Optimizing NEM2.0 for PG&E EV2-A rate

[BGbreeder]

That does sound like a better approximation. But I do not rely on the $$ numbers from the Tesla app, I just want the PW to behave "correctly".

On my EV2-A rates, the discounted partial peak export would still come in higher than off-peak import, and peak export even more. So I would not expect your adjustment to effect the PW export or grid charging behavior.

Or am I missing something here?

Treating the Powerwall gateway algorithm as a black box, I would try adjusting the relative pricing until you get the behavior(s) that you want. I reviewed your prior posts, and I am not sure that I fully understand what you want to achieve, and to what goal, sorry.

All the best,

BG

 

[aesculus]

FWIW, I'm not exporting from my powerwalls.(Not allowed, except for peak demand events.) I did not get reasonable export behavior from my solar/Powerwall system until I modified the pricing, but I am entirely willing to believe it was coincidental.

All the best,

BG

Fair enough. We don't really understand what is going on under the covers at Tesla. Adding the NBC surcharge for my exported power got it to behave properly for me, but I really don't know what or how they do what they do. I also don't do exports and will probably cancel my VPP this season as I don't think it was worth the money for the offset in lifestyle and equipment impacts.

I am pretty surprised at some of their dynamics though. For example today they held back power export even though it was a short peak period in order to supply the house. In real-time they made a decision to do that where last week they ended up not using very much of the PWs at all and we used much of the reserve during the week. They even diverted some solar power into charging the PWs during peak. At the end of peak we were just at my reserve of 20% and then they started charging (at a whopping 600 W) the powerwalls.

And we also know whenever we make a change in the configurations/pricing it can sometimes take days for it to change the behavior.

 

[swedge]

I reviewed your prior posts, and I am not sure that I fully understand what you want to achieve, and to what goal, sorry.

I sized the solar and setting to try and keep the true-up adjustment near zero.

Sorry, I thought my goal of achieving minimum $ to PG&E was clear, and is aligned with the Original Poster's issues:

Optimizing NEM2.0 for PG&E EV2-A rate

Does anyone have experience in ensuring things are optimized for maximum monetary offset? I’m PGE & EV2A rate. My understanding is that PGE has a cap to how much excess generation you can send to the grid each month, based more or less on the PVWatts calculations once all your system...

teslamotorsclub.com

 

[YRide]

That does sound like a better approximation. But I do not rely on the $$ numbers from the Tesla app, I just want the PW to behave "correctly".

On my EV2-A rates, the discounted partial peak export would still come in higher than off-peak import, and peak export even more. So I would not expect your adjustment to effect the PW export or grid charging behavior.

Or am I missing something here?

It does seem like my system isn’t ideal…

Here’s what I’m currently using for pricing…

Originally the system was working fine in with grid charging off (I was pre PTO). So ESS was charging from only sun, and it had plenty of headroom each day. The SoC curves looked good, as it basically hit 100% or near that right around 4p peak rates. Though I could send to grid because I wasn’t PRO.

However, I got PTO the day after that photo…then flipped on grid charging. Initially I thought charging to some level starting at midnight made sense. Below it goes start to 66% SOC, then anticipates Solar getting it right to 100% during the day. This is ideal behavior I think. However, it only did this for a few days right after PTO.

Also, wouldn’t it be better for the ESS to wait for the grid charging until as close to 3p as possible? Then it knows more about that days PV production more accurately. It can minimize grid consumption, and NBC’s.

However, what it eventually wound up doing for last several weeks is this. Basically at straight to 90% after midnight. It doesn’t make any sense to me. It then makes me need the Charge on Solar feature to prevent from generating too much off peak so I don’t exceed the monthly PVWatts limits on generation.

Also, I can’t understand why my system goes straight to 5% reserve (my setting) at 4p. It leaves no SoC above 5% reserve for the 9p-12a shoulder, which isn’t cheap. And almost 25% of the time it actually consumes a bit at peak rates even because it’s dissipated the SOC down to reserve.

Any insights to adjust (rates?) would be appreciated.

I thought about maybe turning off grid charging, but then that won’t ensure I max out SOC each day so I can put max onto grid at peak rates (under the PVWatts threshold) for NEM2 swapping later in winter.

