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Topic: dual axis solar tracker for mobile/portable installation of solar panels (Read 3381 times) previous topic - next topic

Robin2

I strongly support @mauried. The KISS principle is essential.

The sun doesn't do 360deg unless you are above the Artic circle.

If the device is to be deployed at a regular property, instead of a motorhome or boat, then it's utterly improbably that the property owner doesn't know the direction of the sun at midday, and can't find out within a day or two.

Tracking the sun was successfully figured out with great precision 5000 years ago.

The more moving parts the more opportunity there is for something to go wrong - especially something that is exposed to the weather 24/7. Would the "helpless" owner be better with something that has extra energy but breaks down and needs to be fixed by a specialist or something with less output that doesn't break down? Will the extra energy comfortably pay for the breakdown service and leave a significant "profit"?

You need to analyze carefully the extra energy you will get from tracked vs stationary panels. This website can help http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

I have 3x 80w solar panels on my boat and they lie flat on the roof for two reasons. It would be grossly uneconomic to make a strong enough "machine" that could elevate and rotate them. And, while I could orient them manually (lift them with a piece of wood under one side) I would have to readjust them through the day and I would get less output if (as is likely) I forgot to readjust them. As it is they will have paid for themselves in three years by making a very nice contribution to my electricity needs - except, perhaps, in Winter.

...R

Thanks greynomad, mauried, and Robin.

@grey,
Thanks for that information. Do you happen to have a diagram of how to install the motor control shield with the H - bridge?

@ mauried,
The economics that I'm looking at, using this system to maximize efficiency, would be a net increase of about 20-30%. Also when using this system this would translate into an additional of about 150 amp hours on a bank of 12 marine deep cycle 12V batteries.  Whereas adding an extra panel to a stationary array would only give an increase of around 15-20% and an additional 105 amp hours. (according to my research anyway, I'm pretty good with numbers but please let me know if you come up with something different as my calculations may be off.)  also making it automatically adjustable means that you can park your rv/trailer/truck in any position relative to the sun. Press a button and it instantly finds the best position to maximize solar power.

@ Robin,

Simplicity is my aim for this project. I would have only 2 pivot points. X-axis is essentially a lazy Susan with a hole in the middle thru which my power & com wires will run (there's a reinforced conduit for increased stability and securing it to the rv there as well.) I chose this option for the ease of use. It gives you the finest range of motion. No matter your orientation to the sun. And the y-axis is pivoted off the edge to give it better directionality, as well as to allow for a fold flat storage option during transport or high wind storms.

Robin2


Also when using this system this would translate into an additional of about 150 amp hours on a bank of 12 marine deep cycle 12V batteries.  Whereas adding an extra panel to a stationary array would only give an increase of around 15-20% and an additional 105 amp hours.


So all this complexity will get you an extra 50Ah or about 10% compared to the simple solution?

How much is an amp-hr worth to the project?

I'm guessing that 12 marine deep cycle batteries probably have a nominal capacity of 2400Ah - or a realistic capacity of 800 to 1200 Ah. What brand of battery? How many amp-hrs will you move in and out of them in a year?

You will need to look at the overall energy balance. How many Ah will be used each day and how many are  supplied by the sun on the best and worst months. If your consumption is well within the capacity of the solar panels you may have too many batteries and if it is not then you need more solar panels (if the project can afford them). Treat the batteries as consumables rather than assets.

...R

Standard car battery is usually around 40 amp hours. So closer to 4800 amp hours on a bank of 12, (give or take considering battery health and age)  I'll be using 12 marine deep cycle batteries. So you could expect that number to be closer to 5000Ah. If you were running all the appliances in the rv in 12v mode, and all at once, you could expect to see the batteries die within 5 hrs. (less if you want to use the inverter to run a few 120vAC appliances as well.)  This is of course without using the solar power system to recharge the battery bank during use. Now if you use the solar system (without a tracker) you are adding an additional 105Amps per hour to your battery bank. Now let say that in perfect conditions you have a full 8 hours of daylight,  and no clouds.  That comes up to 840Ah per day add a traking system and that jumps to 1200Ah.  Per day. Giving us a total of 6200Ah on our battery bank. Which would give you an additional 1-2 hours using All of the appliances at once. Now this is of course an extreme supposition of the use of power system. So if you were looking at average VS. peak usage you could expect the battery bank to last around 8 hours with average use but peak usage spikes throughout the day could reduce that to about 6 hours.  Now the charging system is a dual stage intelligent 7vDC trickle/10vDC blast charger. It activity monitors the battery bank (charge and load) and applies the correct amount of charge to the battery bank.  This also helps maintain the health of the batteries. The solar system would help maintain a "topped-off" charge level. During the day and allows for full usage of the battery bank at night..

