Using powerwalls for load shifting only

[h2ofun]

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?

solar is solar, and can go to grid. Battery is battery, and no matter how it got charged, it cannot go to the grid, only your house.

 

[slcasner]

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?

PG&E's NEM tariff does not allow export of energy from the storage system.

 

[power.saver]

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?

Because they are not setup to export. So all you can do is use them to run your house and then export all your solar during the peak.

With VPP, Tesla will draw from your PWs to export their energy to the grid, where you get NEM credits. But this only occurs during a VPP event, not everyday.

 

[miimura]

PG&E's NEM tariff does not allow export of energy from the storage system.

This is not technically correct as written. You may export from the storage system if it was charged with solar. This is what the VPP will do. PG&E does not allow you to charge from the grid and export that energy. This is why the Paired Storage billing system now compares your estimated solar generation to your exports. Any exports in excess of you estimated solar generation will be disallowed for NEM credit.

What I stated above applies to small residential ESS. There are more complicated rules for large systems.

 

[h2ofun]

This is not technically correct as written. You may export from the storage system if it was charged with solar. This is what the VPP will do. PG&E does not allow you to charge from the grid and export that energy. This is why the Paired Storage billing system now compares your estimated solar generation to your exports. Any exports in excess of you estimated solar generation will be disallowed for NEM credit.

What I stated above applies to small residential ESS. There are more complicated rules for large systems.

I am still waiting to see since I have not seen a bill yet with my new approved solar and see if the estimated solar generation doubled, as I was told by PGE it should do

 

[aesculus]

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?

Right now the only time you can export your solar energy is when you create it. If I understand this correctly, you could technically sell solar stored energy when they want it, up to your designated reserve.

There is a ruling from the CAPUC to allow this anytime but no solution has been defined for this yet from Tesla. This leaves me to suspect its a Tesla issue rather than a rate plan issue. The only limitation we have is only to sell solar energy back, which the VPP does.

So I am waiting for a more general solution from Tesla rather than just an emergency solution. I am willing to give them back some of my solar at peak, non solar producing times, and hope Tesla changes the Cost Savings mode to support that in the future.

 

[jboy210]

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?

As I understand it, if you take the tax credit for a solar install you can and would get credit for any excess solar production (pending utility approval). But, you cannot sell the power stored in your powerwalls back to the grid.

The only exception is under VPP agreements where an external entity, say Tesla, has negotiated a deal with the power company to sell the output from their Virtual Powerplant, which contains your Powerwalls, during high demand events. In that case, you will get paid for Tesla exporting your power from your Powerwalls. The current program in my area (Tesla & PGE) lists $1/kWh rate during the event.

 

[mikesm]

This is not technically correct as written. You may export from the storage system if it was charged with solar. This is what the VPP will do. PG&E does not allow you to charge from the grid and export that energy. This is why the Paired Storage billing system now compares your estimated solar generation to your exports. Any exports in excess of you estimated solar generation will be disallowed for NEM credit.

What I stated above applies to small residential ESS. There are more complicated rules for large systems.

Interesting. Why is it that others are saying you can't export solar energy to the grid? If all you can do is zero out your own peak use, it doesn't seem like the economics for storage would work. Certainly not for bigger solar systems. What do you mean by "larger systems" in terms of storage?

But it would seem that the PUC would want to have solar generated power flow as much as possible in the peak hour, because the peakers are the most costly and the most environmentally unfriendly. It can't be that it is a control problem, because peakers are by their nature not continuously running.

The economics of solar generation really made sense when the peak hour pricing overlapped solar generation. It's less effective now, but allowing you to store and sell that back to PG&E in the peak would sort of restore that incentive. If PG&E ended up with too much energy coming back in the peak, they could lower prices and that would disincentivize people from buying storage. The market should accommodate this all and reduce the amount of centralized generation needed.

 

[miimura]

Interesting. Why is it that others are saying you can't export solar energy to the grid? If all you can do is zero out your own peak use, it doesn't seem like the economics for storage would work. Certainly not for bigger solar systems. What do you mean by "larger systems" in terms of storage?

