The latent heat of alcohol is also only about 1/3 that of water per unit mass, so not a very dense way of storing energy, even if you were to freeze it. Adding

The latent heat of alcohol is also only about 1/3 that of water per unit mass, so not a very dense way of storing energy, even if you were to freeze it. Adding salt to water reduces the latent heat density too (pure water is hard to beat there), but not as much as adding alcohol does.