Solar panel indexer

[Steamwhisperer]

Love my camping and as my job entails talking to up to 200 people everyday, when we go we like to get to places that have no people which also means no power etc.
I have a fold out solar panel and deep cycle battery that gives us power for the fridge virtually indefinitly.
Holidays generally involve a chair and reading either Old Glory or Australian Model Engineers Workshop :D
Thing is, I have to get up occasionally and move the solar panel out of the shade and re point it at the sun.
Very tiring work.
I have a box with all the gear that I mount on the back of the ute so I figured if I mounted a set up on top of this box for the panel it would get less shade and if I incorporated an indexing arrangement I could get back to sitting and reading.
It involves a pivot, a frame to hold the solar panel and a spring loaded detent to stop it blowing around in the wind.

Phil

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[Michael G]

Sorry Phil - I must be missing a photo. Where's the one with the long bits of string so you don't have to even get out of your chair?

Michael

[jhovel]

What about building a proper tracker, Phil? I seem to remember a mechanical method that involves either gas or liquid expanding as a result of the sun shining on it - and moving the panels as a result. In the morning, the first sunshine swings the thing right around from the position of the previous sunset.... alternatively of course there are electronics and eleictric motors to do that .... less your cup of tea I understand... :)

[Oldneweng]

What about building a proper tracker, Phil? I seem to remember a mechanical method that involves either gas or liquid expanding as a result of the sun shining on it - and moving the panels as a result. In the morning, the first sunshine swings the thing right around from the position of the previous sunset.... alternatively of course there are electronics and eleictric motors to do that .... less your cup of tea I understand... :)

A mate described a system to me a long time ago that is pretty simple. When the sun moves, this idea causes the light to hit a photo diode which operates a motor. When the panel is moved by the motor, so the sun is no longer shining on the photo diode the motor stops.

Dean

[Steamwhisperer]

Sorry Phil - I must be missing a photo. Where's the one with the long bits of string so you don't have to even get out of your chair?

Michael
Thought about that Michael but they would just be another set of ropes that I can trip over in the middle of the night while trying to get 8 hours sleep on a 6 hour bladder. :D


What about building a proper tracker, Phil? I seem to remember a mechanical method that involves either gas or liquid expanding as a result of the sun shining on it - and moving the panels as a result. In the morning, the first sunshine swings the thing right around from the position of the previous sunset.... alternatively of course there are electronics and eleictric motors to do that .... less your cup of tea I understand... :)
I actually looked into that Joe with a timer but after some light reading on the subject my head exploded.
When we were kids, to wake the chooks early up dad used a wind up alarm clock that would turn the light on in the chook shed. As the wind-up handle un wound, it would hit the light switch and on came the lights. That's about my limit on automatic stuff. :D

Phil

[mahgnia]

Why use a sensor?
The sun is pretty regular at 24 hours for each rotation, so just have a timer that triggers a motor to rotate the panel every hour by 15 degrees.

Andrew

[Steamwhisperer]

Hi Andrew
that's what I had planned when it all became too confusing.
Electronics and electricity I just don't get.

Phil

[Steamwhisperer]

A mate described a system to me a long time ago that is pretty simple. When the sun moves, this idea causes the light to hit a photo diode which operates a motor. When the panel is moved by the motor, so the sun is no longer shining on the photo diode the motor stops.

Dean


Thanks Dean, my head just exploded again. Photo dio whatsy:-

Phil

[jhovel]

Two EASY options without electonics:
1. Search Google on info about "passive solar tracking" - I found lots of information about high volatility liquids wich boil off on the sun side and condense on the shade side, until the weight of liquid balances, facing the panels into the sun.
2. Have a look at this video: https://www.youtube.com/watch?v=ljTJqQYSJ8g it used a small electric DC motor and two small solar panels arranged with opposite polarity. They drive the motor in the direction of whichever panel gets the most sun, until they both produce the same amount in opposite polarity, at which point they cancel out. Then the motor tops until there is a difference again.
Very clever, no electronics or control systems at all.
THe second one is particularly easy to adapt to your indexable mount.

[nadroj]

I've heard reported that the trouble with electronic tracking is they need a matched pair of sensors to work - one isn't enough.
If they are matched to begin with, they can drift after a while so as not to be matched any more. Then it doesn't work.
I saw a really big and expensive custom solar tracking installation that stopped working properly because of this.
Andrew's timer idea seems a better bet. Maybe they've worked out a solution to electronic tracking though?

[.RC.]