But it would seem that the PUC would want to have solar generated power flow as much as possible in the peak hour, because the peakers are the most costly and the most environmentally unfriendly. It can't be that it is a control problem, because peakers are by their nature not continuously running.

The economics of solar generation really made sense when the peak hour pricing overlapped solar generation. It's less effective now, but allowing you to store and sell that back to PG&E in the peak would sort of restore that incentive. If PG&E ended up with too much energy coming back in the peak, they could lower prices and that would disincentivize people from buying storage. The market should accommodate this all and reduce the amount of centralized generation needed.

There is a difference between what is allowed by PG&E and what Tesla Powerwalls are programmed to do. The normal Tesla behavior during Peak is to power household loads from the battery while allowing your solar to go to the grid to earn NEM credits. With other battery systems you could allocate energy differently. For example you could calculate how much energy you have available from that day's solar, say 16kWh to discharge during the 5 hours from 4pm-9pm, and simply output 3kW continuously for those 5 hours. Whatever the house didn't use would go to the grid in addition to whatever the solar produces during those hours.

The PG&E NEM Tariffs specify Paired Storage >10kW as "Large AC Coupled Storage Systems". If you have more than 2 Powerwalls, you fall into this Large Storage System category. The NEM2 tariff specifies some limitations and requirements for those Large Systems that don't apply to systems that only consist of one or two Powerwalls.

We have to be realistic about what makes sense and to whom. Rate plans like EV-A on NEM1 were really too good to be true for solar homeowners because we got double the solar kWh to charge our cars overnight because of the Part-Peak schedule during generating hours. PG&E wasn't going to let that stand while more and more customers were getting solar. So, they kicked out as many customers as they could and put them on the EV2 rate plan that was Off-Peak through most solar generating hours.

Whether avoiding Peak usage is sufficient for you to make the economics of storage work for you is completely dependent on your usage pattern. In my personal case, having the batteries compensated for being kicked out of EV-A and losing that solar value. Since I am a significant net consumer, it significantly reduces the amount I owe at true-up.

 

[aesculus]

The current program in my area (Tesla & PGE) lists $1/kWh rate during the event.

Do you have link to this? I could not find it. It would require some sort of rate adjustment by PG&E for it to work, since they are the ones paying you. Tesla can only support the function. They have no monetary role in this.

And my fear with PG&E is that anytime you do anything with them they will use it against you to pull you off the plan you are on. The only time that worked in my favor is when I put in solar in 2018 and got a few years of grandfathering in EVA1. Otherwise in every other case it was a net negative to me to "tweak" my rate plan.

 

[jboy210]

Do you have link to this? I could not find it. It would require some sort of rate adjustment by PG&E for it to work, since they are the ones paying you. Tesla can only support the function. They have no monetary role in this.

And my fear with PG&E is that anytime you do anything with them they will use it against you to pull you off the plan you are on. The only time that worked in my favor is when I put in solar in 2018 and got a few years of grandfathering in EVA1. Otherwise in every other case it was a net negative to me to "tweak" my rate plan.

On the new 4.0 app I installed on my iPad it shows under the "Settings" menu. Under the sub-item "Tesla Virtual Power Plant (Beta)" there is a button labeled "Get compensated while supporting California's electric grid". If I press that the $1/kWh is listed in the summary.

 

[GenSao]

Do you have link to this? I could not find it. It would require some sort of rate adjustment by PG&E for it to work, since they are the ones paying you. Tesla can only support the function. They have no monetary role in this.

And my fear with PG&E is that anytime you do anything with them they will use it against you to pull you off the plan you are on. The only time that worked in my favor is when I put in solar in 2018 and got a few years of grandfathering in EVA1. Otherwise in every other case it was a net negative to me to "tweak" my rate plan.

Unfortunately, Tesla's VPP terms on the website is "generic" and does not include the PG&E specific language reproduced below. Note, I (got a little lazy and) did not fix all the formatting from the copy and paste.

Join Tesla & PG&E to Create a Virtual Power Plant​

Grid emergencies are forecast in California this summer. Powerwall can support your state while earning you compensation and maintaining your energy security.

