Vehicle-to-Home Load Shifting $14k 6-yr savings?

[Mardak]

People have been talking about Vehicle-to-Grid as a potential for Tesla and customers to make money selling to the grid when demand is high leveraging long life cycles of 2+ million mile batteries. V2G would be a superset of what one could do with Vehicle-to-Home, which instead of selling to the grid, one could shift one's own electricity peak demands to off peak times. But even with this lesser capability, V2H seems to have a lot of potential value in some places that have significant time-of-use electricity price differences, e.g., California which is likely to continue to be a large market for Teslas.

If Tesla sells cars that can at least power the house, owners would be able to return home and pull from the car's batteries instead of paying Peak and Partial-Peak pricing to then recharge the car during Off-Peak times. Some people have done this already with Powerwalls, but it's a little bit more complicated as those batteries normally charge only from solar generation in the US for tax purposes: Grid Charge Powerwall with Solar

To put some numbers, PG&E charges California EV2-A owners 48¢/kWh for summer Peak rate from 4pm to 9pm and 37¢/kWh for Partial Peak and 17¢/kWh for Off-Peak midnight to 3pm. Taking an average pre-EV consumption of 30kWh/day split equally between summer/winter Peak/Partial-Peak rates, this would normally be $4200 for the year vs $1800 if everything was Off-Peak instead. Over 6 years, this would exceed $14k in savings even with some inefficiencies.

Here's a example of potential savings:

Alternatively, a 72-month 2.5% loan for a $38k vehicle would normally be $600/mo, but $200/mo load shifting savings would reduce the effective payment to $400/mo which would be more like a $24k vehicle purchase price.

(Even better is if your work covers the cost of your EV charging… )

 

[miimura]

I'm pretty sure you're over-estimating your arbitrage potential. I do have Powerwalls, so I have done the calculation. I only save about $700/year because of my limited winter solar production.

Some notes:
1. EV2-A Summer season is only 4 months. (~122 days)
2. You have to recharge the battery from Off-Peak, unless you're using energy recharged by your employer. So, you have to subtract the Off-Peak cost from your Peak cost to calculate your savings.
3. I doubt you're using 30kWh/day between 3pm and midnight unless you use a significant amount of A/C.
4. Part-Peak is 3-4pm and 9-12pm. Peak is 4-9pm.
5. If you're using the car, you can't take energy out of it if you're not at home. That may push out your offset hours to 6pm-12mid Mon-Fri??

Summer Peak Arbitrage = Peak kWh * ($0.47861 - $0.16611)
Summer Part-Peak Arb. = Pt.Pk kWh * ($0.36812 - $0.16611)
Winter Peak Arbitrage = Peak kWh * ($0.35150 - $0.16611)
Winter Part-Peak Arb. = Pt.Pk kWh * ($0.33480 - $0.16611)

If you assume 10.0kWh Peak, 8.0kWh Part-Peak in the Summer, you save $578 for the entire Summer rate season.
If you assume 8.0kWh Peak, 6.0kWh Part-Peak in the Winter, you save $609 for the entire Winter rate season.
That's only $1,187 for the entire year. Less than $100/mo on average.

 

[wjgjr]

While I agree in principle that it could save money in some cases by arbitraging between peak and off-peak, the issue is not as simple as just plugging in the car and having the car charge your house. At the least, there would be significant costs involved in installing something like the existing powerwall gateway hardware, which would be required to ensure the car battery plays nicely with the grid. (And while you describe it as V2H, it is still a type of V2G, since your home is on the grid, so any energy you are introducing into your home can impact the grid.)

Then, there is also the question of how utilities will respond to such a product. Some utilities seem more enthusiastic about PWs for load shifting than others. And it gets pretty complicated if you also have solar, as some utilities apparently will not allow PWs to be charged from the grid, which could be an issue with an EV (which in this usage is like a large PW.) Plus, over time, it is likely that the gap between peak and off-peak would shrink if and as enough storage becomes available to actually smooth the peak.

I would also suggest the assumptions on savings are high in that they would require the vehicle to be tied to the home except during off-peak times (and they need some off-peak time to charge.) In the above example, if somebody is out of the house from 8am-6pm (perhaps a "typical" example, pre-pandemic) they would have to use peak energy when the car is off-grid. (Of course, maybe the house has solar and/or dedicated PWs, but then at some point you max out the amount of power that can be shifted.)

