No need napkins for it. Because of friction and other forces the dynamo does not generate enough energy to lift the balls back up and have extra to be stored fo

No need napkins for it. Because of friction and other forces the dynamo does not generate enough energy to lift the balls back up and have extra to be stored for other uses. In short, you use more energy to lift them than produced. If anyone could invent such a device, the world hunger and money wouldn't be problems anymore and we would be traveling to the end of the universe already.