I spent some time last week helping a third grade class with science projects. One group was trying to power a small electric fan with a cell made from an aluminium can and a copper sheet in salt water. Needless to say, it wasn’t working very well. They were able to produce about one tenth the minimal current needed to turn the motor.
To alleviate the suffering, I built a new motor. This one has a battery inside. The transistor turns the motor (powered by the battery) on when a potential difference is placed between the two leads. It’s cheating — and I’m not sure whether it was a good idea. But at least the team were able to present their work at the science fair.