I thought Steamwhisperer already had an automatic solar panel tracker. Otherwise known as a wife. :D:D

[Michael G]

Why use two then? - If you put one sensor at the bottom of tube (ID painted matt black), then as the sun moved away, the output would drop. Unless Phil visits parallel universes (or the northern hemisphere I suppose), we know which way the tube (and so the array as it is attached to it) has to drive to maximise output, so it should be straightforward to use a wiper motor or something to move the array around.

:blowup: whoops - there goes Phil's head again...


Michael

[nadroj]

Dunno. What if a cloud caused the shadow?

[Michael G]

What if a cloud caused the shadow?

Getting more complicated again (and beyond my limited electronic knowledge) but if you compared the output of the panel with the output of the sensor that should be able to tell you whether it is a cloud (both outputs drop) or the sun moving (sensor drops faster than the panel).
You would not necessarily have to use a sensor when I think about it. If you had another panel that had some closely spaced vertical fins over the collecting surface if the sun was not directly overhead (that is, the fins were throwing more than minimum shadow) the output would drop. You could then compare the output to the unshaded panel.

Sort of like the traffic lights where the shield has fins in it to stop glare and/ or motorists seeing that light if they are not stopped at it.

Michael

[nadroj]

It's still 2 sensors, if a panel is regarded as a sensor.

[Oldneweng]

Why use two then? - If you put one sensor at the bottom of tube (ID painted matt black), then as the sun moved away, the output would drop. Unless Phil visits parallel universes (or the northern hemisphere I suppose), we know which way the tube (and so the array as it is attached to it) has to drive to maximise output, so it should be straightforward to use a wiper motor or something to move the array around.

:blowup: whoops - there goes Phil's head again...


Michael


This is basically what I described except that the sun's movement means that it shines on the sensor. Only one sensor required. When the panels are in position the sun does not shine on the sensor. It moves to the point it is shining on the sensor, which kicks in the motor.

The design as explained to me had 2 sensors, but the second one was to swing the entire unit back again in the morning. Phil could get his wife to do this for him as he drinks his wake up coffee. I think it was also to fit a parabolic reflective water heater.

Dean

[eskimo]

how will it know where to point if the day begins very overcast and doesnt clear till late afternoon

[Oldneweng]

In that case it won't matter where it points. :D

Dean

[eskimo]

how will it know where to point if the day begins very overcast and doesnt clear till late afternoon

Ahah
it can all be controlled using astro telescope software at any time day or night......the actual setup costs maybe prohibitive tho
maybe freeware is available????

[eskimo]

In that case it won't matter where it points. :D

Dean

but the panels could be missing out on 6 or so hours of sunshine. If the panels face east in the morning, along with the sensors with no sun due to heavy cloud cover, how will it know that it must/might have to face west in the arvo when the sun comes out?

[bob ward]

These guys in Laidley do a lot of farm and industrial solar systems. In their yard they have this 'look what we can do' fully tracking solar panel. The panel is probably 12' x 10' and is fully articulated around a centre pivot, it tracks dawn to dusk, winter to summer. Pretty cool. Photo was taken at 9am.

http://i237.photobucket.com/albums/ff28/sirrobertthegood/IMG_0171_zpsxyhsnoyi.jpg (http://s237.photobucket.com/user/sirrobertthegood/media/IMG_0171_zpsxyhsnoyi.jpg.html)

http://i237.photobucket.com/albums/ff28/sirrobertthegood/IMG_0172_zpszbvkod4l.jpg (http://s237.photobucket.com/user/sirrobertthegood/media/IMG_0172_zpszbvkod4l.jpg.html)

[nadroj]

That's a lot of hardware to improve panel efficiency.
I'm guessing the cost would be more than that of some more panels, statically mounted, with the same output and better reliability.
Good advertisment, but it made more sense when panels were expensive.

The aim here though isn't to improve efficiency, but to make camp life more pleasant by getting around the need to re-aim a small array.

Any chance you could ask how the self-tracking is done?

[simonl]

Nice work Phil!

I looked into a solar tracker project a few years ago that used 2 Cds (Cadium disulphide) cells. Each cell sits inside a tube facing the sun and the two tubes are separated by a barrier. The output is fed into a comparator. The comparitor output is then buffered and sent to an electric motor. If one cell has more sun than the other then the comparitor switches power to a small motor which rotates the panel. The motor stops when both cells are "roughly" equal in resistance, indicating they are equally facing the sun…..

Well, as you can see I really couldn't be bothered and since solar panels are so cheap these days I just ended up buying a bigger panel!

