How do I prioritize solar for self consumption when using Time Based Control?

[RKCRLR]

I have solar and Powerwalls and I've been TBC for a while now. I'm on PG&E EV2A and have set the times and buy rates to match EV2A. I set the sell rate rate at $0.03 less to account for NBCs.

When recharging the Powerwalls in the mornings it works the way I want. It prioritizes my solar consumption to the house over running it from the grid and only runs from the grid when there is no solar or it thinks the Powerwalls aren't going to get recharged before 3 pm. However during partial peak and peak it exports all solar to the grid and my house runs off the Powerwalls. During partial peak and peak hours I want it to self consume the solar, send the excess to the grid, and only draw from the Powerwalls when I'm not producing enough solar.

Someone suggested setting the sell price to accommodate round trip losses so I set off partial peak and peak sell prices to the buy price minus 10% minus $0.03. Nothing changed.

Someone said that setting the sell price to 15% lower than the buy prices would make it prioritize self consumption of solar during peak hours so I tried that. It ran just like when I had the sell prices set to $0.03 lower or included round trip losses.

So then I tried setting the sell price to $0.10 across the board for off peak, partial peak, and peak to see what happened. That caused me to run off the Powerwalls during off peak and run off the grid during peak.

So then I tried setting the sell prices to 20% lower than the buy prices. That worked! - for one day. Then it reverted to exporting all solar to the grid during partial peak and peak hours.

People have claimed that they have been able to prioritize self consumption of solar during partial peak and peak hours by manipulating the rates. What rates do I enter to achieve this?

 

[bemyax]

Usually, someone who knows stuff chimes in by now.

a) I am not that guy.
b) Have you tried switching to self-powered mode for a week to see how that works?

David

 

[RKCRLR]

Usually, someone who knows stuff chimes in by now.

a) I am not that guy.
b) Have you tried switching to self-powered mode for a week to see how that works?

David

I tried self powered a while ago and it didn't work as I wanted. It would draw from the grid during peak hours. I never want to draw from the grid during peak hours unless my Powerwalls are at their reserve limit.

 

[BGbreeder]

This is what I use and we have essentially zero draw on peak.

The result is nothing but trivial draws from the grid when a large load kicks in within the house during peak. 80% for Powerwall use, though we rarely use more than 15% of the total storage on any given day.

 

[RKCRLR]

^^^
Thanks, I'll give those price settings a try. I have my reserve set at 40% and I want to leave it there.

 

[aesculus]

FWIE I have at a 3 cent offset for buy/sell for over a year and it only runs from the PWs during peak on TBC.

EDIT: I have seen a very few occasions where the gateway directed solar to the home during peak periods. It was on a very hot day, early in the period, where it was clear I would not make it to end of peak solely on the PWs. I was surprised it could figure that out.

 

[RKCRLR]

FWIE I have at a 3 cent offset for buy/sell for over a year and it only runs from the PWs during peak on TBC.

EDIT: I have seen a very few occasions where the gateway directed solar to the home during peak periods. It was on a very hot day, early in the period, where it was clear I would not make it to end of peak solely on the PWs. I was surprised it could figure that out.

I'm surprised Tesla doesn't have an option to prioritize solar self consumption over export during peak hours. Instead we have to try to trick it. Once people in California start getting transitioned to NEM3 it will be even more important to be able to prioritize solar self consumption during peak hours.

 

[aesculus]

I'm surprised Tesla doesn't have an option to prioritize solar self consumption over export during peak hours. Instead we have to try to trick it. Once people in California start getting transitioned to NEM3 it will be even more important to be able to prioritize solar self consumption during peak hours.

I think they do with TBC when the financials and potential loads are figured out. It does take about a week after you make changes to "do the right thing - ie learn" IMHO. I also think, but don't have proof, that they are now including weather into the mix, as my few exceptions were during very hot weather events where my cooling load was much larger than normal.

 

[RKCRLR]

I think they do with TBC when the financials and potential loads are figured out. It does take about a week after you make changes to "do the right thing - ie learn" IMHO. I also think, but don't have proof, that they are now including weather into the mix, as my few exceptions were during very hot weather events where my cooling load was much larger than normal.

I left my sell prices 20% lower than my buy prices for well over a week in the hopes that it would work again. It never did.

 

[wwhitney]

During partial peak and peak hours I want it to self consume the solar, send the excess to the grid, and only draw from the Powerwalls when I'm not producing enough solar.

Why? What's the upside to this behavior?

Say you have enough PV during off-peak to charge your PWs from Reserve to 100%. Then you start Peak at 100% PW, and economically you want to end Peak at Reserve level on PWs. The available energy will whatever PV makes after Peak starts plus the PW available energy, (100% - Reserve Level)*PW capacity.
You want to use that energy to cover all the house usage, and export any remainder.

