls reached 100% at about 1pm when they stopped charging, then started discharging at the start of the Peak period at 2pm. I think I took this screenshot because TBC had just been activated and the app updated to show the time periods. The screenshot from the prior week doesn't have the time period shading and Peak/Off-Peak labeling.

View attachment 400823

 

[PBBear]

I'd suggest letting the system run for a week or two on 'self powered' until it learns a bit of history about your average usage profile, and then see if TBC does sensible things.

 

[Frankman60]

This is interesting. Do you set up your schedule this way and do the PWs actually only discharge during peak (2-9 PM in this example)? I’m just making sure that this has been tested and is not just theoretical. Also, what TBC mode (i.e. cost savings or balanced) would be used for these settings, or do both modes get the same result?

If you really want to contain discharge to only the peak (which I do) then simplify your schedule to this:

9pm-2pm = off-peak
2pm-9pm = peak

 

[miimura]

This is interesting. Do you set up your schedule this way and do the PWs actually only discharge during peak (2-9 PM in this example)? I’m just making sure that this has been tested and is not just theoretical. Also, what TBC mode (i.e. cost savings or balanced) would be used for these settings, or do both modes get the same result?

Setting everything to Off-Peak except the Peak hours is truly a brute force approach. The undesirable side effect will be that the house will run from the grid during all those hours too. You can see from my charts up-thread that the following conditions are followed.

1. During Peak, the house is powered by batteries and All Solar goes to the grid.
2. During Off-Peak, the batteries never discharge and All Solar goes into the battery until full.

The shoulder period between Off-Peak and Peak is where the behavior sometimes gets strange.

 

[power.saver]

This is interesting. Do you set up your schedule this way and do the PWs actually only discharge during peak (2-9 PM in this example)? I’m just making sure that this has been tested and is not just theoretical. Also, what TBC mode (i.e. cost savings or balanced) would be used for these settings, or do both modes get the same result?

Yes, this is tested and I have been using it for over 6 months now. It behaves exactly the same every day. The part-peak (shoulder) period is the one where you can sometimes get charging or discharging, and due to round-trip losses, I don't want any discharge except during my peak period (2pm-8pm). All the rest is off-peak, which is charging only until full, then export all excess solar.

 

[Frankman60]

Thanks miimura and power.saver for your advice. I am thinking that there isn’t any reason I would want PWs discharging during shoulder periods, especially within the same shoulder period as miimura described in earlier in this thread. Wouldn’t this create extra wear on the batteries in addition to the round-trip losses that power.saver mentioned, for no benefits? Or am I missing what the benefits would be for discharging during shoulder periods?

 

[Frankman60]

What mode do you set the PW (e.g. TBC Balanced, TBC Cost-Savings, etc) with this approach, or does it matter?

Yes, this is tested and I have been using it for over 6 months now. It behaves exactly the same every day. The part-peak (shoulder) period is the one where you can sometimes get charging or discharging, and due to round-trip losses, I don't want any discharge except during my peak period (2pm-8pm). All the rest is off-peak, which is charging only until full, then export all excess solar.

 

[power.saver]

I use TBC Balanced. I believe that Cost Savings would work the same with this setup.

 

[Late2theGame]

Hello,

I had my dual Powerwalls with Solar in operation for 3 weeks now.
TBC - Cost Savings; PG&E EV-A with Peak, shoulder, and off peak during the week and Peak and off peak on weekends; Reserve is 35%.

During weekdays I see it charge every day when solar kicks in - from solar and during shoulder period until it reaches about 75%. Then it feeds the grid and might intermittently charge some part of the solar to the Powerwall up to ~80%- 85%. During peak it discharges and runs the house and typically ends the peak period with 40%-45% charge. No activity during off-peak. Only time it discharges during shoulder is late on Friday. I assume it tries to empty the tank so it can refill it with the off-peak solar on the weekend as that is more cost effective.

On weekends it charges during off-peak to 100% and powers the house during peak. So Monday morning it has a higher charge than other weekdays.

Overall I am very happy with this behavior as I believe it maximizes storage of solar during cheap periods and discharge during expensive periods. I was pleasantly surprised by the slightly different behavior on Friday evening and during the weekend.

