How to charge powerwalls from grid with solar

[HankLloydRight]

This is being discussed in three or four different threads now.

Please start here: Anyone use Powerwall (with Solar) specifically for TOU savings? San Diego, CA

It *IS* possible to get Tesla to enable charge-from-grid, in the U.S. It's just not easy. See the threads linked above.

 

[wjgjr]

I am not questioning or challenging what you are saying. But how do they/ one or the other know if you took the tax credit?

I think the answer, like a lot of different parts of the tax code, is they will only know if there is an audit. When you submit an ITC claim, you don't even have to prove you actually have solar or PWs, let alone document how the PWs work. As to how likely it is that you will be audited, and that an audit would drill in on the PWs, I have no idea, though I would admit it seems highly unlikely. (Though I do wonder if claiming the ITC does increase your risk of an audit in general.)

I would guess the most likely - though I still would consider it rather unlikely - avenue for them to find out would be if they identified a pattern and contacted Tesla for a list of customers/addresses where powering from the grid is occurring. I suspect this would be why, as I understand it, Tesla was requiring a customer to pledge not to claim the ITC in exchange for enabling the functionality. That way, at least Tesla could claim they were not enabling a tax fraud.

 

[wwhitney]

The primary goal in cost saving is to power the house from PW for the duration of Peak power and send as much solar back to grid during Peak while sun is still up.
If you have excess PW after powering thru Peak, your just sending power to the grid at the same price you charged the PW (solar is charging PW, but you are drawing from the grid at that rate). So, you are losing money to send back to grid at same rate because of the 10% loss in PW

Here's an example:

Say you're on a rate plan with 2 rates, Peak and Off-Peak. Suppose on a given day you're going to use 10 kWh during Off-Peak and 20 kWh during Peak, while your solar is going to generate 30 kWh during Off-Peak and 0 kWh during Peak.

1) With no Powerwalls: you send 20 kWh to the grid during Off-Peak, and you draw 20 kWh from the grid during Peak. So if you are on NEM, you pay 20 P - 20 O (where P is the Peak rate, O is the Off Peak rate).

2) What Tesla currently let you do is charge your Power with ~22 kWh of Off-Peak generation and use that to cover your 20 kWh of Peak consumption. So you draw 2 kWh of Off-Peak and have no net generation/consumption during Peak. You pay 2 O, which is typically less than 20 P - 20 O.

3) However, with enough battery capacity and control over the Powerwall behavior,, what you could do is charge the Powerwalls with your full 30 kWh of Off-Peak generation, and have the Powerwalls regenerate it all as ~27 kWh during Peak. So you'd be drawing 10 kWh of Off-Peak from the grid, and net generating 7 kWh of Peak to the grid. Your bill would be 10 O - 7 P, which is typically less than 2 O.

To pick some numbers, if P = 15 cents and O = 10 cents, then in case (1) you'd pay 100 cents; in case (2) you'd pay 20 cents ; and in case 3 you'd get a credit of 5 cents.

Cheers, Wayne

 

[h2ofun]

Here's an example:

Say you're on a rate plan with 2 rates, Peak and Off-Peak. Suppose on a given day you're going to use 10 kWh during Off-Peak and 20 kWh during Peak, while your solar is going to generate 30 kWh during Off-Peak and 0 kWh during Peak.

1) With no Powerwalls: you send 20 kWh to the grid during Off-Peak, and you draw 20 kWh from the grid during Peak. So if you are on NEM, you pay 20 P - 20 O (where P is the Peak rate, O is the Off Peak rate).

2) What Tesla currently let you do is charge your Power with ~22 kWh of Off-Peak generation and use that to cover your 20 kWh of Peak consumption. So you draw 2 kWh of Off-Peak and have no net generation/consumption during Peak. You pay 2 O, which is typically less than 20 P - 20 O.

3) However, with enough battery capacity and control over the Powerwall behavior,, what you could do is charge the Powerwalls with your full 30 kWh of Off-Peak generation, and have the Powerwalls regenerate it all as ~27 kWh during Peak. So you'd be drawing 10 kWh of Off-Peak from the grid, and net generating 7 kWh of Peak to the grid. Your bill would be 10 O - 7 P, which is typically less than 2 O.

To pick some numbers, if P = 15 cents and O = 10 cents, then in case (1) you'd pay 100 cents; in case (2) you'd pay 20 cents ; and in case 3 you'd get a credit of 5 cents.

Cheers, Wayne

And the ROI for this is how long?

 

[Akikiki]

I think nearly everyone here with far more PW charging experience than I, know what they are talking about - in their area. I simply don't understand how any agency would know if someone took the federal tax credit AND they were charging their PWs from the grid. Not looking at someone's tax records. I don't believe any agency including the IRS is going to dig so deep into someone's utility bill, contact Tesla, or even question the owner (victim) of an audit to discover tax credit and PW charging and take any action. Just don't buy it. I don't think my two cents matters if its believed by me or not. No one cares, but I don't believe it.