 

[BGbreeder]

I think that you need more separation of your buy and sell prices.

FWIW: My math includes the 10% power loss of the storage, plus the NBCs, plus another 10% difference to make sure that the system doesn't do unwanted things like buy peak power. That results in early charging of the powerwalls on off peak solar, that may dribble into mid-peak, followed by mid-peak and peak exports of solar in excess of home usage, and self-powered peak.

All the best,

BG

 

[swedge]

It does seem like my system isn’t ideal…

Here’s what I’m currently using for pricing…

View attachment 958279

Originally the system was working fine in with grid charging off (I was pre PTO). So ESS was charging from only sun, and it had plenty of headroom each day. The SoC curves looked good, as it basically hit 100% or near that right around 4p peak rates. Though I could send to grid because I wasn’t PRO.

View attachment 958280

However, I got PTO the day after that photo…then flipped on grid charging. Initially I thought charging to some level starting at midnight made sense. Below it goes start to 66% SOC, then anticipates Solar getting it right to 100% during the day. This is ideal behavior I think. However, it only did this for a few days right after PTO.

Also, wouldn’t it be better for the ESS to wait for the grid charging until as close to 3p as possible? Then it knows more about that days PV production more accurately. It can minimize grid consumption, and NBC’s.

View attachment 958281

However, what it eventually wound up doing for last several weeks is this. Basically at straight to 90% after midnight. It doesn’t make any sense to me. It then makes me need the Charge on Solar feature to prevent from generating too much off peak so I don’t exceed the monthly PVWatts limits on generation.

Also, I can’t understand why my system goes straight to 5% reserve (my setting) at 4p. It leaves no SoC above 5% reserve for the 9p-12a shoulder, which isn’t cheap. And almost 25% of the time it actually consumes a bit at peak rates even because it’s dissipated the SOC down to reserve.

Any insights to adjust (rates?) would be appreciated.

I thought about maybe turning off grid charging, but then that won’t ensure I max out SOC each day so I can put max onto grid at peak rates (under the PVWatts threshold) for NEM2 swapping later in winter.

View attachment 958282

Wow! Them is some pretty big numbers! 20kW from your 4 PWs, looks like up to 16 kW or so peak to the house, car charging perhaps late on that 6/26 screen shot? Solar is harder to make out, maybe 8kW peak or so.

Also, I can’t understand why my system goes straight to 5% reserve (my setting) at 4p. It leaves no SoC above 5% reserve for the 9p-12a shoulder, which isn’t cheap. And almost 25% of the time it actually consumes a bit at peak rates even because it’s dissipated the SOC down to reserve.

PW dumped the power onto the grid during the 3-9pm peak, credited at $0.53 per kWh. You then re-imported at the partial peak buy rate of $0.45, netting around 8¢ per. Less than that as BG points out due to round trip loss. The alternative would be to not export that energy during peak so as not to reimport it. This is probably what you'll see it do when on the winter prices.Basically at straight to 90% after midnight. It doesn’t make any sense to me.

However, what it eventually wound up doing for last several weeks is this. Basically at straight to 90% after midnight. It doesn’t make any sense to me.

Mine is not doing that, but with only one PW, my solar easily brings it up to 100% these days. Perhaps yours figured out that your solar would not bring it up to 100% and the flat pricing from midnight till 3pm makes it not matter when it charges. Also, my car charger is connected before the gateway, so not backed up, but also not metered by the PW, so that is not included in PW's planning.

If you turn off grid charging, Export Everything will still dump any excess during peak, but the total exports won't exceed the PG&E estimate. In my case, even with grid charging (the one PW) I never get near the export limit. Be glad, though, that PG&E no longer requires a non-export feature or an expensive NGOM (sp?) meter on your solar + storage system.

To minimize NBC, I sometimes charging our Model Y to use, rather than export solar after the PW is full. I set the charge rate to match solar minus house, i.e. what would export if I didn't use it. I set the car charge limit to stop charging at 3 when it is better to export. Tesla has announced but not yet shipped a new "Drive on Sunshine" feature to automate this, so I'm looking forward to that.