I estimate my 50L fridge uses about 25Ah per 24 hour period with the fridge fully loaded and an ambient temp of about 30 deg. I bought a 150W panel and coupled it to a good quality MPPT regulator and just never touch it. It runs the fridge indefinately now and I can restock with drinks on a hot day and not have to worry about it using up the aux battery.

A good quality MPPT regulator is worth the money. Most solar panels have their rated power at 18 - 21V and a standard regulator will just regulate that voltage back down to the required 13 or 14V which means you have lost some of the available power. Multi Point Power Tracking will reduce the voltage to the battery BUT they then boost the current which means a 150W panel has nearly all of it's 150W available. For instance my 150W panel produces its peak power at 18V. At 18V it puts out a max of 8.3A. However, when my battery is very low, the solar regulator puts in 14V (there abouts depending on which part of it's 4 stage charging cycle it's at) at 10A, close to it's max power.

As you would know, realeste is at a premium (especially with 2 kids and a ridgeback) so I have no room for a 150W panel so I built a slide underneath the roof rack and the panel just slides out and a spring loaded stand off rests it on the bonnet. If I face the bonnet at north (which means the fridge in facing south and in the shade) it has the capacity to pump 10A continous into the battery for a good part of the day, although it rarely gets that high a charging rate as the battery always maintains a reasonably high charge capacity. This also means instead of a massive 120Ah aux battery under the bonnet, I can get away with a smaller one and it does not get as deeply discharged meaning my aux batteries last many years.

I like you work Phil! Like you, the solar industry and cheaper prices has made a huge difference to camping for us!

Edit: in the bush, KISS principle works the best.

Simon362365362366

[BaronJ]

Hi Guys, Phil,

I have recently bought a 300 watt panel that I intend to mount on the roof of my camper conversion, though in my case the panel will be fixed. So I was very interested to read your post.

I've already built the converter to take the 56 volts and drop it down to 13.6 - 14.3 for charging the leisure batteries. I hope to be able to run just about everything from the panel during daylight hours.

One solar tracker that I've seen used the voltage difference between two cells/panels to steer the array for maximum sunlight, though unless you can get at the cell wiring, I doubt you could do this for a single panel.

[simonl]

Hi Baron,

Unless you plan on running an aircon or similar, 300W should be more than sufficient to run most things such as fridge, microwave?, recharging of electronic devices, and lighting at night.


I forgot to mention in my previous post, if I was to make a solar tracker for camping I would do as suggested above and just program a PIC to move a smaller stepper motor 15 degrees every hour. It's simple, effective and it only supplies power to the motor once every hour for a fraction of a second. Solar trackers that use Cds cells and the like, if not designed properly may end up trying to update every couple of minutes, and constantly leave the stepper humming if they cannot achieve a satisfactory position. This wastes unnecessary power and reduces the effectiveness of the tracker at liberating more power in the first place.


Also, on those really hot days it's also of benefit to run some water over the panel to cool it down. Panel power is usually rated at around 25 degrees and it's reduces in power at temps above this. If you look at the specs of the solar panel they have three figures, temp coeff of short circuit current (Isc), temp coefficient of open circuit voltage (Vos) and temp coefficient of power (Pmax) So with increases in temp, the current output of the panel increase BUT the voltage output decreases. Unfortunately the max voltage decreases with increase temp at a greater rate than the current increase and so the net effect with all panels is a decrease of their rated power at temps above that of their rated power. To give you an idea, a coefficient of 0.5 W/deg C is not uncommon. If a panel heats to 55 degrees (which is easily done on a hot day) then you have lost 15% of it's available peak power.

On a 35 degree day, my panel can be too hot to touch. running a small amount of water on it can boost it's output by 20% in these conditions. Of course if you are not camped near a river or near a water supply you may not have the luxury of wasting the water!

Interesting, a camping trip many years ago I was camping by myself and I derived a formula where I could plug in the time of year (No. 1 - 12) and my latitude and it would spit out the optimal angle to set the solar panel. I still have that nice piece of work as it's written on the back of one of my maps of the Vic high country.


Simon

[nadroj]

just program a PIC to move a smaller stepper motor 15 degrees every hour. It's simple, effective and it only supplies power to the motor once every hour for a fraction of a second. Solar trackers that use Cds cells and the like, if not designed properly may end up trying to update every couple of minutes, and constantly leave the stepper humming if they cannot achieve a satisfactory position. This wastes unnecessary power and reduces the effectiveness of the tracker at liberating more power in the first place.

on those really hot days it's also of benefit to run some water over the panel to cool it down.

