Time of Use Power Shifting for Powerwall 2

[UberEV1]

@Frankman60 and @liuping : Thanks! Just checked PG&E rates from our August bill - $0.45 Peak; $0.25 Part Peak; $0.12 Off Peak. For the year, your average costs seem much higher down South, but not sure electricity production costs or infrastructure is much different.

 

[liuping]

@Frankman60 and @liuping : Thanks! Just checked PG&E rates from our August bill - $0.45 Peak; $0.25 Part Peak; $0.12 Off Peak. For the year, your average costs seem much higher down South, but not sure electricity production costs or infrastructure is much different.

Well on the plus side, solar pays for itself very quickly here...

Our annual SDG&E bill has been essentially zero for a couple of years now. Solar paid for itself already, so it all free now. We pay about $10 a month for natural gas, but otherwise nothing for the house or cars.

The Powerwall are new/extra and will may never pay for themselves, but I love whole house backup, and control of when we use the grid The combo of SGIP and Federal tax credits made them too hard to pass up.

 

[Jimmy10]

Energy Advisor at Tesla store yesterday insisted that all software is now in place to do time of use shifting. I have an order in for two PowerWall units to specifically do that. Here in SoCal, peak is an amazing $.48/kWh vs $.12 at night, so....

How many years it will be needed to get your investment back?

 

[Frankman60]

I estimate that my payback period for one PW would be about 10 years. The calculation assumes that I would not need to purchase any electricity at the $.54/kWh rate during the 5 month Summer season. Instead, the peak period power would come from one PW that has just enough capacity to get through the 5 hour peak period from 4 to 9 PM. There would also be a much smaller savings during the 7 month Winter season. The calculation is based on the current net cost of installed PWs. People that were able to purchase PWs directly from Tesla and installed by Tesla, would have a shorter payback period because of the reduced costs. And as Liuping said, the ability to have whole house backup during a grid outage Is a nice non quantifiable bonus.

How many years it will be needed to get your investment back?

 

[Dave EV]

There would also be a much smaller savings during the 7 month Winter season.

Don't forget to account for Powerwall efficiency - at 90%, the difference between super-off-peak and on-peak rates during "winter" months for SDG&E you barely come out ahead, about 0.56 c/kWh. If you have solar and are charging the power-wall during off-peak and discharging during on-peak, you lose money. For the record, the current "winter" TOU rates for EVs and Solar are 0.228887 super-off-peak, 0.23893 off-peak 0.24799 on-peak.

 

[Frankman60]

Yes, the cost savings from PW in my calculation is very small during the Winter season (i.e. the rates you listed in your post). However, I did not consider any possible additional savings during the Summer season from new features available in the Tesla app related to TOU. If I am able to direct all of my solar energy produced during peak to the grid (rather than recharging the PW) and draw all needed electricity from the PW, the payback period will be shorter.

Don't forget to account for Powerwall efficiency - at 90%, the difference between super-off-peak and on-peak rates during "winter" months for SDG&E you barely come out ahead, about 0.56 c/kWh. If you have solar and are charging the power-wall during off-peak and discharging during on-peak, you lose money. For the record, the current "winter" TOU rates for EVs and Solar are 0.228887 super-off-peak, 0.23893 off-peak 0.24799 on-peak.

 

[Ed Hart]

How many years it will be needed to get your investment back?

Too complicated to estimate because buying second electric car at the same time. Leap of faith investment.

 

[MorrisonHiker]

How many years it will be needed to get your investment back?

Free for us, thanks to the referral program.

 

[mattack4000]

Hey guys,

While I was supercharging my vehicle yesterday, the guy at the showroom was pushing hard on the Powerwall. I tried to go through all pages of this thread, but some information seems to be outdated and in conflict of what the salesguy told me. Can I ask you guys to answer the following questions please?

I live in CA and has PG&E with the TOD rate. I have a small (1kwh) solar system in a fairly efficient house. I calculated that my system basically pays for all usage except for my AC and my car charging. Any overages are relatively low. I also live in an area with a very reliable grid, so keep that in mind when you answer the following questions.