 

[Frankman60]

I’m not sure I understand why it is good for the PWs to discharge during the Friday shoulder period in preparation for the weekend. I think you may have a weekend rate similar to what I have where the off peak is extended until 2 PM or so. In this case, if the PW retained its charge rather than discharging during Friday shoulder, wouldn’t it be the same outcome except there aren’t any turn-around losses?

Hello,

I had my dual Powerwalls with Solar in operation for 3 weeks now.
TBC - Cost Savings; PG&E EV-A with Peak, shoulder, and off peak during the week and Peak and off peak on weekends; Reserve is 35%.

During weekdays I see it charge every day when solar kicks in - from solar and during shoulder period until it reaches about 75%. Then it feeds the grid and might intermittently charge some part of the solar to the Powerwall up to ~80%- 85%. During peak it discharges and runs the house and typically ends the peak period with 40%-45% charge. No activity during off-peak. Only time it discharges during shoulder is late on Friday. I assume it tries to empty the tank so it can refill it with the off-peak solar on the weekend as that is more cost effective.

On weekends it charges during off-peak to 100% and powers the house during peak. So Monday morning it has a higher charge than other weekdays.

Overall I am very happy with this behavior as I believe it maximizes storage of solar during cheap periods and discharge during expensive periods. I was pleasantly surprised by the slightly different behavior on Friday evening and during the weekend.

 

[Late2theGame]

I’m not sure I understand why it is good for the PWs to discharge during the Friday shoulder period in preparation for the weekend. I think you may have a weekend rate similar to what I have where the off peak is extended until 2 PM or so. In this case, if the PW retained its charge rather than discharging during Friday shoulder, wouldn’t it be the same outcome except there aren’t any turn-around losses?

Here is my logic - and I hope I got it right:

Discharging Friday evening at shoulder rates means more credit/less consumption at shoulder rate and the battery gets replenished at off-peak rate Sat/Sun = less off-peak credit: Effectively shifting off-peak credit to shoulder credit (~8c/kWh for me) - roundtrip penalty removes a little from that.

Not discharging Friday evening means no round trip but more consumption at shoulder rate on Friday and more credit Sat/Sun at off-peak rate as the SOC of the battery Sat morning is higher.

The same reasoning applies to charging the powerwall to 100% on Sunday (and not just enough for one evening peak period like during the week), but that is more obvious: Storing off-peak solar to discharge during peak periods (22c/kWh difference).

Weekday:
shoulder: 7am-2pm and 9pm-11pm
Peak: 2pm-9pm
off-peak: 11pm-7am

Weekend:
Peak: 3pm-7pm
off-peak rest of day
no shoulder

 

[Frankman60]

Thanks for the explanation. What you said makes sense to me. I think that it depends on the differences in electric rates among the different periods. What I presently have during the Winter season are identical peak and shoulder rates ($.24/kWh), and $.09/kWh off peak. In this scenario I just try to defer everything to the off peak period such as charging the EVs, running the dishwasher or clothes washer, etc). I don’t think the PWs will serve much of a purpose during the Winter season except provide backup power if needed. However during the Summer season, things are different. Peak is $.52/kWh, Shoulder is $.28/kWh, and Off Peak is $.09/kWh. What I’m thinking is that maybe it would be good to have Summer and Winter season settings for the PW.

Here is my logic - and I hope I got it right:

Discharging Friday evening at shoulder rates means more credit/less consumption at shoulder rate and the battery gets replenished at off-peak rate Sat/Sun = less off-peak credit: Effectively shifting off-peak credit to shoulder credit (~8c/kWh for me) - roundtrip penalty removes a little from that.

Not discharging Friday evening means no round trip but more consumption at shoulder rate on Friday and more credit Sat/Sun at off-peak rate as the SOC of the battery Sat morning is higher.

The same reasoning applies to charging the powerwall to 100% on Sunday (and not just enough for one evening peak period like during the week), but that is more obvious: Storing off-peak solar to discharge during peak periods (22c/kWh difference).

