"Gravity" EV Charging

bwilson4web

bwilson4web

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Source: https://gravitytechnologies.com/

An interesting approach, the charging electronics looks about the size of a typical, EV motor controller. They are already bi-directional, high power, multi-frequency, and compact.

I like the approach but let's see if they show up.

Bob Wilson
 
I dunno, looks a little pie in the sky/expensive. Maybe I'm missing something. They don't seem to be doing anything all that innovative, basically the offering appears to be a big DC bus with distributed EVSE switching, and a wierd name (DEAP). Assuming the deal is you have all these batteries on the bus (21MWH is a lot of battery) and then you just park and plug in. As the property owner, you just lease out the space, they run all the wire and install all the boxes. They show a Tesla, the stations are spec'd CCS. Looks like a grizzle-e wallmount DCFC but with more juice. There is no particular reason the current crop of DCFC's need to be as large as they are. The problem is storing or generating the electricity to feed 10 cars at 500KW. So they are a little light on the deails of exactly how we get the energy into the battery to then put into the car. Rotate 3 sets of 10 vehicles at 500KW for 30min then what? So why is this cheaper than just hooking up, cause 21MWH of battery is goin to set you WAY back, and this assumes you can get cheaper off-peak, and ... There is a 10-20% loss every time you move the power from battery to battery.

I've long said it would be nice to have a bunch of 25-50KW chargers scattered in those places where you might be parked for 30 min to an hour or so, just to top up. To this point, I have an openevse box that gets turned on whenever my solar batteries hit a sliding charge threshold, and I've programmed it to allow me to bleed off some of my solar battery in the AM, if sufficiently charged, before the sun is up. EV's suck up a lot of electricity, but unless I am traveling I rarely fall below 50%.
 
DEAP is absolutely the correct term because it is a complete paradigm shift for energy distribution. Gravity's business model is absolutely contingent on bi-directional charging as it enables a microgrid, which circumvents traditional load calculations.

It's just really a shame that the CEO comes off very cagey.
 
One of the reasons I went to "May the 4th be with you" was to see if the power electronics of other EVs can be the basis for a fast DC charger. I understand the early SuperChargers used a modified, Model S, motor controller.

I was able to see the Ioniq 5 that uses a clever wiring trick to make the stator into a 2-to-1 step up or down transformer. So I'm convinced a home, fast DC charger is practical. I've got 200 A, 240 VAC service to my house. Limited to 100 A, I should be able to make a 24 kW, fast DC charger . . . except I don't need one.

A better alternative would be to repurpose the 25 kW, two cylinder, motor-generator from a BMW i3-REx. But my Tesla Model 3 has a 55 kWh battery. Do I need a full charge in less than 2 hours?

My home L2 charger provides the 30 and 31 amps which is the maximum the BMW and Tesla can take, 7.2 kW. At most, the Tesla could take ~7 hours to do a full charge. But I only charge to 80% at home, about 6 hours or less. Yesterday, the Tesla returned with a low SOC after a 250 mile trip, ~10 mi remaining.

The BWW is used for local errands and seldom reaches 25% SOC. Usually I'm home with 75% SOC so it is fully charged in less than 1 hour.

I think Gravity has an interesting approach and the size of their boxes are consistent with the typical power controller in an EV. As for a battery buffer, that is what Tesla is doing with their grid storage. I have no problem if Gravity enters that market

Bob Wilson
 
teslarati97 said:
DEAP is absolutely the correct term because it is a complete paradigm shift for energy distribution. Gravity's business model is absolutely contingent on bi-directional charging as it enables a microgrid, which circumvents traditional load calculations.

It's just really a shame that the CEO comes off very cagey.
Click to expand...

Enlighten me as to why this is significantly different than what Tesla is doing with batteries at their superchargers?

There is an EVGO at the "Food City" I shop at about 2 miles from my house. Nothing from the article intimates anything much different, drive over plug in, get power while shopping. Bi-di in a single family home, maybe. Bi-di, at an apartment complex or business, is not something I think I would care about. I must me missing something. For home, I can really care less about charge rate for the most part. At some point I will have 90KWH of solar batteries, that will set me back over $25,000. I can't see anyone putting in a smaller system at their house to charge at a higher rate, unless you just had more money than sense. I could do what I do directly from the grid, charging batteries, then dumping them into a car but why would you want to?

Bi-directional is already floating around using an inverter with your car, but frankly I stand by my other comments, I see no point. If the power is out for more than a few hours, I'm not going to keep it running by dumping the power from my EV so now not only do I not have power, but I can't go anywhere because I killed my EV battery. So I can spend $10K for some odd infrastructure that wipes out my EV, or I can buy a small generator for $1000 that will run everything for as long as I need. It just doesn't compute for me.
 
