Anotherpower.com Forum
Project Journals => User Journals => RossW => Topic started by: rossw on July 17, 2012, 05:43:59 pm
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So.... there I am, sitting quietly working away, minding my own business, when I get accosted in IRC by a regular, wanting help and ideas for controlling the tracking on his solar array...
I pitch in a few ideas, and another regular puts his hands up "I'll have me one of them too!". Then a third....
So I'm planning to document here what I'm planning so others might chip in, pick up on my oopsee's etc.
Step 1 was to decide the basic operation. Sun-followers have ended up being too unreliable. Not because of their design, but because of the environment. Clouds, weather etc. Combined with the reliance on good construction, requiring optics, mounting suitably etc, we ruled that out for this application.
Instead, we've elected to use a time-based positioning system. Sure, it's not as accurate to position as a sun-tracker under ideal conditions, but it's "close enough" virtually all the time, even in broken sunlight, and it won't hunt.
That does imply it needs a clock of some sort, so finding a suitable board was the next stop. It also needs to be programmable so we can make it do what WE want. It needs moderately accurate timing for the drive times, and wait times. It needs enough outputs to operate east and west drive, and optionally elevation if its a 2-axis board. It would be nice if it had inputs for limit switches and/or manual drive. If there was interest or demand, it might be nice to monitor the supply voltage so the actuator drive time can be adjusted automatically if volts are up or down a bit. It might also be nice if it could monitor panel voltage or current, ambient temperature, array temperature or even just sunlight level. It would also be nice if it could be used to log data!
Fortunately, I've used some small "PLC" boards for a number of my own projects, that tick all these boxes. Smallish, reasonably low cost, 8 digital outputs, 8 digital inputs, 3 analog inputs and up to 8 temperature sensors, will take a few thousand lines of program, has a built-in webserver and ethernet interface!
My next step has been thinking about how to make it work out sunrise time sufficiently accurately to be useful, AND so it can be used by multiple people without having to rewrite the code each time. The plc logic engine doesn't have lookup tables, or floating point maths. So I've been playing with some approximation techniques using purely integer maths, and trying to estimate sunrise at an arbitary latitude/longitude to within about 15 minutes. I'm getting close.
Once I have that I'll move on.
The current plan is (starting at sunrise) - drive the arrays west for a small time - around 2 seconds - every 15-20 minutes. The exact times will vary depending on the time of year (length of day).
About half an hour after sunset, to move the panels to a mid-way "park" position. This should minimise the wind loading and maximise the chance that any overnight rain will wash the panels clean. About half an hour before sunrise, drive the panels fully east ready to catch the sun, and so the cycle repeats.
Each night, it will need to recalculate the sunrise/sunset times for the following day.
The board has timekeeping in software, but with its internet connectivity, will go out and synchronise itself with the very accurate internet NTP pool. This means the device won't need backup batteries, or to have its clock set etc. It'll just work. (It will need to be told your lat/long, and the time your actuator takes to drive).
So, any thoughts, comments, "please add" etc - now's the time to do it!
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Thank you Ross for taking time to do this.
I have some old digital readout sensors for my lathe and mill. I out grew the little 3 in 1 machine and sold it. The guy who bought it said he didn't want to mess with them so.... maybe I could make use of one or two of them for feedback as too the trackers current location? Whatcha think?
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maybe I could make use of one or two of them for feedback as too the trackers current location? Whatcha think?
I don't know that the scales are suitable for use outside like that.
If you wanted some feedback, you could rig a potentiometer to give feedback perhaps (a weight on an arm, use it like a gradiometer) back to an analog input....
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I have been working out the pros and cons of a tracker, and in the end the tracker will be the best.
I have most of everything I need at this point, except time.
Any which way, I have also come to the conclusion mine will be built to have a shade for the panels as well.
Your "parking" idea seems like a perfect time to also deploy the shade, as well as anytime NOAA has a warning for hail and/or high winds.
I think I will have a pic controller, interfaced to the PC that can send it a "park and shade" when such a warning is issued.
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I think I will have a pic controller, interfaced to the PC that can send it a "park and shade" when such a warning is issued.
This device has enough inputs that it could easily have a single input pin you drive active to say "Please park, NOW!". It wouldn't even be out of the question to make a "high wind sensor" (little more than a stiff wire, a small sail on the top, and a contact ring around it) that could trigger the board to park. (or in your case, park and deploy the shield - just another output and timer)
You can set outputs from a host on the internet (assuming it's connected of course), so one of your existing servers could make the call that there's a storm comming and send a "shutdown and park" command to the tracker.
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Just so we are on the same page.
Are you thinking along the lines of an antenna like wire with it's lower part inside of a pipe, with a ball of some sort on top thats just large enough to catch the proper amount of wind.
When there is enough wind to flex the wire into the pipe a connection is made.
The PIC would need some logic for how many times this needs to happen or not happen over a certain time period to change between the park, and normal operations.
Am I anywhere close?
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Just so we are on the same page.
Are you thinking along the lines of an antenna like wire with it's lower part inside of a pipe, with a ball of some sort on top thats just large enough to catch the proper amount of wind.
When there is enough wind to flex the wire into the pipe a connection is made.
The PIC would need some logic for how many times this needs to happen or not happen over a certain time period to change between the park, and normal operations.
Am I anywhere close?
Thats about exactly what I was thinking, yes.
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Ross,
How about thinking a little more like a CNC mill or lathe?
