Nothing magic about the numbers, I was just working from I was reading in your specs.
78 square feet (or so) is the area of the dish being exposed directly to the Sun, correct? That was why the pi x R^2 stuff above. The radius of a 10 foot dish is 5, so 5 x 5 x 3.14 = about 78.
The area of your target -- at the focus of the dish -- where the LNA (low noise amp) was located, and where the light will be focused -- is going to be 2 feet X 2 feet, correct? That would be 4 square feet.
Taking the area of the dish and dividing it by the area of the target will give you how much concentration is happening -- 78 square feet of Sun focused into 4 square feet of target -- in your case about 20X. Teton's design works out about 60X or so, as I recall. I think he had some 110+ plus 1 X 1 foot mirrors focusing on a target about a 1.5 X 1.5 foot or so
Typical ranges are from 50X to 150X or so. Generally the further North (or South, below the equator), the higher the concentration should be. Mostly a feature of how fast you can get the heat sucked off from the target.
You can make yours a higher concentration if you want by using a smaller target. That would also save you on material costs, and reduce the weight hanging up there, as well. The water will just have to pump through faster to keep up with the higher concentration and smaller volume. In concept you could make your target as small as your largest mirror.
There are a couple good methods on tracking. It becomes sort of a religion in some discussions. I have used both timers and photocell style sensors and both work fine. Also used freon weight types for PV, but that is not really an accurate way for this.
As far as weatherproofing, etc -- I sort of look to nature on some design. At night a lot of flowers fold down, and wait for the Sun to come back, so that is what I am doing on my designs.
http://www.fieldlines.com/story/2007/8/22/171323/372
Teton's design did not really allow for this and his mirrors wore out from the continued exposure. If you are using the full dish pole mounts and motor, I do not see an easy way for you to fold up, either. The Stirling Engine solar concentrators I have seen use a pole mount like yours and Teton's, but have "petals" the close up over the whole array.
Here (Texas) I figured hail or wind would destroy them if I did not make it close up flat and tight on itself, as well. If you do not mind the additional daily work, you may be able to use the vertical alignment on the dish to tilt it forward every evening, and back up in the morning?
