Storing energy as weight is more difficult than storing it as fuel. It is far more bulky. Consider that you can store enough energy in a litre of fuel, to drive a one ton vehicle about ten miles. It doesn't convert exactly, because a vehicle runs on wheels, but I think you can see that you would have to raise one ton of sand quite high in the air to have the equivalent of just one litre of petrol. People do store energy by pumping water to higher reservoirs, I believe. Someone may have already said this.