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Can Your Electric Car Be Used to Help Power the Grid?

There are more than 200,000 electric vehicles in Southern California Edison’s service area and about 700,000 in the entire state. The newest of these cars have batteries that can hold up to 100 kilowatt-hours of electricity — or enough to power an average California household for nearly a week.

For California to meet its goal to become carbon neutral by 2045, SCE sees the need for 75% of all vehicles in the state to be electric by then.

“With all this potential for stored energy to be connected to the electrical system at some point during the day, either at home or in parking lot charging stations, it’s worth considering whether EV batteries could be a viable source of power for the energy grid,” said Carter Prescott, principal manager of operations for SCE’s eMobility team.

Earlier this year, SCE launched a number of demonstration projects, including one that explores vehicle-to-grid, or V2G, two-way technology that allows EV batteries both to charge and to discharge power onto the grid while they are plugged in, the same way stationary batteries do.

“V2G has the potential to make EV owners energy producers, much like our rooftop solar customers who sell power back to the grid,” said Juan Castaneda, SCE principal manager of Grid Technology Innovation. “But the technology to make that happen is in the developmental stages, and we still have many hurdles to overcome before we’ll be able to tap energy stored in EV batteries as a safe, reliable and efficient resource.”

The demonstration project will attempt to validate whether V2G could actually result in a reduction of customers’ electric bills in exchange for energy they supply from their EV batteries when they are connected to the grid. It will also examine standardization of equipment that would be necessary to make those connections possible.

The project will be conducted using a mix of passenger EVs both at workplace charging sites and under laboratory conditions, as well as electric school and transit buses. The project is being funded through SCE’s administration of the Electric Program Investment Charge, or EPIC, which manages an annual budget of $13 million for demonstrations to further grid advancements that will help meet the state’s energy and climate goals.


Matt Chester's picture
Matt Chester on May 19, 2020

Really interesting stuff going on with EVs and the grid, and it's great to see SCE's leadership in that regard. Thanks for sharing, Michael.

For California to meet its goal to become carbon neutral by 2045, SCE sees the need for 75% of all vehicles in the state to be electric by then

Does this account for all vehicle types (e.g. trucks, government fleets, personal vehicles, etc.), or is this strictly lightweight vehicles like personal cars? And is there a difference in how SCE's program is approaching these different 'classes' of vehicles toward such V2G programs? I would imagine engaging a larger fleet (whether government or private like a fleet of FedEx delivery vehicles, for example) would require a different approach than residential customers? 

Michael Herrera's picture
Michael Herrera on Jun 3, 2020

You're certainly welcome for the share Matt. The project research is being conducted with testing on both lightweight vehicles and larger vehicles. We look forward to the results of this project which will ultimately help guide us on how we approach the different 'classes' of vehicles. 

Benoit Marcoux's picture
Benoit Marcoux on May 20, 2020

V2G pilots have highlighted the cost and the complexity of this idea. The value of peak power (kW, not kWh) varies, but a value of $100 per year per peak kW is in the ball park. For an EV with a 7 kW bidirectional residential charger, this is a potential of $700 per year - not negligible. However, this depends on this EV being available at peak time. Unfortunately, this cannot be guaranteed, with an increasing share of EVs being charge in public or at the workplace (and not at home), EVs being typically charged at home every 2 or 3 days, and drivers not always be home at exactly peak time. Furthermore, this adds electrical costs to the vehicle and the home charger, requires a communication link to control the system, and could shorten the battery life. 

If anyone could pull this off at the moment, it would be Tesla because of its vertical integration (from battery to home chargers, storage and solar panels), built-in telematics in the car, and critical mass. 

Roger Arnold's picture
Roger Arnold on Jun 8, 2020

$100 per year per peak kW is perhaps a reasonable price for capacity, but that's a small part of the "value proposition" for V2G (or for energy storage in general). There's also arbitrage on the stored energy, the value of ancillary services, and the indirect system value of wholesale market stabilization. That last bit is particularly interesting. It's a major factor, but hard to monetize.

Variable renewables suffer from the problem of declining value as grid penetration levels rise. The problem derives from two intrinsic facts: the marginal cost of energy production from VR assets is zero, and their output is strongly correlated on the scale of weather systems. The limiting model is binary: either VR production is higher than demand, or it is zero. In that admittedly simplistic model, the value of VR resources drops all the way to zero. When they are producing in excess of demand, wholesale market prices are driven to the marginal cost of production -- i.e., zero. When they are not producing, the wholesale market price soars, but it all goes to the non-VR resources that remain on the grid. Investors' financial return on VR assets is zero.

