Can 19th-century technology solve the energy storage dilemma?

Energy storage is basically a holy grail for the power system community these days.  If we had cost-effective, large-scale energy storage, many of the challenges that go along with incorporating renewable energy into the grid would disappear.  But, we don’t, and the basic feeling is that we need some sort of new idea to get there…

My bet is that if you ask a grade-schooler about how best to store energy, one of the first ideas they’d suggest is to use roll a heavy rock up a hill when you have excess energy and then, when you want energy later, extract it as the rock rolls down the hill…

Over the last few years I’ve been suggesting to folks that this idea isn’t as crazy as it sounds, and it seems that there were others of similar minds! Dave Rutledge recently pointed me to a new energy storage startup called ARES that does essentially that.

Their tagline is “the power of gravity,” and the basic idea of what they’re suggesting is to fill rail cars with 200-tons of rocks, and then use solar/wind to power the car up a hill and then when the power is needed, they come on back down the hill and their motion powers a generator.  So, nineteenth-century technology to the rescue!

This is one of those simple, but brilliant ideas.  Nearly everything works in its favor.

  • It avoids the environmentally-damaging aspects of other energy storage technologies such as pumped hydro, compressed air, lithium ion, etc.. No noise pollution, no water, no air pollution, no spotlights, no rare materials needed, and the space required is minimal.
  • It should also be able to be very reliable.  In particular, the lifetimes should be very long, since there are no curves in the tracks, no diesel, no high-speed machinery, etc.
  • Costs should work out well too.  A back-of-the-envelope calculation is that $1000 per 200 metric ton load with a drop of 700m would give $2.60/kWh, and $500,000 per 2MW locomotive would mean $0.25/W.  Both of which are very competitive!
  • Finally, the discharge rate should be pretty good too.  Taking a plot from the ARES site, it is quite competitive with compressed air and pumped hydro…ARES_Capacities_2XR2_6

I’ll be very interested to see how it goes… The main nagging issue, it seems to me, will be geography.  Of course, there are lots of hills that should work well for this sort of thing (many of which already have tracks even), but getting transmission lines there may be expensive, which would hurt the cost comparison with other storage technologies.  (Though, it’s not easy to find appropriate sites for pumped hydro either…)



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