As long as it's doing that, it doesn't matter when the PWs discharge during the Peak period. [To first approximation; the existence of VPP and of Part Peak are exceptions.] I'm more or less assuming "Export Everything" is turned on, although for the case that during Peak hours house usage > PW available energy, that doesn't matter.

So what alternate behavior do you want? To maximize PW charge level at end of Peak, while not drawing anything from the grid during Peak? That behavior will cost you money, as you will end up exporting more PV during off-Peak, rather than storing the off-Peak PV in the PWs to export during Peak. But it will increase your PW overnight charge level and thus given you more cushion if there's an overnight power outage.

If that's what you want, i.e. priorities No Peak Grid Draw > Max Reserve for an Outage > Cost Savings, then I'm not sure if the current PW logic supports those choices.

Cheers, Wayne

 

[aesculus]

I'm more or less assuming "Export Everything" is turned on

I have a slightly off topic question about Export Everything. I know with PG&E we are bound by only being allowed to export solar we generate (VPP excepted). But with EE, as it time shifts the solar, is that allowed under our rules? Ie I put it in the PWs during off or partial peak and then TBC dumps the PWs energy to the home and excess to the grid along with currently generated solar? Also does this seem to work? ie will the PW get to the end of peak at the reserve? I guess I need to turn it on and try it.

 

[ArizonaJon]

RKCRLR, I am using TBC. I have a 4 cents offset during peak and my system uses PW during peak. I actually have 4 time periods. In the summer, it is one peak, two shoulder and one super off peak. System has ran correctly for several years.
In the winter it is even messier as we have 2 peak times. Usually it only uses PW for power them. But if I have too much demand in the morning, it has to go to the grid until there is enough solar. I keep a large 60% reserve on my 2 PWs. Good luck with your latest settings.

 

[ucmndd]

The stated intent of time based control is to maximize monetary value given your utility plan. Exporting as much solar as possible to the grid during peak time and powering house loads with the powerwalls is exactly what it should be doing given the large price delta between peak and off peak on EV2-A under NEM2.

Sounds like you’re looking for self-powered mode.

 

[RKCRLR]

Why? What's the upside to this behavior?

Say you have enough PV during off-peak to charge your PWs from Reserve to 100%. Then you start Peak at 100% PW, and economically you want to end Peak at Reserve level on PWs. The available energy will whatever PV makes after Peak starts plus the PW available energy, (100% - Reserve Level)*PW capacity.
You want to use that energy to cover all the house usage, and export any remainder.

As long as it's doing that, it doesn't matter when the PWs discharge during the Peak period. [To first approximation; the existence of VPP and of Part Peak are exceptions.] I'm more or less assuming "Export Everything" is turned on, although for the case that during Peak hours house usage > PW available energy, that doesn't matter.

So what alternate behavior do you want? To maximize PW charge level at end of Peak, while not drawing anything from the grid during Peak? That behavior will cost you money, as you will end up exporting more PV during off-Peak, rather than storing the off-Peak PV in the PWs to export during Peak. But it will increase your PW overnight charge level and thus given you more cushion if there's an overnight power outage.

If that's what you want, i.e. priorities No Peak Grid Draw > Max Reserve for an Outage > Cost Savings, then I'm not sure if the current PW logic supports those choices.

Cheers, Wayne

I'm a net producer so I only get compensated at ~$0.07/kWh at true-up. So sending power back to the grid during peak hours vs non-peak hours is less important as long as I have enough credit in dollars so I don't wind up negative at true-up. So round trip efficiency and NBCs become more important. My NBCs are the biggest part of my bill.

Sometimes I draw power from the grid when the Powerwalls are recharging in the mornings. The lower their level the more power I draw from the grid and thus more NBCs.

I live in an area of frequent power outages. I currently have my reserve set at 40% which lets me squeak through the night on my reserve if the power goes out in most but not all circumstances (50% would be better). Prioritizing solar to the house during peak hours would provide a higher level of charge in the Powerwalls at the end of peak hours and more cushion in keeping the house running during an outage especially in the winter where I may not be producing much solar in the morning. Even without an outage it would give me a higher likelihood to make it through the peak periods in the winter without drawing from the grid.

And all this is ignoring additional cycles (potential life reduction) on the Powerwalls that may be unnecessary.

 

[ucmndd]

I'm a net producer so I only get compensated at ~$0.07/kWh at true-up. So sending power back to the grid during peak hours vs non-peak hours is less important as long as I have enough credit in dollars so I don't wind up negative at true-up. So round trip efficiency and NBCs become more important. My NBCs are the biggest part of my bill.

Sometimes I draw power from the grid when the Powerwalls are recharging in the mornings. The lower their level the more power I draw from the grid and thus more NBCs.

