Friday, May 09, 2008

AirCooled Solar Tower: No Cooling Water Needed

One of the big problems of desert solar thermal is the need for cooling water to maintain the heat cycle efficiencies of steam turbines. This "solar tower" approach from Bright Source utilises air cooling instead of water cooling. Advantage Bright Source.
The stated advantages of power tower technology seem to make a lot of sense. The solar field of mirrors require no plumbing going to each mirror, containing a thermal transfer fluid, because the two-axis tracking mirrors point to a central boiler. This saves considerable expense to install and maintain plumbing throughout the solar field.

Also, because each mirror sits atop a single independently placed post, the ground underneath the solar field can be left relatively irregular and uneven. With parabolic trough technology, for example, the ground beneath the troughs must be almost perfectly smoothed, meaning far more site preparation is required.

Less obvious but also significant are the costs saved by utilizing super heated steam coming from one central boiler atop a tower, because this design allows the water to be air cooled instead of water cooled. In order for solar thermal power to require minimal input of water, the water needs to be continuously recirculated - it heats up in the boiler, drives the turbine, then must be cooled and condensed before returning to the boiler for heating. If this isn’t done, in a closed loop the back pressure of the steam after passing through the turbine would largely counteract the pressure of the incoming steam, ruining the efficiency of the device.

...Not only is Bright Source Energy using what could emerge as the most cost effective solar thermal design, but they are well on their way to implementing their technology. Their pilot plant in Israel, with a 60 meter tower and 1,600 mirrors, is in testing currently and will go active in mid-June. The plant will generate 5.0 megawatts of thermal energy, which with a boiler efficiency of 74% and a turbine efficiency of 45% will output 1.5 megawatts of electricity. That is just the beginning. __Read the rest at EcoWorld
It looks as if Bright Source may have solved some of the main problems of implementing solar thermal on a large scale. The modular nature of solar towers (from 1.5 MW upwards) allows each plant to match the needs of the community and region. Without heavy water demands for cooling, this approach is far more applicable to extremely arid regions.

Bright Source is applying for a permit to build a 400 MW facility in the Mojave desert near the California/Nevada border. If California doesn't grant the permit, Nevada is likely to do so.



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