In any event, you now get the joy of the "Black and White" detailed bill, which is more of an obfuscation that an illumination. But there are things there you should probably keep an eye on, such as the accumulating balances, NBCs and such. There are a number of threads here on TMC to help decode the B&W bill and True-Up accounting.

You are doing great, coming up to speed on your new personal power plant. We have a neighbor with a PW for several years now, but we just fixed an installation error which had the PW thinking the house was often consuming a negative amount of power. You are years ahead of the game!

SW

 

[YRide]

Wow! Them is some pretty big numbers! 20kW from your 4 PWs, looks like up to 16 kW or so peak to the house, car charging perhaps late on that 6/26 screen shot? Solar is harder to make out, maybe 8kW peak or so.


PW dumped the power onto the grid during the 3-9pm peak, credited at $0.53 per kWh. You then re-imported at the partial peak buy rate of $0.45, netting around 8¢ per. Less than that as BG points out due to round trip loss. The alternative would be to not export that energy during peak so as not to reimport it. This is probably what you'll see it do when on the winter prices.Basically at straight to 90% after midnight. It doesn’t make any sense to me.

Mine is not doing that, but with only one PW, my solar easily brings it up to 100% these days. Perhaps yours figured out that your solar would not bring it up to 100% and the flat pricing from midnight till 3pm makes it not matter when it charges. Also, my car charger is connected before the gateway, so not backed up, but also not metered by the PW, so that is not included in PW's planning.

If you turn off grid charging, Export Everything will still dump any excess during peak, but the total exports won't exceed the PG&E estimate. In my case, even with grid charging (the one PW) I never get near the export limit. Be glad, though, that PG&E no longer requires a non-export feature or an expensive NGOM (sp?) meter on your solar + storage system.

To minimize NBC, I sometimes charging our Model Y to use, rather than export solar after the PW is full. I set the charge rate to match solar minus house, i.e. what would export if I didn't use it. I set the car charge limit to stop charging at 3 when it is better to export. Tesla has announced but not yet shipped a new "Drive on Sunshine" feature to automate this, so I'm looking forward to that.

In any event, you now get the joy of the "Black and White" detailed bill, which is more of an obfuscation that an illumination. But there are things there you should probably keep an eye on, such as the accumulating balances, NBCs and such. There are a number of threads here on TMC to help decode the B&W bill and True-Up accounting.

You are doing great, coming up to speed on your new personal power plant. We have a neighbor with a PW for several years now, but we just fixed an installation error which had the PW thinking the house was often consuming a negative amount of power. You are years ahead of the game!

SW

Lots to read here and digest. Good thing I have a 16hr flight coming. Many thanks for all your insights @swedge

Just now realizing that my inverters appearing to by overheating and clipping out multiple times a day after lunch. This is definitely more involved then I thought! The EE degree is paying off now?

 

[swedge]

Lots to read here and digest. Good thing I have a 16hr flight coming. Many thanks for all your insights @swedge

Just now realizing that my inverters appearing to by overheating and clipping out multiple times a day after lunch. This is definitely more involved then I thought! The EE degree is paying off now?

View attachment 958436

Something else strange about that solar graph: Before around 1, during the time the PowerWall was still charging, the drop-outs didn't appear to decrease the total solar production, but rather went to charge the PW instead. What it is showing there is large drops in the blue line, which is house draw, and the PW soaking up the difference.

After the PW stopped charging, around 1PM, the actual solar appears to drop down temporarily.

This suggests that the solar may not be the source of the glitches.

Strange...

Did you have a 747 circling overhead, casting shadows on you solar? Gremlins? Or maybe power line glitches, like a PG&E crew bumping lines together in a belated 4th of July Spark-Works display?

Seriously, though, look at each of the component graphs to see which is glitching. And bear in mind that the PowerWall Gateway actually measures the solar, the grid, and the PowerWall flows (with current transformers), but it calculated the house consumption flow as the net of the other three. This makes measurement errors give baffling results. But the grid and solar number can often be cross checked with the PG&E meter and the inverter's display respectively, and the PW flow is controlled by the gateway and so is probably reliable. The displayed data is in 5 minute intervals, and may be interpolated a bit.

