# The Lapse Rate Power Tower

## Abstract

Our atmosphere has a natural property called the lapse rate which causes air temperature to drop with increasing altitude. This temperature differential is used to lift water vapor to high elevations where it condenses at ambient temperature. Gravity then pulls the liquid to ground level in a column, generating a large pressure used to spin a turbine. The power cycle mimicks the Earth's hydrological cycle and therefore sustains operation indirectly through solar radiation, making it a form of solar power which can operate even at night.

## This Is Clearly Insane... Right?

Right.

But if you think of it like a Rube Goldberg Machine, it becomes a whimsical way to generate electricity.

This project all started with the incredibly boring barometer, which was intriguing to me because of its ability to lift water with a vacuum (ie nothingness). Somehow nothingness was able to lift water over 32 feet in the air! Surely, I thought, there must be some way to use this trick to generate power... So being young, naive, and brazen, I naturally tried to find a way to break the first law of thermodynamics and create a perpetual motion machine. This did not end well for me.

But the exploration of the relationships between pressure, temperature, and phase led me down the path to a device that mimicked the earths water cycle. The motivation to learn the required thermodynamics provided me with valuable practice that allowed me to stay employed in the energy industry. So while this particular idea may have been a dead end, the lessons learned from it were incredibly beneficial to my career.

This machine is ridiculous in its proportions and would never be practical purely for power generation. It could possibly play a role in geo-engineering as a tool to lower the Earth's surface temperatures, but lets hope we never need to do that! For more perspective on just how big the Burj Khalifa tower is:

Two opposing forces are required to sustain an energy producing cycle.
1. The lapse rate is a thermal gradient that flows vertically upward.
2. Gravitational potential energy flows vertically downward.
Water is constantly in flux between these two energy gradients, forming the Water Cycle.

## The Water Cycle

The Earth's water cycle provides a perfect example of how water can be moved great distances with these two forces. Water is raised high into the atmosphere as a low density vapor, then pulled back down after condensing into a high density liquid. Water is only light enough to “ride” the thermal gradient upward while in the vapor phase. Equally important, only liquid water is dense enough to be pulled back down to the ground, overcoming the upward push of the thermal gradient. Humans harness energy from the water cycle by damming rivers to drive turbines. Unfortunately, damming rivers is damaging to the environment in many ways.

## The Power Cycle

This power cycle is a closed system using water as the working fluid. The only interaction with the environment is heat transfer in the condenser at the top and in the evaporator at ground level.
1. The vapor riser column (2) is at very low pressure causing water to boil at atmospheric temperatures. Heat is absorbed from the atmosphere at ground level.
2. Water vapor flows upward to fill the low pressure void created from vapor condensing to liquid at step 3.
3. The condenser (3) is at a higher altitude than the boiler (1) where the ambient temperature is colder, allowing water to condense. Heat is released to the atmosphere.
4. A small upper liquid reservoir is needed to equalize pressure between vapor riser column and atmosphere and smooth out transient disturbances.
5. Liquid water flows into vertical column and increases hydrostatic pressure at the inlet to the turbine.
6. High pressure liquid drives the turbine before exiting to atmospheric pressure. The turbine drives an electric generator.
7. Liquid water remains in lower reservoir until being pulled back into boiler, thus completing the cycle.

## Size

Compared with all other forms of solar power this power tower has a very small footprint. The height requirement is the real killer of this technology. High altitudes are required to achieve a large enough temperature differential between the evaporator and condenser.

## The End?

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