Solar Thermal Energy System in Mojave Desert

These gain most of their energy from the heat of the sun rays, right? Heat of the Sun rays is maximum at the late morning to noon to early afternoon.

If this was a setup for the photovoltaics I could understand.

Wouldn't they achieve more by maximizing the number of parabolic throughs, reducing the distance and making them function at the high-intensity points of the day?

I thought about the shadow thing, I still feel its a great distance by which they have been separated. They probably have a lot of spare land available, like Redfred says. And yea, I forgot about the servicing space they would need

While its true there is more heat during mid-day, that does not mean there is not plenty of usable energy available in the morning hours as well. Since there is plenty of available land space in the desert, they really don't need to 'pack them in'. Simply calculate the number of mirrors needed get the maximum input the central collection device can handle (thats going to be the limiting factor), then space the mirrors for maximum usable daylight hours.

First, when you have lots of available space there is no need to maximize efficiency.

You should also realize that the image is from a high elevation angle. I suspect that the view at sunrise or sunset on the Winter Solstice the shadow lines will likely be almost touching each other. Even though this is desert, there probably will still be sparse flora growing under the array that will help to secure soil from erosion.

The placement is to allow the modules to be serviced...Troughs...and, of course, the shadows as mentioned....

Oh well, I did forget the servicing. Probably they calculated the right distance.

Are they Parabolic or Hyperbolic reflectors?

Parabolic. If they are hyperbolic the reflections wouldn't end at the single foci. Hyperbolic reflectors find use too of course - like in the Cassegrain reflector - which has two one hyperbolic and one parabolic.

I agree that, mathematically, placing the troughs closer together will increase the power output per unit area.

But practically, I trust the judgement of the engineers in charge of planning the placement of the troughs. At certain tipping points, other variables may become more important in determing the extent of spacing between troughs.

Isn't there is a need for space between the troughs to allow for servicing, replacement, repairs and regular check ups? Peharps the desolate locations where these troughs are usually located are not prime real estate therefore the need for maximizing land mass isn't as important as we(you) may think, as compared to the need for accessing the mirrors for the aforementioned purposes.

Another similar system in California: http://www.nrel.gov/docs/legosti/fy98/22589.pdf

Would anyone have an estimate on the cost-density of a single parabolic through? By cost density I mean, average-energy/US$ for a single parabolic through, assuming it to be connected to the necessary supporting system.