Time shifting on SRP (Scottsdale, AZ)

[cyr0nk0r]

I've read in various threads on this forum that SRP has a rule that you can't charge powerwalls from the grid if you also have a solar array.
I got a call from SRP solar dept. today discussing my rate plans and asked them about this. The guy said he had never heard of this rule. He also reached out to their 'distributed energy' department (DER) to ask about it and they relayed to him that SRP does not have any such rule requirement in place.

Can anyone that has both solar and powerwalls that is on SRP here in Phoenix, AZ confirm this? I know other utilities allow this based on user experiences in other parts of the country, but didn't think SRP allowed this at the moment.

 

[h2ofun]

I thought if you got a federal tax write off you could not charge your PW's from the grid if you had solar?

 

[cyr0nk0r]

I thought if you got a federal tax write off you could not charge your PW's from the grid if you had solar?

oh interesting. so maybe this isn't a utility rule issue but a federal tax credit issue. interesting.
Ok, so who is checking if I get a federal tax credit to let me charge the powerwalls from grid or not? Is this an honor system thing?

 

[getakey]

the Tesla app won't allow you to charge from grid unless in Stormwatch

 

[jjrandorin]

oh interesting. so maybe this isn't a utility rule issue but a federal tax credit issue. interesting.
Ok, so who is checking if I get a federal tax credit to let me charge the powerwalls from grid or not? Is this an honor system thing?

as @getakey says, the tesla app will not allow charging from the grid if you have solar, unless in stormwatch mode (which is triggered by tesla itself).

Recently, someone posted a bit of a "hack" whereby you could theoretically log into the gateway with the installer password (something the end user normally does not have, but a few here have), and make some changes, but they did not recommend leaving it in that state as there might be some other issues with it left that way (and no idea if it charges from solar if left like that, etc).

The short answer is, its likely you wont be able to charge from the grid if you have solar.... but saying that, the one person I remember reading about getting tesla to allow that for them, had a letter from the utility specifically allowing it, and pestered tesla into it. I also believe that person was somewhere in Arizona but I may be mis remembering that.

In general, though, grid + solar = no powerwall charging, disabled by tesla.

 

[cyr0nk0r]

I'm fine to be a squeaky wheel to get SRP to give me some kind of written authorization that I can present to Telsa. Can you elaborate more on the installer password? Is it the same across the board or unique to each installation?
Any threads you can point to that mention what you're talking about with the user getting Tesla to enable the feature?

 

[wjgjr]

My understanding is that there are several issues at play. First, as noted above, the ITC seems to require that you not charge from the grid (technically, even storm watch could be seen as violating the rule.) It appears there is a 5-year period after which you would probably be free to use the PWs as you want without violating the ITC. As to the question about enforcement, I would agree it is unlikely the IRS is going to get into those details unless there is something bigger going on. (I could imagine for a large enough ITC claim, they might look to pursue it.)

Second, also as noted above, Tesla seems to block grid charging. However, this is not a hardware limitation, but something in software. My understanding is that grid charging is allowed in other countries, and there have been users who have reported Tesla allowing it in specific circumstances in the US upon request. So I would consider this a hurdle, but not an insurmountable one.

Third is the utility rules. Some may have very specific rules disallowing some combination of charging to PW from the grid, discharging from PW to the grid, or using the PW to shift load. This could come in the form of an outright ban or it could be accomplished by disallowing battery storage in rate plans where there would be a monetary incentive to do the above. Other utilities seem to be more accommodating, though in some cases even then, they have specific programs (like one mentioned elsewhere that a CT utility has) or rules to follow.

I do think this is something Tesla will need to reckon with in the US. While it seems like a lot of people want to claim the ITC, the 5-year window is probably expired or soon expiring for existing installs, and there is the possibility the ITC will itself be gone starting in 2022. And we know there is a benefit to shifting loads to off peak times, with or without solar. (Somebody recently posted about a VT utility subsidizing PWs just for this purpose.)