I'm not sure, but brief grid outages might look like this. If PW is full, solar has to shut down because there is no where else for it to go. But while PW is charging, it will take over and keep the solar running and will absorb the excess by charging. It takes a couple minutes for solar to resync when the grid comes back. Anyway, this is just a hunch. Oh, the app can show a history of backup events, at the bottom of the Impact page.

Good luck figuring this one out! Hopefully not a problem with your hardware or installation...

SW

 

[swedge]

Lots to read here and digest. Good thing I have a 16hr flight coming. Many thanks for all your insights @swedge

Just now realizing that my inverters appearing to by overheating and clipping out multiple times a day after lunch. This is definitely more involved then I thought! The EE degree is paying off now?

View attachment 958436

I did a little experiment. At around 4 pm, I took my PW off-grid for just a moment. The conditions were different from yours: my home had been running on solar and was just switching to battery to take full advantage of the peak (EV2-A) rate. But here is what it looked like.

The battery was fully charged, solar was running the house and exporting the excess. When I took it off-grid, the solar stopped and the battery took over the house. I quickly reconnected to the grid, and a couple minutes later things returned to normal.

Here is the view from the grid point of view:

Solar had been exporting, it went to zero briefly, the solar restarted exporting, and the battery started its 4pm export everything dump. I think my system limits export to 5kW because that is what the PW can do and what the interconnection design specified.

So it looks pretty similar to your strange glitches. Perhaps you went off-grid a few times, maybe just because of a line surge or something. Perhaps your solar re-syncs faster than my flock of 20 micro inverters.

Anyway, good luck watching for repeats and figuring out your glitches.

SW

 

[YRide]

I did a little experiment. At around 4 pm, I took my PW off-grid for just a moment. The conditions were different from yours: my home had been running on solar and was just switching to battery to take full advantage of the peak (EV2-A) rate. But here is what it looked like.
View attachment 958507
The battery was fully charged, solar was running the house and exporting the excess. When I took it off-grid, the solar stopped and the battery took over the house. I quickly reconnected to the grid, and a couple minutes later things returned to normal.

Here is the view from the grid point of view:View attachment 958508
Solar had been exporting, it went to zero briefly, the solar restarted exporting, and the battery started its 4pm export everything dump. I think my system limits export to 5kW because that is what the PW can do and what the interconnection design specified.

So it looks pretty similar to your strange glitches. Perhaps you went off-grid a few times, maybe just because of a line surge or something. Perhaps your solar re-syncs faster than my flock of 20 micro inverters.

Anyway, good luck watching for repeats and figuring out your glitches.

SW

In my case those cutouts were at regular intervals every day after about 12p for the last two weeks it seems. So I really don’t think this is a grid down issue, seems way too periodic & consistent.

Also, when I went to the app it looks like Tesla must have detected something…I didn’t file this:

Let’s see where this goes…I’m losing about 10-12kWh generation per day on this.

 

[YRide]

Tesla Energy finally acknowledged a problem with HW. Scheduled an appointment with me in September to come fix it.

In meantime, one of three Y’s got “Charge on Solar”, as did Powerwalls/GW2. So been playing with that. Actually, added ChargeHQ ($5/mo plan) on top of that to handle the other two Y’s that don’t have the CoS FW (2023.26.x). So far it’s all kinda working together nicely, I’m impressed.

I also reduced the sell rates down by a few cents across the board to account fit some of the RT loss. New rates:

Still a few things perplex me…

1) why is the powerwall still charging yo 90% right after midnight each night? Isn’t that causing excessive grid pull (NBC’s) and also making extra daytime generation of PV that draws down from my monthly PVWatts generation limit at lower NEM2 rates?

2) why is the powerwall dumping to 5% (reserve) immediately at 4p? This is causing me to pull some peak kW from the grid just before 9p, and also even more from shoulder 9p-12a.

Do I need to basically adjust the sell rate of Peak (currently 51c/kWh) to be below the buy rate of Mid-Peak (currently 45c)? Will that cause the PW to save a little power above reserve to get me through Peak + Mid Peak without any grid pull?

 

[miimura]

Just for your own education, I would suggest disabling Grid Charging and Export Everything just to see how it behaves without those. If you have an actual need for either one, turn it back on after you see what the "Normal" operation looks like. I would only need Grid Charging during the darkest 3 months of Winter. I have not used it because I took the tax credit that technically required the batteries to be charged 100% from on-site renewable energy. That is no longer a requirement for the IRA authorized tax credit.

