Bidirectional home chargers

Mjhirsch78

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With the Quasar charger at CES pushing the idea of chargers at home that can turn the Rivian into a battery for the few times a year we lose power, what hurdles do we have to this becoming a reality? For those of you with a broader knowledge of all the options and hurdles, what are we up against to make this a reality? Even my wife who generally tunes me out when I go into another “EVs are amazing” rant was excited about that idea.

P.S. If this has been covered in these forums, forgive me and direct me to that conversation. Thanks!
 

CappyJax

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With the Quasar charger at CES pushing the idea of chargers at home that can turn the Rivian into a battery for the few times a year we lose power, what hurdles do we have to this becoming a reality? For those of you with a broader knowledge of all the options and hurdles, what are we up against to make this a reality? Even my wife who generally tunes me out when I go into another “EVs are amazing” rant was excited about that idea.

P.S. If this has been covered in these forums, forgive me and direct me to that conversation. Thanks!
Just hope the power doesn't go out right after you get home from a long trip.

I wanted to build a light weight tiny home that used the Rivian as the battery source, but that would require Rivian to have some sort of high output feature. I believe the 120V plugs will be a mere 500 watts, and I think 3,600 watts would be the absolute minimum you would need for a small tiny house. For a large home, you would probably need a 12,000 watt plug.

A better way would be to make the DC voltage of the battery available and have the inverter in the house.
 

ajdelange

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This has been discussed if not "covered" in various fora but there are so many I wouldn't know where to direct you.

A major hurdle right now is that the NEC requires EVSE installed in the US to have circuitry that prevents backfeed of energy from the EVSE to the circuit feeding it. This is, of course, in direct opposition to the intent of the Quasar concept. I believe that prior to NEC doing this there would have to be development of standards that insure interconnectability between vehicle, EVSE, house wiring and grid. This latter might be a major one as the utilities aren't much interested in having homeowners feeding them power. It's electrically quite doable (inverter in the EVSE) and is, I believe, being done experimentally in Asia and Europe.

Then you would have to convince the market place that it wants this technology. I want my house electrical system to keep my BEVs charged - not discharge them. Seems to me that Power Walls and similar setups are better solutions for load shifting. micro grids etc. but that's just my opinion.
 

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If a Rivian can charge another Rivian, couldn't you also route the power through an inverter connected to a home?
 

skyote

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If a Rivian can charge another Rivian, couldn't you also route the power through an inverter connected to a home?
Probably depends on control protocol. Might not be compatible (and definitely not optimal) with vehicle to grid.
 

ajdelange

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It is not at all difficult to pass power from a DC source (such as a BEV battery) to the grid. In fact I have 58 little boxes on my roof that do just that. The power interface is a couple of transistors and a wee transformer. The challenge is in coming to terms with the utility on how much power you will pass to them and when. They don't want your power and they don't need your power until the government tells them they do at which point they begin to come up with all kinds of requirements relating to the protection of their equipment and personel. Not all these requirements are frivolous. If the grid goes down and you vehicle or my solar panels continue to supply power to it this is potentially dangerous. So the interface has to detect when the grid is misbehaving and shut down if it does. As interfacing equipment needs to be able to connect vehicles and solar panels from several manufacturers to utilities all over the US there has to be an agreed upon way of meeting these various requirements and that's where standards committees come into play. The utility, the government agencies that regulate it, the OEMs and the NEC all have to agree on how this is to be done. Some parts of it are covered and some are not, Standards still have to be worked out.

The most relevant consideration is that you don't really want the battery in your BEV being used as part of an emergency electrical system. That's not what it is designed to do. If you want a battery based backup power system buy a PowerWall (or other maker's) system. It is designed for this type of service and is able to charge from solar panels when the sun is out, from the mains when it isn't, to supply any excess solar to the grid in a way and in quantities that the utilities have agreed to accept and to supply power to the house when the grid is down. There is talk of provisioning these systems with batteries whose performance is degraded by aging beyond the point where they are useful for traction. That alone should tell you something.
 
