New Powerwall Advanced Options [Toggles for charging from and discharging to grid from powerwalls]

[jboy210]

We had no particular issues getting Powerwalls added to our existing solar, except for delays in getting PTO (during which the Powerwalls were operating normally). According to the statistics in the mobile app, we've had a total of 8 days of outage, so a little under 200 hours of outage since commissioning. The longest outage event was 3 days. You seem to imply that the only benefit we got from having Powerwalls was backup protection, but we bought ours originally for cost savings. They continue to perform in that role every day.

I'm quite happy with my investment in battery storage. As I wrote earlier, everyone's needs are different, so I would not claim that this approach is good for everyone.

(And I'm conscious of the fact that this is deviating somewhat from the thread topic, apologies for contributing to that topic drift.)

Bruce.

I don't think this topic drift, or at least not much. We have a new charge from grid option. This feeds into the discussion of should one get batteries at all and everyone's needs are a bit different.

We work from home and have for nearly a decade. For us losing power equates to losing work time which equates to potential loss of income. That is one of our reasons for having Powerwalls. Since getting them we have not lost a minute of worktime (billable or non-billable) due to Power outages.

 

[jboy210]

What good is the credit at the rate in force if they are paying 4 cents no matter the time? I don’t quite follow.

I had a bit of a time understanding this at first, and here is my understanding.

They are offsetting your usage with the energy you sent back. If you generate excess solar (say in Spring through Fall), then they use they credits to offset your usage during the winter months when you are pulling more grid then you send to the grid. So, this is effectively a credit at the market rate at time of use, such as $0.24/kWh. The only time the $0.04 rate comes in is if you still have excess credits at the "true-up date". That is, kWh credits paid @ $0.04 = kWh sent to grid - kWh used.

Someone please fix this if my understanding is faulty.

 

[jjrandorin]

What good is the credit at the rate in force if they are paying 4 cents no matter the time? I don’t quite follow.

You are mixing two things up (which is common as it relates to this specific topic). There is a difference between "how much credit you have on your account" and "how much you might potentially get a check cut for at the end of the year".

The credit credit goes on your account, with the "intention" being that you would be using it at some point during the year, NOT getting a check for it at the end of the 12 month true up period.

You get credit for it at the rate in force at the time its generated, and that credit is on your account for you to draw from when you are not generating solar energy. Thats why it matters what rate you get for the PV energy generated when its generated.

At the end of the 12 month true up period ( and ONLY at the end of your 12 month true up period), if you still have remaining credit, meaning you were a net generator for the 12 month period, at that time (and ONLY at that time) they can pay you for the over generation that is left on your account. They will only do so, however at the wholesale rate for the credit you didnt use during your 12 month period, not at the rate generated.

ONLY at the 12 month true up is that done, and its in relation to your yearly total (for most utilities anyway, I have heard stories of some that true up monthly).

I do; however, the increase in export during peak hours still would be offset by use later in the day so would simply be shifting use toward off peak hours… as would be anticipated with any solar system on a TOU plan. The effect might be a little more dramatic if charging from the grid, but the pattern is nothing unique that would suggest charging from the grid.
Do utilities really have time/resources to spend on monitoring/investigating this when a) it benefits them and b) it is the IRS that actually cares?

If you took the ITC towards the PW it is supposed to be charged with 100% PV. If you didn’t take the ITC, no worries.

It appears that you already know "whats supposed to be done" and are asking, in effect " Do I have to do what I am supposed to do? Is anyone going to care or is anyone tracking this? Will the utility report me somehow if I choose to not comply?"

I am not touching that part of the discussion because I dont know. I know what taking the ITC says we are supposed to do, and I know the utility knows how much power you export to them if you are exporting, and when you export it. Whether they will report, not report, etc or whether "someone will get caught" if they took the credit and are charging from the grid regularly anyway, I dont know.

To me, thats like asking if someone is going to check the deductions on your taxes, or if you would be found out if you have some deductions on your taxes you cant quite prove. Thats up to you, and your finances, and its not really something anyone else can advise on.

 

[wwhitney]

At the end of the 12 month true up period ( and ONLY at the end of your 12 month true up period), if you still have remaining credit, meaning you were a net generator for the 12 month period,

Have a remaining $ credit at true up is not the same as being a net generator in kWh. You only get paid if you are a net generator in kWh and have a $ credit, and then you are paid per the surplus kWh, regardless of the $ credit. If you are a net consumer of kWh, but have a $ credit because you net exported during Peak and net imported during Off Peak, you get nothing (but owe nothing).