#19
Jan 27, 2014, 06:55 am Last Edit: Jan 27, 2014, 07:00 am by Fauxfire27 Reason: 1
Okay, I think that we've gotten well off track. The reasons why I need to build this are all, because I want to. What I need is help getting it put together. As I said I'm not an electronics engineer, nor a programmer. I need help understanding the basics of building the control board, so that it reads the inputs from the PE sensors and controls the motors. I also need some help programming it. i know what I want it to do, but I don't know how to make it do it.  These are the points of my project in which I need guidance.

@greynomad And @tom

I want to take this opportunity to thank you for your time and patience with me :-) I know that dealing with noobs is difficult. You have been very helpful and I have a few more ideas on how to connect my motors to the uno board. Now all I really need is the electronic parts and figure out how to connect everything and then figure out how to program it. :-)

Any suggestions?

Graynomad

Quote
The reasons why I need to build this are all, because I want to.

And that's all the reason we need to do stuff eh?

I can't recommend an actual shield because I've not used any of them, so unless someone pipes up and says that the X shield is great you'll have to start searching and reading reviews. I will advise against buying stuff from any vendors that don't have good documentation and support. This means most eBay vendors. Personally I'd rather spend $30 for a board from somewhere like Adafruit or Sparkfun that has an active forum and good support  (I assume, I've not required it from them) than pay $3 from Foo Bar Electronics and get no support. That's not to say there isn't a $3 vendor with good support, just don't let your wallet do the thinking.

So to get the ball rolling you need the following

Rotary mount -  Lazy-susan or other type of thrust bearing. The bigger the better because that reduces the mechanical advantage things such as wind loading will have. Or a small bearing and some form of dolly-wheel support as far from the pivot point as possible.

Azimuth control - Probably a worm gear I think. That will give you a high gearing and unlimited rotation. Can be driven by a DC motor or a stepper. I don't think direct drive is an option because this may get pretty heavy and the inertia will be very high.

Azimuth detection - At the very least you need to have a single detection point so you can resync the device for parking. Say an opto interrupter at the "north" location.

Altitude control - You said linear actuators, good as anything but 180 degrees is not achievable I think as at the ends of travel the three pivot points will be in line (they may even go over centre) and the actuator will be working against the hardware. Also when the pivot points are almost in line (ie at the start or end of travel) the force required is huge compared to that required once the panel is raised a few degrees, this means a lot of stress and larger actuators. Some careful thought needs to be thunk here, unless there's some clever mechanism I've not seen (possible) sticking to ~90% will be much easier, and as I said before all you need anyway.

NOTE: All the above is moot if you use say another worm gear instead of a linear actuator. But a worm gear will be small and thus have very poor mechanical advantage, once again causing a lot of stress and as well no matter how well you make it there will be play and this will manifest as a large movement out at the end of the panel(s)  and large shock loading in the wind.

Altitude detection - Not really required I suppose, just limit switches for end of travel in both directions.

Arduino stuff - Arduino Uno, stepper shield, motor shield, LDRs, opto interrupter, limit and control switches, that's probably about it for starters.

Note that this approach is not really scalable, meaning that if you design for one panel you can't just start adding panels. You have to decide now on the max panels that will be needed and design for that number. The difference between a mechanism to handle 1 panel and that for 8 will be huge.

That's all I can think of for now.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

Robin2

12 x 40 was 480 when I went to school, not 4800. Maybe I need a new calculator for the new maths.

If you imagine for one moment that (say) a 100Ah battery will give you 100Ah of useable power you are sadly mistaken. Discharging any battery (including deep cycle batteries) completely will damage it.

Many people who use batteries for their main power source will recommend that they are never discharged below 50% but that is a rather simplistic approach for deep cycle batteries. As far as I can see the life of a battery depends on how many amp-hrs are put through it. It is also essential to ensure the battery is fully recharged at least once every 7 to 14 days (more often is better) and that it is not discharged excessively (I suggest no lower than 30%). It is relatively easy to charge a battery back to about 80% but the last 20% will take 8 hours or so at a relatively low current flow - large solar panels are no help at that stage.

