About Solar Towers

Solar towers use many large, computer controlled, sun tracking mirrors (heliostats) to focus the suns energy on a receiver located at the top of a tower.  A heat transfer fluid, usually molten nitrate salt, is heated in the receiver and used either to drive a turbine/generator to produce electricity or to provide high temperature thermal heat.  The molten salt can be used to store the thermal energy for producing electricity at night or during cloudy weather. Commercial power plants would be sized from 50 MW to 200 MW each.

A ten MW plant, Solar One, located near Barstow CA operated for six years demonstrating the viability of solar towers.  It used a heat transfer fluid to transfer the heat to the generator.  Solar Two, shown left, was a retrofit of solar one, built to demonstrate the advantages of molten salt for heat transfer and solar storage.  At one point it delivered power to the grid for seven days, 24 hours a day during cloudy weather.  Molten salt solar towers are well suited to peaking power applications, being able to generate power when most needed, day or night, cloudy or sunny.

In a molten-salt power tower, the molten nitrate salt, which is a clear liquid with properties like water at temperatures above its 240^oC (464^oF) melting point, is pumped from a large storage tank to the receiver, where it is heated in tubes to temperatures of 565^oC (1049^oF). The salt is then returned to a second large storage tank, where it remains until needed by the utility for power generation. At that time, the salt is pumped through a steam generator to produce the steam to power a conventional, high-efficiency steam turbine to produce electricity. The salt at 285^oC (545^oF) then returns to the first storage tank to be used in the cycle again.

The following paragraphs were excerpted from the Solar Power Tower report referenced at the end of this post.

The Solar Two receiver is comprised of a series of panels (each made of 32 thin-walled, stainless steel tubes) through which the molten salt flows in a serpentine path. The external surfaces of the tubes are coated with a black Pyromark™ paint that is robust, resistant to high temperatures and thermal cycling, and absorbs 95% of the incident sunlight. The receiver design has been optimized to absorb a maximum amount of solar energy while reducing the heat losses due to convection and radiation. The design, which includes laser-welding, sophisticated tube-nozzle-header connections, a tube clip design that facilitates tube expansion and contraction, and non-contact flux measurement devices, allows the receiver to rapidly change temperature without being damaged. For example, during a cloud passage, the receiver can safely change from 290 to 570ºC (554 to 1,058ºF) in less than one minute.

The salt storage medium is a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate.  Molten salt can be difficult to handle because it has a low viscosity (similar to water) and it wets metal surfaces extremely well. Accordingly, Solar Two is designed with a minimum number of gasketed flanges and most instrument transducers, valves, and fittings are welded in place.

Reference:

Technology Characterization - Solar Power Tower (pdf 304 KB), SolarPACES

Technocrati tags: solar, thermal solar, renewable, alternative energy

Comments

[brian donnelly]

published reports on steam generation and heat recovery. all available. more news to soon.

[Anant Joshi]

Is it possible to get detail design/ design features of steam generating heat exchangers
of Solar one and solar two.

alternate ID: ajoshi101@hotmail.com

[Martin Glass]

Solar 2 cost $48.5M in 1996 and produced 10MW, and was later decommissioned and converted to a telescope.

Why was it decomissioned, why are they not springing up all over the world, and why are they being sold in South Africa by the 100MW with claims of $1M per MW cost?

[Kit P]

MG

There was a time when only a few nuclear power plants bragged about performance and production cost. The interesting thing about good performing plants is that they had great safety records too. Now every plant is performing better than the top quantile 10 years ago.

Now the debate is about plants lasting 80 years and how fast we can build new plants.

When the solar industry starts discussing performance instead of potential, we can then debate the roll of solar power. The short answer to MG's question, solar does not work. Great for cool pictures.

[Martin Glass]

Solar stand alone PV works, where the cost to run grid to a site needing power exceeds or is close to the cost of a PV system to supply the energy required, or where the OPEX costs of running a diesel power plant exceed the CAPEX finance costs of a PV plant.

Outside of this, I agree, makes for great pictures, and one of the greatest ways to be seen to be green.

[subhash narang]

i think much year ago but i cant tried i seen hear you done first

[Ray Garris-Shoemaker]

this is a great site i go here for everything for science

[Kit P]

Like I said,

“``Natural variations over the next 10 years might be heading in the cold direction,'' Wood said. ``If you run the model long enough, eventually global warming will win.''

The world will become at least 2.5 degrees Celsius warmer by 2100, compared with the pre-industrial period, Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change, said in March.”

http://www.bloomberg.com/apps/news?pid=20601087&sid=aU.evtnk6DPo&refer=worldwide

I want to the AGW zealots call these folks denialist. What is not know and will never be know is the magnitude and environmental impact of the human portion. What is very well established is the benefit of an adequate energy supply.

[Marcus]

Just because there are uncertainties KitP does not make it any less of a problem. Since we know how much CO2 we are contributing to the atmosphere we can estimate the temperature change due to our efforts. Read the latest IPCC report.

[Kit P]

“less of a problem”

Marcus provides an example of negative thinking. Mathematical “uncertainties” does not make the something more of a problem either.

Drunk drivers not wearing seat belts have a lower risk of getting alcohol cancer than I do because they will more likely to die in an accident before they develop cancer.

AGW zealots like Marcus are afraid of gradual change in climate something the planet has always adapted for. If life on earth can adapt between summer and winter, then “ 2.5 degrees Celsius warmer by 2100” should not be too hard. Marcus please stop telling me to read something when you ignore the results. If AGW is a crisis, then the word 'crisis' has lost it is meaning.

[Martiin]

"The world will become at least 2.5 degrees Celsius warmer by 2100"

Very safe predictions to make - like maybe the sky will turn green by 2100. If you're wrong, who cares, you'll be long gone and so will those who heard the prediction.

The earth is in equilibrium, whatever the doomsayers who make fortunes out of our fears would have us believe.

The ocean warms up, so Antarctica, Iceland and The Artic dump huge ice cubes into it, and the ocean cools down.

"Natural variations over the next 10 years might be heading in the cold direction"

Now here is a short-term prediction that the writer will probably be around to defend in 10 years time - because it is most likely based on evidence, rather than fearmongering speculation.

And all of these negative theories presuppose that there is no God, who loves us and created everything around us for our benefit. But then trusting God wouldn't be good for business, would it?

I'm not saying we shouldn't act responsibly with our environment, but if the planet heating up is our fear, consider that it will cool down soon enough once there are no more fossil fuels to burn. But perhaps not in our lifetimes - while we are alive, in the eyeblink of a lifetime when compared with eternity, our concern should not be of things which we cannot change, but of things we can.

Things within ourselves.

[Pankaj]

well the salt which is used is to generate power.is it possible to use any other salt which is low cost and can be used for steam generation purpose.please reply.

email id:pankaj7on7@gmail.com

[Pankaj]

if i have a boiler which is working 24 hrs and i need to minimize its use,is their some process where i can use molten salt to convert water to steam along with the boiler...???please reply.

email id:pankaj7on7@gmail.com