Solar Power Tower – Tower that Generates Power

ps 20 solar power tower
PS20 Image by Tom Raftery

The Solar Power Tower is another concept for generating electricity by using the solar energy in the form of heat. This technology has seen and presently going through developments. Tower Power technology is less mature as compared to the technology of electricity generation using parabolic trough collector or sterling dish collectors. They are even known by the name Solar Updraft Tower.

History of Power Towers

Power Towers have been implemented the world over on an experimental basis since the past two decades. The basic purpose of the implementation was to demonstrate the feasibility of application and economic usefulness of the power tower technology.

The concept of a solar updraft tower was put forth in 1903 by Isidoro Cabanyes. He served as a Colonel in the Spanish Army. He discussed the concept in the Spanish Magazine La energía eléctrica.

After Isidoro Cabanyes, a german author named Hanns Günther made a description of a solar chimney power plant in 1931.

Robert E. Lucier applied for patents on solar power towers during the period 1978 to 1981. As these patents were expired they were granted again in US, Israel, Canada & Australia.

System Description

A Solar Power Tower generates electricity by using the solar energy in the form of heat. A large number of heliostats are used to generate heat from sunlight. The Heliostats concentrate incident light on a tower mounted Receiver.

Molten salt is stored in a “cold storage tank” in a molten salt based solar power tower. The temperature of the salt in the liquid state is around 290°C to 300°C. This molten salt mass is pumped to the overhead receiver where it gets heated to a temperature of around 550°C to 565°C. Upon heating it is transferred to a “hot tank”. Where it is either stored for further use during the day or is used for power generation during peak loads.

Now when power is required the salt in liquid form is pumped to a system which generates superheated steam. This superheated steam then acts as the prime mover to a “Rankine Cycle” Turbine coupled to a generator system.Thus generating solar electricity.

The molten salt is taken back to the “cold” storage tank, which can be transferred to the receiver for reheating and the process keeps on repeating.

solar power tower system
Solar Power Tower System

Other Important Facts

The number of heliostats and the area of the heliostatic field depends on the requirement of the generating station. That means higher the Mega watt power generated larger the heliostat area. For any particular tower power system, the harvesting of solar energy takes place much more than the steam required for powering the turbine.

Thus the storage system can continue to work even when the system is busy generating electricity using the superheated steam.

The ratio of thermal capacity of the heliostatic field to the peak thermal power required by the turbine is termed as solar multiple.

The higher the solar multiple ensures that the plant continues to generate electricity even after sunset or during cloudy days.

About Solar Power Tower Projects

The very first of the solar tower project was the “Solar One”. This project operated from 1982 to 1988, it was also the world’s largest tower plant in capacity i.e. 10MWe. In all there were 1818 heliostats installed in the heliostatic field. Each heliostat had a reflective area of 39.3 Sq mtr. The annual efficiency of Solar One was a meager 7%.

Further advancements due to the research work in the power tower led to the commissioning of Solar Two.

Solar Two was implemented using the molten salt heat transfer system. Solar Two had a capacity of 10MW similar to Solar One. In 1996 Solar Two was grid connected. The tower situated receiver for Solar Two was designed by Boeing’s Rocketdyne division. The receiver is optimized in such a way that almost the entire concentrated solar energy would be absorbed by the receiver. The Thermal capacity of the Solar Two is 110MWt.Solar Two started power production in the second half of 1997.

Other solar power tower plants include Sierra SunTower situated in Lancaster, California. It has a capacity of 5MW.

Solar Tres Power Tower is a 17MW capacity plant coming up in Spain.

Recently Internet Giant “Google” has invested $168 Million in the World’s largest solar power tower plant. It has a mammoth capacity of 392 MW. This plant is scheduled for completion in 2013.

The technological advancements and innovations have increased the ease of generating solar thermal electricity. Land costs, Subsidies by Governments and System Costs alongwith Economical Constraints will always have a major role to play.

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