SageBrush
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Location: Colorado

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

Thu Apr 13, 2017 1:17 pm

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.
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alozzy
Posts: 292
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017

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

Thu Apr 13, 2017 1:26 pm

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.
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VitaminJ
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Re: Rocky Mountain Institute and Evgo fleet and tariff analysis (relates to DC FCing)

Thu Apr 13, 2017 2:26 pm

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.
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alozzy
Posts: 292
Joined: Fri Jan 20, 2017 4:25 pm
Delivery Date: 18 Jan 2017

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

Thu Apr 13, 2017 5:44 pm

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!
Canadian with a US 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Big grin, enjoying my first BEV :D

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