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Is This The Best Answer Yet To The Energy Storage Question?

Every so often an item appears in Blowout Week that’s worthy of further discussion, and Blowout Week 118 has one. It’s the article on ARES – Advanced Rail Energy Storage – a simple combination of three proven technologies – railroads, potential energy release and regenerative braking – which reportedly has a number of advantages over its numerous energy storage competitors:

• All it needs is a rail line, heavy rail cars with regenerative braking, and a hill. It needs no reservoirs, pump houses, penstocks, underground cavities, salt mines, submarine bladders or even water.

• Environmental impacts are usually minimal, energy efficiency, costs and ramp rates are reportedly comparable to pumped hydro, there are no limits on the number of charge/discharge cycles and no degradation with time.

• There’s no lack of ARES natural resources (hills) in many parts of the world. Storage capacity can be made as large or as small as needed in these areas.

The ARES concept has been tested at a pilot project in Tehachapi, California. No results are provided but some intriguing images are:

(Click to enlarge)

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The ARES gravity train used at the Tehachapi, California, pilot plant

So let’s take a closer look at ARES:

First, sources of data. As is common with “first posts” I have used a number of basic data sources that tend to be repetitive, and rather than burden the text with lots of duplicate references I am listing all these sources below:

ARES Press Kit

Pahrump Rail Energy Storage Project

America’s First Commercial-Scale Rail Project Receives Approval

Advanced Rail Energy Storage uses heavy train cars to store power

Gravity train as energy storage

ARES system to put energy storage on the right track

ARES performance

Plus a potted overview from Utility Week:

Technologies vying for the bulk storage market

Now on with the show. The Blowout Week article describes how Advanced Rail Energy Storage LLC has just been granted a right-of-way lease by the US Bureau of Land Management for a 50MW rail storage project in Pahrump, Nevada. The approval came after an Environmental Assessment concluded that the project would have no significant impact (it disturbs only about 70 hectares). Details of the project are summarized on the list below and on the following project layout map:

1. A single 9.2 km long track with an elevation change of approximately 640m.

2. Six 300-ton trains made up of rail cars with regenerative braking capability.

3. 50MW peak output, 12.5MWh storage with the option of scaling up to 1 GW.

4. Capital cost $55 million ($1,100/kW installed. I can find no information on costs/KWh.)

5. “A lower life-cycle cost than batteries, a higher energy-to-power ratio than flywheels, and a greater efficiency and faster ramp-rate than pumped-storage.”

6. An 8-month construction time, project life 30-40 years.

7. “The project has all private financing, no government loans or grants.”

(Click to enlarge)

ARES Pahrump project layout map

The project will be grid-connected and designed to provide “fast response energy to assist the balancing of intermittent renewable energy [solar and wind]” and handle “momentary changes in demand”, which probably explains why the storage lasts for only 15 minutes at 50MW output. Long-term storage could, however, presumably be achieved simply by parking trains at the top of the hill and leaving them there.

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And here’s what I understand to be an artist’s impression of what the rail yards for a 1GW system would look like:

A 1GWh(?) ARES facility

An entertaining video of how the rail cars are shunted around to compensate for changes in PV output as clouds pass over the panels is also available here. I can’t post a direct link to the video but it’s the image at the bottom. There are more images of interest above it.

Other technical features of the ARES system include:

Reactive Power Production – The shuttle-trains onboard Dual 3-Level Active Rectifier/Invertors are capable of supplying 25 percent of generated system power as reactive power for grid VAR support in full discharge mode and in excess of 100 percent of system power as reactive power while synchronized to the grid in standby.

Heavy Inertia – When in direct grid synchronization the ARES shuttle-trains provide beneficial heavy inertia — augmenting grid stability against the loss of heavy generating facilities and increasing reliance on solar energy.

High Efficiency Regulation – While providing Regulation-Up and Regulation-Down support to the ISO a separate dedicated pool of loaded ARES shuttle-trains are available to dispatch from mid-system elevation complying with ISO regulation commands without having to overcome the efficiency loss of operating on pre-stored energy. As such an ARES facility is able perform a round-trip regulation Reg-Up/Reg-Down command at over an 86 percent operating efficiency.

Variable Output at Constant Efficiency – Unlike CAES and pumped-storage hydro there is no loss of system pressure during discharge. ARES system efficiency is constant over the full range of discharge and power output.

It’s nice to know that ARES considered and apparently resolved its grid stability issues before starting construction, which is more than can be said for another project Energy Matters has been discussing recently.

And the System Ratings image below reportedly demonstrates the superiority of ARES over all other energy storage technologies except pumped hydro:

ARES system rating versus other energy storage system ratings.

But ARES has a major advantage over pumped hydro too. Pumped hydro needs favorable topography and water, an increasingly rare combination, while ARES needs only favorable topography. And while there isn’t much favorable topography in such places as Florida, the Netherlands and the Nullarbor Plain, it abounds in the southwestern U.S. Consider for example the Google Earth view below, which shows the 70km by 3o km “prospective area” surrounding the ARES Pahrump project on the west side of the Spring Mountains:

Pahrump “pediment”, showing area prospective for ARES installations

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This 70 x 30km area covers an area of roughly 2,000 square kilometers where the land drops regularly at gradients of 5-10 percent over distances of up to 30km as we move away from the edge of the mountains, forming what we U.S. desert geologists call a “pediment”. I’m now going to guess that half of this area, or 1,000 sq km, could accommodate ARES storage projects. How much ARES storage could be developed on 1,000 sq km? We can make the following rough calculations:

- One 12.5MWh ARES system takes up 70 hectares
- 1,000 sq km (100,000 hectares) will therefore accommodate 100,000/70 = 1,400 systems
- Total potential storage therefore amounts to 1,400 * 12.5 MWh = 17,500 MWh, or 17.5 GWh

Now we are getting somewhere. 17.5 GWh represents approximately two Dinorwigs, and with ARES we get these two Dinorwigs from a patch of waterless desert that makes up only a tiny fraction of the total prospective ARES area in the American southwest. Potential for the development of ARES storage in the numerous surrounding “pediment” areas is clearly unlimited.

There’s just one problem – cost.

1,400 ARES systems at $55 million each will cost seventy seven billion dollars.

Okay, we can maybe take a half or maybe even a third of this number to allow for economics of scale and incremental technological improvements with time (there won’t be any major breakthroughs with technologies this mature). But we’re still looking at roughly $25 billion, which seems like a prohibitive amount to spend for enough storage to supply Nevada’s demand for only four or five days.

Although ARES might always get lucky at the tables. The city in the bottom right quadrant of the last image is Las Vegas, after all.

By Roger Andrews via Euanmearns.com

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  • David Hrivnak on April 11 2016 said:
    Very cool idea and relatively low tech.

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