 

[wwhitney]

Sounds like you're saying "It's not wrong if they can't catch me." I would not agree.

Wayne

 

[h2ofun]

I think nearly everyone here with far more PW charging experience than I, know what they are talking about - in their area. I simply don't understand how any agency would know if someone took the federal tax credit AND they were charging their PWs from the grid. Not looking at someone's tax records. I don't believe any agency including the IRS is going to dig so deep into someone's utility bill, contact Tesla, or even question the owner (victim) of an audit to discover tax credit and PW charging and take any action. Just don't buy it. I don't think my two cents matters if its believed by me or not. No one cares, but I don't believe it.

Again, from what I understand, has NOTHING to do with credit. Do you have solar? If so, telsa will not config units to charge from grid from what I have been told, period. Yep, I have asked

 

[Akikiki]

Sounds like you're saying "It's not wrong if they can't catch me." I would not agree.

Wayne

I don't think that's what I am saying. So, let me add. That's not what I am saying. I don't know what agency is saying they can't charge from the grid. I guess its the local PUC and the local utility. I just don't think its got anything to do with federal tax credit. And I am going to add again, my opinion about this doesn't matter, because either way, my opinion doesn't change anything. There. Better?

 

[wjgjr]

Again, from what I understand, has NOTHING to do with credit. Do you have solar? If so, telsa will not config units to charge from grid from what I have been told, period. Yep, I have asked

I think this thread (or one that points to it) was linked earlier, but Grid Charge Powerwall with Solar refutes this. It appears it is possible, provided the utility allows it and the customer promises not to claim the ITC. It does not appear to be an easy process (and I suspect much of Tesla is told it is not possible because it isn't something they can normally configure.)

But, in any case, the Tesla position seems to be designed to be aligned with the ITC, which clearly only subsidizes solar and related equipment that solely supports solar.

 

[wwhitney]

I just don't think its got anything to do with federal tax credit.

The IRS has indicated that the solar FTC can be taken for a Powerwall if it is only charged from solar.

Because of this, Tesla has decided to configure Powerwalls to only charge from solar if solar is present.

Cheers, Wayne

 

[wjgjr]

I don't think that's what I am saying. So, let me add. That's not what I am saying. I don't know what agency is saying they can't charge from the grid. I guess its the local PUC and the local utility. I just don't think its got anything to do with federal tax credit. And I am going to add again, my opinion about this doesn't matter, because either way, my opinion doesn't change anything. There. Better?

There are two issues here. First, some utilities do have rules restricting or prohibiting grid charging/discharging to/from powerwalls. Second, the IRS rules - regardless of how easy it is for them to detect - seem very clear that PWs can only be claimed as part of the ITC if they are exclusively used with solar power. And this makes sense as the purpose of the ITC is to promote alternative energy. As it is, it is fortunate for us that the IRS didn't decide to disallow PWs for the ITC.

As this applies to Tesla, their base assumption is that all customers installing solar+PW want to use the PWs for their solar so they can claim the ITC on them. And, given the discussions on this forum, it seems a correct assumption for the vast majority of customers. For the minority who want to do otherwise, Tesla seems to have a convoluted process for enabling grid charging which requires, among other things, disclaiming the ITC. I do think this process/choice should be more straightforward (and this will become a bigger issue if and as the ITC winds down and ends.)

 

[getakey]

Here's an example:

Say you're on a rate plan with 2 rates, Peak and Off-Peak. Suppose on a given day you're going to use 10 kWh during Off-Peak and 20 kWh during Peak, while your solar is going to generate 30 kWh during Off-Peak and 0 kWh during Peak.

1) With no Powerwalls: you send 20 kWh to the grid during Off-Peak, and you draw 20 kWh from the grid during Peak. So if you are on NEM, you pay 20 P - 20 O (where P is the Peak rate, O is the Off Peak rate).

2) What Tesla currently let you do is charge your Power with ~22 kWh of Off-Peak generation and use that to cover your 20 kWh of Peak consumption. So you draw 2 kWh of Off-Peak and have no net generation/consumption during Peak. You pay 2 O, which is typically less than 20 P - 20 O.

3) However, with enough battery capacity and control over the Powerwall behavior,, what you could do is charge the Powerwalls with your full 30 kWh of Off-Peak generation, and have the Powerwalls regenerate it all as ~27 kWh during Peak. So you'd be drawing 10 kWh of Off-Peak from the grid, and net generating 7 kWh of Peak to the grid. Your bill would be 10 O - 7 P, which is typically less than 2 O.

To pick some numbers, if P = 15 cents and O = 10 cents, then in case (1) you'd pay 100 cents; in case (2) you'd pay 20 cents ; and in case 3 you'd get a credit of 5 cents.

Cheers, Wayne

In #2, I believe you did not account for the excess solar going to the grid during Off Peak. Also, you assume no solar during peak. In reality that is never the case. If you are always charging PWs at Off Peak, you are storing electricity at Off Peak rate. When you use PW to power house at peak, you pocket the Peak minus Off Peak. How can you ever pocket difference between storing Off Peak and sending to grid Off Peak?