 

[swedge]

Still a few things perplex me…

1) why is the powerwall still charging yo 90% right after midnight each night? Isn’t that causing excessive grid pull (NBC’s) and also making extra daytime generation of PV that draws down from my monthly PVWatts generation limit at lower NEM2 rates?

2) why is the powerwall dumping to 5% (reserve) immediately at 4p? This is causing me to pull some peak kW from the grid just before 9p, and also even more from shoulder 9p-12a.

Do I need to basically adjust the sell rate of Peak (currently 51c/kWh) to be below the buy rate of Mid-Peak (currently 45c)? Will that cause the PW to save a little power above reserve to get me through Peak + Mid Peak without any grid pull?

1) Mine does not do this. And yes, it will cost you in NBCs. I'd suggest turning off Grid Charging, which should prevent any such. The rate screen shot came out pixelated, so I can't read the prices. But I think you have them right.

It is as if your PW does not trust it'll have enough solar beyond your consumption to charge to 100%. Two ideas here. First, I wonder if the wacky solar dropouts are confusing the PW. The other is if PW is planning to discharge to the car?

Mine also does not show car charging. Is that a 2023.26 thing? i.e. does it include all your cars, or only the CoS car? Is the red line CoS?

2) Also strange. Mine does start discharging to the grid at 4, while I would expect it to do this later. (Since the export is limited to a certain rate, and the export will include a variable and unpredictable amount of solar, it may have trouble estimating when to start dumping.) But getting down to reserve before the price drops is undesirable. It might do this occasionally if your consumption is higher than PW predicts, but that should only happed on unusual days. Here too, I wonder if the car charging is making it hard for PW to guess what is going to happen.

I was quite surprised to see mine grid charge one day when the previous days had been sunny. It sure seeded to have used the local weather forecast to decide what to do. My point is that with some settings and rate plans it will need to guesstimate timing and sizes of loads and generation. Mine may behave more predictably because I had my car charing wired outside of the gateway and it's metering, so my PW doesn't know anything about our sporadic car charging.

I'm sorry I don't have good answers for you. Hopefully getting your inverter drop-outs fixed will simplify things a bit.

 

[swedge]

Just for your own education, I would suggest disabling Grid Charging and Export Everything just to see how it behaves without those.

YRide,

I agree with miimura here. Observe your system's behavior in various situations and with various settings to see what the settings do.

Much depends on your system and your usage. Solar size, home and car consumption and timing, for example.

NEM also takes a bit of study too, and the optimum strategy also depends on the details of your particular situation. What works for me is irrelevant to h2ofun, for example. He has 30kW solar and 7 Powerwalls to my 5kW and one PW. But he also has heat pumps for heat and cooling, while I have a gas furnace and ventilation cooling. So our objectives and settings are quite different.

Besides, all of it is guesswork till you get your annual true-up. I did a detailed forecast for my year, and tracked forecast vs actual as the year progressed. When I got my first NEM2 true-up this June, PG&E did not follow their own rules and undercharged me a couple hundred $, as far as I can figure out. Oh, and then they trued me up again in July! Talk about unpredictable. In another posting here on TMC, there was a surprise true-up of several $k due, it turned out, to a malfunction in his heat pump. So, try as you might, getting close is the best you can try for.

The bottom line is that each situation is different, so you get to figure yours out as you go along. Oh, and once you do, Tesla may well introduce a new feature which upset your applecart. Charge on Solar is just the most recent such, and may help me somewhat reduce my NBCs, which were (incorrectly I think) the basis of my recent true-up.

On the other hand, most PW owners just set it and forget it, and don't care enough to optimize. A friend in Santa Cruz had an $1,800 true-up. When I looked at his settings, I found he had 75% backup reserve setting. The made it so his 2 PWs could not cover even his peak period consumption. It had been that way for 3 years. One tweak of the slider will save him hundreds, maybe thousands. But he could afford not to notice, so it was OK.

You are paying attention, finding glitches, and learning quickly. Good on you.