The real case, of course, isn't nearly so black and white. VR production rarely falls all the way to zero, especially when VR capacity is a mix of solar and wind. But the binary model does capture the essence of a real problem. Declining value of VR assets at higher levels of grid penetration has led to stagnation or even decline in investment in VR capacity in regions that have reached substantil levels of grid penetration -- think Germany and California. The level of diminishing returns, unfortunately, is only a fraction of the level that would be needed for a "100% renewables" energy economy.

A remedy, or partial remedy, for that problem is online energy storage. Charging can provide responsive demand to consume excess production -- a form of DSR (Demand Side Regulation). It doesn't actually take a great deal of storage (relatively speaking) to stabilize wholesale market prices. At current penetration levels, four hours at rated capacity for new wind and solar assets is enough to keep them from "stepping on each other's toes" and forcing curtailment. 

V2G potentially offers the most cost-effective way to meet the storage levels needed to enable higher levels of VR contribution to world energy. Although "V2G" is perhaps a misnomer. It isn't cost-effective to include the high power rectifier and inverter capacities in the vehicle and the high capacity AC service to homes that would be needed to support a "true" V2G capability.

What works is bi-directional charging between the vehicle and a smaller stationary storage package. The stationary package includes the more modest rectifier and inverter functions required for bi-directional connection to the grid in a typical residential home with 200 amp service. Tesla's PowerWall 2, with 13.5 kWh of storage capacity, is an example. 13.5 kWh is only a fraction of the capacity of a longer range BEV, but in being always on line, it addresses the connection timing issues that afflict the "raw" V2G model.

Jim Stack's picture
Jim Stack on May 21, 2020

Yes I love V2G. We recently found out the On Board Charger in all Tesla model 3 and Y have V2G capable bult it. The ACPrpoulsion T-ZERO that was used to start the Tesla Roadster had V2G built in. So did the BMW MIMI-E and Xbox Scion all coverted by ACPropulsions. 

   The University of Delaware has been doing a V2G Demo for over 8 years with the MINI-E vehicles. I have been trying to have a Phoenix Arizon V2G Demo project. All it takes is 5 or 10 kWh from an EV to make a big difference in the Duck Curve. I made a website about it.

Gary Hilberg's picture
Gary Hilberg on May 21, 2020

Jim - this was a good find, but when and how will Tesla open access to their technology?  Nissan is doing Leaf trials in Australia, but it is not clear whether their new Leaf models in the US support V2G.  A limiting factor is that modifying the existing fleet could be hard and push the cars out of warranty, particularly the battery warranty which is so critical to most EV buyers.  

Joe Steinke's picture
Joe Steinke on May 21, 2020

If Tesla's EV battery is used as a staionary power source, the battery warranty is voided according to Tesla.  Other manufacturers require charging with an approved charger.  If V2G is done, what will be done for an "odometer" reading on the batteries?  Cycling batteries 1000 times over a decade of driving an EV in normal driving results in significant decay.  If used in V2G on daily cycles, this can occur in a few years.  I think that trials should be done to see how much electricity can be contributed, the cost of bi-directional high capacity metered chargers (cost = $10K+), and the impact on battery life.  


Bob Meinetz's picture
Bob Meinetz on May 22, 2020

Joe, good points all. Don't forget:

Line losses from grid and back
Battery resistance losses
Bi-directional inversion losses
Never knowing how much "fuel is in the tank"

It would be a miracle if V2G was 60% efficient overall - meaning either 1) ratepayers, or 2) car owners are paying the price for the luxury of having intermittent "green" electricity on the grid. A non-starter.

John Benson's picture
John Benson on May 21, 2020

Hi Michael:

Thanks for the post.

Among other categories, I write frequently on EVs, and I'm currently working on a post for early in June on all things Elon. One of the miscellaneous pieces of information is that Tesla has apparently enabled V2G in their recent model cars and chargers. Go through the link below.


Jim Stack's picture
Jim Stack on May 23, 2020

A few others think the parts seen my Marco were not what he had guessed. They don't there really is bi directional charging in the Tesla 3 or Y. 

Yet an interesting note is that the original design and inverter Tesla used in the Roadster had V2G. It was made by ACPropulsions in San Dinas Califorina. The also converted the MINI-E for BMW  that also has V2G. 

Michael Herrera's picture
Michael Herrera on Jun 3, 2020

Hi John: 

Thank you for the reply and for sharing the post. The future of this possible solution certainly appears promising. We look forward to the results of our research. 