With the powerwall, I want to see if it can do the following in order for it to make sense economically.

#1 Does the powerwall have to be installed close to the main panel? I assume the closer, the cheaper the installation is?

#2 I was told I need 2 powerwall for full power backup since 1 powerwall can only push out about 22amps. In theory, if I limit my power output. I can get away with one?

#3 Powerwall doesn't qualify for the 30% tax credit since I already have solar?

#4 Going back to #2, does that mean I need 2 to power an AC compressor let say? This leads to my next question.

#5 For it to make sense economically, I essentially need this system to shift my load off the peak period (5PM-9PM) and some partial peak time. I can do this by charging the battery with the grid during off peak hours and slowly let it out during peak time. As long as I am not creating a negative number, PG&E should just offset my bill to zero. Is that allow or possible? Last time I checked they said the firmware needs to be updated before it can happen, but I want to make sure it is actually out and PG&E will let me do this? (Peak rate is about 30 cents more expensive compare to off peak)

#6 How is the overall experience with the powerwall?

Thanks for the help.

 

[cwied]

1.I think they will figure out a way to install it anywhere, but close to the main panel is best. Tesla seems to be bidding incredibly low rates for installation. They installed a load panel, generation panel, the gateway and two Powerwalls in my garage for $900. That included some sheetrock work to cover some wiring.

2. They won't connect a single powerwall to a load panel that contains breakers greater than 30 amps. If you want whole-house backup, you probably will need two.

3. You can qualify for the Investment tax credit with just a battery installation, but that commits you to charging from solar only, which may not be compatible with your TOU plans (if Tesla actually implements TOU the way we hope).

4. Probably.

5. You will always be subject to minimum charges from PG&E ($10 per month for me). You can't ever get to $0. This is why it often doesn't make financial sense to offset 100% of your usage.
Now here's the kicker: the current Tesla firmware doesn't support TOU yet. Rumor has it something will be released in March. It is not clear what they will do for solar customers. Their current website states that a Powerwall installed with a solar system will not charge from the grid. Unless this changes, full TOU functionality like you want (charging at the cheapest rate, discharging at higher rates) will not be possible.

6. I've only had my powerwalls for about a week, but I've been able to test them out for a couple of OhmHours. They worked great - offsetting my usage during the demand reduction period. My main reason for wanting the powerwalls is actually backup, so I'm not expecting to ever get my investment back, but if I can get the effective price down to that of a generator, I'll be happy.

 

[miimura]

Hey guys,

While I was supercharging my vehicle yesterday, the guy at the showroom was pushing hard on the Powerwall. I tried to go through all pages of this thread, but some information seems to be outdated and in conflict of what the salesguy told me. Can I ask you guys to answer the following questions please?

I live in CA and has PG&E with the TOD rate. I have a small (1kwh) solar system in a fairly efficient house. I calculated that my system basically pays for all usage except for my AC and my car charging. Any overages are relatively low. I also live in an area with a very reliable grid, so keep that in mind when you answer the following questions.

With the powerwall, I want to see if it can do the following in order for it to make sense economically.

#1 Does the powerwall have to be installed close to the main panel? I assume the closer, the cheaper the installation is?

#2 I was told I need 2 powerwall for full power backup since 1 powerwall can only push out about 22amps. In theory, if I limit my power output. I can get away with one?

#3 Powerwall doesn't qualify for the 30% tax credit since I already have solar?

#4 Going back to #2, does that mean I need 2 to power an AC compressor let say? This leads to my next question.

#5 For it to make sense economically, I essentially need this system to shift my load off the peak period (5PM-9PM) and some partial peak time. I can do this by charging the battery with the grid during off peak hours and slowly let it out during peak time. As long as I am not creating a negative number, PG&E should just offset my bill to zero. Is that allow or possible? Last time I checked they said the firmware needs to be updated before it can happen, but I want to make sure it is actually out and PG&E will let me do this? (Peak rate is about 30 cents more expensive compare to off peak)

#6 How is the overall experience with the powerwall?