Help create the largest distributed battery in the world and keep California’s energy clean and reliable. Opt-in to the Tesla Virtual Power Plant (VPP) pilot with PG&E, and your Powerwall will be dispatched when the grid needs support. Through the pilot, you will receive $1 for every additional kWh your Powerwall delivers during an event. Adjust your Backup Reserve in the Tesla app to set your contribution while maintaining backup energy for potential outages.

Benefits of Participation​

• Stabilize California’s Grid: The extra capacity your Powerwall provides could help avoid or reduce blackouts in a severe emergency. This way, Powerwall can help keep the lights on for both you and your community.
• Clean the Grid: Tesla will dispatch your Powerwall when the grid is in critical need of additional power and avoid use of inefficient generators.
• Unite as a Tesla Community: Team up with other Powerwall owners who are accelerating the world’s transition to sustainable energy and help form the largest distributed battery in the world — potentially over 50,000 Powerwalls. As part of the VPP, your Powerwall will have an outsized positive impact on the grid over traditional demand response programs.
• Keep Your Energy Security: Powerwall will discharge during VPP events but won’t discharge below your Backup Reserve. Adjust your Backup Reserve in the Tesla app to control your contribution while maintaining backup energy for outages.
• Earn Compensation: Through the Tesla & PG&E VPP pilot, you will receive $1 for the incremental kWh that your Powerwall provides during events. You are not required to change your energy usage behavior to participate.

Event Behavior​

When an event is scheduled, you will receive a push notification informing you of event times. Depending on the forecasted severity of the event, your Powerwall may prioritize charging from your solar system in advance of the event to help shift your home’s energy use from the grid to earlier in the day. If Powerwall fully charges before an event, your solar system will resume powering your home and export any excess power to the grid.

When the event begins, you will receive a push notification reminding you of the event end time, and your Powerwall will begin discharging to support the grid. Your Powerwall will continue to discharge until the event ends, or when it discharges to your selected Backup Reserve level. No action is required on your part to participate in the event, but you may raise or lower your Backup Reserve level at any time during the event.

Events​

Tesla and PG&E will call upon the VPP when the California grid operator, CAISO, declares an alert, warning or emergency in response to challenging grid conditions. Tesla and PG&E may also call events at other times. These additional events may be necessary to prove the effectiveness of VPPs and ensure that participants have an opportunity to earn compensation in the Tesla & PG&E VPP pilot, even if no grid emergencies occur.

The Tesla & PG&E VPP pilot will have a minimum of 20 hours of events in 2021.

Compensation​

The Tesla & PG&E VPP pilot will compensate you $1 for the incremental kWh that your Powerwall delivers during events. You have the potential to earn more compensation by participating in all events and reducing your Backup Reserve to only the amount you expect to need.

Your compensation depends on several factors, including:​

• How many Powerwalls you own and your Backup Reserve, since this determines the total capacity you can provide during an event.
• The size of your solar system, since your solar system charges your Powerwall. The VPP will only export as much power as your solar system does in order to minimize negative grid impact while providing support.
• Your Powerwall’s typical behavior, since the program only pays for incremental kWh excluding the energy that your Powerwall would have delivered in the absence of the event.

Considering these factors, compensation earned during an event will vary from customer to customer. For reference, a two-Powerwall system that can deliver half of its energy capacity may earn approximately $10 per event.

Eligibility​

The Tesla & PG&E VPP pilot is available to PG&E residential customers who own Powerwall and solar and who are not on a medical baseline energy rate. Participants must not be part of a conflicting program, which may include another virtual power plant or demand response program run by PG&E, a Community Choice Aggregator or another party. Enrolling requires the Tesla app version 4.0.1.

If you are running Tesla app version 4.0.1 and do not see the opportunity to enroll, PG&E and Tesla may be unable to verify your eligibility. You can call PG&E at (800) 743-5000 to inquire about your eligibility for the pilot.

Frequently Asked Questions About Tesla VPP​

How do I enroll in the Tesla Virtual Power Plant?​

Step 1: Open the Tesla app, and switch to your home.

Step 2: Tap ‘Settings.’