I derived a formula where I could plug in the time of year (No. 1 - 12) and my latitude and it would spit out the optimal angle to set the solar panel. I still have that nice piece of work as it's written on the back of one of my maps of the Vic high country.

Simon

Another compelling reason to ditch sensor-based tracking. A timer is simple and reliable, and it uses less power.

Interesting to hear about benefit of cooling the panels.

May we please have your optimum angle formula?

Jordan

[Steamwhisperer]

First up I would like to thank everyone for their input with regards to tracking. It has been an interesting read and I actually understood some of it.
I'll probably stick with the manual way though for a while as I agree with Simon, the KISS principal in the bush is the best.
I will have to read your post quite a few more times Simon before I can comprehend some parts of it but some great info there.
I have a 180 watt fold out panel with MPPT feeding a 120 amp/hour deep cycle and like you the fridge runs indefinitely even with reloading during the day. Overnight the battery will lose 0.5 volts worse case scenario.
Using the panel on the ground just gave me 'something else' to step over on the odd occasions I actually got up out of the chair. :D
Mounting this to the top of the box on the back of the ute gives me less shadows to contend with as well.
One of the blokes at work has the same solar panel as me and a very old 100 amp/hour battery and a kid that is genetically predisposed to opening the fridge for no reason and still manages to keep it running indefinitely.
I think if I was to get all high tech I would go with the stepper motor and a timer (of some sort) that fires up at predetermined intervals as you suggest.
Camping sure is easier nowadays.

Hi Baron
300 watts, wow, I can only dream of that sort of power. :D
I was just thinking that mine, being a fold out panel, is actually two panels which I have to plug together (I think that's what I'm plugging together) when I set it up so maybe a possibility further down the track...no doubt a lot further down the track. :-

Thanks again everyone for the input.

Phil

[simonl]

Another compelling reason to ditch sensor-based tracking. A timer is simple and reliable, and it uses less power.

May we please have your optimum angle formula?

Jordan

See if I can dig it up and take a pic of it...

[simonl]

It was on the back of my Walhalla Adventurer map!

1st pic shows the finished formula and the list of variables. I actually worked it to the nearest day. Don't ask me why, mathematical completeness I suspect and the fact I was alone camping and had a bit of time on my hands!

The second pic shows some of my workings. It's obviously a sinusoidal curve. I used serveral boundary conditions to help. The fact that the earth tilts back and fourth by 23.5 degrees, summer solstice at 22/12, winter at 22/06 and two equinoxes at 22/03 & 22/09. The curve had to satisfy those conditions. The 30.4 figure represents my mathematical average number of days in a year and 365.4 represents the average number of days in a year including leap years although looking at that, perhaps it should be 265.25 (one extra day every 4 years) but it's not going to make a big difference to the angle. Like I said, it was more a mathmatical challenge for me than a practical application.

One way of testing the equation was to plug in a lattitude of the tropic of capricorn and the date of 22/12 and it should return a value of 0 degrees. 22/6 and it should be 23.5 degrees and so on. remembering that the angle is between the panel and the ground.


Enjoy!

Stupid computer still not letting me upload! I'll try again later..

[simonl]

Well I can't seem to attach pics ATM so here's the equation:

Panel angle = lat - 23.5COS(((m-1)x30.4 + D + 10)x 2pi/365.4)

Where:

lat = current position in latitude (decimal degrees)
m = month of year (1 - 12)
D = day of month (1 - 31)

Answer is angle of panel to the horizontal….

Cheers,

Simon

[BaronJ]

Hi Guys,


Hi Baron,

Unless you plan on running an aircon or similar, 300W should be more than sufficient to run most things such as fridge, microwave?, recharging of electronic devices, and lighting at night.

Simon

I am installing hot air heating, water heater, fridge, TV, shower and an electric step. So a fair bit of electrical consumption if everything is running.



Hi Baron
300 watts, wow, I can only dream of that sort of power. :D
I was just thinking that mine, being a fold out panel, is actually two panels which I have to plug together (I think that's what I'm plugging together) when I set it up so maybe a possibility further down the track...no doubt a lot further down the track. :-

Thanks again everyone for the input.

Phil

The panel that I bought is a poly crystalline one, exactly the same size as one you would see on a house roof assembly. I chose this panel because of it's cost compared to one of half the wattage and four times the price, just because it was sold as a camper specific product. It cost me less than £100.00p delivered from the local solar panel distributor. I also got the clamps and fittings supplied as well.

The additional costs was the aluminum channel that I bought to make the rails and the clamp fittings that hold it to the van roof.