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EVian

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To counter the point about aging,I heard something, probably in one of the Fully Charged videos, possibly from Nissan, that the profile of discharge in a vehicle to grid situation is very different from that when driving (of course) and can actually help to preserve the life of the battery - my inference (I think it was my inference and wasn’t explicit in the video) was that it gives some respite from the heavy discharge under acceleration, and to some extent allowed the battery to be conditioned. No idea on the science (or lack thereof) behind that, but that’s what the fella said.

I don’t see the difference between a powerwall and a Rivian. Except one will be much nicer to drive... One is a mobile battery, the other is an immobile battery. Why not use the Rivian as backup power? Or actually in reality, more likely grid balancing. Tesla seems to be showing, for their chemistry and setup at least, that battery degradation isn’t as bad as first thought, and if you have as battery the size of a Rivian, you don’t need to take much of the top off its charge to get a meaningful amount of energy, so if taking a limited amount of energy then there should be little degradation.

I see grid-connected cars as a major part of the future grid.
 

ajdelange

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There are certainly some ways to discharge and charge batteries that are better than others but I expect that there is a rather high correlation between chemical total round trip current.

FWIW Tesla's current recommendations are to use Super Chargers only when there is no alternative (suggesting that high speed charging has been determined to be more damaging than previously supposed) and to plug in whenever one is at home thus minimizing the total round trip current as keeping the 12V battery charged etc will be handled from shore power rather than the main battery. There is still phantom drain however and the main battery does get frequent shallow charges to cover that.
 

ajdelange

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I should have added last night the reason I think round trip current is the culprit. When you charge a battery at any level you suck electrons out of the cathode and transfer them onto the anode resulting in the anode becoming more negatively charged and the cathode more positively charged. This results in Li+ ions migrating from the cathode to the anode. During discharge the opposite conditions exist with electrons flowing back to the cathode thus atttracting Li+ ions to it as well. The electrons flow through an external circuit which contains the motor and charger. The problem is that not all the shuttling ions make it to the cathode or anode. A small fraction react irreversibly with the electrolyte and are thus taken out of the available pool which means the capacity of the battery goes down. My Tesla X battery is warranted to lose no more than 30% of its charge in 150,000 miles. It has a 100 kWh battery and a range of 351 miles per full charge thus we can calculate its consumption at 100000/351 = .280 Wh/mi. To go 150,000 miles we would have to withdraw (and subsequently, of course, replace) 0.280*150000 = 42,000 kWh equivalent to discharging and recharging the battery 420 times. Thus if the battery loses 30% of it's range in 420 cycles it must lose 30/420 = 0.07% per cycle. This is, of course, just a stab at the degradation rate. Keep that in mind when looking at the numbers to follow.

Last month I used 2667.3 kWh electricity. My peak demand was 27.36 kW though my average consumption was only 3.59 (with standard deviation of 2.79) for a crest factor of 8.52 sigmas. So let's suppose that the greenies get hold of the State Corporation Commission and decree that the utility will cover you to 1.5 sigmas above your average use and beyond that you are on your own. The tree huggers rejoice because the utility, which must meet peak demand, can be sized way down and everyone can easily cover his peak demand with his Rivian battery - right? For me 1.5 sigmas is 7.8 kW and I exceed that only 10% of the time. The graph below shows how my March loads were distributed. It says that of my total March Consumption of 2667.3 kWh, only 757.32 kWh (28%) were taken at a level more than 1.5 sigmas above the average. Spread out over the 31 days that's only 24.4 kWh or a quarter of my Tesla's battery capacity. Why worry about that? And perhaps one shouldn't. But that 757 kWh represents 7.57 cycles of charge/discharge of that battery and thus loss 0.07*7.57 = 0.53% of my battery's capacity which means that my 351 mi range X is now a 349.14 mi car. At the end of a year I've lost 6.4% so that my X is now a 329 mi range car.