Cheers, Wayne

 

[BruceHulkBanne]

You are mixing two things up (which is common as it relates to this specific topic). There is a difference between "how much credit you have on your account" and "how much you might potentially get a check cut for at the end of the year".

The credit credit goes on your account, with the "intention" being that you would be using it at some point during the year, NOT getting a check for it at the end of the 12 month true up period.

You get credit for it at the rate in force at the time its generated, and that credit is on your account for you to draw from when you are not generating solar energy. Thats why it matters what rate you get for the PV energy generated when its generated.

At the end of the 12 month true up period ( and ONLY at the end of your 12 month true up period), if you still have remaining credit, meaning you were a net generator for the 12 month period, at that time (and ONLY at that time) they can pay you for the over generation that is left on your account. They will only do so, however at the wholesale rate for the credit you didnt use during your 12 month period, not at the rate generated.

ONLY at the 12 month true up is that done, and its in relation to your yearly total (for most utilities anyway, I have heard stories of some that true up monthly).





It appears that you already know "whats supposed to be done" and are asking, in effect " Do I have to do what I am supposed to do? Is anyone going to care or is anyone tracking this? Will the utility report me somehow if I choose to not comply?"

I am not touching that part of the discussion because I dont know. I know what taking the ITC says we are supposed to do, and I know the utility knows how much power you export to them if you are exporting, and when you export it. Whether they will report, not report, etc or whether "someone will get caught" if they took the credit and are charging from the grid regularly anyway, I dont know.

To me, thats like asking if someone is going to check the deductions on your taxes, or if you would be found out if you have some deductions on your taxes you cant quite prove. Thats up to you, and your finances, and its not really something anyone else can advise on.

Thank you!

 

[getakey]

Think of your NEM as a PayPal account that you only pay up once a year. Some months you sell more than you buy (at retail $/kWh rate) and you accrue a credit. Other months you buy more than you sell and either draw against the credit or go positive on the account. At your true-up pay up time, if you have a negative balance, it just goes away and adjusts to zero to start the new year. If it is positive, you pay the amount due. Being a net producer or net user is an independent calculation based on total net kWh for the year. If you over produced (produced more than you used), you get paid the $.04/kWh. If you used more than you produced, there is nothing additional than your NEM bill. In my case, my NEM was negative, but I was NOT a Net Producer.

 

[wwhitney]

Being a net producer or net user is an independent calculation based on total net kWh for the year. If you over produced (produced more than you used), you get paid the $.04/kWh.

While being a net producer/consumer is an independent calculation, you only get paid the $0.04/kWh if you are both a net producer and have a credit $ balance (which gets erased and replaced by the $0.04/kWh). If you owe money at true-up, you just pay that amount, regardless of being a net producer/consumer. If your loads are more skewed towards Peak than your PV production is (assuming no production time-shifting), then you could end up with a balance due while being a net producer.

Cheers, Wayne

 

[getakey]

While being a net producer/consumer is an independent calculation, you only get paid the $0.04/kWh if you are both a net producer and have a credit $ balance (which gets erased and replaced by the $0.04/kWh). If you owe money at true-up, you just pay that amount, regardless of being a net producer/consumer. If your loads are more skewed towards Peak than your PV production is (assuming no production time-shifting), then you could end up with a balance due while being a net producer.

Cheers, Wayne

hmm - did not realize that you would not get the $.04 if your NEM balance was positive. Thanks for the clarification

 

[skepticcyclist]

Been following this thread since it was started and I still don’t have advanced options or grid charging option.

And my virtual power plant option has also been removed.

 

[Shwood]

If you import mostly off-peak, and export some solar at peak, it is possible to get more $ credit for exported solar than you owe for imported power, but at the annual true-up they just take away that excess credit.

Thanks/understood, but winter in Pittsburgh will take any credit I get from summer. (I also may be one of few EV-PV-PW setups in my utilities area, so might get more scrutiny charging from grid than I would in CA.)
That said, I think this may create another issue: if I charge off peak, end export more solar during peak, I pay supply/distribution/transmission when I charge, and get paid only the supply amount (I think) when I export. As a net user, this means I end up paying distrib/transmit charges to use energy that I could’ve just held onto if I hadn’t exported as much during summer months. If that is true (?), I’d actually lose money by charging off-peak and then paying transmit/distrib costs later when I need that energy.
Am I missing something?

 

[wwhitney]

hmm - did not realize that you would not get the $.04 if your NEM balance was positive. Thanks for the clarification

Yeah, if you owe them money under NEM, it doesn't matter if you're a net kWh exporter, you've already gotten NEM credits for those kWh. So you don't get a bonus $0.04 for them.

