3 ms·

My understanding is that electric power is very efficient at moving heavy rail cars up a mountain, so surprisingly little power gets stored.

beat 10y ago
What you mean is that little power gets lost, not little power gets stored. The goal is to reduce thermal losses. Beyond that, it's just a matter of throwing mass at the problem. These aren't ordinary rail cars. They're designed to be generators, so they optimize for efficiency. Adding mass increases storage, but we don't want to waste more energy than necessary in the storage process.
- woodandsteel 10y ago
  Yes, you are right that I should have said little power gets lost. I thought about it some more, and I think the underlying problem is that even these very heavy rail cars don't have nearly enough mass. Compare them with the literally millions of tons of water in an even moderate-sized reservoir.
  - beat 10y ago
    Water is 1000kg/m^3. Cast iron is 7300kg/m^3, so there's a substantial density difference. More important, though, is geography. A place with long, steep, relatively straight slopes isn't necessarily a good place to build a reservoir.
    - woodandsteel 10y ago
      Density doesn't matter for storing power by lifting up weight, what matters is total weight lifted, and how far. As far as I can tell, the problem with the heavy rail car method is that it costs too much for the amount of storage you get. One reason I say that is that if the economics if it were good (and I assume they are pretty easy to calculate), then articles that talk about different methods for storing all that renewable energy we are getting would include it, but they rarely if ever do. Also, unlike other methods like lithium-ion batteries and flow batteries, the various technologies involved in heavy rail cars are already well-developed, so there is little room for improvement once the first few models are developed. I mean, it is not like anyone is likely to develop cheaper ways of making rails or railroad cars.
      - beat 10y ago
        Density reduces the volume for total weight lifted. It may not affect the physics, but it greatly affects the engineering.

beat 10y ago

What you mean is that little power gets lost, not little power gets stored. The goal is to reduce thermal losses. Beyond that, it's just a matter of throwing mass at the problem. These aren't ordinary rail cars. They're designed to be generators, so they optimize for efficiency. Adding mass increases storage, but we don't want to waste more energy than necessary in the storage process.

woodandsteel 10y ago
Yes, you are right that I should have said little power gets lost. I thought about it some more, and I think the underlying problem is that even these very heavy rail cars don't have nearly enough mass. Compare them with the literally millions of tons of water in an even moderate-sized reservoir.
- beat 10y ago
  Water is 1000kg/m^3. Cast iron is 7300kg/m^3, so there's a substantial density difference. More important, though, is geography. A place with long, steep, relatively straight slopes isn't necessarily a good place to build a reservoir.
  - woodandsteel 10y ago
    Density doesn't matter for storing power by lifting up weight, what matters is total weight lifted, and how far. As far as I can tell, the problem with the heavy rail car method is that it costs too much for the amount of storage you get. One reason I say that is that if the economics if it were good (and I assume they are pretty easy to calculate), then articles that talk about different methods for storing all that renewable energy we are getting would include it, but they rarely if ever do. Also, unlike other methods like lithium-ion batteries and flow batteries, the various technologies involved in heavy rail cars are already well-developed, so there is little room for improvement once the first few models are developed. I mean, it is not like anyone is likely to develop cheaper ways of making rails or railroad cars.
    - beat 10y ago
      Density reduces the volume for total weight lifted. It may not affect the physics, but it greatly affects the engineering.