Weekday:
shoulder: 7am-2pm and 9pm-11pm
Peak: 2pm-9pm
off-peak: 11pm-7am

Weekend:
Peak: 3pm-7pm
off-peak rest of day
no shoulder

 

[Late2theGame]

Thanks for the explanation. What you said makes sense to me. I think that it depends on the differences in electric rates among the different periods. What I presently have during the Winter season are identical peak and shoulder rates ($.24/kWh), and $.09/kWh off peak. In this scenario I just try to defer everything to the off peak period such as charging the EVs, running the dishwasher or clothes washer, etc). I don’t think the PWs will serve much of a purpose during the Winter season except provide backup power if needed. However during the Summer season, things are different. Peak is $.52/kWh, Shoulder is $.28/kWh, and Off Peak is $.09/kWh. What I’m thinking is that maybe it would be good to have Summer and Winter season settings for the PW.

I see. If you have only 2 different rates all days of the week, then treating Friday different or round-tripping in the powerwall during periods with identical rates makes no sense. PG&E's EV-A has 3 rates during the week and 2 rates on the weekend all year round (varying rates), which opens this minor opportunity for special Friday behavior.

My other point really was - having read how many people see odd behavior - that after a little thinking I believe mine worked reasonably well out of the box - fingers crossed.

 

[miimura]

Thanks miimura and power.saver for your advice. I am thinking that there isn’t any reason I would want PWs discharging during shoulder periods, especially within the same shoulder period as miimura described in earlier in this thread. Wouldn’t this create extra wear on the batteries in addition to the round-trip losses that power.saver mentioned, for no benefits? Or am I missing what the benefits would be for discharging during shoulder periods?

You've got it right. There is no logical reason to charge and discharge again in the same shoulder period. It is just wearing out the battery and incurring round trip conversion losses for no reason. IMHO, when it reaches the SOC that it wants to be at ahead of the start of the Peak period, it should just go into Standby. That will let the solar power the house and let the surplus go to the grid to earn NEM credits. Charging and discharging is reducing the Part-Peak credits by the conversion losses. Also, I would always prefer to have the battery cycle at the higher end of the SOC range so that there is more reserve for outages. It could accomplish this by simply continuing to charge through the Part-Peak period. Maybe only on Thursdays and Fridays should it stop charging before it gets full.

During the Winter I set the reserve higher so that there was just a little more capacity headroom than I had ideal generation. I couldn't make it through the Peak period on battery before it hit the Reserve, but over a period of days it didn't matter because I simply didn't have the generation capacity to do it. I was going to be bouncing off the Reserve anyway, so why not bounce between 75% and 95% instead of 25% and 45%. As the solar generation increased according to the season, I gradually dropped the Reserve. Now I have less Peak period consumption than daily generation, so the algorithm is doing these strange things like charging and discharging during Part-Peak. Oh well.

 

[hodad66]

Great thread to learn from....

 

[csanders90D]

Thanks for the explanation. What you said makes sense to me. I think that it depends on the differences in electric rates among the different periods. What I presently have during the Winter season are identical peak and shoulder rates ($.24/kWh), and $.09/kWh off peak. In this scenario I just try to defer everything to the off peak period such as charging the EVs, running the dishwasher or clothes washer, etc). I don’t think the PWs will serve much of a purpose during the Winter season except provide backup power if needed. However during the Summer season, things are different. Peak is $.52/kWh, Shoulder is $.28/kWh, and Off Peak is $.09/kWh. What I’m thinking is that maybe it would be good to have Summer and Winter season settings for the PW.

During the winter (on SDGE rates) you can still get the difference between the $.24 and $.09 rates on the weekends because the off-peak goes until 2PM. Fill up weekend mornings and discharge in the afternoons. I configured both peak and shoulder times as "peak" in the app, since the price is the same.

If you get a bit fancier, you can also use the 10AM-2PM off-peak during March and April weekdays to charge, but that requires gaming the time of day and reserve settings to make it work. Hopefully they'll update to allow 2 peak periods per day before next March rolls around.

 

[Frankman60]

Do you use Balanced or Cost Savings settings? My understanding is if you use either of these two profiles, and only configure Peak and Off Peak (no shoulder) periods, the PWs will only discharge during the defined Peak period. Is that what you have experienced? I’m assuming that you are going to change the setup on June 1st when the Summer season begins.

