Funiculaire Neuveville-St.Pierre in Fribourg, Switzerland
There are often simple, low-tech solutions to difficult problems, including some ingenious ones from the great age of engineering in the last half of the nineteenth century. Kris at Low Tech Magazine explains how furniculars, those cable trains that were built up the sides of hills and mountains, often ran on water! The two cars were connected by cables, so you added 400 gallons of water to the one at the top, to make it heavy enough to roll down the hill while pulling up the lighter one at the bottom.
That is how the famous furniculaire de Montmartre worked in Paris until 1930 when the water system was replaced by engines. The water systems still required energy to pump the water up the hill, so there probably was not that great a gain in energy consumption.
In Fribourg, Switzerland, they had a much better idea. One area in town is at the top of a hill, and the other at the bottom, separated by about 375 feet of elevation. And if there is one thing that is always flowing from the top to the bottom, it is sewage. Instead of running in a pipe, they pump some of it into the car at the top; at the bottom, they open it up and let it run into the lower sewer.
They have been doing this virtually without a break since 1899, using the one energy source that we will probably never run out of.
It is an ingenious solution, using the weight of waste. Perhaps we could use it in elevators; instead of a solid counterweight, install tanks that are filled from the toilets of the upper floors of buildings. From Low-Tech Magazine and Funimag