> a per hour storage cost of $103/kWh
Ouch!
Ouch!
These units would be consistent with other reporting for grid-scale battery systems costing ~$250/kWh to construct:
http://cleantechnica.com/2013/12/18/utility-scale-battery-st...
As for operating costs, I'm assuming that the nameplate storage capacity is the output. So if you have a 100kWh system with ~60% throughput efficiency, you'd need 160kWh of input at your standard energy rates and then the energy coming out would be 'free' -- of course there'd be costs for maintenance and depreciation too though.
I think the idea is that this is storage for renewables. As such, you wouldn't need more "input at your standard energy rates" than what it might take to charge the system for overnight use.
Compare against Beacon Energy's 25kWh flywheel storage units, which have a cost of $10,000 per kWh.
There are trade-offs. Beacon's system is very highly responsive (flywheels can pretty much take up or deliver as much energy as you want, with response in the second to sub-second level) directly receive and deliver electrical energy, and have extremely high round-trip efficiency (90%+, approaching 99%). As an alternative to spinning reserve they have benefits.
http://www.beaconpower.in/html/technology.html http://beaconpower.com/
The problems are the limited capacities of individual units (25 kWh isn't that much power at grid scale), engineering problems, notably precession (the Earth's own rotation about its axis is a concern for the units), and interesting failure modes (preferred deployment is burying the units in below-grade concrete containment with massive lids -- you neither want systems flying apart nor wandering about the neighborhood at 16,000 RPM should the come unmoored).
Flywheels are among the more expensive energy storage options available, but at least at first glance the cooling option looks reasonable.
Your average, underfunded community or educational theater has 150-200 lighting dimmers, each at 2.4 kW. I can consume half a megawatt (200 circuits x 20A x 120V = 480kW) in 6 keystrokes.
http://www.energycentral.com/generationstorage/energystorage...
The other factor is that when you're operating at grid scale, it's overall changes to the grid flow that you're concerned with. A large city might have a peak load of 2000 MW, and the plant here could handle a fluctuation of 10% -- given the law of large numbers, that's a lot. Sure, you might be turning on a slew of light banks in any given period, but someone somewhere else could be cycling down a cooling plant, or resistance heater, or the like.
I suspect large rapidly cycling loads might also be at issue -- with electrified transit, light rail and trolley buses make high instant demands on the grid, and then return energy through regenerative braking. I don't know how such loads are managed, but they're substantial and I do know that utilities tend to segregate these from other residential and commercial circuits.
"With a capital cost of only $618/kW for 6 hours of storage ($375/kW power machinery and $40/kWh stored energy) and a round-trip efficiency in excess of 90% this is the cheapest and most efficient form of energy storage."
If it's $103/GWh, on the other hand, then we're talking about only ~10% overhead on costs.
The article states 30% cheaper, not 30% more efficient.
> If it's $103/GWh, on the other hand, then we're talking about only ~10% overhead on costs.
The article states $103/kWh, not per GWh. To calculate overhead costs you would need to know life cycle costs which were not disclosed.
The question is, what are the life cycle costs? If it's on par with pumped hydro, then we are talking.
There's probably a standard interpretation, but it's not obvious to a lay reader like me.