I live in an area of frequent power outages. I currently have my reserve set at 40% which lets me squeak through the night on my reserve if the power goes out in most but not all circumstances (50% would be better). Prioritizing solar to the house during peak hours would provide a higher level of charge in the Powerwalls at the end of peak hours and more cushion in keeping the house running during an outage especially in the winter where I may not be producing much solar in the morning. Even without an outage it would give me a higher likelihood to make it through the peak periods in the winter without drawing from the grid.

And all this is ignoring additional cycles (potential life reduction) on the Powerwalls that may be unnecessary.

So again, it sounds like what you’re looking for is self powered mode, not TBC.

“Minimize draw from the grid” is the stated purpose of that configuration, and what you appear to be looking for.

 

[RKCRLR]

^^^
I want to maximize my savings while also maximizing my SOC for outages. I don't think self powered will do that.

 

[ucmndd]

I want to maximize my savings while also maximizing my SOC for outages. I don't think self powered will do that.

Seems to me that’s precisely what TBC plus your reserve setting accomplishes. Maybe I’m missing something.

If you want more reserve or less cycling of the batteries, you should set the reserve higher. If you set it high enough, the PW learns what it needs to get you through peak time and will send solar to the house if necessary to not draw from the grid during peak.

 

[RKCRLR]

Seems to me that’s precisely what TBC plus your reserve setting accomplishes. Maybe I’m missing something.

If you want more reserve or less cycling of the batteries, you should set the reserve higher. If you set it high enough, the PW learns what it needs to get you through peak time and will send solar to the house if necessary to not draw from the grid during peak.

I used to have my reserve at 50% but I would often wind up drawing from the grid during partial peak. Drawing from the grid during partial peak may not hurt me at true up but I would have to monitor it and make adjustments to make sure. I'd prefer to have a setting that I can set and forget. Allowing me to to prioritize solar to my house could make this a more set and forget while having a higher SOC in case of power outages.

Maybe I'm missing something. If someone wants to provide an example where I'd be better off without prioritizing solar to my house during peak hours when I'm a net producer but still maximizing SOC for power outages I'd be in interested in seeing it.

As I mentioned, I think people transitioning to NEM3 will be even more interested in this.

 

[wwhitney]

I tried self powered a while ago and it didn't work as I wanted. It would draw from the grid during peak hours. I never want to draw from the grid during peak hours unless my Powerwalls are at their reserve limit.

So, the issue is that in self consumption mode, the control algorithm doesn't pay attention to peak vs non-peak, and doesn't prioritize failures to self-consume to occur during non-peak? Do you know for sure that this peak grid draw behavior would result in greater dollar costs to you? As if you'd still be at a net credit at True-Up, then I believe you'll get your kWh based compensation regardless, and you'll just pay for NBCs and minimum monthly charges.

Or for a more extreme example, if you're a net producer of kWh, do you know that setting the PWs to Backup Only would be more expensive than using the PWs to time shift load or production?

Cheers, Wayne

 

[RKCRLR]

So, the issue is that in self consumption mode, the control algorithm doesn't pay attention to peak vs non-peak, and doesn't prioritize failures to self-consume to occur during non-peak? Do you know for sure that this peak grid draw behavior would result in greater dollar costs to you? As if you'd still be at a net credit at True-Up, then I believe you'll get your kWh based compensation regardless, and you'll just pay for NBCs and minimum monthly charges.

Or for a more extreme example, if you're a net producer of kWh, do you know that setting the PWs to Backup Only would be more expensive than using the PWs to time shift load or production?

Cheers, Wayne

No, it is a valid point that I don't know if using self-consumption mode would knock me below the rate threshold and cause me to owe money at true-up. In fact I don't know if prioritizing solar for self-consumption wouldn't knock me over the threshold. The problem is the calculations are so complicated and there are so many variables that I don't know how to accurately predict it. The only way I know would be to monitor it and intervene if it looks like I would break the threshold.

What I do know is when I was in self-consumption mode there were times when the system drew a significant amount of power from the grid during partial peak and peak periods.

Perhaps my evaluation is too simplistic. Here's the way I look at it assuming I don't break the rate threshold for not owing money at true-up:

Self consuming solar costs $0.07/kWh. This is what I would get compensated at true-up if I sent the power to the grid instead of using it.

Self consuming power from the Powerwalls costs me $0.077/kWh. That includes what I would get compensated at true-up if I sent the power to the grid instead of consuming it plus the 10% round-trip efficiency loss.

Consuming power from the grid costs me $.010/kWh. That includes what I wouldn't get compensated for at true-up when I draw from the grid plus $0.03/kWh for NBCs.

So, my cheapest power is when I self-consume solar, it costs me a little more to use solar from my Powerwalls, and my most expensive power is from the grid. The main advantage of self-consuming solar vs consuming from the Powerwalls would the higher SOC at the end of off-peak. This could either be used for more margin if the power were to go out or reduced consumption from the grid (and lower NBCs) overnight by extending the off-peak hours through the night.