 

[h2ofun]

The IRS has indicated that the solar FTC can be taken for a Powerwall if it is only charged from solar.

Because of this, Tesla has decided to configure Powerwalls to only charge from solar if solar is present.

Cheers, Wayne

Now, the question I have been asking my installers, and have yet to get a clean answer, is what if one is getting batteries from the SGIP program with NO FTC!!! Why cannot these be configured to charge from the grid?

Now in my case I would have 2 gateways with my 400 amp service. The design had one from my solar, and the other grid charge enabled. I continue to ask them why both cannot have grid enabled, not that I would ever use, since I am not doing FTC via the SGIP process I would use having them be 100% free.

 

[Akikiki]

First, some utilities do have rules restricting or prohibiting grid charging/discharging to/from powerwalls.

Good I can see some utilities doing that. I bet not utility in the country is doing that simply because we in this country we can't get everyone to agree to do even one thing. You said, some utilities. I would agree.

Second, the IRS rules - regardless of how easy it is for them to detect - seem very clear that PWs can only be claimed as part of the ITC if they are exclusively used with solar power.

Sounds like someone is simply making an assumption here. Sorry, I won't believe this part until I see it in writing from IRS. You don't have to produce it for me. I don't care enough to look for it, and I surely don't expect you to prove it to me. And I say again, my two cents don't matter.

I have more solar and produces more that I can use. Thank goodness. Its under NEM and I am happy to be one of those that have NEM considering they closed that program. And I am working now on installed more solar for a parallel/separate system to power two PWs, just for house backup. Don't think it will be configured to overflow to grid. Only care that I have power when the grid is down, and don't really care if its for an extended period when the grid goes down. Just keep my radio running (and beer fridge) running, when the big blow comes through.

 

[h2ofun]

Good I can see some utilities doing that. I bet not utility in the country is doing that simply because we in this country we can't get everyone to agree to do even one thing. You said, some utilities. I would agree.

Sounds like someone is simply making an assumption here. Sorry, I won't believe this part until I see it in writing from IRS. You don't have to produce it for me. I don't care enough to look for it, and I surely don't expect you to prove it to me. And I say again, my two cents don't matter.

I have more solar and produces more that I can use. Thank goodness. Its under NEM and I am happy to be one of those that have NEM considering they closed that program. And I am working now on installed more solar for a parallel/separate system to power two PWs, just for house backup. Don't think it will be configured to overflow to grid. Only care that I have power when the grid is down, and don't really care if its for an extended period when the grid goes down. Just keep my radio running (and beer fridge) running, when the big blow comes through.

If I read your last paragraph, that is a lot or money to spend to just keep the radio and beer fridge running?

I heard a comment from a person that made so much sense. Why are so many spending so much to save 100 bucks worth of food in the fridge? Radio, c batteries. Lights, flash lights? I did not have a good answer back to this person.

 

[Akikiki]

Oh, yeah, I need to charge my phone too.

But yeah, you are right. A lot to spend on beer fridge. Don't deny it.

 

[h2ofun]

Oh, yeah, I need to charge my phone too.

I have like 15 phone bricks I have ready, and used for my phones? Again, I am just trying to understand the ROI process folks use to buy this expensive stuff.

 

[wwhitney]

In #2, I believe you did not account for the excess solar going to the grid during Off Peak.

In case #2, there is no excess solar going to the grid during Off Peak. The solar generates 30 kWh per the assumed data, and 22 kWh is used for Powerwall charging, 10 kWh is used for consumption, so 2 kWh comes from the grid during Off Peak.

Also, you assume no solar during peak. In reality that is never the case.

That was just to make the math easier to follow. If you assume, say, 10 kWh of Peak generation, and an additional 10 kWh of Peak consumption, those cancel in all cases and the numbers are the same.

If you are always charging PWs at Off Peak, you are storing electricity at Off Peak rate. When you use PW to power house at peak, you pocket the Peak minus Off Peak.

Correct, after you account for the 10% round trip Powerwall losses. The point is the you maximize this arbitrage within the PG&E rules by both (a) time shifting all consumption to Off-Peak and (b) time shifting all generation to Peak. Tesla Powerwalls do (a), but the current software does not support (b).

How can you ever pocket difference between storing Off Peak and sending to grid Off Peak?

That has not been proposed, obviously, as there is no difference.

Cheers, Wayne

 

[Akikiki]

I have like 15 phone bricks I have ready, and used for my phones? Again, I am just trying to understand the ROI process folks use to buy this expensive stuff.

But its okay if we do spend our money on this expensive stuff?

 

[wwhitney]

And the ROI for this is how long?

Varies, but the ROI for time shifting both consumption (supported) and generation (unsupported) would be less than the ROI for time shifting just consumption.

Cheers, Wayne