 

[YRide]

1) Mine does not do this. And yes, it will cost you in NBCs. I'd suggest turning off Grid Charging, which should prevent any such. The rate screen shot came out pixelated, so I can't read the prices. But I think you have them right.

It is as if your PW does not trust it'll have enough solar beyond your consumption to charge to 100%. Two ideas here. First, I wonder if the wacky solar dropouts are confusing the PW. The other is if PW is planning to discharge to the car?

Mine also does not show car charging. Is that a 2023.26 thing? i.e. does it include all your cars, or only the CoS car? Is the red line CoS?

2) Also strange. Mine does start discharging to the grid at 4, while I would expect it to do this later. (Since the export is limited to a certain rate, and the export will include a variable and unpredictable amount of solar, it may have trouble estimating when to start dumping.) But getting down to reserve before the price drops is undesirable. It might do this occasionally if your consumption is higher than PW predicts, but that should only happed on unusual days. Here too, I wonder if the car charging is making it hard for PW to guess what is going to happen.

I was quite surprised to see mine grid charge one day when the previous days had been sunny. It sure seeded to have used the local weather forecast to decide what to do. My point is that with some settings and rate plans it will need to guesstimate timing and sizes of loads and generation. Mine may behave more predictably because I had my car charing wired outside of the gateway and it's metering, so my PW doesn't know anything about our sporadic car charging.

I'm sorry I don't have good answers for you. Hopefully getting your inverter drop-outs fixed will simplify things a bit.

I’ll turn off grid charging and see what that does. Long term, I don’t think this is an option. Peak summer, no clouds, I’m generating about 62kWh. So I’ll definitely need Grid charging for 51kWh (4x PW with a 5% reserve). Even for cloudy/rainy days in spring and fall I don’t think I’ll be able to top off the powerwalls.

Yes, red is cars that are now CoS eligible. It seems like Tesla is now tracking that.

I’ll need to figure out how to get the powerwalls to hold charge further into the evening. It doesn’t make sense to pull from the grid peak or even shoulder I think. I suppose if I adjust the sell rate of peak to below the buy rate of shoulder, then the PW’s should try to plan for having enough charge from 3p all the way until midnight.

 

[swedge]

I suppose if I adjust the sell rate of peak to below the buy rate of shoulder, then the PW’s should try to plan for having enough charge from 3p all the way until midnight.

It can make sense to discharge to export during peak and then re-import during partial peak. Saving PW capacity to run the house through partial peak means less export during peak.

When I first tried Export Everything, this was a surprise for me too. I was quite happy with the standard Solar Export Only keeping us off-grid for the entire peak and partial peak time. So to see it now drawing from the grid during partial peak caused a bit of head scratching. Now I'm bald. ;-)

This behavior is a result of the cost savings calculation the PW makes for Export Everything, so adjusting the prices will probably change the behavior. Easier might be to just set the peak time to go all the way to midnight. Either way will mess up the $ numbers on the impact pages, but I've not found those useful anyway - they know nothing about true-ups. But I think you will find it saving you a bit less on your true-up.

 

[YRide]

It can make sense to discharge to export during peak and then re-import during partial peak. Saving PW capacity to run the house through partial peak means less export during peak.

When I first tried Export Everything, this was a surprise for me too. I was quite happy with the standard Solar Export Only keeping us off-grid for the entire peak and partial peak time. So to see it now drawing from the grid during partial peak caused a bit of head scratching. Now I'm bald. ;-)

This behavior is a result of the cost savings calculation the PW makes for Export Everything, so adjusting the prices will probably change the behavior. Easier might be to just set the peak time to go all the way to midnight. Either way will mess up the $ numbers on the impact pages, but I've not found those useful anyway - they know nothing about true-ups. But I think you will find it saving you a bit less on your true-up.

That’s a good point, could always just change the time windows. Though I guess the more accurate way would be just really calculate the round trip loss + the NBC offset, and let the algorithm do it.

I guess basically if the true rates (inc RT losses) basically are that peak sell is still > mid-peak buy, then it financially makes sense to sell during peak and then re-import during later mid-peak. That’s not accounting for wear and tear on system of course.