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Here are some pictures of the roof rack and support pillars that I made.
The pillars are 35 mm round bar drilled right through and threaded with a slot machined in one end to fit the studs welded into the van roof. They are secured with a grub screw down the middle. The cross rails are simply nut and bolted to the long rails. The last picture shows the panel mounting brackets on the cross rails.

[simonl]

Sounds like a nice setup there Baron.

Are you using electricity to heat the water for a shower or is the power just for the pump?

If it's just for the pump then the intermittant use of the pump actually uses very little power compared to running a fridge anyway. When I camp, 90% of our power use goes into running the fridge, 9% into recharging the kids devices and 1% for our LED lighting at night!

Your heater might chew some juice, is it a diesel heater with a fan?

Edit: I agree about purchasing solar panels from camping shops. Buy a panel from a commercial solar panel supplier and you may get it for just over a $1 per watt. Then go to Rays or Anaconda and you pay $10 per watt. Ridiculous. Just realised, you may not know who Rays or Anaconda are. They are camping shops here in Aus.

I have a small gas instantaneous water heater which I use in my shower setup. Only gets set up on trips lasting more than about 5 days though. I have a small 4aH LiPo battery to run the pump, a small 1.25 LPG bottle for the shower heater and if I camp near a river then I just throw the hose into the river and I have virtually unlimited hot sowers.

Hi Phil, I wouldn't too bogged down with the figures I quoted. I just that when I go camping I really like to get my brain working with facts and figures. Before I purchased a solar panel, I would have to find a reason to go for a 2 hour drive every 3 days just to charge up the battery!

Friends of mine have a small Honda EU10i inverter generator which is a really nice (and expensive) piece of kit but they need to run out extension leads and drag it out of the trailer and then you hear a humm in the background. I like the quietness and simplicity of solar. Even on overcast days I still get enough charge to get me through.

I recently did a 4 day hike to Lake Tali Karng. I left the car at Mcfarlane saddle with the fridge and supplies to last another week of camping after we got back from the hike. The weather was all over the place, warm, cold, overcast and sunny. I was worried that we would get back with next to no food left in our packs and find our fridge out of battery and all our food perished. I took a chance and when I came back the battery was still full and the fridge nice and cold. We got back and I did a roast lamb in the camp oven. Happy Days! Love my solar panel!!!

Cheers,

Simon

[BaronJ]

Hi Simon, Guys,


Sounds like a nice setup there Baron.
Thanks.




Are you using electricity to heat the water for a shower or is the power just for the pump?


I bought a "Truma" device, it heats water using gas or/and electricity. The electric pump provides water, via the Truma, for the shower and sink. The Truma also provides hot air heating. I have fitted tanks for fresh and gray water, roughly 65 liters each. The gas tank is under the floor and contains 25 liters of gas at 80% fill, which is the maximum allowed in that size tank.



If it's just for the pump then the intermittant use of the pump actually uses very little power compared to running a fridge anyway. When I camp, 90% of our power use goes into running the fridge, 9% into recharging the kids devices and 1% for our LED lighting at night!

Your heater might chew some juice, is it a diesel heater with a fan?


Yes I think the fridge is going to be the biggest consumer of electricity, being a 12V compressor type, and the Truma the biggest consumer of gas with the hob being next.



Edit: I agree about purchasing solar panels from camping shops. Buy a panel from a commercial solar panel supplier and you may get it for just over a $1 per watt. Then go to Rays or Anaconda and you pay $10 per watt. Ridiculous. Just realised, you may not know who Rays or Anaconda are. They are camping shops here in Aus.

I have a small gas instantaneous water heater which I use in my shower setup. Only gets set up on trips lasting more than about 5 days though. I have a small 4aH LiPo battery to run the pump, a small 1.25 LPG bottle for the shower heater and if I camp near a river then I just throw the hose into the river and I have virtually unlimited hot showers.



Before I purchased a solar panel, I would have to find a reason to go for a 2 hour drive every 3 days just to charge up the battery!

Me neither :)





Friends of mine have a small Honda EU10i inverter generator which is a really nice (and expensive) piece of kit but they need to run out extension leads and drag it out of the trailer and then you hear a humm in the background. I like the quietness and simplicity of solar. Even on overcast days I still get enough charge to get me through.

Happy Days! Love my solar panel!!!

Cheers,

Simon

I have one of those generators as well, however in many places in Europe you are not allowed to use a generator, purely from a noise point of view. Hopefully when I get my new van sorted there won't be any need to have it.