Step 3: Scroll down to ‘Tesla Virtual Power Plant.’

Step 4: Tap the switch on, and follow the prompts to enroll.

How do I suspend my Powerwall’s participation in the Tesla Virtual Power Plant?​

Step 1: Open the Tesla app, and switch to your home.

Step 2: Tap ‘Settings.’

Step 3: Scroll down to ‘Tesla Virtual Power Plant.’

Step 4: Tap the switch off to suspend the Powerwall’s participation.

You may tap the switch back on at any time during the program.

What can I expect my Powerwall to do when there is an event?​

You will receive push notifications informing you when an event is scheduled and when it begins. Events will be scheduled a few hours prior to discharge when possible, and discharge will typically take place during the grid’s peak hours in the afternoon.

Tesla will securely command your Powerwall to discharge to the grid up to the maximum power approved by your utility. Most Powerwalls will discharge at levels similar to peak solar production on summer days. Prior to some events, your Powerwall may reduce the power it provides to your home to maximize the amount of energy it can discharge during the upcoming event.

Can I opt-out of dispatches?​

Yes — during an event, you can increase your Backup Reserve level to limit your Powerwall’s discharge. You can also tap the VPP Virtual Power Plant switch off to opt-out. As the Tesla Virtual Power Plant (beta) continues to evolve, you can expect to have more ways to control your participation.

How do I ensure that I will have enough energy for backup power?​

A push notification will inform you that there will be a VPP event. You can adjust your backup reserve level then or at any time, based on your own risk of outage.

If rotating outages occur due to grid emergencies, and your home is in a curtailed block, an outage can last about 1 to 1½ hours. Other grid blackouts or Public Safety Power Shutoff (PSPS) events may be longer in duration. If outages are planned, check with your utility for the expected duration.

If an outage occurs during the event, your Powerwall will still provide you with energy security using its stored energy.

Will participation in this program impact my electric bill?​

Tesla expects most events this summer to occur during typical peak hours for many time-of-use rate plans. Participating in the event will shift energy exports to periods that are later in the day compared to typical exports. If you are eligible for compensation under a NEM program, you may earn different credit for exporting at different times.

How will I get compensated?​

At the end of the VPP pilot (toward the end of the year), PG&E will calculate your contribution and incentive payment based on your Powerwall data. You can expect to receive payment from Tesla before the end of February.

​

Tesla & PG&E Virtual Power Plant Pilot Customer Participation Agreement​

Thank you for your interest in Pacific Gas and Electric Company’s (PG&E) Demand Response Emerging Technology Battery for Load Management Study (Study) implemented by Tesla, Inc. (Tesla). The Study involves only residential PG&E-selected participants who have one or more Tesla Powerwall(s) (Device) Tesla can remotely control during Demand Response (DR) events (Event). Participation is subject to your agreement to be bound by these terms and conditions with PG&E and Tesla (Terms).

By clicking “Accept Enrollment” or “Accept Updated Terms”, you (“Participant”) acknowledge that you have read these Terms and agree to be legally bound by them.

1. Eligibility
   PG&E in its sole discretion shall determine Participant’s eligibility to participate in the Study and shall have the right to not select Participant for any reason. Notwithstanding the foregoing, to be able to participate the Participant must:

a. Receive electric service on a PG&E residential rate schedule and not receive service pursuant to Medical Baseline or Life Support rate schedules, where continuous service is necessary and critical.

b. Have a PG&E electric SmartMeter that is read remotely and approved for electric grid interconnection and exports under PG&E Electric Rule 21.

c. Participant is not and will not enroll or participate in any other PG&E DR program, Community Choice Aggregator, DR Auction Mechanism Seller, or third-party DR program while participating in the Study.

