Kottke brings news of a novel way to store electricity for later use using cranes and concrete blocks. During times of excess solar/hydro/wind generation the electric powered crane lifts these huge weights as high as it can. Then, when there's a lull in energy the crane drops the weights, spinning turbines which generate electricity for the grid. What's striking is they claim to be recovering 85% of the electricity used to lift the blocks, compared with 90% when it's stored in lithium batteries. I always assumed these systems lost much more through noise, friction, etc, so that's good to know.
There's also the train-full-of-rocks approach, where a train full of rocks is slowly driven up a hill and then, when the energy is needed, rolls back down.
But reservoirs and hills take up a lot of space. The crane system really caught my eye because it doesn't have a large footprint. You simply need to lift something up. And we have plenty of structures that can house a up-lifty thing. Imagine if every building over 3 stories had a shaft containing a dense block of metal. On top of the building is a solar array and/or wind turbine which, if its energy isn't being used, lifts the block. And then, at night or when the wind drops, the block starts its descent.
This sort of micro-conservation of energy has a lot of potential. Cities absorbed insane amounts of heat this summer which just sat there in the concrete making everyone uncomfortable. Couldn't that energy be captured and stored in a kinetic system?