As someone interested in engineering and renewable energy, I’m not sure how I went this long without knowing about tide mills.
Using running water to turn a water wheel is about as simple and ancient a renewable energy idea as you can get. Normally, you need to stick your turbine somewhere water is already flowing downhill, like a river or waterfall. That water was originally carried uphill by clouds and dumped as rain or snow.
The genius of tide mills is that the responsibility of dragging some water uphill is shifted to the moon. Tides aren’t subject to droughts or competition from irrigation. Every high tide lets you recharge a giant battery, which you can then discharge in a controlled manner.