I'm TRACKING!

[Volvo farmer]

if you had to choose one as more important...would you have seasonal adjustment or tracking?  it appears if i only track, a traxle would be ideal (no shading of/from other racks).  if i wanted seasonal, single poles would be easier and shading wouldn't be as much an issue if not tracking.  i wonder if i had the 3 single poles in a triangular fashion, i could maybe limit the tracking angles to reduce shading.  if i am picturing it correctly, the most shading would occur during tracking when the arrays are tilted further (putting one side of the array high into the air).  fixed arrays seem as if they could be closer w/ less shading than trackers.

That's a tough question! Tracking adds complexity. Seasonal adjustment adds almost no complexity. I really like tracking, but it does come at a price. Someday you will look at your array and it will not be pointing at the sun because something is busted... then you have to fix it. I actually built a second array fixed at optimum for winter sun that neither tracks nor seasonally adjusts

Are you off grid? The funny thing about tracking is that it helps least in the winter, when you most desperately need the watts.  I have read arguments that even seasonal adjustments don't help the off-grid person as much as you'd think because if you size your array to get you by in January, the amount of extra sunlight available in the summer more than offsets the inaccuracy of the angle of the array to the sun's rays.

Also, if you are off grid, and you need to set up E-W arrays, you can position them so that you get the shading in the long days of summer, when you'll have power to spare.

[rossw]

The funny thing about tracking is that it helps least in the winter, when you most desperately need the watts.

Yes, but that not withstanding, I get a LOT more watt-hours in winter with tracking than without.
My linear array is 1.2kW, made of exactly the same panels I use on each tracking array.

Morning and afternoon, I usually see close to full output from the tracking arrays (5-6 amps per array) when the linear arrays are only returning 1-2 amps.
Middle of the day, I'm seeing 6-6.5 amps from everything.
So to me, it's MORE than worth the effort - I start sticking power back in my batteries earlier, and can defer drawing down from them later.

I have read arguments that even seasonal adjustments don't help the off-grid person as much as you'd think because if you size your array to get you by in January, the amount of extra sunlight available in the summer more than offsets the inaccuracy of the angle of the array to the sun's rays.

True, to a limited extent. I find that in summer I have more things that need power - water pumps etc, and in summer I get to spend more time in the workshop with lathes, welders and assorted power tools. I also don't really have enough solar for winter - but then, who does?!

[pyrocasto]

I'm excited to see everyone tracking! I made one from a satellite dish mount fairly easily about 6 years ago. I was 19 at the time. It was only up for 6 months or so and I still have it in storage. Been out of the energy world for a while. I'm waiting to close on a house come end of September where I'll finally get her back out for testing and use. Super excited.

The mount is 4" square tubing 1/4" wall, plenty heavy enough. Though I get morning sun starting at 930 so I'll miss those early and late hours being in the valley.

http://pyronet.50megs.com/RePower/panel%20on%20barn4.jpg

[defed]

i am on grid.  this is mostly a hobby for me, an expensive one at that!  currently am going to batteries, but may grid tie some day.

i found my chart, i think it will help me lay out multi arrays...on one axis it has solar elevation, on the other it has solar azimuth.  then there are lines (bell curves) for each month to show the compass direction and solar elevation per hr of day per month.  i believe you enter your lat/long and it gives you a chart per location.  you stand at your array location, face the compass direction, and then use an angle finder and if you see obstructions, it will shade the array.  you plot that point on the graph, then connect the dots and it will tell you your shading times.

feb through november, i have pretty much no shading from 9am on.  jan and december on the other hand, i am only CLEAR from 10am to 2pm.  i think i can use this to make some shadow drawings on the array layout as suggested.

on top of balancing the need for seasonal/daily tracking, i need to use a layout that doesn't sprawl all over the yard!  i'm sure i am going to have to compromise somewhere.

