Rocky Mountain Institute and Evgo fleet and tariff analysis (relates to DC FCing)

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cwerdna

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Thanks to a post on https://www.facebook.com/groups/rav4ev/, from http://www.rmi.org/Press%20Releases press release at http://www.rmi.org/Content/Files/EVgo_press_release_2017.pdf.

Report at http://blog.rmi.org/Content/Files/eLab_EVgo_Fleet_and_Tariff_Analysis_2017.pdf.

Excerpt of press release
RMI Publishes Report with EVgo on Utility Rate Structures to Support
Growth of EV Fast Charging
Los Angeles and Boulder, Colo., April 11, 2017 – EVgo, the nation’s largest public electric vehicle (EV)
fast-charging network, and Rocky Mountain Institute (RMI) have released a report regarding the future
of EV fast-charging utility rates. The report, titled EVgo Fleet and Tariff Analysis, found that public fast-charging
infrastructure is critical to EV deployment; however, California’s state legislators and regulators
must make future adjustments to allow for more cost-effective fast-charging services. More cost-effective
utility rates ultimately will help support the state’s efforts to move toward an electrified
consumer vehicle fleet and simultaneously cut emissions.
...
RMI’s study found that, under certain electricity tariffs, current demand charges can make up as much
as 90 percent of the monthly bill of operational public DC fast chargers, driving the cost of delivered
electricity as high as $1.96 per kilowatt-hour (kWh) during summer months in some locations. These
charges are nearly seven times as high as the current gasoline equivalent cost of $0.29/kWh, meaning it
is difficult for DC Fast charging providers like EVgo to remain competitive with the costs of operating
petroleum-fueled vehicles.
 
I've often wondered if a high rpm (100k +) carbon fiber flywheel, combined with an EVSE, could be a way to supplement the peak output. I don't think there's enough kinetic energy in a flywheel to last for a full half hour charge, but it could still help.

The EVSE enclosure would include an electric motor that slowly accelerates the flywheel whenever the EVSE is idle, so it's ready to add energy for the next charge cycle.
 
From page 19 of the report, under Recommendations:
It is clear from our analysis that demand charges, more than other rate components, are the primary reason why it is
economically challenging to operate public DCFC profitably in California
. As our analysis of chargers on the SDG&E ALToU
Commercial rate clearly demonstrates, demand charges make up the vast majority of the bill, regardless of the
charger’s utilization
. The fact that the proposed new EV-specific tariffs eliminate demand charges for a period of time, or
for “Option R” charger installations, which also feature on-site renewable energy generators, indicates that the utilities
understand this issue.

Switching to the proposed SDG&E and SCE tariffs that rely on dynamic adder charges rather than more conventional
demand charges seems to solve many of the problems inherent in the existing tariffs. These new tariffs better align the
utility costs with charges paid by EVgo, and could produce a fairer outcome in which it is possible for DCFC operators like
EVgo to obtain a flatter, more predictable cost structure.

The question that remains is whether or not the new tariffs that the California IOUs have proposed can enable a profitable
business for public DCFC charging companies
, and whether there may be alternative approaches to rate design that would be more attractive. . . .
 
Looks like a commercial product is already in the works that incorporates flywheels with EVSEs to reduce demand load on the grid and the accompanying fees:

https://media.wix.com/ugd/56cf92_27c5e75a110a4f5098329bcfb2ab166f.pdf
 
SageBrush said:
Enter stage left: Tesla batteries
Yep just put a battery buffer in the DCQC. The local electric go-kart track does this, they have charging stations for their karts which have a big battery in them. The storage battery charges up slowly while the kart is not being charged or out on the track, then when the kart needs to be charged up quickly for the next race, the charging station dumps it's stored charge into the kart all at once, and then goes back to filling itself up slower from the grid.
 
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Supplementing EVSEs with flywheels seems like a more long term, environmentally friendly solution to me
 
Interesting table. I wonder how they plan on building a flywheel that can store energy for hours and still be "totally green." No high strength alloys? No carbon fiber or resins? No precision machining required? Where did you get that from?

And check out these "flow batteries" with a liquid electrolyte that has 0 degradation with age. It can also be used from 100% to 0%, full depth of discharge.

https://www.youtube.com/watch?v=4OHstY_kKUY
 
I referenced the source in a PDF URL above.

This is just one commercial example I found, another is Stornetic.