 

[jjrandorin]

I'm fine to be a squeaky wheel to get SRP to give me some kind of written authorization that I can present to Telsa. Can you elaborate more on the installer password? Is it the same across the board or unique to each installation?
Any threads you can point to that mention what you're talking about with the user getting Tesla to enable the feature?

I dont have the installer password, I just know some do. You can read through this thread regarding someone in AZ getting that setup, but i dont know what utility.

Grid Charge Powerwall with Solar

That is the one person I remember getting tesla to allow grid charging when connected to solar (keep in mind that one is not supposed to take a tax credit in that configuration as the powerwall is only eligible for tax credit if charged from renewables).

 

[getakey]

why do you want to charge from the grid?

 

[cyr0nk0r]

because I can charge the powerwalls at 2am when im paying 0.02 cents per kw hour and then use that stored energy at 2pm when the cost is 0.15 cents per kw hour or more here in Phoenix, AZ

 

[heems]

why do you want to charge from the grid?

Cloudy days + tou plans (cheap grid charging at night).

 

[getakey]

because I can charge the powerwalls at 2am when im paying 0.02 cents per kw hour and then use that stored energy at 2pm when the cost is 0.15 cents per kw hour or more here in Phoenix, AZ

Thought that might be the reason and you would have to get exception as stated in previous posts. Our lowest rate at 2am is 15 cents. Peak is 54 cents and partial peak is 37 cents. You guys are lucky

 

[wjgjr]

I understand the idea behind the load shifting, but it is worth noting that if the difference is really only $0.13/kWh (I know it is "or more" for peak, so I don't know how high it goes) and you can only do one cycle a day (up to 13.5 kWh, but probably closer to 12 kWh with reserves,) this comes in under $600/year. So, over the 10-year warranted lifetime of the battery, it won't pay for itself. Of course, it hopefully will last longer, but the capacity will likely be significantly lower by then (I believe they guarantee 70% at 10 years.) Along with its other benefits for outages, it might make it worthwhile, depending on circumstances.

The example posted for CA with a $0.39/kWh difference makes break-even much easier, just on load shifting.

The other question I would have is with battery only, does the Tesla app make it easy to force the battery to discharge during peak and recharge overnight? Certain of the options I have with solar + PW should encourage this behavior, but Tesla abstracts away a bit from having direct control. It would nice to just explicitly say "from noon to 8 PM, discharge the PW; from midnight to 6 AM, charge from grid."

 

[jjrandorin]

I understand the idea behind the load shifting, but it is worth noting that if the difference is really only $0.13/kWh (I know it is "or more" for peak, so I don't know how high it goes) and you can only do one cycle a day (up to 13.5 kWh, but probably closer to 12 kWh with reserves,) this comes in under $600/year. So, over the 10-year warranted lifetime of the battery, it won't pay for itself. Of course, it hopefully will last longer, but the capacity will likely be significantly lower by then (I believe they guarantee 70% at 10 years.) Along with its other benefits for outages, it might make it worthwhile, depending on circumstances.

The example posted for CA with a $0.39/kWh difference makes break-even much easier, just on load shifting.

The other question I would have is with battery only, does the Tesla app make it easy to force the battery to discharge during peak and recharge overnight? Certain of the options I have with solar + PW should encourage this behavior, but Tesla abstracts away a bit from having direct control. It would nice to just explicitly say "from noon to 8 PM, discharge the PW; from midnight to 6 AM, charge from grid."

I think the people who want to do this see a world where they are charging overnight on TOU cheap rates, using that energy to power their homes during peak AND because their batteries are "full" from cheap energy at night, forcing all of their solar to the utility.

Totally not the spirit of what NEM is about, at least in my opinion, and one of the reasons so many utilities are rushing to put in place things to specifically block this.

EDIT: To clarify a bit, by "block" I actually mean "de value solar production more" and "add more non bypassable charges".

 

[miimura]

I understand the idea behind the load shifting, but it is worth noting that if the difference is really only $0.13/kWh (I know it is "or more" for peak, so I don't know how high it goes) and you can only do one cycle a day (up to 13.5 kWh, but probably closer to 12 kWh with reserves,) this comes in under $600/year. So, over the 10-year warranted lifetime of the battery, it won't pay for itself. Of course, it hopefully will last longer, but the capacity will likely be significantly lower by then (I believe they guarantee 70% at 10 years.) Along with its other benefits for outages, it might make it worthwhile, depending on circumstances.