Cheers, Wayne

 

[wwhitney]

Am I missing something?

The Tesla app lets you set buy/sell rates for each TOU period. So the optimal behavior with just two tiers depends on 4 numbers.

For example, say off peak you can buy a kWh for $0.20 and you get to sell one for $0.15, and on peak you can buy a kWh for $0.40 and sell one for $0.35. [Made up numbers.] You generate 1.1 kWh off-peak. You can (a) use it to offset $0.22 of energy you'd otherwise buy while it's being generated (b) sell it for $0.165 immediately (c) put it in a battery to displace a kWh you'd have to buy later during Peak for $0.40, or (d) put it in a battery to sell it later for $0.35.

With the above numbers, economically c > d > a > b. So you want the system to fill the battery from off-peak solar, if it can, and to use excess instantaneous solar to the extent possible. Then you want it to cover all your house loads during peak, and export everything else (while never drawing from the grid).

I think on residential the billing interval is 1 hour, and I think that the NBCs (the reason for a NEM2 difference in buy vs sell) are also only charged on that 1 hour net usage. So the above reckoning really only applies hour by hour, rather than instantaneously.

Cheers, Wayne

 

[wwhitney]

I think on residential the billing interval is 1 hour, and I think that the NBCs (the reason for a NEM2 difference in buy vs sell) are also only charged on that 1 hour net usage. So the above reckoning really only applies hour by hour, rather than instantaneously.

Actually, I'm not sure about the above, maybe someone with NEM 2 could tell me. Does each hour just generate a single number of kWhs, + or -, or does it generate two different numbers, kWhs imported and kWhs exported? The latter based on a much shorter sampling period (how long?) and adding up the imports and exports separately.

Cheers, Wayne

 

[miimura]

In the NEM-PS billing, you can see there are "Channel IDs" that accumulate import (A suffix) and export (C suffix) quantities. I have never checked to see if the sum of the positive interval data for each TOU period equals exactly the A channel figures and the negative values equal exactly the C channel figures. If you have a large import at the beginning of the interval and large export at the end of the interval, it may be possible for the meter to accumulate those flows separately from the reported interval net value. Also, if PG&E feels that there is very peaky usage, they can move you to 15 minute intervals, even for residential accounts. At various times over the years since I got solar, my Green Button data has been reported in hour intervals and 15 minute intervals.

 

[ptdusn]

Been following this thread since it was started and I still don’t have advanced options or grid charging option.

And my virtual power plant option has also been removed.

Same here, no grid charging option. We are on SRP's E-13 plan. Which pays us $.03kW instantaneously, unless we over produce. Which at the end of the month they even things out. Right now we switched to Summer hours, peak time is 2pm to 8pm, ($.25kW), rest is off peak, ($.08kW).

 

[swedge]

so might get more scrutiny charging from grid than I would in CA

Shwood,

Much of the discussion here, certainly what I post, relates to California. Your utility certainly has somewhat different rules, so you'll need to talk with them or look those rules up for yourself. (Both of those suggestions are fraught: often our utility customer service reps get it wrong, and the tariffs are some of the most convoluted text ever published.)

Tesla says the grid charging option is only available in regions where it is allowed, so if your app has the grid charging option, you might just assume Tesla knows it is allowed for you. The ITC, on the other hand they suggest you check yourself. (Link)

The best strategy depends on the prices, rate periods, solar production, consumption, so it can be complicated. The exact behavior of the PW in Cost Savings mode is not described by Tesla, and not fully explored yet by us tinkers, so it might not behave exactly as we would hope.

Using mine as an example, since I am grandfathered on an old NEM1 tariff, my buy and sell prices are equal but do vary by time of day. PW would discharge to cover our consumption during peak price times, but only if there was enough charge from solar. So, during the winter I started charging from the grid as soon as the rate dropped to off peak at midnight. This means I import more and export more than if I didn't grid charge, but since the price is the same (and PW efficiency is pretty good) it costs very little extra. But it means I have a full charge when peak period arrives, so I don't need to import any peak price power. So far, it appears that my PW grid-charging option works the same way, charging up to 100% starting at midnight.

(I am still waiting for Tesla support to fix my account so that the Export Everything option is available on my app, and then I'll have to figure out how to set it up to export as much as possible during peak times. Wish me luck...)

Your situation, with lower export compensation, is different. You probably still want to get to 100% before the rates jump up, but want as much your solar to go into the battery or consumption as possible, so as to minimize export. One would hope the PW Cost Savings algorithm would do a good job, but skepticism is in order.

