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 Youtube.com 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.

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.

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.

Final photo group showing the back and front views of the finished array

Good job michael

It sounds and looks very sophisticated. Quite an accomplishment.

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?

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

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

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

Interesting. I guess I've heard it all now. Some places pay more for the energy you produce than what you pay for it. Some pay the same, and obviously as your case is, they pay less. Oh, I guess there are places that still don't pay anything, so at least you get something! :)

One additional note: Early in the design phase of this project when we were first working with the sellers of the panels, I spoke of my desire to build a tracking array based on calculations that showed I could achieve a 25% gain in generation over a fixed array. We were told that it would be easier to simply increase the number of panels by 25%. It would have been easier, true, but it would have added another $6k to the project, and we were out of room because the array was already planned to be 65' long and a tight fit as it was.

For two years now, we've generated an average of 24kWh per day. The normal maximum generation on a clear day is about 4800 watts even though the array is rated at 230 x 24 = 5520 watts. It has gone as high as 6000 watts on certain days when a strange "edge-of-cloud" phenomenon happens, and the sun's light seems to be concentrated or focused by shining past the edge of passing clouds. I'm imagining pouring a concrete pad in front of the array on which I'll place reflective mylar to boost the generation during winter months while the array is in a fixed, steep angle as the sun is in a low arc. The array is wired in three strings of eight panels each, so I'll start with an experimental reflector on one of the strings in order to compare the efficacy of the reflector to the panels without a boost. The generation rate of the panels rises as the temperature falls and vice versa, so boosting generation via reflected light may not work in summer, but it has a good chance of working in cooler weather as the additional heat on the panels would be more easily dissipated.

I have a "Kill-a-watt" type device on the generation loop, so I can see instantaneous generation, and it keeps a record of daily watt-hour totals.

I've always heard of people wanting to experiment with reflective surfaces to increase output of solar panels, but I've never seen anyone actually DO it. I look forward to seeing what you come up with!

I'll see what I can do to satisfy your curiosity. mm


I just noticed that I put in the youtube search name incorrectly. The instructions should have been to search TrackingQT1 on youtube.

Michael,

I thought, I gave a lot of thought to my install. My install.

Out standing job!

I wanted a one axes system, just did not have the time. I did come up with a manual North / South tilt, it helps a little, not like yours. Once I built the platform, I had a company that installed Sun Power panels for $5k, included under ground 1 1/2" pipe to electric panel.

I have observed the magnifying effect of the clouds and the sun also. Very cool when it happens.

Had my system this Feb, 2013 for full 3 years. Last month 'Feb' bill was $2.00. I really don't pay for electricity. :eek:

With Sun Power you get free monitoring, here.

Check out, month and year values on link, cool.

Vern

Do you get any shadows during part of the day and/or year? If so, how much shadow on a group of three panels can occur until you lose the output from that group?

Since your panels are probably much cooler than roof mounted systems, you can then probably tolerate a bit more heat gain from using a reflector. I missed how the tracking is controlled - is it real time, or is it on a timer?

Another thought: does the tracking motor typically end the day at the same angle as the beginning of the next day will need? Can you "park" the angle as steep as possible in the winter overnight to minimize snow - if you ever get snow?

Hello Vern2, Nice installation! While visiting in Vemont a couple years ago, I stumbled across a utilities company that had a large array of solar panels with a seasonally adjustable north-south orientation. A couple of workers with wrenches could change the tilt of these huge arrays. You can see it from above if you go to Google Maps and look for the point where Westminster Heights Road exits going north from I-91 near Bellows Falls.

Thanks for the links. mm

Hello NeilBlanchard, The array gets a few shadows early in the morning during a short part of late fall and early spring as well as some late in the day shadows during summer when it is awake until late. The panels are in groups of eight, and it takes only a little bit of shadow on the corner of one panel to knock out the whole group. If I were doing it again, I would look more seriously into panels that have individualized inverters attached to the panel so that each panel's reaction to shadows would not affect any other panel. In our situation, shadows are only present at the very beginning or end of the day, so the loss is quite minimal.

The tracker is based on real time, that is, it connects to a GPS satellite each morning to collect the time and date, and it continues to check throughout the day. We don't have snow here...well, once every ten years or so we might get an inch or two, but in general there's no snow. The tracker parks the panels at night in a near vertical position to limit the collection of dust from cars passing on the nearby gravel road. In the morning, each day's setting comes from a look-up table based on the date and time string from GPS and varies by season. mm

Spent a few days in mendocino ten years ago on vacation .... good hippy ville :)

I always thought tracking by computer would be better then the sensors following the sun

Good job

The problem I had with sensors tracking the sun was coming up with an alternative means of finding the correct orientation when the weather is overcast. Even on an overcast day, it's somewhat better for the array to face where the sun is behind the clouds. There may be a great alternative; I just couldn't think of one. The look up tables, however, are error free and very precise, and the controller can sleep between moves which is a very low power state. It wakes every hour, moves to the place where it will be exactly facing the sun in half an hour, and after a five second motor move, goes back to sleep.

Michael,

My panels can be adjusted between 7 to 30 degrees. I need wrenches and some help to change angle. The offset of sun to panel angle is small, going back and forth between those two angles. So basically I have a summer and winter tilt only. I'm at a 31 degree latitude.

That is a BRILLIANT installation. Hard to believe it is DIY.

Michael, you obviously know your stuff and have thought through this project way more than I ever could. You make me doubt my conclusions about one axis tilting to match the sun's inclination.

I used pvwatts to estimate how close a manual tilt 4 times a year would come to daily continuous, and IIRC I thought > 90% of ideal collection would be achieved with manual. What do your numbers and calcs say ?

I am unhappily surprised to hear the price you paid. I thought panels were under $1/watt these days; from your post it sounds like you paid closer to $4/watt.

Ugh, I lost my post.
Here is a recreated spreadsheet that uses PVWatts to check insolation using various tilt strategies. I get that 4 season manual N-S adjustment is ~ 92.5% of continuous N-S.

Sound about right, Michael ?

Hello ELGo, Thanks for your kind words. No one was more disappointed than I was to pay $4 per watt for our installation, but I just read an article that reported that the average installation of residential or small commercial solar arrays in 2011 was pegged at $6.10 per watt. That's when ours first went online. My numbers, as you call them, are a dimly remembered event from three to four years ago, so I can't answer your questions with any degree of certitude, but I'd agree with your figures. I plan to build a smaller, seasonally adjusted array in the near future and consider it good enough. mm

I envy you :thumbup:

If your smaller array could take advantage of E-W tilting, your DIY skills would really pay off.

What is your estimated $/watt for this new array ?

I poked around on the web a little, and came up with:
$1/watt panels
$0.70/watt Enphase inverter
$0.50/watt manual tilting support to put on the end of a pole

This is a sweet... install it looks great.