I have been living from batteries charged by a diesel engine for 5 years and I have solar panels for the last 2.5 years. The solar panels save a lot of diesel in summer. I have two battery banks so that one is on top-up charge (the last 20%) while the other bank is in use and I swap them regularly.

...R

Graynomad

Yes all true AFAIK.

Quote
It is relatively easy to charge a battery back to about 80% but the last 20% will take 8 hours or so at a relatively low current flow - large solar panels are no help at that stage.

Exactly why with my next camper build I will use LifePo4 Lithiums, none of those issues.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

#23
Jan 27, 2014, 11:59 am Last Edit: Jan 27, 2014, 12:14 pm by Fauxfire27 Reason: 1
You are correct, it would be 480. Which means that my calculations for the relative usage time frame is very far off. Which also means that the solar efficency needs to be at its peak for as long as possible. Which compounds the need for an accurate automated solar tracking system. I Thank you for the correction. I think that I may need to upgrade my solar power system with supplemental wind turbines now as well. I've been looking at some options for Mag-Lev vertical axis wind turbines. I'll also need to upgrade my charging system to accept additional power inputs.

Robin2

I have a very simple philosophy for wind generation.

If you are using a mobile home or a boat where there is sufficient wind to make a wind generator worthwhile you should move to somewhere more pleasant where there is less wind. :)

In an attempt not to be entirely negative I am using US2200 golf-buggy batteries which seem to last reasonably well in spite of my abuse. They are 6v batteries so you have to use them in pairs to get 12v. They have a very clever device for getting the lids off the cells easily so you can top up the electrolyte. When it is tedious to get at the cells you won't check them up often enough.

...R

Graynomad

Yeah turbines are a big fail with motorhomes. You should have them on a huge pole (5-6M at least) which is a pain to set up and they are noisy as hell. Everyone I know who has tried them binned them after a while.

And +1 to not being in a windy place anyway :)

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

Yes, I would have to agree with you on the wind turbines, at least traditional wind turbines anyway. I believe that I have found a viable option in a frictionless (not friction-free) Mag-Lev vertical axis wind turbine. Depending on the design it can work on either AC or DC and in less than 3 mph winds. I'm studying the designs right now. But I still need help with the solar tracking system. I have ordered an uno board and the design faze of the panel mount, pivot,  and turntable is complete. I have a 48 inch linear actuator for the y-axis and a 12 volt drive servo/motor (I'm designing this portion like a bike drive chain &  sprocket, except with pulley wheels and a drive belt)  for the 360 degree rotational x-axis and I have purchased several limit switches. I now only need help with wiring everything together (diagrams would be greatly appreciated)  and programming the software. (once again, any suggestions or diagrams would be greatly appreciated.)

Nick_Pyner


Yes, I would have to agree with you on the wind turbines, at least traditional wind turbines anyway. I believe that I have found a viable option in a frictionless (not friction-free) Mag-Lev vertical axis wind turbine. Depending on the design it can work on either AC or DC and in less than 3 mph winds. I'm studying the designs right now.


If you are short of watts, I submit you will be better off studying how you can install another pv panel or two, rather than fartarsing about with wind turbines, because fartarsing is all its going to be.  It's just Popular Mechanics stuff. Indeed, one of the the better justifications you have for going to so much trouble with tracking PV as you propose, is that it helps you avoid having a wind turbine.  There is more fantasy written about wind turbines than any other source of power, which goes quite some way to explain why all those turbine-on-every-rooftop projects never happen.

mauried

Before you even think about any kind of vertical axis wind turbine , make sure you examine closely the
power output versus wind speed for the turbine you are considering.
All VAWTs fall into 2 categories.
They are either a Savonious rotor design, which are fairly common , but extremely inefficient as they are a drag rotor and need
hi wind speeds to make any usuable amount of power.
The other type is a Darrieus vane which do work well, but are extremely large and need very substantial mounting structures, so are not viable for most people.

Robin2

There is no point making a wind turbine that works at 3mph because there is f__k-all energy in wind at 3mph. It's just an entertaining garden ornament.

Useful wind turbines are big (100kW and over), mounted on tall structures and located at sea or on mountains.

Small turbines may be useful for trickle charging batteries when a property is not in use or running small sensors at remote locations - though I suspect solar panels are more economic.

...R

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