Roger Arnold's picture
Roger Arnold on May 24, 2020

There's a recent Youtube video titled "Bidirectional Charging in a Tesla Model 3? BUSTED". It's relevant to this discussion, and I recommend it. It doesn't discount the possibility that Tesla vehicles could support V2G, or at least bidirectional charging, in the near future. However, reports that it's already implemented in the Model 3 power electronics appear to be mistaken. Key components that an investigator took to be power MOSFETs that would support bidirectional charging are actually diodes. Which won't. 

It's confusing, because the components in question evidently DO use the pckaging form factor of power MOSFETs. It's as if the board had been designed to support bidirectional charging, but diodes were substituted where MOSFETs would be needed for bidirectional operation. Diodes are cheaper than MOSFETs for the same current and voltage ratings. The cost difference would be small, but if you didn't want the battery pack to be used for bidirectional charging the substitution would make sense. For later production, the feature could be added by changing just those particular components, without producing a new board design. That's just my speculation, however.

I've no real doubt that Tesla will soon be getting into the V2G business. They might not particularly want to, in that they'd "sort of" be competing with their own PowerWall product line. But if half the rumors are true about the "million mile battery" technology that's about to be rolled out on "battery day", the case for doing so is pretty compelling. The "million mile" feature is so far above the requirements of the EV itself that it obviates the cycling wear issue from V2G operation.

It would make both technical and business sense to link the V2G capabilities with a new model PowerWall. The EV would not support V2G directly, but would support bidirectional charging. That would allow it to serve as a large capacity extension for the PowerWall. The PowerWall already implements the necessary bidirectional AC interface to the grid, but its battery capacity currently is many times less than that of a full range EV  (6.4 or 13.5 kWh, vs. 50 - 125 kWh). 

Matt Chester's picture
Matt Chester on May 26, 2020

A link to the video Roger is referencing:

Bob Meinetz's picture
Bob Meinetz on May 28, 2020

Thanks for the link Roger, I'm always amazed when someone is willing to disassemble his $50,000 vehicle just to learn how it works (and void the warranty).

"It would make both technical and business sense to link the V2G capabilities with a new model PowerWall."

Whether it makes environmental sense is a question no one is asking, and they should be.

The best AC-DC converters on the market are 91% efficient; the worst, 70%. That means in the best possible scenario, 18% of every kWh that travels G2V-V2G is wasted; in the weorst case, half is wasted. 1 kWh in, .5 kWh out.

In terms of emissions, that lost electricity has to be generated again. Thus, electricity coming out of your car battery has up to twice the carbon footprint of the electricity that went in.

But wait, there's more! That's only counting the bi-directional inversion losses. Add in resistance losses within  the battery (6% for PowerWall), 2-way transmission losses (18% in California) and we end up with electricity that is 62% dirtier. 

There are some who claim when the Glorious Renewable Future arrives, only 100% pure, golden solar energy will be stored V2G. Then, there are some in oil company boardrooms who claim a 62% increase in natural gas sales, if V2G is used grid-wide, means $billions in added revenue. Which is more accurate is anyone's guess, but 100% of my money is on the guys who have consistently made profit their #1 priority.

Roger Arnold's picture
Roger Arnold on Jun 4, 2020

The best AC-DC converters on the market are 91% efficient; the worst, 70%. 

Not really. The article you referenced was talking about relatively low power commodity converters of the sort a designer would use for a computer power supply or for small electronics equipment. Efficiency isn't too important for those applications.

Until recently, serious high power power AC - DC converters based on IGBT switching devices were 95 - 96% efficient. The new generation of converters of the sort Tesla uses employ silicon-carbide MOSFET rather than IGBTs. The best designs can now manage 97 - 98%. Inverters for DC to AC are if anything slightly better.. That's for power levels in the range of 10's of kW to low MW.

I believe that 6% linternal resistance losses for PowerWall is worst case, for the highest spec'd charge and discharge rates. The coming generation of "million mile" batteries is rumored to feature markedly lower internal Supposedly they will tolerate almost supercapacitor rates of charge and discharge.

Jim Stack's picture
Jim Stack on Jun 4, 2020

Calculating round trip loss is a very limited view of electrical knowledge. In the real world electricity flows to the closest area of nedd, your neighbors home and pool pump. It has no round trip lose. It improblves Power Factory Control PFC.  It also reduces transmision losses  it's is very valuable. 

  The price of batteries is dropping very fast and the life increasing. They are the best thing to ever happen to the GRID. Get all the FACTS. Think outside the cenralized power center. 

Bob Meinetz's picture
Bob Meinetz on Jun 4, 2020

Jim, the portion of line loss attributable to energy on the grid, no matter where it goes in or comes out, is very close to the system-wide average.

Unlike water, electrical energy "flows" at the speed of light, so proximity is irrelevant. That's the real world.

Michael Herrera's picture

Thank Michael for the Post!

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