Thanks for the help.

1. The closer the PowerWall is to the main panel, the cheaper the install will be. The PowerWall itself does not have to be that close, especially if the rest of the panels and Gateway can be installed close to the main panel.

2. The installation design is limited by what can be backed up. One simple limitation is that you cannot have any single breaker backed up that is more than 30 amps per PowerWall. For example, if you want to back up an AC unit that has a 40A breaker, you need two PowerWalls. If you don't want to back up any large loads, but lots of small ones, you can probably get away with one PowerWall.

3. If you charge the batteries only from solar, you can get the 30% tax credit even if the solar is already installed. If you want to charge from the grid, you do not qualify for the tax credit.

4. Backing up the AC depends completely on how big the breaker is on it and whether it has a soft start or inverter drive.

5. PG&E EV rate Peak hours are 2pm-9pm. I have no problem using the PowerWall to drive my usage to zero during these hours. However, until there is a software update, I have to interactively change the reserve percentage to get the PowerWall to do what I want. Primarily, I want to avoid PowerWall discharge during Off-Peak, but allowing the grid to power the house during Part-Peak allows the battery to fill before 2pm and generate some Peak hour solar credits.

I noticed another fine point that was not clear to me before I looked at the behavior of my install. The power monitoring current transformers that Tesla uses to balance the house load and the PowerWall output are placed on the backup gateway in a location where it can only measure the backed up loads. Therefore, the PowerWall will not offset the usage of any loads that are not backed up. It can probably be moved, but there is a limit to how long the leads are between the Neurio monitoring device in the Gateway enclosure and the CT. I would like to add another Neurio in my main panel so that those loads can be offset as well, with a RS-485 linking it back to the Gateway. However, I'm pretty sure this is not currently supported. My reason for bringing this up is that if you left your AC outside the Gateway so that it is not backed up, its usage would also not be offset by the PowerWall. If I had AC, that would be a big problem for me. As it is, the primary loads outside my Gateway are my EVSEs and I would never want to charge the cars from the PowerWall energy anyway.

 

[Frankman60]

I’m not sure I understand what you said about Neurio. I presently have a Neurio for use with my PV system and I will be getting two PWs installed in the near future for whole home backup. Do I need to be concerned about the Neurio system that has been working great for the past few years at monitoring usage and solar generation? Will the PW installation affect it in some way? Presently the Neurio CTs are connected to the solar breakers and the main Utility feed to the meter.

I noticed another fine point that was not clear to me before I looked at the behavior of my install. The power monitoring current transformers that Tesla uses to balance the house load and the PowerWall output are placed on the backup gateway in a location where it can only measure the backed up loads. Therefore, the PowerWall will not offset the usage of any loads that are not backed up. It can probably be moved, but there is a limit to how long the leads are between the Neurio monitoring device in the Gateway enclosure and the CT. I would like to add another Neurio in my main panel so that those loads can be offset as well, with a RS-485 linking it back to the Gateway. However, I'm pretty sure this is not currently supported. My reason for bringing this up is that if you left your AC outside the Gateway so that it is not backed up, its usage would also not be offset by the PowerWall. If I had AC, that would be a big problem for me. As it is, the primary loads outside my Gateway are my EVSEs and I would never want to charge the cars from the PowerWall energy anyway.

 

[miimura]

I’m not sure I understand what you said about Neurio. I presently have a Neurio for use with my PV system and I will be getting two PWs installed in the near future for whole home backup. Do I need to be concerned about the Neurio system that has been working great for the past few years at monitoring usage and solar generation? Will the PW installation affect it in some way? Presently the Neurio CTs are connected to the solar breakers and the main Utility feed to the meter.

