Using Tesla car as a Powerwall - Is it possible?

[sparkypete]

I live in the UK and have a Model 3 reservation.

I'm looking at the benefits of a combination of installing solar panels, Powerwall and using cheaper overnight electricity (called Economy 7 in the UK).

Due to our climate in the UK, solar payback periods are quite long and apart from weekends most of the generated electricity won't be usable and will be exported at about a third of the cost of buying it back. Powerwall 2 would solve this but payback on that at the moment is working out at just under the service life of the unit so I'm not convinced.

There would definitely be savings if I could use Economy 7 electricity at night to charge the Tesla (I'll need about 10kwh per day Mon-Fri and more at the weekends) but the increased cost of peak usage on these tariffs may negate the gain. My commute is about 30 miles a day.

A real cost benefit would be if I could use the spare capacity in my Tesla as a Powerwall when I'm not using it. If I could set a system up to allow me to specify the residual charge that must be kept in the Tesla (say 50%), I could use cheap electricity overnight to keep it fully charged, then when I come home, plug it in and draw power from the Tesla for powering the house until midnight, then use cheap electricity again to charge the whole thing up.

This would be great for the grid as a whole, allowing energy companies to use more renewables due to the storage effect.

I'm sure this isn't a new idea but I couldn't find anything online. Does anyone know whether / how this can be done?

 

[sparkypete]

Ah - found some stuff on this. It seems it's called V2G (Vehicle to Grid). Not looking possible at the moment. See Using my 90D as emergency power for my house? | Tesla Motors

 

[Ibrido]

These kits turn your Prius into an emergency generator

I also remember Google had done this experiment of using multiple Prius cars to occasionally supply grids.

So should be possible with Tesla too with some additional hardware.

 

[OBX John]

I wish they would just give us a 120 volt outlet in the car!

 

[dutchinchicago]

I wish they would just give us a 120 volt outlet in the car!

The main issue is that batteries are heavy and a car has to carry the batteries around with it. This means that battery efficiency is really important. If you loose 10% efficiency in a home battery that is not a big deal but if you loose 10% efficiency in a car battery then that is a huge issue. Therefor you don't want to use your car as a home battery as the additional usuage will degredate the battery a lot faster.

 

[Ampster]

Therefor you don't want to use your car as a home battery as the additional usuage will degredate the battery a lot faster.

It probably depends more on how much of a full cycle you put it through. Unless you have huge loads at your home the kW draws from a home are a lot less than acceleration or high speed driving. Of course all of that is moot sonce Tesla has not announced V2G yet. For example if your car consumes 300 Watts per mile at 100kph then in an hour your car will use close to 20 kWh of energy versus a home that normally would be less than 5kW per hour.

 

[WannabeOwner]

most of the generated electricity won't be usable and will be exported at about a third of the cost of buying it back

Its a while since my PV was installed, so it may have changed?

I get a rebate for 50% of the units I generate - i.e. it is assumed that I Export 50%, I don't have a meter that actually monitors what I do export. Can't remember what the export rate is, but I thought it was generous - surprised that you mention Exporting being only 1/3rd the value of Import?

the increased cost of peak usage on these tariffs may negate the gain

Unless you are using a lot of electricity during the day I doubt this. (You mention better savings of Solar at weekend, so I assume you are out at work during the week, and thus day time usage is negligible)

You may need to install some timers etc. so you can run Dishwasher, Washing machine, etc. overnight (that said: all my white-goods have integral delay-timers), but since we have had Solar, and more recently EV charging overnight, I now use all things such as Washing machines during the day - to use up Solar power (as my Rebate is on the assumed 50% export, so the more I use, and the less I export, the better off I am - I still get the same Rebate)

Charging a car on E7 will be (depending on how good your E7 rate is and how poor the MPG is/was of your equivalent ICE) something between 4x and 8x cheaper than petrol. The differential that I might gain by being smart and shuffling things between Sun-shining, sun-not-shining and E7 periods I don't think is enough for me to either a)worry about or b) provide a payback for me investing in some sort of automatic switching system, let alone a storage system. If there was a smart switch that didn't require rewiring the whole house! I'd be interested, but even trying to use something like the hot water immersion heater to soak up spare Solar PV costs a lot - both the kit and the install (unless everything is all within a few feet of each other, sadly that's not the case in my house).

