Parabolic Trough Lens

TOP technique.

You have not told us how elaborate your system is. Will this work for you?

[edit] I see admin has altered the title of your thread. No lens involved.

Check Mother Earth News. You can use photocells and motors, or small tanks and a heat-sensitive gas like freon. It can be kept simple.

Line it up East-West, tilted from the vertical by an angle equal to your latitude.

At the end of the trough, on the axis that it is rotating about, fix an assembly with a sheet to form a shadow and behind it two small photovoltaic panels:-

Use the power from the panels to drive a small bi-directional DC motor which is then geared down hundreds of times to rotate the trough.

As the sun rises a little light will fall on the top panel: use the current to tilt the trough up. If there is a period of cloud cover then when it passes a lot of light will fall on the top panel and the trough should tilt up fairly quickly. Vice versa as the sun falls.

since the sun travels at a set rate the cheapest way would be to set the angle ie up down and then use a geared motor drive to pan the unit to follow the path of the sun, then when the end travel has been attained fit a micro switch to return unit to start position then a timer to allow for night time then start again