This NASA video gives a good overview of the concepts, although it doesn't get into details about RPM, diameter of the flywheel, weight, power generation, etc:

https://www.youtube.com/watch?v=mz_7UF4KQpk

This one is decent too:

https://www.youtube.com/watch?v=eCtlfj4kMJs

Flywheels are an ancient technology, but adding a vacuum sealed chamber, a strong carbon fiber rotor, and magnetic levitation for near zero friction makes them a very interesting energy storage solution.

Specifically for DCQC providers, marrying an EVSE to a modern flywheel design might allow them to avoid a lot of demand charges as EV charging seems like an ideal fit for that - short peaks of demand followed by periods when the flywheel can be "energized" for the next charge cycle
 
Flywheels may indeed make for an excellent energy storage, although I don't know conversion losses from and to electricity and a motor/generator would have to be added in addition to electronics and control devices. I've also seen hydraulics proposed for energy storage.

Batteries lend themselves to easy grid integration, and have value to the grid itself which reduces their net cost.
 
Yup, a hydraulic accumulator system could also deal with reducing peak demand for a DCQC, if coupled with a hydraulically driven electric motor, but accumulators have pretty high heat losses. With a near zero friction flywheel spinning in a vacuum, the loses are comparatively low.
 
Thanks for the videos, I had actually already seen the NASA one, or one like it. The NASA video makes a point pretty well that I was alluding to earlier. There looks to be a very, very expensive very shiny piece of high tech kit sitting on the floor there. What do you think that baby cost to make? The other video shows an immense installation with underground chambers and a command bunker.

Flywheels need some expensive and hard to build components: a vacuum chamber, high strength magnets, extreme precision manufacturing. They suit some needs perfectly, but others less perfectly. I think a DCQC is a bad application for them based on these factors.

The flow batteries are pretty much a revolution. There is no degradation over time and they deliver full discharge capacity. The biggest benefit is that they have a liquid electrolyte. That's not ideal in a car where weight and size is important, but for energy storage it's almost better. Freshly charged electrolyte can be pumped in to the battery to instantly recharge it. You can add capacity to the battery just by adding a larger fluid tank and filling it up with electrolyte. If there is unusually high demand, a company truck can come to the site and pump in fresh fluid to meet demand. A network of pipes could be set up to share fluid between stations and charging facilities.

What happens to your flywheel system overnight or when there is a break in traffic? Batteries can keep their energy stored for days or weeks or longer.

There is far more untapped potential in new battery technology than in flywheels. As you say they are an old technology but it hasn't really been adopted. In Formula 1, where no expense is spared, most teams are using battery driven KERS and only 1 team is using a flywheel KERS. The flywheel system is also about 20% more efficient than the battery system but the teams prefer battery systems so far. They have been using KERS since 2009.
 
The flow battery concept is interesting. The company rep mentions in the video that each zcell has 10kWh of stored energy. I found a diagram on their website that has indicates a discharge rate of 100A @ 48v, or 4.8kW, can be drawn for 30 mins.

For a 25kW DCQC EV solution, for which you wanted to bump up the charging rate to 50kW and sustain that for a 1/2 hour EV charge cycle, one would need 6 ZCells. That would take up quite a bit of space and you'd only be able to charge one EV at a time. Seems better suited to micro-grid applications.

It will be interesting to see what happens with flywheel technology, as perhaps materials like graphene will make power densities for flywheels more compelling. Based on the research I did, it seems like the power density isn't quite there yet to make them very useful for DCQC applications. The awesome thing with flywheels is that they are ideal for delivering high energy output over short periods of time, which is what got me thinking about their use with DCQC applications in the first place.

It's fun batting this stuff around, learned a bunch of new info!
 
(thread resurrection)
cwerdna said:
Thanks to a post on https://www.facebook.com/groups/rav4ev/, from http://www.rmi.org/Press%20Releases press release at http://www.rmi.org/Content/Files/EVgo_press_release_2017.pdf.

Report at http://blog.rmi.org/Content/Files/eLab_EVgo_Fleet_and_Tariff_Analysis_2017.pdf.
Unfortunately the rmi links are 404 now but there is a copy of the report at https://web.archive.org/web/20170412053900/http://blog.rmi.org/Content/Files/eLab_EVgo_Fleet_and_Tariff_Analysis_2017.pdf.
 
Wasn't sure if I should start a new thread or just a new EVgo one, but I stumbled across this PDF from them. I've only skimmed tiny bits of it but it does relate to the RMI study in the OP.

The Costs of EV Fast Charging Infrastructure and Economic Benefits to Rapid Scale-Up
https://www.evgo.com/wp-content/uploads/2020/05/2020.05.18_EVgo-Whitepaper_DCFC-cost-and-policy.pdf
 
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