I agree, if my EV would just be my house-power-source from dusk to bedtime, and then recharge on E7 from midnight onwards, that would be spot-on. Don't think that's on the cards with the current generation of EVs though and, like you, I cannot make the numbers work for any sort of storage solution. My next-spend is more likely to be increasing generating capacity, rather than trying to store / offset what I already have.

If you don't already do so I think it would be worth reading your meter regularly (I have read mine weekly for years) and perhaps also doing some readings Day/Night and weekday/weekend, particularly during Winter, to see how much you are using at various times of the day / days of the week. That will provide a decent baseline at least.

 

[brucet999]

Whether M3 might or might not stress its battery if put into service as a power wall is a moot point. You won't be able to do it anyway.

Tesla did not allow Roadster, MS, or MX to connect to any third party output. Why would they change with M3?

Tesla makes purpose-built power wall products with proper controls to use as emergency backup, time shifting of Grid power or to store PV-generated power for use at night. Why would they facilitate using your M3 instead of buying a Power Wall?

Tesla probably doesn't want the liability exposure of people back-feeding their house current by plugging the car in. Besides the possible damage to house and/or car by such ad hoc do-it-yourself connections, there is the problem of endangering electric utility workers trying to repair some fault in the neighborhood circuit but finding it still energized after they had disconnected from their transformer. Power Wall switching equipment automatically isolates the house when it takes over during a Grid power failure.

 

[Schumpeter]

One of the challenges is the costly charging infrastructure when creating such as solution In its early days, Tesla has done pilots with vehicle2grid but stopped these..

A company from the Netherlands jedlix.com works together with Tesla for regular smart charging (basically postponed charging), directly through the connected car. They are probably planning to go to the UK as well. I have used it and it works pretty well; they help balancing the grid and pay a compensation to me.

 

[Aussie]

The reason why you would not want to use your car as a Powerwall is the impact on cycle life. The car only has battery which lasts less than 1000 cycles. So you really don't want to waste them to power your home if you can get a battery which is designed for this application for a relatively cheap price. Better to go with a Powerwall2 or sonnen unit for you in the UK.

 

[Ampster]

Tesla did not allow Roadster, MS, or MX to connect to any third party output. Why would they change with M3?

Because if they could aggregate that power and make the grid more resilient and provide better value to M3 owners. It has fewer financial risks as a concept now that Supercharging is not free.

 

[Ampster]

A company from the Netherlands jedlix.com works together with Tesla for regular smart charging (basically postponed charging),

In California I am on a pilot with Ohm Connect and it will tell my car not to charge if the grid is stressed. (They call it an Ohmhour when a peaker plant is running)

 

[brucet999]

The reason why you would not want to use your car as a Powerwall is the impact on cycle life. The car only has battery which lasts less than 1000 cycles. So you really don't want to waste them to power your home if you can get a battery which is designed for this application for a relatively cheap price. Better to go with a Powerwall2 or sonnen unit for you in the UK.

Your point would be another reason for Tesla not to allow it, as the risk would exist of their having to replace some over-cycled traction batteries during the 8-year unlimited miles warranty.

 

[brucet999]

Because if they could aggregate that power and make the grid more resilient and provide better value to M3 owners. It has fewer financial risks as a concept now that Supercharging is not free.

I think you missed the point of my post. What would be the advantage to Tesla?
Why would Tesla allow their cars to back-feed the Grid instead of people having to buy the Tesla Power Wall that is purpose-made for load balancing?
What has paid supercharging to do with allowing M3s to back-feed the Grid?

 

[brucet999]

I live in the UK and have a Model 3 reservation.

I'm looking at the benefits of a combination of installing solar panels, Powerwall and using cheaper overnight electricity (called Economy 7 in the UK).