1. Authority
   Participant should not participate in the Study unless Participant has the authority to control the Device and is the customer of record for the utility account associated with the address at which the Device is installed. By accepting these Terms, Participant confirms that Participant has that control and is the customer of record in that manner, and that Tesla and PG&E can rely on those confirmations in connection with the Study.
2. Participant Device Control Requirements
   By accepting these Terms, Participant grants each of PG&E and Tesla remote access to control on an exclusive basis the enrolled Device to enable Tesla during an Event to automatically charge and/or discharge the Device during the Study. Participant will have the ability to set a minimum level of charge as a backup reserve (“Backup Reserve”). Tesla will not draw Participant Device’s state of charge below Participant’s designated Backup Reserve and will not discharge Participant’s Device when the state of charge is below the Backup Reserve. Except for honoring Participant’s Backup Reserve, Tesla may charge or discharge Participant’s Device at any time and to any level.
3. Study Term
   The Study begins upon the Participant’s acceptance of these Terms and will continue until midnight of February 28th, 2022, unless expressly extended by PG&E or terminated sooner.
4. Payment
   The Study will only compensate the Participant $1 for every incremental kilowatt-hour PG&E and/or Tesla discharges from Participant’s Device during the Study Term. Tesla will pay the Participant any compensation earned upon the completion of the Study and later than midnight on February 28th, 2022. Those payments, if any, are the only compensation that Participant will receive from Tesla and PG&E for its participation in the Study. Participant is responsible for all other costs that may involve participating in the Study, including but not limited to, the cost of electricity to charge Participant’s Device and the general use of Participant’s Device.
5. Participant Device Data and Other Information
   Participation in the Study involves PG&E and Tesla having access to certain Participant personal identifiable information and energy use data that will include, but may not be limited to, their name, address, energy usage, utility account number, Device information, data generated from the Study, and other personal information, collectively referred to as Confidential Information. Participant authorizes PG&E and Tesla, and their employees and representatives, to use and exchange the Confidential Information to administer the Study and in accordance with Tesla’s Customer Privacy Policy (Privacy and Legal | Tesla) and PG&E’s Customer Privacy Policy (Privacy Policy). (Even though those policies are separate documents from these Terms, they are considered part of these Terms.) Participant further authorizes PG&E and Tesla to provide any Confidential Information to the California Public Utilities Commission upon its request or as otherwise required by law. Provided the Confidential Information is anonymized and does not contain any Participant personal identifiable information, such anonymized information may be used by PG&E and Tesla and that use does not require the Participant’s consent.
6. No Warranty; Disclaimer
   PG&E and Tesla expressly disclaim all warranties of any kind relating to the Study, whether express, implied or statutory including but not limited to any implied warranties for conditions, merchantability, fitness for a particular purpose, title, non-infringement or misappropriation of intellectual property rights.
7. Limitation of Liability
   In no event will Tesla or PG&E be liable for any direct, indirect, incidental, special, or consequential damages, arising in connection with the Study, including but not limited to Participant’s Device reduced charge during a power outage causing a loss of power or any other loss of power for whatever reason. If Participant is dissatisfied with the Study, any of these Terms, or believes Tesla or PG&E has breached these Terms in any way, Participant’s sole and exclusive remedy is to discontinue participation in the Study.
8. Termination
   PG&E or Participant may terminate Participant’s participation in the Study at any time for any reason, by PG&E providing notice to the Participant or the Participant sending an email to Tesla – [email protected]. Participant will receive compensation owing under Section 5 of the Terms for participation in the Study up until the date of termination.
9. General
   a. Entire Agreement. These Terms are the entire agreement between PG&E, Tesla and Participant concerning the Study’s eligibility and participation requirements.

b. No Assignment. These Terms may not be assigned by Participant without PG&E’s prior written consent.

c. Severability and Waiver. If any provision herein is invalid or unenforceable, the remaining provisions will remain in full force and effect.

d. Survival. Termination in the Study will not affect the obligations and rights under these Terms which are intended to survive such termination.

e. Governing Law. This Agreement is governed by California law.

