This is about a clean, environmentally benign, cost effective way to capture energy which is otherwise lost.
Cisterns are normally considered to be rainwater storage devices either underground, or at ground level. Also, cisterns are not involved with the production of electricity.
The 12 continental U.S. places with the most annual rainfall are all on the west coast. Their average figures range from 105.6” at Grays River Hatchery, Washington state, to 130.6” at Aberdeen Reservoir, also in Washington.
What if a rather large cistern were placed at the top of a 200’ tower, just offshore in Washington state, where the rainfall was 108” (9 feet) per year? What if this device collected rainfall, and periodically allowed the accumulated water to escape by way of turbines just above the water’s surface? The turbines would be connected to the nearest power transmission lines
How much electricity could such a cistern/turbine combination generate in one year? Let’s talk about one acre in size, nine feet in depth. One acre is 43,560 square feet. This is not much larger than the average putting green at a golf course.
One acre filled to a depth of 9’ is 392,040 cubic feet. Each cubic foot of water weighs 62.4 pounds, meaning 392,040 cubic feet would be 24,463,296 pounds. This weight of water, falling 200’ to the turbine, would be (24,463,296 * 200), or 4,892,659,200 foot-pounds of energy.
How much electricity would be generated by 4.9 billion foot-pounds of water? Close to 2 million watt hours: 1,842,654, to be exact. This may appear to be considerable, but for a full year’s accumulation of rainfall it is probably not cost effective. However, scaling up would change the equation:
• Make the tower arbitrarily taller, with a greater fall meaning more power. How much taller? The engineers would know best.
• Enlarge the surface area and capacity of the cistern. Again, the optimum would be determined by engineers.
• After a pilot test, build several more towers at the site, all linked to each other and to the power transmission line on the shore.
The above steps would make the cistern project practical and cost effective. Although it would not reverse global warming, this project would be a marginal, worthwhile contribution to reduced reliance on fossil fuels.