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44 comments on And who is that, riding to the rescue?

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stalkylittleboy on October 17, 2005 - 8:48pm Permalink | Subthread | Comments top
A question for you energy production gurus:

Take a bunch of mirrors and mount them on hardware which can rotate and tilt.  Hook them all up to a controller which tracks the sun and knows where the mirrors are located.  The controller can then use the mirrors to collect sunlight from a large area and concentrate it into a small area for effecient conversion into electricity.  I don't really know how you'd do that, but I'd think maybe you could use a steam turbine?

It seems intuitively that this would give you cheaper and more scalable solar to electric conversion than, say, photovoltaics.

But since nobody does this, there must be more to it.  Why doesn't this work?

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throwaway92614 on October 17, 2005 - 8:57pm Permalink | Subthread | Parent | Comments top
Already tried, tested, etc. Info available at:

http://www.solarpaces.org/publications/sp99_tec.htm

Scroll down to the "Power Tower Plants"

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stalkylittleboy on October 17, 2005 - 9:09pm Permalink | Subthread | Parent | Comments top
Interesting, thank you.  I'm surprised they are not in wider use.  They seem like they'd be pretty cheap to build, and in the right areas (like a desert) you could set up large farms of them with little environmental impact.
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TJ on October 17, 2005 - 9:02pm Permalink | Subthread | Parent | Comments top
It does work.  It's been done somewhere in California on a small scale, IIRC.  It's not done more because the initial investment is high.
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stalkylittleboy on October 17, 2005 - 9:11pm Permalink | Subthread | Parent | Comments top
I don't understand why the initial investment should be so high.  Conversion of heat to electricity is a mature technology, and aimable mirrors don't seem very expensive.
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TJ on October 17, 2005 - 9:27pm Permalink | Subthread | Parent | Comments top
The higher the steam temperature the better your thermal efficiency for your generating cycle.  It takes a lot of mirrors to get high temperatures.
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robertmcleod on October 17, 2005 - 9:46pm Permalink | Subthread | Parent | Comments top
Mirrors are expensive actually.  They are basically a pane of  glass with an aluminium coating and an anti-reflective coating on top of that.  The electrical actuators used to track the sun are also expensive.  Futhermore, mirrors don't work when it's cloudy.  That limits concentrating systems to locations like the Sonata and Sahara deserts.  Concentrators can be highly effective in those high insolation environments.

Photovoltaics have no moving parts so they don't require much maintenance.  You just have to hose off the bird droppings every once and a while.  

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Joseph Somsel on October 18, 2005 - 11:24am Permalink | Subthread | Parent | Comments top
I interviewed for a job as startup engineer on the "Power Tower" in the Mohave Desert run by Southern California Edison back in the late '70s.

What a loser!  I declined as the performance was so marginal. It's still there - you can see it from the freeway or if you take Amtrak's Southwest Chief:
http://www.amtrak.com/servlet/ContentServer?pagename=Amtrak/am2Route/Horizontal_Route_Page&c=am2 Route&cid=1081442673827&ssid=132

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ericy on October 18, 2005 - 8:10am Permalink | Subthread | Parent | Comments top
Also see http://www.stirlingenergy.com/ for a similar idea.  They have contracts to build two plants - one is  300-900 MW.  The other is 500-850MW.

The design here is for 38 foot diameter dishes, with a stirling engine at the focus of the dish.  Very modular as each dish is independent of the others, so as soon as the first dish is complete they will start getting electricity.

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Murray on October 18, 2005 - 11:31am Permalink | Subthread | Parent | Comments top
See http://www.energypulse.net/centers/article/article_display.cfm?a_id=864  Murray
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