Building a Solar Parabolic

[DonRotolo]

To aim a dish 'antenna' at a celestial object, a Polar Mount is used. The track of the sun is quite predictable, an arc across the sky.

Imagine the front of a bicycle, the handlebar/front fork assembly. It turns in a single plane, left or right. If you mounted a dish to the front of the handlebars, you'd easily be able to scan across the horizon, right?

OK, now tilt the assembly backwards, so the dish points into the sky when the handlebars are straight ahead. But when you turn left or right, the dish points lower and lower until it looks at the horizon again - this happens both left and right.

This is called a polar mount. There is some error in pointing here, but for a solar collector it is certainly manageable. (If pointing error is unacceptable, you'd use an Azimuth-Elevation (Az-El) antenna rotator system, controlled bya computer. Readily available from Amateur Radio stores in the under-$1500 range)

You use a Linear Actuator to move the polar mount side to side. These are readily available from people who sell satellite TV antennas of 2 meters or larger. Kind of rare these days, what with DirecTV and such, but they're still out there. I saw a linear actuator in a surplus catalog for $40 recently. The actuator can be made to move slowly enough that it is always moving during the day, just really slowly, thus tracking the sun. At midnight, it runs for 2 or 3 minutes to reset the dish for the next sunrise.

The angle of the tube is simple: At the solstices the peak of the arc is at its highest or lowest, so normally one would pick an angle between the two, and careful observation and measurement shows that this equals your latitude. Funny how that works...

Here is a link to a Polar Mount installation instruction
Here is a Link to a Linear Actuator, just a good photo of one


OK, now that you have all that...using a dish like that is a bad idea.
The temperature at the focus of an 8 foot diameter dish will be enough to melt aluminum, possibly to melt steel if you are careful when applying your reflective coating. This is dangerous, and difficult to extract energy from. Maybe some engineering calculations are in order - I'll leave that to you. But take a google at commercial solar collectors, see how THEY do it, and copy that.

In fact, you can make a linear system (a ling line-like collector) that doesn't need to move at all. Think of a rain gutter at the edge of a roof. Make a gutter that's a parabola, and put a tube right at the focus. Then, turn the assembly so it goes from the peak of the roof to the eaves. Then tilt it up at the magic angle (your latitude) and face it due South. This setup will be nearly as efficient as a tracking array, with half the cost (so you can aoofrd to put up more of them). Great for hot water generation. You need to use anti-freeze in those pipes if it gets cold where you are, though.

I think that's enough to get you started.