To me, taking into account the infrastructure costs and the need to have the car plugged into the house to get the savings, it is not likely to be a huge money-maker for most people. I think in some ways the bigger benefit might be having it available as an option during an outage either short-term if you don't have PWs, or long-term if your solar over-produces. But I would not be surprised if some of the complexities around utility rules might also make even that a challenge.

 

[miimura]

@wjgjr you are correct that you need some expensive equipment to power a house from an EV. You need at least an inverter and a disconnect switch. My assumption is that you can get around the utility argument by simply disconnecting the grid and using the EV to power the house completely during the desired hours. However, the inverter then needs to support surge demand like starting an air conditioning compressor.

As I have stated in other places in this forum, arbitrage is meaningful to me because I was lucky enough to get Powerwalls with a large SGIP rebate and the 30% tax credit on the balance of costs.

 

[Mardak]

1. EV2-A Summer season is only 4 months. (~122 days)
3. I doubt you're using 30kWh/day between 3pm and midnight unless you use a significant amount of A/C.
5. If you're using the car, you can't take energy out of it if you're not at home. That may push out your offset hours to 6pm-12mid Mon-Fri??

The main difference with your numbers from mine is that I just flat estimated 15kWh for each of summer peak, summer partial-peak, winter peak, winter partial-peak; but indeed I did incorrectly do 6 months of summer instead of 4 as PG&E's xlsx file seemed to indicate May-Oct for summer.

The 30kWh average I searched for US average, but I do see a California specific number of about 20kWh, which does indeed bring the potential savings closer to $100/mo than $200/mo.

Theoretically, one shouldn't need to use the A/C or electricity in general if nobody is at home, but yes there will be some draw that cannot be offset if the car isn't plugged in at home.

 

[ra88it]

I'm assuming no one has a TEG2+ Powerwalls +Gen3 charger + Y/3 after Xmo of 2019?

 

[Mardak]

Some utilities seem more enthusiastic about PWs for load shifting than others.

Yeah, I wonder if utilities would be willing to front the cost of installing the hardware, e.g., charger, inverter, disconnect; and this could potentially be for the utility to access your battery during peak times for "free" while giving the customer most of the arbitrage benefit. Tesla would likely design some custom/streamlined version to reduce parts and labor costs too.

At least with Tesla Demand Response Terms of Service | Tesla Support it seems like Tesla is deploying something related at a smaller scale already.

 

[jboy210]

I'm assuming no one has a TEG2+ Powerwalls +Gen3 charger + Y/3 after Xmo of 2019?

I have Teg1 + 2 PWs + 2020 Model 3 + Gen2 charger. Does Teg2 and Gen 3 charger give you V2G/V2H?

 

[jjrandorin]

Im totally NOT interested in using the expensive battery in my car, which was designed to run my car, to power my or anyone elses home, except for an emergency. I remember reading somewhere that battery chemistry for the car batteries is different than for powerwalls, due to the different use case (car acceleration, vs home electricity usage.

I would be interested in plugging in my car in an outage situation to assist my powerwalls in powering my home, but as a "general use, mobile powerwall" situation, no, not interested even in the slightest bit.

 

[wjgjr]

Yeah, I wonder if utilities would be willing to front the cost of installing the hardware, e.g., charger, inverter, disconnect; and this could potentially be for the utility to access your battery during peak times for "free" while giving the customer most of the arbitrage benefit. Tesla would likely design some custom/streamlined version to reduce parts and labor costs too.

At least with Tesla Demand Response Terms of Service | Tesla Support it seems like Tesla is deploying something related at a smaller scale already.

There are various programs where utilities or states share the costs for PWs - a number of people have mentioned programs in CA, and I know there is a program in parts of New England that allows utility access to PWs (ConnectedSolutions | Tesla). And MD, for example, provides a state rebate for PWs. The difference I see, though, is these PWs are permanently attached to the grid, so they are more of a known commodity. I don't see the same benefits to utilities or to the grid in general (which may be relevant to legislatures as they set policy and incentives) of "mobile batteries."

In some future where your car can self-drive and can plug itself in on request to help the grid, maybe there is at least something of an argument, but for now it feels like it would be premature for governments and utilities to be subsidizing this kind of scheme. I do think dedicated battery farms, along with tapping private PWs (from owners who accept the incentives for such programs) are the better approaches for stored energy that Tesla can support.

 

[ra88it]

Im totally NOT interested in using the expensive battery in my car, which was designed to run my car, to power my or anyone elses home, except for an emergency. I remember reading somewhere that battery chemistry for the car batteries is different than for powerwalls, due to the different use case (car acceleration, vs home electricity usage.