1. Tesla Arbitration Requirement

Agreement to Arbitrate Please read this part carefully because it means you are agreeing that any unresolved dispute between you and Tesla will not be decided by a judge or jury in a public courtroom, but instead by a single arbitrator in a private arbitration. If you have a dispute arising out of or relating to any aspect of the relationship between you and Tesla, Inc. or its affiliates (which we call “Tesla”), please send us an email to [email protected], describing your dispute and how you would like it resolved. If it is not resolved within 60 days from the date of your email, you agree that your dispute can only be resolved by a single arbitrator in an arbitration administered by the American Arbitration Association (AAA) under its Consumer Arbitration Rules. This includes claims arising before you ordered your System (such as claims related to statements Tesla made about our products). We will pay all AAA fees for any arbitration, which will be held in the city or county of your legal residence. To learn more about the Rules and how to begin an arbitration, you can call any AAA office or go to www.adr.org. The arbitrator can only resolve disputes between you and Tesla, and cannot consolidate claims from others without consent from you, Tesla, and the others. You can only bring claims in arbitration against Tesla in your individual capacity and not as a plaintiff or class member in any class or representative action (and the same is true for Tesla). If a court or arbitrator decides that any part of this agreement to arbitrate cannot be enforced as to a specific claim for relief or remedy (such as what lawyers call “injunctive” or “declaratory” relief), then that claim or remedy (and only that claim or remedy) will be carved out of the arbitration and can be filed in court; all other claims must be arbitrated. If you prefer, you can take your individual dispute to a small claims court instead. If you don’t want to agree to arbitration, you can "opt out” of arbitration by sending us a letter within 30 days after placing your initial order for your System. Please send the letter to Tesla, Inc.; P.O. Box 15430; Fremont, CA 94539-7970 and include your name, your order number, the name of the product you ordered, and a statement explaining your desire to opt out of arbitration. If you do not opt out, your agreement to arbitrate overrides any different arbitration agreement between us, including any arbitration agreement in a lease or finance contract.

 

[aesculus]

Unfortunately, Tesla's VPP terms on the website is "generic" and does not include the PG&E specific language reproduced below. Note, I (got a little lazy and) did not fix all the formatting from the copy and paste.

Yeah. This is clear as mud and not even legal in some sense I suspect. But what I can get out of this and the corresponding web page:

Tesla Virtual Power Plant With PG&E | Tesla Support

Participate in the Emergency Load Reduction Program (ELRP) pilot offered by Pacific Gas and Electric Company (PG&E) and support the grid while also earning compensation and maintaining your energy security.

www.tesla.com

Is that Tesla is acting as an aggregator. They claim they are not doing this for any monetary gain. That may be true initially and that could easily change. Plus the value they are going to get using their customers systems and behavior as an experiment is worth a lot more than they would gain skimming a % of the returned energy at this early stage.

This statement is still confusing though:

• Export Credits During Peak Periods: You don’t need to change your home energy usage behavior to participate. Additionally, if you’re part of a net energy metering (NEM) program, you may earn net metering credit for your energy sent to the grid during events.

 

[GenSao]

This statement is still confusing though:

• Export Credits During Peak Periods: You don’t need to change your home energy usage behavior to participate. Additionally, if you’re part of a net energy metering (NEM) program, you may earn net metering credit for your energy sent to the grid during events.

I believe the $1/kWh VPP rate is on top of the prevailing NEM rates at that time. So for someone on PG&E's, EV2-A rate schedule, they would earn $1.50/kWh ($1.00 VPP + $0.50 NEM).

Technically, it is a bit of a wash for NEM since "solar only" export early in the day is swapped (or delayed) for exporting stored power during a VPP event later in the day (when the sun is down).

 

[mikesm]

So I am trying to do some estimates of the economic case. Given peak pricing at $0.51/KWh, and off-peak at $0.19/ KwH, that gives a spread of 32 cents/KWh that is available from loadshifting. If we have 3 Powerwalls, and each gets filled with 13.5 KWh of capacity, and sent to the grid during the peak hour (or offsetting peak consumption), that yields 13.5*3*30/days/month*12m/yr*.9 (to cover roundtrip losses in the PWs) = about $4199/yr in savings. Did I get that right given the assumptions?

Each PW is about $7500, plus $1K for the gateway, so this is about 3*7500+1000 or $23500 for the hardware alone yielding a 5.5 year payback. Not very good economics for doing this, though if the spread increases I guess it would get better, but if the spread decreases, then it would make even less sense.

Is there a federal tax credit that could make this a better business case? Did I miss something in the analysis?

