I received the following question by email so I thought it helpful to post the question here - as my original comments about water use by solar steam generators was not clear. Thanks for the interest!

Question: "How do these generators work - why isn't water in closed system? I was thinking solar heats enclosed water > steam >drive turbines(??) > condense > repeat. Obviously not the case. maybe you could expand ..."

Response:   The steam loop is closed.  It is important to keep the steam loop closed because, if it were open, minerals would be deposited in the steam pipes when the water in the loop evaporated, eventually leading to clogged piping (just like the minerals which deposit in the bottom of your tea pot). 

However, because the ambient air temperature can vary between 32 and 120F in the desert, the difference in temperature between the very low pressure "waste" steam and the air  is not sufficient to create an efficent condenser in a small "pipe to air" radiator envelope (which would at least need to be shaded and fan cooled).    It is much less costly to construct a "wet" cooling tower, where water circulates in contact with (but on the outside of the steam loop).  The cooling water condenses the steam back to a liquid so it can be pumped again through the solar heaters.  The warmed cooling water is then sprayed  down through a natural draft (hyperbolic shaped like Perry Nuke) or fan drafted cooling tower.  Some cooling water evaporates, taking away heat into the air, and the rest of the air cooled cooling water is collected and recirculated.   

At the Boron solar steam electric facility fan drafted wet cooling towers are used.  It is from these cooliing towers that large amounts of moisture are lost throught evaporation (see two towers of 6 at the facility in photo with Joshua tree above). 

The same type of evaporative loss takes place from the Perry Nuclear generator - millions of gallons per day of Lake Erie water are evaporated from Perry - and lost from the Great Lakes Basin.  These evaporative losses were one of the main water "diversion" issues addressed recently by the Great Lakes Basin Compact signed into law on October 3, 2008 by President Bush.

Here is a link to a list of SEGS plants from NREL    You will notice to to ensure  "dispatchability" these plants have natural gas powered back up generation - so they are not entirely "green" facilities.

Kudos to you Jeff for posting a header with notes. Not only do we learn about what we're looking at, we also learn via discussion and dialogue.

Whomever sent the question, I hope you will continue your inquiries here and add your knowledge. Sometimes questioning is the more powerful aspect of knowledge building, eh? At least, in this case, it was for me.

We also learned that someone found the  header images link and perchance the contact form. Cool!

Solar Heaters work on two principles. First the absorption of Solar energy by black surface and Second is the Heat trapping principle called Greenhouse Effect.

solar energy panel