Summary: The following summarizes the sizing of solar panels to get energy for my EV and the design of a tracking solar panel array.

A PV array that tracks the sun's passage is preferable, because the outpur per day is about 30% more than a fixed collector. Some tracking arrays utilize a sun sensor. It looks for the hot spot in the sky. I have chosen an alternate approach, namely to move the array, keeping it at righ angles to the sun. The choice of rotating axis makes the control simple or complex.

A complex, 2 axis tracker is here. The link is a 3-D model which is zoomable, and rotateable.

A simple, 1 axis tracker is here. The link is a 3-D model which is zoomable, and rotateable.

Notes on the 1 axis tracker: The single axis tracker is set up to where a manually adjusted axis tilts the array's rotating axis to where it is parallel to the earth's axis. This way, the tracking of the sun is accomplished through a slow RPM motor / gearbox. The math is as follows: If I use a motor that rotates at 72 RPM, I need to gear it down to 1 revolution per day. This ratio is 103680. 103680 = (72 REV/Min) * (60 Minutes / Hour) * (24 Hours / Day). How do I get this rather lartge ratio? Through a combination of gearing and pulsing the drive motor. In order to stiffen the tracker from high wind loads, I need a gearbox. Wind loads are not transmitted back to the motor. They can not get through the gearbox. The motor has a gear ratio to the gearbox of 3:1. The gearbox has a ratio of 129:1. Then another timing belt with a 3:1 ratio. The 3 ratios, multiplied, are 3 x 3 x 129 = 1161. The remaining ratio needed is 103680 / 1161 = 89. So, I turn the motor on for 1 second, and leave it off for 89 seconds. This is how to get the overall ratio of 103680. The controller is programmable as to the "on" and "off" time. This way, if an end user uses a different gearbox, the system can pr programmed for those ratios.

So, literally, the movement is incremental, but on average 1 revolution per day.

What about pointing accuracy? With a solar panel, the apparent area is the actual area x cosine of the error angle. The error angle is 1-2 degrees. cosine(2degrees) = 0.999. Indeed, if the error were 10 degrees, cos(10) = 0.984. I have heard of people using a deer feeder programmer, which can be turned on 4 times per 24 hours, to tilt an array. If you are gimballing mirrors, such as in the solar power tower, pointing accuracy is critical. Play the video at the link. Here is a parabolic mirror that requires good pointing accuracy.

Controller: A friend is developing a microcontroller, to gimbal my array, using an Arduino, programmed in the language called "c". It will be programmed to start up in the morning, and " bump" the array throughout the day, until it encounters a limit switch. Then it will reset the array to a start limit switch. In the morning, the process will be repeated. The program will have compensation for time of sunrise. When developed and tested, it will be offered for sale in kit form.

Notes on the 2 axis tracker: The golden sphere represents the sun. In order to track the sun, both motor / gearboxes turn. One motor rotates the array about a vertical axis. The other motor / gearbox moves the array about a horizontal axis. In the morning and afternoon, most of the turning is with the horizontal axis. At mid-day, most of the turning is about a vertical axis.

I will use solar panels coupled with this micro-inverter from Enphase. On this company link, scroll down, and in the section listing individual panels, note that you can sort panel costs on different categories - for instance $/Watt or total cost. Just click on the column head.

Instead of the traditional installation, which consists of an array of panels feeding one inverter, the alternate method is purchasing one panel, electrically tied to one micro-inverter. The latter takes the panel power, and inverts it, feeding the incoming power line - 240 vac. The initial cost is less than having many panels feeding one inverter, and, the benefits are better conversion efficiency and lower entry level costs.

Here is a picture of a sundial, that I built, located in Galveston, Texas. Scroll to Texas, and look at the one in Galveston (Photo). In this dial, the operator turns the analemma to a position facing the sun. The time is read on the time ring, opposite the shadow cast by the figure 8 - the analemma. The time increments are 5 minutes.

Questions, e-mail me. See www.hstech.biz Thanks