 

[jboy210]

So I am trying to do some estimates of the economic case. Given peak pricing at $0.51/KWh, and off-peak at $0.19/ KwH, that gives a spread of 32 cents/KWh that is available from loadshifting. If we have 3 Powerwalls, and each gets filled with 13.5 KWh of capacity, and sent to the grid during the peak hour (or offsetting peak consumption), that yields 13.5*3*30/days/month*12m/yr*.9 (to cover roundtrip losses in the PWs) = about $4199/yr in savings. Did I get that right given the assumptions?

Each PW is about $7500, plus $1K for the gateway, so this is about 3*7500+1000 or $23500 for the hardware alone yielding a 5.5 year payback. Not very good economics for doing this, though if the spread increases I guess it would get better, but if the spread decreases, then it would make even less sense.

Is there a federal tax credit that could make this a better business case? Did I miss something in the analysis?

You cannot just sell the power out of your Powerwalls to the grid at will.

Most plans restrict you to only sending power to the grid from your solar system's excess production. Excess production = Solar Production at moment - (home use + powerwall charging).

The only exceptions I am aware of are things like the Virtual Power Plant (VPP). Perhaps others know of other ways to sell power from a Powerwall.

 

[aesculus]

Is there a federal tax credit that could make this a better business case? Did I miss something in the analysis?

@jboy210 did a great job of explaining the current situation with only being able to send back the power when you create it. While nothing restricts the utility from buying all of your solar any time you want to send it to them, other than VPP, it does not work that way today. We are hoping Tesla will fix that soon.

And yes you may qualify for the Solar Tax Credit for your Powerwalls which will reduce the ROI period.

 

[h2ofun]

So I am trying to do some estimates of the economic case. Given peak pricing at $0.51/KWh, and off-peak at $0.19/ KwH, that gives a spread of 32 cents/KWh that is available from loadshifting. If we have 3 Powerwalls, and each gets filled with 13.5 KWh of capacity, and sent to the grid during the peak hour (or offsetting peak consumption), that yields 13.5*3*30/days/month*12m/yr*.9 (to cover roundtrip losses in the PWs) = about $4199/yr in savings. Did I get that right given the assumptions?

Each PW is about $7500, plus $1K for the gateway, so this is about 3*7500+1000 or $23500 for the hardware alone yielding a 5.5 year payback. Not very good economics for doing this, though if the spread increases I guess it would get better, but if the spread decreases, then it would make even less sense.

Is there a federal tax credit that could make this a better business case? Did I miss something in the analysis?

Plus install, permits, etc. Its a lot more

 

[miimura]

As stated above, you cannot just sell your entire Powerwall energy content every day. My math works out about like this considering my actual usage during Peak hours:

• 4 months Summer rates $0.50-$0.19=$0.31 difference offsetting 10kWh/day -> $0.31 * 10kWh * 120d = $372
• 4 months Spring/Fall on Winter rates $0.37-$0.19=$0.18 difference offsetting 10kWh/day -> $0.18 * 10kWh * 120d = $216
• 4 months Winter rate $0.18 difference, limited by generation to average 5kWh/day -> $0.18 * 5kWh * 120d = $108

Approximate Arbitrage Savings Total: $696 per year

If you have significant A/C usage during the Summer, you could save a lot more in that season. If you have a larger solar system, you could save more in the Winter.

 

[h2ofun]

As stated above, you cannot just sell your entire Powerwall energy content every day. My math works out about like this considering my actual usage during Peak hours:

• 4 months Summer rates $0.50-$0.19=$0.31 difference offsetting 10kWh/day -> $0.31 * 10kWh * 120d = $372
• 4 months Spring/Fall on Winter rates $0.37-$0.19=$0.18 difference offsetting 10kWh/day -> $0.18 * 10kWh * 120d = $216
• 4 months Winter rate $0.18 difference, limited by generation to average 5kWh/day -> $0.18 * 5kWh * 120d = $108

Approximate Arbitrage Savings Total: $696 per year

If you have significant A/C usage during the Summer, you could save a lot more in that season. If you have a larger solar system, you could save more in the Winter.

so how many years payback?