The example posted for CA with a $0.39/kWh difference makes break-even much easier, just on load shifting.

The other question I would have is with battery only, does the Tesla app make it easy to force the battery to discharge during peak and recharge overnight? Certain of the options I have with solar + PW should encourage this behavior, but Tesla abstracts away a bit from having direct control. It would nice to just explicitly say "from noon to 8 PM, discharge the PW; from midnight to 6 AM, charge from grid."

If you don't have solar, you can use Time Based Control to power the house from battery during Peak and recharge from the grid during Off-Peak. I assume it does nothing during Shoulder periods.

 

[cyr0nk0r]

I think the people who want to do this see a world where they are charging overnight on TOU cheap rates, using that energy to power their homes during peak AND because their batteries are "full" from cheap energy at night, forcing all of their solar to the utility.

Totally not the spirit of what NEM is about, at least in my opinion, and one of the reasons so many utilities are rushing to put in place things to specifically block this.

that's not really what im looking to do. It's more about the ability to run the house on the batteries for longer. If I'm not having to use the batteries during the peak part of the day then the solar can be covering the house at those times. Then during the evening / early morning I can be using batteries.
I'm not looking to try and get the system to make me money, but be as close to break even on my electrical usage as possible.

 

[getakey]

that's not really what im looking to do. It's more about the ability to run the house on the batteries for longer. If I'm not having to use the batteries during the peak part of the day then the solar can be covering the house at those times. Then during the evening / early morning I can be using batteries.
I'm not looking to try and get the system to make me money, but be as close to break even on my electrical usage as possible.

do you have net metering? Do you get credit of solar pushed back to the grid? If so, at what rate?

 

[cyr0nk0r]

depends on my use plan. SRP has plans where its 1:1, I would get credit back for exactly what I pay retail for it.
I mean, yeah, if during the hottest parts of summer if for some reason my solar is making more than what the house is using and the batteries of are full, then cool, I get the meter running bardwards. But that's not what the main goal is.
The main goal is to have the solar run the house during the hottest parts of the day when im peak A/C, then use batteries in the morning / evening rather than grid.
Then just charge the batteries at night.

 

[wjgjr]

It seems like regardless of the reason, the idea of charging off-peak for use during peak is simple math in terms of payback" (peak - off-peak)*amount*0.9. This would be true whether or not you have solar. "amount" would be the lower of the battery capacity or actual use during peak. And the "0.9" reflects the loss in converting the energy to DC and back.

I do not know what the peak times are in AZ, but the typical use for PWs with TOU rates is to charge them up in the morning from solar, before peak, and then discharge them in the afternoon/evening during the peak. This would likely be more consistent with utility NEM rules. However, I don't see it as an abuse to use PWs as proposed, as long as the installation follows the utility rules and doesn't try to claim rebates/credits that would be disallowed by the use. In some areas utilities want, or are at least indifferent to, the idea of customers grabbing energy at night and using it during the day. It makes a lot of sense for utilities in some areas to support this.

If you don't have solar, you can use Time Based Control to power the house from battery during Peak and recharge from the grid during Off-Peak. I assume it does nothing during Shoulder periods.

Thanks - wasn't certain how that worked.

 

[getakey]

depends on my use plan. SRP has plans where its 1:1, I would get credit back for exactly what I pay retail for it.
I mean, yeah, if during the hottest parts of summer if for some reason my solar is making more than what the house is using and the batteries of are full, then cool, I get the meter running bardwards. But that's not what the main goal is.
The main goal is to have the solar run the house during the hottest parts of the day when im peak A/C, then use batteries in the morning / evening rather than grid.
Then just charge the batteries at night.

The Cost Saving mode in the Tesla app does just about the opposite. You charge batteries from solar before peak, then run house from batteries during peak and "sell" solar back to grid at peak rates.