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michael 03-24-13 04:43 PM

DIM 5500 w PV Array
The following photos chronicle in a spotty fashion a single axis tracking solar array I finished recently. It took two years to design and build. It serves two residences and generates slightly more electricity than the two homes use. It is grid tied, so we use PG&E as our battery pack. The panels are 230 w Sunpower, and were installed on the array by a local company, Mendocino Solar. I built all of it myself, but I had lots of help. I used Parallax microcontrollers, and received help and guidance from the Parallax Users' Forum, from a local generous neighbor, Jonathan Peakall, and from my son, Patrick Moreland. Those are the folks who were given the daunting task of teaching me how to write code for the microcontroller. The motor, which has an additional microcontroller in it, was provided by the robotics company for which my son works. A very short video of the array working can be viewed by going on and searching "trackingQT1."

There was a good deal of welding involved, and the photo of the rocker arms shows a bit of the welding set up. I used a TIG welder for all the mild steel, which I later had galvanized, the stainless and the aluminum.

Each morning the controller wakes a bit before sunrise, elevates the array until it hits a limit switch which sets the beginning point for the day. It takes a few minutes to establish contact with a GPS satellite to determine the day and exact time, checks look-up tables that were derived from sun charts to find the correct orientation to begin the day, and sets the array to that angle. It corrects the position hourly until just after sunset when the array is returned to its steepest angle (to help prevent dust build up), and goes to sleep.

I'll be happy to answer questions, and I'll be happy to share any part of the programming code.

michael 03-24-13 04:45 PM

6 Attachment(s)
First photos: These include the beginning stages of preparing for the frame, the concrete base, and finally a shot of the home-made rocker arms before they were galvanized.

michael 03-24-13 04:56 PM

6 Attachment(s)
Photo group 2: Prototype of array mover where I learned how to connect with GPS and how to control the motor. Views of the control box showing the microcontroller and GPS modules. View of the limit switches to set the day's motion as well as to disable the power in case of an error.

michael 03-24-13 04:57 PM

2 Attachment(s)
Final photo group showing the back and front views of the finished array

greif 03-24-13 10:16 PM

Good job michael

Exeric 03-25-13 02:17 PM

It sounds and looks very sophisticated. Quite an accomplishment.

Daox 03-25-13 03:33 PM

Very impressive setup.

What made you go with vertical tracking, but not horizontal tracking?

Also, would you care to share how much $ you have into that setup?

michael 03-25-13 05:05 PM

Hello Daox, If you mean why single axis vs two axis tracking, it was far too complicated for me to design a two axis tracker, and it wd have taken several to mount 24 panels. Also, our local codes allow a nearly permit free array as long as it isn't taller or higher than 6'. If you mean why an east west axis vs north south axis, I had a couple of reasons. First, the site lent itself to an east west axis; that's where the room was. Second, we're in a bowl created by surrounding trees that blocks the sun until it is 15-20 degrees above the horizon. N-S axes turn the panels directly toward the sunrise and sunset, those are the best angles, and those were the times when we had least access to the sun.

We have quite a bit of money in the set up, as you might guess. The panels cost about $900 each. I think I built the array for about $3000, and most of that went into the aluminum I beam and channel. None of the metals were cheap! And that doesn't count the cost of the TIG welder that I bought used for about $1500. We got a rebate from the electric company for about $5000 and a tax credit of about $11000, both of which mean that folks like you helped me build this thing, I'm ashamed to say. The solar industry has got to get off welfare, but for that matter, the same is way overdue for the oil industry. In the end, we were out of pocket about $28k for the thing, all the little details included. It's rated to last a minimum of 30 years, but unless electricity goes up a bunch, it will never pay for itself because our electric bill was only about $1200/year before the array; now it's zero. It just seemed like the right thing to do with the cash we had at the time, and it was the most fun, challenging thing of that sort that I've ever done. I guess the failure to break even aspect of it was just the price of admission. mm

Daox 03-25-13 09:09 PM

If you over produce, do you get paid by your utility?

michael 03-26-13 01:16 AM

Theoretically, yes. State legislation requires PG&E to pay consumers for overproduction. In the past, at the annual settlement date, the utility kept the overproduction but charged for any underproduction. Now, by contrast, they are required to pay, but they pay at a rate they call "wholesale." For the last two years, we've had a credit balance at the end of the year of $400, but the wholesale value for that has been $20, so you can see there's a pretty good mark-up in the utility business. The practical answer to your question is: "No!" mm

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