The other part that makes me think the algorithm isn’t fully adjusting…wouldn’t it be more advantageous to the user if the PW waited until a little into the peak window to basically finish full discharge right at 9p end of peak? One, you want to always deist discharge until the last possible moment in case a power outage. Two, similar, in case there’s a last minute / emergency VPP you want to have as much SoC as possible in PW ( note, I missed two recent VPP’s because Tesla announced them at like 845p and I was already at 5% reserve…it’s almost like they knew this). Three, it could allow the system to better account for both predictable and unpredictable home usage in the peak window.

FWIW, one day into having Grid Charging off has allowed me to fill the 4x PW’s to 100% SoC just at 3p, start dumping the twilight solar straight to grid, then at 4p dumping the full powerwall to reserve. And that is with my inverter issues currently which seem to account for a 10-12kWh loss in PV production per day. So this will greatly reduce NBC’s for extra import.

So this could work. But I think as we get toward fall/winter, I’ll need grid charging back on.

 

[swedge]

That’s a good point, could always just change the time windows. Though I guess the more accurate way would be just really calculate the round trip loss + the NBC offset, and let the algorithm do it.

Right. But there are a few true-up scenarios which depend on full year cumulative totals, which PW can't know till the end of the true-up year.

I guess basically if the true rates (inc RT losses) basically are that peak sell is still > mid-peak buy, then it financially makes sense to sell during peak and then re-import during later mid-peak. That’s not accounting for wear and tear on system of course.

You've got it.

The other part that makes me think the algorithm isn’t fully adjusting…wouldn’t it be more advantageous to the user if the PW waited until a little into the peak window to basically finish full discharge right at 9p end of peak? One, you want to always deist discharge until the last possible moment in case a power outage. Two, similar, in case there’s a last minute / emergency VPP you want to have as much SoC as possible in PW ( note, I missed two recent VPP’s because Tesla announced them at like 845p and I was already at 5% reserve…it’s almost like they knew this). Three, it could allow the system to better account for both predictable and unpredictable home usage in the peak window.

I agree. I was thinking today that perhaps it dumps early because it is not predicting that solar decreases predictably as evening approaches. Export is typically limited in the PTO, so how much the PW can export is limited by solar production. So to insure it can do the full dump, it starts early, just in case the sun decides to stay up late. I'm with you, later export would be better.

FWIW, one day into having Grid Charging off has allowed me to fill the 4x PW’s to 100% SoC just at 3p, start dumping the twilight solar straight to grid, then at 4p dumping the full powerwall to reserve. And that is with my inverter issues currently which seem to account for a 10-12kWh loss in PV production per day. So this will greatly reduce NBC’s for extra import.

I generally leave Grid Charging enabled. But then my car charging is not visible to my PW. Since home use is fairly predictable, while car charging is large and can occur at different times, your PW may be trying to conserver SOC in case you decide to charge the car late in the day. Just a guess on my part.

So this could work. But I think as we get toward fall/winter, I’ll need grid charging back on.

Yeah. That is what I see mine doing.

In terms of clarifying what is going on, consider turning off both Export Everything and Grid Charging for a few days. PW should behave in ways that make much more sense, essentially time-shifting your consumption to minimize or eliminate your peak and partial peak imports. Then, when you turn these back on, you can see how the effects of also time-shifting the solar to export during peak: when PW can export to the grid, the buy/sell difference becomes relevant and makes things more complicated.

Back to your original question about optimizing, the real issue is the true-up. The goal is to minimize the True-Up Adjustment. Zero is as low as it can go, with a minor exception if you export more than you import and get a small Net Generation credit. Both Export Everything and Grid Charging help. I am finding that car charging during solar production also can help a little by reducing NBCs, which were the basis of my $67 true-up adjustment in June. But that is small change. Solar production is the big gain, PW helps a lot by using TOU and importing only off-peak, EE and GC help a bit, and car charge timing is fine tuning. We can discuss more as you go.

 

[YRide]

Right. But there are a few true-up scenarios which depend on full year cumulative totals, which PW can't know till the end of the true-up year.

You've got it.

I agree. I was thinking today that perhaps it dumps early because it is not predicting that solar decreases predictably as evening approaches. Export is typically limited in the PTO, so how much the PW can export is limited by solar production. So to insure it can do the full dump, it starts early, just in case the sun decides to stay up late. I'm with you, later export would be better.

