Friday, February 14, 2014

A Functional Death Ray

Or you could think of this as just another green bird killer. Back when I worked for a Big Aerospace Company, one of the cleverer mechanical engineers there got us into the "power Tower" idea. This involves several acres of mirrors focusing sunlight onto a heat  exchanger which would be used to boil water, etc, etc. It was fairly ambitious as it involved writing software that would control a lot of individual mirrors very precisely over a long period of time during which the sun inconveniently would appear in a different spot not only as it moved across the sky, but every day the arc would be slightly different, more so as the day does not mesh with the year on this planet.

Getting the thing started involved first bringing the mirrors part way up to a "cleaning" position to allow the window washers to remove the previous days dust, then bringing them up to a preliminary position with the entire field focused slightly off to the side of the tower with the heat exchanger in it while overall field orientation was checked, then swinging the entire field over to place the focus on the heat exchanger. If the field is not focused on a single spot, the power would be degraded. Likewise if the spot wasn't centered properly. One other thing: If the preliminary focus was good but the transfer to the heat exchanger ran slow or if the daily tracking algorithm didn't work during the preliminary setup, the focus of the beam would track slowly across the concrete tower. Concrete, though tough and generally durable, was never meant to stand up to this kind of heat.

I asked one of the engineers on the project and yes, the occasional bird would fly through the beam. Halfway through anyway, and would be replaced by a shower of burnt feathers. The local predators must have thought this was manna from heaven with KFC ranging from rare to well done falling out of the sky. The saving virtue of this is that the "stay out" zone varies in intensity and birds approaching from the right direction would quickly learn to stay away.

We sold one commercial installation to the Chinese who from what I heard, never finished it. Current estimates are that power produced in this manner will cost about twice what conventional power runs which in the green world is remarkably cheap. The local power company has a contract to buy the power and the costs will be passed along to the grateful consumers which would include Las Vegas and Los Angeles.

We have covered the roof of the building where I work with solar panels and while the fixed photovoltaic panels do not directly compare to the dynamic mirrors at the Ivanpah facility, there is a large screen inside that shows exactly what we are getting. Without exact numbers, I would guess that on a clear day we get about 2 hours of full rated capacity around noon, plus 3 hours of average 50% capacity in the morning and evening. This adds up to 5/8 rated capacity for an 8 hour period while the sun is up which further works out to 20.8% rated capacity over a 24 hour day. On a cloudy day this can drop by between 2/3 and 1/3 depending on the cloud cover.

Lotta money for something with 6-21% efficiency.

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