Regenerative braking on Locomotives with AC transmission

[rollingstein]

Don't know about MGM Grand's power rating but MGM's Mandalay Bay has a connected load of approximately 30 MW.

I quote:

"MGM Resorts International has partnered with NRG Energy on the planned installation of a large rooftop solar photovoltaic array at the Mandalay Bay Resort Convention Center in Las Vegas. The 20,000 panel, 6.2 MW installation will be MGM Resorts’ first commercial solar project in the US, and it will be among the largest in the world, MGM said. At peak production, the rooftop array is expected to produce nearly 20 percent of the Mandalay Bay’s power demand."

http://www.energymanagertoday.com/m...ns-6-2-mw-roof-top-solar-installation-093352/

 

[mheslep]

I've never heard of commercial use of capacitor / flywheel based systems on mainline rail. So your analysis showing it doesn't make sense is probably right.

The two ways to make regen pay are: (a) feed it back to transmission line (obviously can't do for diesels) &

(b) feed it to hotel load (only for PAX trains)

Or eventually feed regen power to batteries in some future diesel-electric. There have been some attempts apparently; I suspect the battery tech is not quite there yet. Given the problems transmitting power along the train (as discussed above) only energy from the locomotive would be economic to recover, and then the loco-batteries would have to be particularly inexpensive to justify.

 

[rollingstein]

Or eventually feed regen power to batteries in some future diesel-electric.

My impression was batteries were not a practical solution yet for those sort of capacities.

But I just dug up some numbers. I see $ 11 / kWh mentioned as the cost of storing in a NiCd battery (1000 cycle life assumption). Assume a braking load of 3000 kW as per Jim Hardy's calculation previously in the thread. That's a steep slope & say we design for storage capacity for 60 minutes of this downhill run.

That's 3000 kWh which would cost $33,000 worth of NiCd batteries. That doesn't sound too bad. What gives? Am I using a bad estimate of storage cell cost?

This other graph let's me estimate the weight of such an assembly. 50 Whrs/kg sounds typical. That would weigh 60 tons. Not a lightweight but is that a game killer. A loco weighs upwards of 200 tons.

If you bill power at even a cheap 3 cents / kWhr that's a $250 saving on every such 1 hr downhill run. If you factor in start stops & lesser hills etc. say, you are saving $500 / day. That'd mean a 2-3 month payback. Not bad.

I assume I'm getting some numbers wrong?http://batteryuniversity.com/learn/article/cost_of_power

http://www.mpoweruk.com/images/energy_density.gif

 

[mheslep]

The problem in this case is the unit cost of power with batteries, not so much energy. Your source has Li-ion batteries currently at $1000/kW, or $3 million for your 3000 kW loco braking application, and continued fast charging typically shortens the battery life. Capacitors on the other hand are excellent for quick charge/discharge and sustain millions of cycles. Capacitors are inferior to batteries for energy density (per unit mass, unit cost). So, eventually regen braking might pay for locomotives but not yet.

 

[Doug Huffman]

What does Battery University have as LiPo cycle life? Last I looked, and BU is my go to, it was still =<500, twice your 1000.

 

[rollingstein]

What does Battery University have as LiPo cycle life? Last I looked, and BU is my go to, it was still =<500, twice your 1000.

I used the 1000 cycles life for NiCd not Li. Battery University reports a lower cost per kWh for NiCd than Li. $11 / kWh vs $24 / kWh

Should I not be using NiCd? With Li cost would double approximately but that still means a 6 month payback. Not too shabby for such projects?