I am aware of some PW owners in Australia and in Arizona who do charge from solar and the grid, but use a third party service to continuously monitor their PW and adjust the settings on the fly to optimize the behavior. We can hope the PW Cost Savings algorithm does grid charging well, but I think that is yet to be proven.

I did calculate that my grid charging last year was only "necessary" a few days, when the solar production was less than my peak period consumption, so the savings from doing that was less than $100 for the entire winter. Not a bid deal. As far as I know, only one other person in the US even tried to grid charge, so it is probably not really big a deal. But, again, I don't live in Philadelphia.

What I did was I installed the PW to cover us during power outages, which PG&E was forcing on us for days at a time due to fire risk. I had been on a non-time of use rate, but with the PW, PG&E put me on an EV, TOU rate. I soon noticed the savings due to discharging to cover our peak needs, cool, an added bonus! Then winter came and I noticed sometimes PW got down to reserve before the end of peak, and so got curious how to fix that, hence my interest in grid charging. My point is that we tend to learn as we go, and then learn only as much as we want to.

SW

 

[swedge]

The Tesla app lets you set buy/sell rates for each TOU period. So the optimal behavior with just two tiers depends on 4 numbers.

Wayne,

Does the PW actually use those prices in it's Cost Savings decisions? (I'm still waiting for Tesla Support to get rate plan, cost impact and export options to appear in my app, so I can not yet experiment.)

I think on residential the billing interval is 1 hour, and I think that the NBCs (the reason for a NEM2 difference in buy vs sell) are also only charged on that 1 hour net usage.

My understanding is that they accumulate import and export separately in each TOU rate period for the entire month, and then apply the pricing to the monthly totals. (Ah, unless the rates change during the month, in which case they do it twice, for the accumulations before and after the rate change.) I am on NEM1, so there is no NBC on my bill, but I believe it appears as just a discounted rate applied to the accumulated monthly export during each TOU window, off peak, partial peak and peak.

If I am right about this, each hour is not used in the billing, only the accumulated import and exported energy in each TOU period.

SW

 

[wwhitney]

Does the PW actually use those prices in it's Cost Savings decisions? (I'm still waiting for Tesla Support to get rate plan, cost impact and export options to appear in my app, so I can not yet experiment.)

Don't know if they do yet, just that the interface supports entering it, so the info is available for them when their software is ready.

My understanding is that they accumulate import and export separately in each TOU rate period for the entire month, and then apply the pricing to the monthly totals.

There is certainly hourly data reporting, but the question over what time period is the "import vs export" differentiation made? E.g. if a net is counted for the hour, then just one number per hour gets reported. But instead the meter could be sampling power every second (or faster) or 15 seconds or whatever, and then accumulating two registers over the hour, imports and exports, and then reporting two numbers per hour. As I'm on NEM1 as well, I don't know.

Cheers, Wayne

 

[skepticcyclist]

I’m wondering if I remove my TOU settings if this option will appear?

 

[cwied]

Don't know if they do yet, just that the interface supports entering it, so the info is available for them when their software is ready.



There is certainly hourly data reporting, but the question over what time period is the "import vs export" differentiation made? E.g. if a net is counted for the hour, then just one number per hour gets reported. But instead the meter could be sampling power every second (or faster) or 15 seconds or whatever, and then accumulating two registers over the hour, imports and exports, and then reporting two numbers per hour. As I'm on NEM1 as well, I don't know.

Cheers, Wayne

I believe it's not aggregated over any period, just the total for the month.
Here's my data from last month. The Powerwall data is using the site_energy_exported and site_energy_imported numbers for the billing period (3/31 00:00:00 - 5/2 00:00:00):
1. PG&E White Bill: import 625, export 705
2. Powerwall CTs, no aggregation: import 622, export 704
3. Powerwall CTs, 5 minute aggregation: import 613, export 698
4. Powerwall CTs, 15 minute aggregation: import 613, export 696
5. Powerwall CTs, 1 hour aggregation: import 601, export 683

I hope I got the math right for the aggregation. If anyone feels like proofreading my InfluxQL, here is the query I used. The parameters are for 5 minute aggregation export. I had to filter out large numbers because a software upgrade during the billing cycle inserted a 0 into the data:

SELECT SUM(net) FROM
 (SELECT i - x as net FROM
   (SELECT DERIVATIVE(first("site_energy_exported")) as x, DERIVATIVE(first("site_energy_imported")) as i
    FROM "forever"."http_1m"
    WHERE $timeFilter
    GROUP BY time(5m))
   where x < 100000 and i < 100000 and x > -1000000 and i > -1000000)
  where net < 0