I assume a new PowerWall installation would ignore any existing monitoring devices, your Neurio included. It appears to me that the default install communicates between the Tesla factory installed Neurio and the Tesla Gateway with RS-485. There was some discussion about the WiFi Signal quality of the Neurio antenna inside the Gateway's enclosure, but it is probably irrelevant. They will probably have to re-locate your solar circuits to the Generation Panel anyway, so slapping on another set of CT's is not a problem.

Of course, the fact that you have a Neurio that is already monitoring the Utility feed would make my proposed dual Neurio setup all that much easier. However, like I said before, I don't think it's supported. I will probably approach Tesla Energy about this possibility after my setup is completely finished and all inspections, interconnect agreements, and rebates are complete.

 

[ianaz1]

1. A PW2 with solar will only charge from solar. You can see that in my chart above.
2. If you have solar production during Peak hours and the PW2 is capable of absorbing it all, it will do that. There will be no solar export until the battery is full.

#2 above is why I want to avoid PW discharge during Off-Peak. You're losing money to negative arbitrage because the solar was generated during Part-Peak and you're using it during Off-Peak. That's a losing proposition. If you avoid Off-Peak discharge, then the battery will be full earlier in the afternoon so that you can earn Peak credits. Those credits will only be the excess from your household consumption. In theory, Tesla could allow PW discharge during the Peak period to match your household consumption and allow the solar to ALL go to the grid and earn credits. However, I don't really expect them to do that even though there is probably no regulatory reason they couldn't, even with a non-export interconnect agreement.

 

[mattack4000]

Thanks for the information guys. I guess powerwall wouldn't make sense for me economically. For one, my system is small (1kw). I am guessing I generate 5kw per day conservatively. Even if I generate half of it before peak time at 2PM, at most I can make is like $1 per day. The problem is even worse as I will need a second powerwall given I have a 40A on my 100A subpanel and the solar panel and AC hooks to the 200A main panel. I am better off just doing the netmetering.

 

[dhu1]

I assume a new PowerWall installation would ignore any existing monitoring devices, your Neurio included. It appears to me that the default install communicates between the Tesla factory installed Neurio and the Tesla Gateway with RS-485. There was some discussion about the WiFi Signal quality of the Neurio antenna inside the Gateway's enclosure, but it is probably irrelevant. They will probably have to re-locate your solar circuits to the Generation Panel anyway, so slapping on another set of CT's is not a problem.

Of course, the fact that you have a Neurio that is already monitoring the Utility feed would make my proposed dual Neurio setup all that much easier. However, like I said before, I don't think it's supported. I will probably approach Tesla Energy about this possibility after my setup is completely finished and all inspections, interconnect agreements, and rebates are complete.

There is a new post that has information on what the TOU controls. From what I can tell, if you have solar, it does not give you the option to charge from the grid thereby killing significant portion of the rate arbitrage. I have not taken the the ITC since I wanted to charge from the grid but might now that charging from grid may not be an option.

 

[abasile]

A Tesla Energy electrician came for a site visit yesterday, in preparation to install our Powerwalls next week.

We do have a solar PV system. However, the Tesla Energy installer clearly told me that the "TOU" feature will enable us to charge the Powerwalls from the grid at night, when rates are low, and use that stored energy when rates are higher. While I wouldn't bank on this, as the software isn't out yet and the installer may be mistaken, it would be nice if he's right. We do quite a bit of EV driving and charging, so we owe money to SCE at the end of the year and it would be nice if the Powerwalls can help us reduce our net electric bill further.

The Tesla installer also seemed to indicate that when our PV system is producing power, our home will use that power first, before drawing from the Powerwalls or from the grid. If true, that may represent a reasonable compromise with the utilities, as an alternative could have been to use the Powerwalls to meet daytime home demand while enabling all PV production to be exported.

 

[nswfugitive]

The Tesla installer also seemed to indicate that when our PV system is producing power, our home will use that power first, before drawing from the Powerwalls or from the grid. If true, that may represent a reasonable compromise with the utilities, as an alternative could have been to use the Powerwalls to meet daytime home demand while enabling all PV production to be exported.