I would be interested in plugging in my car in an outage situation to assist my powerwalls in powering my home, but as a "general use, mobile powerwall" situation, no, not interested even in the slightest bit.

Same batteries as Model 3/Y, discharged at 30a MAX. haha. You're worse off hitting that supercharger once a year.

 

[jjrandorin]

Same batteries as Model 3/Y, discharged at 30a MAX. haha. You're worse off hitting that supercharger once a year.

Even if thats the case, I am still not interested in the slightest at using my car instead of my powerwall batteries... and if I didnt have powerwalls I would only want to use the car for power as emergency backup, not for 'everyday load shifing". Im just not interested in using a car for such a feature on a regular basis. Emergency, sure, regular basis, on some sort of "demand response "program, no, not unless the car was basically free to me, which it wouldnt be.

 

[jjrandorin]

Even if thats the case, I am still not interested in the slightest at using my car instead of my powerwall batteries... and if I didnt have powerwalls I would only want to use the car for power as emergency backup, not for 'everyday load shifing". Im just not interested in using a car for such a feature on a regular basis. Emergency, sure, regular basis, on some sort of "demand response "program, no, not unless the car was basically free to me, which it wouldnt be.

Also, for full disclosure, I am also not the least bit interested in any sort of "demand response" program for my powerwalls, either. Im not interesting in the utility paying to cycle my powerwalls when they want to. I played that game in reverse with the AC before I had solar and powerwalls, and it was horrific. I swore I would never do that again, for the miniscule amount of amount that SCE paid for for the privilege of ensuring I was miserable on every hot day.

 

[ra88it]

Also, for full disclosure, I am also not the least bit interested in any sort of "demand response" program for my powerwalls, either. Im not interesting in the utility paying to cycle my powerwalls when they want to. I played that game in reverse with the AC before I had solar and powerwalls, and it was horrific. I swore I would never do that again, for the miniscule amount of amount that SCE paid for for the privilege of ensuring I was miserable on every hot day.

Why anyone sells power back to the grid at a reduced rate and drives an EV is beyond me.

Order enough PV/RE and storage to suit your needs 100%, in winter. It's simple. Using a spare model 3/y to supply power to my roadster at night after the powerwalls are all drained isn't an issue to me with a 100k mile battery warranty.

Bummer you were just open enough to buy a tesla but just closed minded enough to shut down at any potential savings you'd have.

I hope you have a wonderful night.

 

[jjrandorin]

Why anyone sells power back to the grid at a reduced rate and drives an EV is beyond me.

Order enough PV/RE and storage to suit your needs 100%, in winter. It's simple. Using a spare model 3/y to supply power to my roadster at night after the powerwalls are all drained isn't an issue to me with a 100k mile battery warranty.

Bummer you were just open enough to buy a tesla but just closed minded enough to shut down at any potential savings you'd have.

I hope you have a wonderful night.

Money means different things to different people. For "me" the car is a major purchase, and I hope to have it many years. I dont see any reason to put extra drain / fill cycles on it unnecessarily. We know for a 100% fact that batteries degrade over time, from use. This is a 100% fact. Why put extra "use" on the car battery I dont need to? Thats the purpose of the powerwalls.

If I wanted more storage for at home, I would buy more another powerwall, which I am considering doing. As I said, I also would like to be able to use the car battery to power the home in an emergency situation. For me, that an emergency constitutes "appropriate situation to introduce additional undriven charge cycles on the battery". "Charging my other car / powering my home while grid is up / sending power to grid to power someone elses home" does not = an appropriate situation to introduce additional undriven charge cycles to the battery (again, for "me").

I dont have a "spare" model 3. I have my "model 3 commuter car" that I hope to drive and own for years. Not sure how not wanting additional uneeded charge cycles on the cars battery that are not driven makes me "close minded", when this is all a hypothetical discussion anyway. If "potential savings" = enough to buy a new model 3 every 5 years I would obviously consider it, because it would buy me a new car every 5 years. For the (extreme in my opinion, as already pointed out_ example in OPs post of 14k saved over 6 years, yeah I am not interested in that "savings" on wear and tear on my car battery. If I could achieve that amount of savings by load shifting, I would just buy another couple of powerwalls and have them paid for by that program.

/shrug. Yeah I realize I am being a bit sensitive being called "close minded" because of all the things I have been called by people, thats not one of them.