[defed]

http://www.wattsun.com/reference.html

i found this site...scroll down to the "free design tools" section.

the "solar tracker spacing" is a spreadsheet where you enter your data, space the arrays and then can advance the sun at different times of the year and see the shadows created.  it's a bit awkward, and you don't get alot of flexibility in placing the arrays (1st one is fixed in a odd spot)...but it is pretty neat.  i had to save the .xls and then open it to get it to work.  if i just opened it from the website, it was 'read only' mode, and you can't edit the parameters.

a few items further down is the "sun path chart".  this gets you the chart i mentioned before, with the bell curve of the solar elevation vs azimuth at different times of the day and different months.

[defed]

what exactly is dual axis tracking?  to me, a single axis tracker would be set at a tilt angle, 45 degrees for example, and then just spin on top of a pole, always tilted at 45 degrees no matter what compass direction it points.

if that is the case, would a polar mount from a satellite dish be considered dual axis?  when aimed at the horizon, the dish is vertical, when pointing due south, it is tilted back about 45+ degrees.  it is not being 'actively' tracked in both directions, but the nature of the mount makes it move in both directions.

a traxle seems to be in between the two.

i'm back on the traxle kick after thinking of a new way to seasonally adjust the tilt...we'll see how it pans out as i think about it more.

[rossw]

what exactly is dual axis tracking?  to me, a single axis tracker would be set at a tilt angle, 45 degrees for example, and then just spin on top of a pole, always tilted at 45 degrees no matter what compass direction it points.

if that is the case, would a polar mount from a satellite dish be considered dual axis?  when aimed at the horizon, the dish is vertical, when pointing due south, it is tilted back about 45+ degrees.  it is not being 'actively' tracked in both directions, but the nature of the mount makes it move in both directions.

a traxle seems to be in between the two.

i'm back on the traxle kick after thinking of a new way to seasonally adjust the tilt...we'll see how it pans out as i think about it more.

Dual-axis tracking adjusts the azimuth (east around through north/south to west), AND elevation (angle above horizon) to keep the panels square to the sun all day, every day.
A proper polar mount should do the same, but requires frequent adjustment of the elevation for best results.

[SparWeb]

I came across this beast while on vacation, near Ottawa Ontario:





I thought you guys would get a kick out of it!

[TomW]

Quite interesting.

A good bit of sail there but it looks up to the task.

Thanks for the share!

Tom

[defed]

where is everyone drawing the power from for their tracker motor?  main battery bank?  separate battery at the array w/ a small charging panel?

[TomW]

where is everyone drawing the power from for their tracker motor?  main battery bank?  separate battery at the array w/ a small charging panel?

I use a feed from my main bank @24V for the RedRok and 36 volt satellite jack.

Tom

[Elby]

separate battery at the array w/ a small charging panel?

That's how mine is intended to run, at least as soon as I can figure out how to get panels for the main array with no money.

[rossw]

where is everyone drawing the power from for their tracker motor?  main battery bank?  separate battery at the array w/ a small charging panel?

I'm actually cheating.

My battery banks are 48V.
My panels are connected for a nominal 100V to run my MPPT (flexmax-80) charge controller
My actuators are nominally 36V.

My control circuitry is in with the batteries, and runs all the arrays positioners in parallel from one controller. It uses a single drive (interlocked) for 'west' and one for 'east'. The actuators are connected to the 24V (midpoint) on the batteries, and switch to either 0V or 48V to drive them at 24V. Because time to drive east is the same as time to drive west, the power taken out of the batteries over a 24 hour period is the same so keeps the banks balanced without doing anything clever, and no wasted power in stepping down to lower voltages, and no complex H-bridge switching.

[RP]

Because time to drive east is the same as time to drive west, the power taken out of the batteries over a 24 hour period is the same so keeps the banks balanced without doing anything clever, and no wasted power in stepping down to lower voltages, and no complex H-bridge switching.

I never thought of that (balanced use going east and west).  Awesome simple bipolar power supply!   

[damian]

Inspiration

http://www.youtube.com/watch?v=IKyBEPbIgzY