This is definetly correct, your first point about charging from the grid is questionable based on restrictions in the US that I've seen quoted on this forum. You can charge from the grid in Australia though - but that does you little good.

 

[miimura]

A Tesla Energy electrician came for a site visit yesterday, in preparation to install our Powerwalls next week.

We do have a solar PV system. However, the Tesla Energy installer clearly told me that the "TOU" feature will enable us to charge the Powerwalls from the grid at night, when rates are low, and use that stored energy when rates are higher. While I wouldn't bank on this, as the software isn't out yet and the installer may be mistaken, it would be nice if he's right. We do quite a bit of EV driving and charging, so we owe money to SCE at the end of the year and it would be nice if the Powerwalls can help us reduce our net electric bill further.

The Tesla installer also seemed to indicate that when our PV system is producing power, our home will use that power first, before drawing from the Powerwalls or from the grid. If true, that may represent a reasonable compromise with the utilities, as an alternative could have been to use the Powerwalls to meet daytime home demand while enabling all PV production to be exported.

The way it works today is that the Powerwall(s) will absorb all surplus solar until they are full. Then, the surplus solar (excess of what your house is consuming) will be exported. As the solar output decreases below your household consumption, the Powerwall will fill in power so that your net grid consumption is zero. It will continue to do that until either your consumption exceeds the power limits of the Powerwall(s) or it reaches the Reserve you have set in the app. At that point, the Powerwall(s) will go to Standby until a grid outage or the solar starts producing again. Today, I set the Reserve high to stop the Powerwalls from discharging during my Off-Peak rate period. In addition, my installation does not measure the power consumed through my EVSEs, so the Powerwalls never try to provide that power either.

In this image you can see my Powerwalls charging up past the 90% reserve at about 11:30am and 100% at about 1:30pm when the solar started going to export. I usually change the Reserve to 50% at lunchtime and back to 90% after the Peak rate period (2-9pm) ends, usually around 10pm before I go to bed.

 

[UCIBtheG]

2. The installation design is limited by what can be backed up. One simple limitation is that you cannot have any single breaker backed up that is more than 30 amps per PowerWall. For example, if you want to back up an AC unit that has a 40A breaker, you need two PowerWalls. If you don't want to back up any large loads, but lots of small ones, you can probably get away with one PowerWall.

4. Backing up the AC depends completely on how big the breaker is on it and whether it has a soft start or inverter drive.

Hi miimura, I'm scheduled to have my PowerWall2 installed June 1st, and was really hoping to have a whole house solution on one PowerWall. My Inside Energy Advisor guy from Tesla had echoed what you said, that one PW2 would not back up my air conditioner as it is on a 50 amp circuit. I've dug up some info on my air conditioner, and found that the RL Amps (compressor + fan motor combined) is 16.4 amps, which should be well within the range of one PW2. But the LR Amps (which seem to have to do with the brief inrush of current when first turned on) is 86.3 amps combined. Somehow this does not blow the 35 amp fuse that the air conditioner is connected to, I'm assuming because it's a slow blow fuse?

In any case, after reading what you had said above about a soft start, I found an "EasyStart 364 Soft Starter" for about $300. This device would seem to bring the LR Amps down within spec, with the added bonus of silencing the annoying noise the air conditioner makes when it first turns on. My air conditioner unit is 36,000 BTU, which is sized just right for this device's capacity.

My questions: Is this EasyStart 364 box the best device for the job, or is there something else you'd recommend? If I were to have this soft start box connected to my air conditioner, would that allow Tesla to proceed with covering my air conditioner with the one PowerWall? Would that require a change from the 35 amp fuse to a 30 amp fuse, and/or the 50A breaker to be replaced to a 30A breaker? It would probably be a better question for my Inside Energy Advisor, but do you think these changes (including the soft start box install) could be added to the PW2 install scope of work?

I was disappointed when I was told that I'd need a second PW2 just to cover my air conditioner, but this gives me hope that a workaround is within reach.