Due to our climate in the UK, solar payback periods are quite long and apart from weekends most of the generated electricity won't be usable and will be exported at about a third of the cost of buying it back. Powerwall 2 would solve this but payback on that at the moment is working out at just under the service life of the unit so I'm not convinced.

I had a similar first reaction to the cost of solar panels on my roof. Since my power use is fairly low anyway, the break-even point would have been about 12 years. Solar companies suggested that it was not worth it. But when I looked at it not as a cost to be recovered, but as an alternative investment, the returns became far better.

I would have had to take money out of securities investments to pay for the solar array, so I looked at it as an alternative investment. Suddenly, a 12-year break-even on cost turned into an 8% annual return on investment - tax free. My conservative securities portfolio was earning around 5% to 6% of which state and Federal income tax took away over 30%. The money that I would no longer pay for Grid electricity would not be a taxable event, so that 8% savings would be equal to finding a risk-free taxable investment yielding 11.4%.

 

[Ampster]

I think you missed the point of my post. What would be the advantage to Tesla?
Why would Tesla allow their cars to back-feed the Grid instead of people having to buy the Tesla Power Wall that is purpose-made for load balancing?
What has paid supercharging to do with allowing M3s to back-feed the Grid?

The advantage would be greater capacity that could enhance an Powerwall installation and provide better value to the Tesla customer. Tesla might be able to collect some fee for aggregating power. My comments apply to the market in California which is incentivizing storage.
With free supercharging some people might be tempted to fill up at SC and run their house off free SC energy.
I am not disagreeing with you, and with the success of their powerpack installations at a utility scale there is not much likelihood of them doing this in the near future.

 

[WannabeOwner]

the risk would exist of their having to replace some over-cycled traction batteries during the 8-year unlimited miles warranty.

I get that (and presumably Tesla could bake something into the warranty small print ...)

The thought I wanted to add is that, compared to driving, I figure the amount that my car battery would have to contribute to my house is pretty small. I'm the whole Atlantic away from USA so apologies if I have this wrong, but seems to me that USA averages more Electricity use per capita, so might not work there, but our house (which aint small my any metric ...) is rarely using above 2kW and more commonly 1kW. If car powers house from, say, 6PM to 10PM (i'm guessing that is come-home-time to grid-peak-tail-off - Off Peak here starts at midnight) I'm looking at about 4 - 8 kWH per evening, or about 12 - 24 miles of driving.

My figures may be way off, I'm outside my skillset!, if so I would be pleased to have them corrected. If my figures are correct I'm not sure it would be that big a deal for Tesla warranty (assuming they have a limit of some sort on V2G usage)

EDIT: The point I think I may be missing is the Tesla Battery discharging into the grid ... that could easily be more than my house's 1kW requirement ... so perhaps what I am thinking of is just to reduce MY consumption instead.

 

[WannabeOwner]

The car only has battery which lasts less than 1000 cycles

Is that about 200,000 miles? The Tesloop taxi clocked up 200,000 miles and only degraded about 6%.

Tales from a Tesla Model S at 200k miles

 

[brucet999]

Is that about 200,000 miles? The Tesloop taxi clocked up 200,000 miles and only degraded about 6%.

Tales from a Tesla Model S at 200k miles

Wow! Thanks for posting that link.

 

[DFibRL8R]

The reason why you would not want to use your car as a Powerwall is the impact on cycle life. The car only has battery which lasts less than 1000 cycles.

I'm not sure this is accurate (feel free to provide evidence to the contrary of course).
The concept of a charge "cycle" is really a poor way to think about what is happening with the Tesla battery in normal use. While driving, there is frequent switch between discharge and charge due to regenerative breaking. These mini charge cycles shouldn't have much impact at all. It seems extremes of charge state (100% or approaching 0% SOC) are more damaging to the pack over time so I would think as long as the battery is kept in it's normal operating ranges it wouldn't matter too much if it was used for V2G.

Personally, I have a hard time justifying buying additional home battery storage when I already have so much in the car.