 

[ElectricCyclist]

I am personally more in @jjrandorin camp when it comes to just offsetting my TOU usage and will shortly have 2 powerwalls installed which I will set to make sure I don't pay electricity at those high rates of 4-9PM (reside in SCE territory).

What I disagree on is I think Powerwalls and eventually our cars would be much more lucrative investments if the systems were setup to be very responsive demand response assets. I think that we can eventually more than pay for our powerwalls if we are able to allow Tesla to group these assets and provide service to the electrical grid during peak usage and get paid for it not just remove the usage charge if we were to use electricity but get paid to provide electricity to the grid.

Regulatory systems will need to be setup to make this happen but to have so many powerwalls installed throughout California and not be able to call on them to discharge instead of ramping up a dirty gas peaker plant that is expensive to run just seems like great business and gives back more to the customers who installed them.

 

[Ampster]

Does Teg2 and Gen 3 charger give you V2G/V2H?

There were reports that the charger in the model 3 was bidirectional. Several sources have said that is not the case. My opinion is that it is not in the plan for Tesla.

 

[Mardak]

I would only want to use the car for power as emergency backup, not for 'everyday load shifing". Im just not interested in using a car for such a feature on a regular basis.

Also, for full disclosure, I am also not the least bit interested in any sort of "demand response" program for my powerwalls, either. Im not interesting in the utility paying to cycle my powerwalls when they want to.

The former with load shifting is what I was trying to differentiate as Vehicle-to-Home vs latter demand response as Vehicle-to-Grid. At a high level, they both trade battery life for some monetary compensation, but with load shifting, the utility was going to charge you the higher rate anyway, so using your existing battery asset is to reduce your expenses. In contrast, demand response feels more like you're "helping" the utility by offering your batteries for additional income.

Of course people should have a choice to participate or not.

Trying to put some more numbers for context, 20kWh battery cycling every day is similar to adding an extra 30k miles on your battery "odometer" each year. So a 2 million mile battery would last for over 60 years from this load shifting usage. Add in a high 20k annual driving mileage (Tesla owners enjoy driving more?), that would still be 40 years of battery usage. Although degradation curves do vary based on usage, but existing packs do seem to level off at 90% for a while already.

 

[jjrandorin]

The former with load shifting is what I was trying to differentiate as Vehicle-to-Home vs latter demand response as Vehicle-to-Grid. At a high level, they both trade battery life for some monetary compensation, but with load shifting, the utility was going to charge you the higher rate anyway, so using your existing battery asset is to reduce your expenses. In contrast, demand response feels more like you're "helping" the utility by offering your batteries for additional income.

Of course people should have a choice to participate or not.

Trying to put some more numbers for context, 20kWh battery cycling every day is similar to adding an extra 30k miles on your battery "odometer" each year. So a 2 million mile battery would last for over 60 years from this load shifting usage. Add in a high 20k annual driving mileage (Tesla owners enjoy driving more?), that would still be 40 years of battery usage. Although degradation curves do vary based on usage, but existing packs do seem to level off at 90% for a while already.

my existing model 3 is not a "2 million mile" battery or a "1 million mile" battery as defined by tesla, though, so for the purposes of the discussion I think it would be fair to think of the existing fleet as "500k mile" batteries. So, if the existing batteries are 500k miles, and by your estimation that puts an additional "30k miles" a year on "my batteries odometer", while I myself drive between 17k-19k miles a year, that is almost double my normal driving usage.

Or said another way, in order for that to make sense, I would have to receive enough compensation to pay for the car itself in the time I would expect to own it, since I am cutting its battery life in 1/2.

Maybe when there is such a thing as a 2million mile battery that makes more sense, or, we get paid enough for doing that to buy the car, but buying powerwalls is cheaper than buying the car.

 

[ra88it]

Trying to put some more numbers for context, 20kWh battery cycling every day is similar to adding an extra 30k miles on your battery "odometer" each year. So a 2 million mile battery would last for over 60 years from this load shifting usage. Add in a high 20k annual driving mileage (Tesla owners enjoy driving more?), that would still be 40 years of battery usage. Although degradation curves do vary based on usage, but existing packs do seem to level off at 90% for a while already.

I would disagree that 20kWh of battery cycling is going to add 30k miles a year. We're not talking about 300A+ draws here. We're talking about sub 48A (at the most, being that GEN3 is 60A breaker) backfeeding into the home.

Japan and Europe have chademo V2G/V2H, it's only a matter of time before the US gets with the program.