[mikec3010]

I wonder if you could compromise and use powdered concrete in a closed system? High powered fans could blow the fine powder upward in a silo so it would act like a liquid. Then large paddlewheels catching the powder could power a generator coming back down. I have no idea if powder going up a tube has less friction than blocks on a cable/pulley, however.

[effie]

That's not a good idea. You would have turbulent airflow with dust, most energy would get lost, resulting in low efficiency. Weights on cables pulled by electric motors is as efficient as it gets. Not to mention dust bucking up the gears and sockets.