A company called ARES is working on a system that basically consists of automated electric trains carrying bricks uphill to store and then coasting back downhill with them to retrieve power. Basically pumped hydro but without a need for large quantities of water (and really ideal for installation in the desert, where there's a lot of open land with gentle slopes). They say efficiency near 80% with a first installation going in in Nevada in 2017.

This is comparable efficiency to batteries but less expensive and with significant reuse of well-established technologies and industries (e.g. most of the construction work can be done by existing rail contractors).

Although battery technology continues to advance, my suspicion is that large-scale electricity storage is going to tend to be mechanical for cost reasons.

Huh. That's some pretty impressive efficiency. I don't know why, but the thought of a train carrying a brick uphill only to bring it back down again strikes me as a little bit comical :)

Very interesting though. I wonder how far those trains travel, and if there's some way to use them simultaneously as energy storage and transmission infrastructure. I guess it depends on how the energy is recaptured. I'm just wondering because that could solve some of the cost issues associated with putting big solar arrays out in the middle of the desert...

Something like a linear alternator maybe?

https://en.wikipedia.org/wiki/Linear_alternator

Is this the ARES you mean? http://www.aresnorthamerica.com/

Love that they call it the ‘Sisyphus Railroad’.

Other than Wikipedia, no; I was hoping you would. That's why I asked. :)

https://en.wikipedia.org/wiki/Grid_energy_storage

I think it's an interesting field though.

David Mackay's "Sustainable Energy - Without the Hot Air" has good numbers comparing many different forms of energy storage:

http://www.inference.eng.cam.ac.uk/withouthotair/.

It's a "hard-headed" engineering look at our energy options written by a physicist. It might be a bit outdated (published in 2008), but when it came out it was the best compendium I'd seen.

Thanks. This has been recommended to me in the past, though I haven't yet taken the time to read it.

Note that some of the statements there (e.g. estimates of areas needed to provide power from solar energy) are not technology-dependent (ie. are about physical limitations).

MacKay's estimate of areas needed to provide power from solar energy are technology-dependent. See for example:

http://www.inference.phy.cam.ac.uk/withouthotair/c6/page_41....

"If a breakthrough of solar technology occurs and the cost of photovoltaics came down enough that we could deploy panels all over the countryside, what is the maximum conceivable production? Well, if we covered 5% of the UK with 10%-efficient panels, we’d have 10% × 100 W/m^2 × 200 m^2 per person ≈ 50 kWh/day/person.

I assumed only 10%-efficient panels, by the way, because I imagine that solar panels would be mass-produced on such a scale only if they were very cheap, and it’s the lower efficiency panels that will get cheap first."

This assumption was invalidated by the actual trajectory of solar power since 2008. Nobody is building solar farms with 10% efficiency panels any more. Low efficiency is too expensive -- because it requires more glass and aluminum for the panels, more cabling, racking, and labor for installation. Low cost, low efficiency Chinese panels, like the GCL Poly ones used at India's giant new solar farm that HN just had an article about, are now in the mid-teens. (I looked up the data sheet after getting a glimpse of the GCL shipping crates on that Indian project site):

http://www.solarpanelsplus.com/PV-Specials/GCL%20245.pdf

If they used the middle-of-the-road GCL‐P6‐60‐240 that's a 14.7% module; 47% better than MacKay estimated as the best one could hope for from large scale solar projects. And the minimum competitive efficiency for even low-price panels is still creeping up. (Though large scale storage sufficiently affordable to get UK energy primarily from PV is still but a dream.)

MacKay also made the challenge look even bigger than it is by estimating the energy consumption of a "typical moderately-affluent person" and then multiplying that value by the whole population of the UK: http://www.inference.phy.cam.ac.uk/withouthotair/c2/page_22....

This leads to large over-estimates relative to actual measured UK energy consumption, particularly from air travel and automobile travel.

Fair point. He says that the 20% estimate is unlikely to be revised upward, but it's "unlikely because you can't get more than 30% using reasonable approaches to PV" and not "unlikely because you can't get more than 30% due to thermodynamics" (I can't find what's _that_ limit quickly).

> MacKay also made the challenge look even bigger than it is by estimating the energy consumption of a "typical moderately-affluent person" and then multiplying that value by the whole population of the UK (...)

Here I'd agree with him: we need to find energy sources that will deal with projected future demands.

Projected future demands for energy per capita in the UK and other developed countries grow very slowly, or even decline. Primary energy consumption per capita in the UK has actually declined since 2008 when MacKay wrote his book (you'll need to select countries yourself to see the data):

http://www.tsp-data-portal.org/Energy-Consumption-per-Capita...

You might think that's just because the UK doesn't do manufacturing any more, but look at manufacturing powerhouses Japan and Germany: they also have seen per-capita declines since 2008.

Ecologists and economists alike seem to have a default assumption that human resource consumption is insatiable; they just have different attitudes about that assumption. I don't know how many years of trends like the one I just linked it will take before they reassess resource satiety.

Me too. I recently read about these hybrid battery-capacitor thingies that sounded pretty promising. I'll see if I can dig up the link.

EDIT: here we go - http://www.nature.com/articles/srep04315 . Lithium iron phosphate batteries (LiFePO).

Although I'm assuming this particular combination doesn't provide favourable enough economics (or it would probably be a household name already), I can definitely see how this approach in general could. You could have the best of both worlds: cheap, but slow charge/discharge storage combined with the ability to very quickly scale up to meet peak daily demand for a limited (but sufficient) period of time.