During the winter (on SDGE rates) you can still get the difference between the $.24 and $.09 rates on the weekends because the off-peak goes until 2PM. Fill up weekend mornings and discharge in the afternoons. I configured both peak and shoulder times as "peak" in the app, since the price is the same.

If you get a bit fancier, you can also use the 10AM-2PM off-peak during March and April weekdays to charge, but that requires gaming the time of day and reserve settings to make it work. Hopefully they'll update to allow 2 peak periods per day before next March rolls around.

 

[Frankman60]

Miimura you mentioned that the undesirable side effect of only defined Peak and Off Peak periods (i.e. no shoulder periods) will be that the house will run from the grid during the Off Peak hours. In this context, the Off Peak hours would be all hours except what are defined as Peak (2 periods only). I’m trying to understand why this would be undesirable. If the PWs sometimes are unpredictable during shoulder periods (.e.g charge and discharge in the same shoulder period), wouldn’t a good way to handle this is to not define any shoulder periods?

Setting everything to Off-Peak except the Peak hours is truly a brute force approach. The undesirable side effect will be that the house will run from the grid during all those hours too. You can see from my charts up-thread that the following conditions are followed.

1. During Peak, the house is powered by batteries and All Solar goes to the grid.
2. During Off-Peak, the batteries never discharge and All Solar goes into the battery until full.

The shoulder period between Off-Peak and Peak is where the behavior sometimes gets strange.

 

[csanders90D]

Do you use Balanced or Cost Savings settings? My understanding is if you use either of these two profiles, and only configure Peak and Off Peak (no shoulder) periods, the PWs will only discharge during the defined Peak period. Is that what you have experienced? I’m assuming that you are going to change the setup on June 1st when the Summer season begins.

I'm using TBC balanced. The Powerwall charges from all solar during off-peak, running the house from grid until the battery hits 100%, then it goes into standby until peak time. During peak, it runs the house from battery and exports all solar to the grid until the battery hits reserve.

I'll be changing the time periods tomorrow because the weekday 10-2 off-peak is going away, then I'll have to change settings again on June 1st.

 

[miimura]

Miimura you mentioned that the undesirable side effect of only defined Peak and Off Peak periods (i.e. no shoulder periods) will be that the house will run from the grid during the Off Peak hours. In this context, the Off Peak hours would be all hours except what are defined as Peak (2 periods only). I’m trying to understand why this would be undesirable. If the PWs sometimes are unpredictable during shoulder periods (.e.g charge and discharge in the same shoulder period), wouldn’t a good way to handle this is to not define any shoulder periods?

I'm starting to think it's not as undesirable as I said before. Look at the two charts below. The first one is yesterday, a Sunday where the real rate schedule is all Off-Peak and Peak. The system is very well behaved and it charges until the batteries are full, then exports the surplus. When the Peak rate period begins, the batteries power the house. With Net Metering, there's really no economic problem with this. Whatever you take from the grid in the morning is just offset by the exports in the early afternoon. Contrast that with the second chart from today. The system can't decide what it's doing. The cause of the problem is that it started the day at about 85% SOC and a reserve of 25%. I thought about raising the Reserve so the available energy would be less confusing to the algorithm, but I decided not to. I'm starting to think that I should just take away the shoulder period to avoid this craziness. I guess I'm just hoping that Tesla will see this and improve the system so that it doesn't happen like this.

Truly, this crazy behavior is not good for the grid. When the starting SOC is high, the system should start the shoulder period as if it's in Self-Powered mode. I don't mind that little blip of charging before 7:00am. I also would not mind the batteries discharging in the morning while the consumption is higher than the generation. However, after 9:00am when the solar is clearly greater than the household consumption, there is no good reason for it to be whipsawing back and forth between charging and discharging unless that is a demand response signal from the utility. I'm pretty sure that is not the case today in Northern California.

I suppose this brings me back to the Advanced Mode that was proposed earlier in this forum. This time of year when the generation is sufficient to cover all the shoulder and Peak period usage, I would like to set the system to Self Powered during the shoulder period with a "Do not Discharge Off-Peak" rule. That would be the most kind to the grid and would minimize the battery cycling while still providing arbitrage.