Say, a Gecko driver board and some NEMA 23 stepper motors and toothed belt drive. You'll need some sort of positioning sensor, like you say maybe a pot and an AD converter or even an encoder for a feedback loop.
All readily available and reasonably cheap.
Simple plot for a curve, say about 20-30 points, should put you very close.
Program says "It's 10:15AM, where should I be?", look at the pre-plotted table and go there.
Kevin
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Ross,
How about thinking a little more like a CNC mill or lathe?
*WAY* more expensive and complicated than the vast majority of people want/need.
MOST people just use a conventional linear actuator. They're cheap, weatherproof already, and designed for the job. Don't require any fooling around.
The controller board I've already got 5 or 6 of them around my place, running 24/7 for more than a year.
I've got 30 or 40 of them out on other sites also running 24/7, in all sorts of environments, and have never had one fail. Only ever had one that has spontaneously rebooted (although I'm still not sure it wasn't something else that caused that). That's the sort of reliability I want. And for under $60 for the board, there are not too many other options around that include ethernet.
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the Sat jacks have encoders on them or all mine have. Either a microswitch or a mag pickup. So feedback is possible with those.
I am currently using time based tracking track 8 seconds every hour between my shade areas. I don't get as many hours of sun as I would like but trees grow and create shade. The curse of living "in" the timber.:o
Tom
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And if you do not have ethernet available to the solar panels????
Ralph
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And if you do not have ethernet available to the solar panels????
Ralph
Ralph;
Why would you need a network connection @ the panels? They most likely already have wires to carry a positioning signal and power to the motivator? Mine run from a computer and I simply switch the power leads to the actuator from inside the building. The thing needs battery power anyway so is simple to just switch that. I don't see the ethernet point here? This computer is my local file server so it runs anyway and a simple crond job handles the switching via a USB relay board.
It really helps folks understand if you "quote" the post you are responding to. Every post has a "quote" button for this very reason.
More geeky folks probably have network everywhere on their place. Plus there is wireless networking.
Just saying...
Tom
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And if you do not have ethernet available to the solar panels????
Ralph
I will not need Ethernet at the panels. I doubt anyone will really unless they decide to put their batteries and everything right at the pole. I will simply run the control/signal wires from the relay board to the actuator itself. Most use electric linear actuators from the c-band satellite days. These actuators ran from power supplied by the receiver in the television room. So, the power required was usually by way of a couple of 16 gauge wires along side the lna/b etc cables depending on the distance from the receiver to the dish.
My system will be a bit different due in part to having a 4kw array on one pole and tracker. I will be using a hydraulic scheme. However, it too will be close enough to my battery/electronic shed as I will not need any communication network at the pole.
Hope this helps.
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I will be using a hydraulic scheme.
G'day Watt.
Ages ago I saw a hydraulic PV tracker setup that didn't need ANY brains to operate, the guy simply put a tube by the panels and when the sun heated that said pipe the oil heated and expanded and thus moving the cylinder causing the tracker to move. As far as parking goes at night the oil cools down and the unit automatically parks.
Simple design but one can see many slabs of beer to get one going......
Cheers Bryan
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I will be using a hydraulic scheme.
G'day Watt.
Ages ago I saw a hydraulic PV tracker setup that didn't need ANY brains to operate, the guy simply put a tube by the panels and when the sun heated that said pipe the oil heated and expanded and thus moving the cylinder causing the tracker to move. As far as parking goes at night the oil cools down and the unit automatically parks.
Simple design but one can see many slabs of beer to get one going......
Cheers Bryan
Sweet Bryan, I look forward to the beer part! Great idea too.
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Ages ago I saw a hydraulic PV tracker setup that didn't need ANY brains to operate,
I've seen several, but from all my reading, these totally passive devices seem "twitchy" at best. Often lethargic and slow, frequently confused by even a light breeze... but to each their own!
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I helped a friend put together a single axis tracker. We didn't want to mess with sun tracking either. We used and old Motorola Oncore GPS for the time and date. Accelerometer for panel angle. If I was to do again I'd probably use a DS3231 for the time, I just used one of those and was happy with it. Might have to correct the time occasionally, that was nice about the GPS, always on time.
Jonathan
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I will be using a hydraulic scheme.
G'day Watt.
Ages ago I saw a hydraulic PV tracker setup that didn't need ANY brains to operate, the guy simply put a tube by the panels and when the sun heated that said pipe the oil heated and expanded and thus moving the cylinder causing the tracker to move. As far as parking goes at night the oil cools down and the unit automatically parks.
Simple design but one can see many slabs of beer to get one going......
Cheers Bryan
They are not exactly great.
At least one major retailer in the US stopped selling them, and refused to accept returns purchased from ther retailers.
(who accepts returns of items from other retailers?)
Here, the temp has almost nothing to do with where the sun is, ever.
I am just saying a temp based system wouldn't work in this area.
Co/Amanda had the right idea, if/when combined with a slow tracker or time delay.
I have my own related circuits/sketches somewhere, if I can find them.
Simple stuff.
G-
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Been a while between posts. This project hasn't died. The first couple have shipped, and waiting on delivery to their owners.
Have had a few additonal features that have gone in, which includes manual east/west, improved code for parking that will enable it to UNPARK and resume tracking after a specified time, an alarm to warn you to move your fingers before it moves (can also be used to operate the hydraulic pump for hydraulic systems, or to release the brake, or enable power etc) - for a variable time before any movement is made.
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Ross has added another feature to this tracker for us. That is a " Wash " mode. This will be handy for folks like me who only get rain a few times a year.