Lot's of us want to hold on to those miles as if they were diamonds. Silly really I suppose. I'm all for the idea of load leveling at home (it's the utility that's against it here) but I'd do it with 4 power walls for 52 KWh capacity and 32 kW peak load. This easily handles the estimated daily round trip load of 24.4 kWh (even after the batteries have degraded to 46%).

Does this matter in the great scheme of things? That's up to you to decide. But I hope you now better understand what the difference between a Power Wall and an automobile battery in the load leveling application and why many of us won't be interested in using our cars for it.

UseDistrMcL.jpg
 

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Yeah, I'm starting to wonder if relying near-exclusively on public chargers will take too much of a toll on the battery but I'm renting a condo so don't really have much control over things like adding an EV charger to the property. We have like 3 volta locations with a total of 6 stations nearby and it's not unusual to see them open. I think 4 of them might be the newer 100kw ones.
 

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IN CASE THINGS GO BAD

In my case and perhaps in the cases of many others, using our Rivians as a backup source of electricity would only occur when things go wrong. Maybe this would happen a couple of times a year when there's an electrical power outage. While it may be inadvisable to use a Rivian as a routine power source, in power outages, blackouts, brownouts and the like, having a Rivian as a backup makes a lot of sense.

Everyone's situation is different, but in my case with an unreliable electrical power company (PG&E), a Rivian as a backup source of electricity is very appealing even if it wouldn't be put to that use very often. In case things go bad, a Rivian in the driveway could be handy and dandy.
 

JackA

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V2G (Vehicle to Grid) is still being studied. https://cleantechnica.com/2018/11/29/nissan-using-vehicle-to-grid-technology-to-power-us-operations/ Nissan via the CHAdeMO interface is the only manufacturer actually working with the idea in the real environment that I am aware of. The advantage for electrical utilities is that they could by contract have access to some percentage of your parked EV's battery to use in smoothing the demand curve. Usually the matching of production to high peak demand is accomplished by increasing production; as in, firing up diesel generators. If the utilities can find a solution we as EV drivers might benefit because the "Demand Charge" for short term high draw customers like EV Level 3 charging stations could be lowered or eliminated. In Chelan County, WA the cost of a kWh is about $0.03 but the Tesla Super Charger in Leavenworth, WA gets hit by enough Demand Charge add on that the cost is close to $2.85. The rate schedule is here: https://www.chelanpud.org/docs/defa...ment-library/electric-rate-schedules-2019.pdf
 

ajdelange

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I understand that some of you are only thinking of the two way feature for use in emergency situations. There are, IMO, other, better ways to cover those but the best reason I have found so far (no math involved) in on p 175 of the X owners manual;

"Caution: Do not use the Battery as a stationary power source. Doing so voids the warranty."

The reason for this is, of course, that the warranty they offer is possible within the round trip charge/disharge range they expect in normal operation as a motor vehicle. The additional 2* 757 kWh hour round trip load I calculated earlier is equivalent, in terms of battery aging, to an extra 2500 mi per month (30,000 miles per year). This is more than the average American would drive the car on the road.
 

DucRider

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Per kWh???
Demand charges are for the peak kW draw during any given 15 min period and are assessed per meter and per billing cycle.

Using the data linked:
General Lighting and Power (Schedule 2),
If during the month, the maximum draw at a Supercharger meter was 500 kW (4 simultaneous vehicles charging @ 125 kW), the monthly demand charge would be 500* $2.40 or $1,200. Add in $25.35 meter charge and 2.35¢ per kWh.

I'n not sure under what schedule Superchargers are set up and billed. I know that some DCFC stations is Oregon were allowed to be set up under the Agricultural Irrigation schedule to lower demand charges.

Demand charges are more of an issue for infrequently used charging stations. A station that used just a few times a month could have a demand charge split between only a few charging sessions. A busy Supercharger will have it's demand charges split among hundreds of sessions.
 
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