What are Energy Towers?

The energy tower is to the solar updraft tower as the high road is to the low road: two different approaches to the same goal. In this case, that goal is cheap electricity. Being inverse of the updraft tower, it follows that energy towers are also called downdraft towers because the air flows down the tower to spin a turbine at the base. How does it do that?

Photo Credit: EnergyPlenty.com

How it Works

First of all, an energy tower is designed much like an updraft tower with a very tall, very wide, very hollow cylinder (tower). A water spray system sits at the top. Pumps lift the water to the top where it is sprayed into the inside of the tower. This subsequently cools the warm air that hovers at the top of the tower, forcing this newly weighted air down through the tower to spin a turbine at the bottom. That turbine drives a generator which creates electricity.

The methods here are really quite similar to that of solar updraft technology. In fact, energy towers are often considered a form of solar power because the heated air that is wetted and cooled is generated by the sun.

Pros and Cons

Photo Credit: Umair Mohsin

One advantage an energy tower does have over other solar technologies is its ability to work at night because air retains some solar heat after dark.

One disadvantage, however, is how it is affected by changes in humidity; whether by a rainstorm (typical of any solar application) or by a decrease in temperature. That latter problem is significant in terms of geographic potential (i.e., an energy tower would not function properly in cold climates regardless of annual sunshine because the cold ambient air would negate the entire process).

This susceptibility to temperature fluctuation limits the potential usefulness of energy towers to hot arid climates. To tighten things even more, energy towers require a lot of water as well — further limiting them to hot and dry climates that also have access to a bountiful water supply.

Salt water can be used but very careful attention must be paid to corrosion, which could seriously affect the lifetime and efficiency of the tower.

Energy towers, like their updraft cousins, require a lot of space. The greater the temperature differential between hot and cold air, the more energy produced. So the larger the tower the better — dimensions discussed involve towers roughly 3,000 meters tall and 400 meters wide. So space, combined with climatic and geographical factors discussed above, severely limits an energy tower’s scope of influence. Furthermore, this arid and remote land where an energy tower could be erected would require significant upgrades in electricity transmission to deliver power to populations that needed it.

Costs

Photo Credit: zzzack

Like updraft towers, much of the investment is in initial construction. Very little maintenance would be required from then on, a key to selling the idea. Due to the sheer scale of such a project, a good deal of energy would likely be produced.

Estimates as to the cost of electricity generated by an energy downdraft tower range between 1-4 cents per kilowatt-hour. That is much cheaper than other energy sources, although that estimate relies on generous conversion efficiency estimates. There are currently no energy towers in use in the world, so no real data can be gathered. Because solar updraft towers and energy towers, however opposite in use, utilize the same physical principles, one can speculate that conversion efficiencies would be the same. So far data on existing pilot updraft towers hover around 0.50%; not the most promising data.

Source: Wikipedia.org

Posted on April 23rd in Solar Information by Dan.