Gravity uses the existing downtown infrastructure for 200kW+ DC fast charging. Several megapacks + solar canopies generally won't fit in downtown NYC supercharger site. By being bi-directional, Gravity can leverage the Distributed Energy classification and circumvent the demand/load requirements.

If your grid is relatively stable, then the small generator should be sufficient. In other cases, solar + battery + backup gets you that sweet 30% tax credit and bi-directional charging could mean 1 Powerwall vs 3+ Powerwalls.
 
teslarati97 said:
Gravity uses the existing downtown infrastructure for 200kW+ DC fast charging. Several megapacks + solar canopies generally won't fit in downtown NYC supercharger site. By being bi-directional, Gravity can leverage the Distributed Energy classification and circumvent the demand/load requirements.

If your grid is relatively stable, then the small generator should be sufficient. In other cases, solar + battery + backup gets you that sweet 30% tax credit and bi-directional charging could mean 1 Powerwall vs 3+ Powerwalls.
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This just sounds cool. "Gravity can leverage the Distributed Energy classification and circumvent the demand/load requirements." They should put that in their investor briefings. I'm still missing where the electrons are coming from "Bi-directionally". You either stuff electrons into your EV from the grid or from a battery. So by eliminating 2/3's of my batteries and adding "bi-directional" I can somehow charge more cars? Energy cannot be created from thin air, thus my question remains, from whence cometh the joules. "Bi-directional" would seem to indicate robbing peter to pay paul, and I still don't have a clear explanation as to how that helps me charge more vehicles? If I need 60KWH of power to charge my car how does a "bi-directional" DC grid help provide the additional joules to do it without umm additional DC storage?

The problem with electrical DEMAND is umm DEMAND. Once you reach a certain scale there are not any huge troughs and spikes during high demand windows that are going to be all that effective for load shifting. The only thing I could see is that this could somehow use batteries to buffer demand spikes in the grid somehow letting you take advantage of the power delta as demand spikes and drops. The problem is this is generally hours long not minutes, thus at the end of the day we are load shifting power from low-demand times to high demand times. This is exactly what Tesla is already doing at some of it's charging stations without the fancy acronyms.

Define "small generator"? If I put in 10 parking spaces with an average 40% active charging occupancy charging at 100KW I need a constant 400KW of power from somewhere. Demand issues are not unique to the power companies here, but Suppose all 10 slots are in use at one time. Now I need a megawatt from somewhere, and you took away my batteries because "bi-directional" is going to handle it. Bottom line is at some point the power company is going to need to give me a MWH or so of power to charge up these cars. So I guess I'm stupid, but I still don't get it.
 
That's okay, I was trying to say that the bi-directional is mostly for legal purposes and not for the flow of electrons. Most (if not all) of the power will be coming from the grid. Gravity is basically operating as a Distributed Energy ("micro substation") for several downtown buildings. Whether or not you want to replace bi-directional charging with battery energy storage, solar panels, hydro electrics, and/or wind turbines might make it easier to understand. So yes the Distributed Energy Access Point is the correct term as it implies the DEAPs are connected to the Gravity "micro substation" directly, but it is certainly a confusing term! Probably a visual diagram would make it much easier.
 
Okay, so this outfit wants to go into the electricity distribution business as a private entity putting in substations, maybe with a modicum of battery presumably to somehow improve EV charging access, in a way that doesn't bypass the laws of physics, glad we are past that part. Because they add some battery and create a small 'bi-directional' power bus they can market what they are doing to take advantage of some Government largess in the form of tax credits and/or subsidies?

Hmmm. So Jorge my block/cement guy with the beater ICE truck makin' a livin' gets to subsidize some company putting in some additional power substations in some urban areas for an EV he has no plans to buy?

I'm still not seeing where this is any kind of improvement for society/the city, because the power company still has to bring in the infrastructure to provide the actual power, at which point they could just bring in the wire and a couple of transformers and some off-the-shelf charging pedestals, for a fraction of the cost and charge the same number of vehicles.

If you are trying to sell me this idea, I want to buy in. I'm not trying to be obtuse. Thus far I've not seen anything that is changing a paradigm or doing anything different than what we already do. The charging problem is lack of generation capacity coupled with the lack of infrastructure to deliver enough power to where it is needed. I don't see how this helps resolve that. Does this shunt power from substation to substation somehow? If so, how would that be better than building out infrastructure to both?