I generally leave Grid Charging enabled. But then my car charging is not visible to my PW. Since home use is fairly predictable, while car charging is large and can occur at different times, your PW may be trying to conserver SOC in case you decide to charge the car late in the day. Just a guess on my part.

Yeah. That is what I see mine doing.

In terms of clarifying what is going on, consider turning off both Export Everything and Grid Charging for a few days. PW should behave in ways that make much more sense, essentially time-shifting your consumption to minimize or eliminate your peak and partial peak imports. Then, when you turn these back on, you can see how the effects of also time-shifting the solar to export during peak: when PW can export to the grid, the buy/sell difference becomes relevant and makes things more complicated.

Back to your original question about optimizing, the real issue is the true-up. The goal is to minimize the True-Up Adjustment. Zero is as low as it can go, with a minor exception if you export more than you import and get a small Net Generation credit. Both Export Everything and Grid Charging help. I am finding that car charging during solar production also can help a little by reducing NBCs, which were the basis of my $67 true-up adjustment in June. But that is small change. Solar production is the big gain, PW helps a lot by using TOU and importing only off-peak, EE and GC help a bit, and car charge timing is fine tuning. We can discuss more as you go.

Just got home from out of town and realized another reason I want to leave Grid Charging on even in mid summer…

The 52kWH of PV generated a day (normally 63kWh if my inverters aren’t having issues) is just enough to fill the 4x PW with a 5% reserve…BUT…on the full day cycle. If I want the PW’s filled to 100% SoC by 3pm , not by say 730p, I need some grid charging with the size of my PV array. That way at 4p I can dump full PW + dwindling solar at 4p peak rates.

It would be cool if you could fine tune PW behavior, say a max grid charge import per day. Perhaps ChargeHQ will do something like this? Or Tesla. But I guess they would rather have the algorithms control this.

 

[swedge]

Just got home from out of town and realized another reason I want to leave Grid Charging on even in mid summer…

The 52kWH of PV generated a day (normally 63kWh if my inverters aren’t having issues) is just enough to fill the 4x PW with a 5% reserve…BUT…on the full day cycle. If I want the PW’s filled to 100% SoC by 3pm , not by say 730p, I need some grid charging with the size of my PV array. That way at 4p I can dump full PW + dwindling solar at 4p peak rates.

It would be cool if you could fine tune PW behavior, say a max grid charge import per day. Perhaps ChargeHQ will do something like this? Or Tesla. But I guess they would rather have the algorithms control this.

I think you are right, that grid charging will probably help you.

Much of your PW discharge is due to Exporting Everything, i.e. discharging to the grid. Since grid charging should be done during off-peak, and PW export during peak, that extra export will reduce your NEM Charges, aka Cumulative Energy Charges and Credits. However, if you do so much of this that your cumulative is negative, i.e. a credit balance when true-up comes around, that will be ignored, and you will pay for the NBCs. So, if you do too much grid charging, the benefit goes away but the smaller NBC costs continue.

My theory is that they made this hard to predict so that we can't figure out the optimum approach. Off optimum means more $ for PG&E while the total solar and consumption are gonna be what they're gonna be.

If you can do a year long estimate of your solar production and house/car consumption, you may be able to estimate your true-up. I did this once, using monthly history data including breaking it down into TOU periods, but I don't really recommend it. Back of the envelope probably makes more sense. First you want to know if you are going to be a net generator or are going to owe a bunch at true-up.

In my case, while the NEM and NBC balances matched my projection pretty well, and was expecting a few hundred $ of true-up adjustment. But PG&E surprised me by truing up based on the NBCs even though the NEM balance was larger, adjusting only $67. Good news for me, but if they are going to do the same thing next time, I maybe should reduce the NBC's rather than strive for more NEM credits. This would suggest I do more car charging during the day directly from solar, and less grid charging, even though this latter would mean less peak period export. I am still trying to sort out the implications and cause of my strange NBC true-up, though. We all thought they true up to the largest of the NEM, NBCs, MDCs, and maybe Minimum Energy Charges. But that is not what they did for me, so confusion reigns when true-ups are near zero.