EV's suck a LOT of electricity when charging. My house in Phoenix in July, burns as much as 120KWH per day (at the absolute worst). So basically a house-day of power to charge a Tesla and a half IN AN HOUR! That's the demand problem. The only way I can see to get around the demand is to either generate more electricity or store it when demand is low and deliver it when demand is high.
 
Keith Smith said:
I'm still not seeing where this is any kind of improvement for society/the city, because the power company still has to bring in the infrastructure to provide the actual power, at which point they could just bring in the wire and a couple of transformers and some off-the-shelf charging pedestals, for a fraction of the cost and charge the same number of vehicles.
Click to expand...
Gravity will predominately operate in the downtown core as a retrofit solution where physical space is a constraint. In terms of demand, it's less of an issue for downtown cores because the power/load is over allocated. If you take a collection of 1,000 condos/apartment units with 100A service, that would be theoretically a max load of 1,000 * 240V * 100A * 80% = 19.2MW. Realistically speaking, I don't think every single unit (of the 1,000) is asking for 19.2kW of power 24/7.

This just speaks to how we currently manage power by setting a theoretical load ceiling. In the case of Gravity, if there is excess demand, the DC fast charging could be curtailed and allocated back to the individual buildings as needed. If there are multiple substations, then yes the energy could be curtailed between multiple substations on a grid power shortage alert. It's probably not a lot of power, but it's still something.
 
It's a management platform, I see that.

Power is always over-subscribed. As the number of subscriptions goes up demand peaking becomes less volatile. 1000 apartments with 100A service is not going to get 100,000A @ 240v of service (24MW) all to itself, it is already shared (and monitored) by the power company. There is nothing "Theoretical" about a load ceiling, it is a physical limit. If I run 1000MCM to a complex, the wire is rated at 800A direct burial. That is a hard limit for the infrastructure to that grid. Assuming that is for a 480v 3-phase feed I have a physically constrained max load of 384KW. It isn't theory, exceeding that limit will overheat the wire and could cause a fire. The power company is monitoring the big *** 480V 800A 3-phase transformer, and knows pretty much, how much power it is drawing give or take a percentage or two, and brings capacity on and offline to feed the thing as demand shifts. Do you think they just kick all the power generation they have on full blast and see what gets used? All that rhetoric sounds swell, but power generation and distribution has simply defined hard limits and capacity numbers. There aren't any 'extra' electrons floating around in one grid that you can float over to another to take advantage of. You have to either generate it or store it for delivery later.

Further, your still running fat wire to a service panel somewhere thru some conduit, so I'm not sure what the 'space-constraint' angle is about. The current large charging pedestals are that way because they are outside and exposed to the elements. I've seen smaller ChargePoint DCFC's deployed in interior spaces/parking garages, I can assure you they are monitored, and the power company can shut them down under high demand if they need to. You can't 'retrofit' your way into a bigger feed cable and transformer. If your feed cable and transformer will already handle the load, then you are just adding wire and switching, and I still don't see where the 'bi-directional' comes in unless you are digging up the floor/street or running even more conduit and wire to shuffle the electrons between the various power grids. Nothing wrong with that, neither is it innovative or a particlarly novel approach.

Thus I conclude this is just another company with a gimmicky management platform that wants to get into the EV charging game. I don't really see anything particlarly novel in the approach rather just a fresh application of what other folks are already doing. If you see something I don't you can invest, I see another Soylyndra.
 
teslarati97 said:
Good conclusion. In Elon Musk we trust!!
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:pHardly, but they without a doubt are miles ahead of the competition in the charging space. This really peaked my interest, because charging in high density areas is problematic for the reasons outlined above. Better management is obviously desirable but it's being sold as some sort of power-shift, that will improve availability of power, but frankly the only way it works is with massive batteries, because the urban grid is already over-subscribed.

Digital Realty took over an old newspaper plant downtown here in Phoenix a long time ago. They cool from a chilled-water loop under downtown, that uses off-peak power and a zillion compressors on every roof running all night long. None-the-less back when, as the server density increased they had serious power problems for the longest time because the infrastructure simply was not there to feed the power needs of the servers in the building, which compared to charging a few hundred EV's. . . Bottom line is we need to bring in more cables, and feed those cables with more generation. Tesla is using solar and batteries to buffer the need already in various places. I will give these guys credit for copying some of those ideas. No reason you can't cover the roof of these tall buildings with solar panels either. Promising to charge 10 cars at 100+ KW at the same time without fresh power is pie in the sky. It's just a lot of effing electricity.
 
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