Virtual Tracker panel arrangement

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Re: Virtual Tracker panel arrangement

Postby APR » Sun Feb 07, 2016 8:51 am

Hi Gordon, what does your tracker do as far as orientation is concerned on overcast days? Does it still point at the Strongest source of the defused light or does it go horizontal, or does it stay at the current position until there is directional light so it can orient itself?
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sun Feb 07, 2016 9:06 am

In heavy overcast it generally goes to the meridian, which is almost straight up in summer, and towards the N in winter (as the declination adjustment is done manually), as that's where the strongest light comes from.
Once I get the azimuth drive onto the new tracker (dual axis drive), it will probably automatically point to near overhead in overcast winter weather. By having sufficient delay programmed into the tracking, it doesn't try to follow any brief bright patches of cloud.
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Re: Virtual Tracker panel arrangement

Postby APR » Sun Feb 07, 2016 9:40 am

Thanks Gordon. I am looking at trying to build a tracker to hold 9 panels and have been chewing over some of the issues that need to be addressed. If I get to build it I will most likely find a lot of issues I have not foreseen.

One issue that I am considering is what can I do to eliminate galvanic corrosion. I am considering making the main structure out of steel, and using alloy panel mount rails off a steel frame to attach the panels, but I also wonder about fixing the panels straight to a steel frame.

I am also wondering whether I should build a 2 axis system with it's added complexity, or go for a single axis system. I like the idea of being able to place the panels in the horizontal in heavy wind, and also in overcast weather. I need to think this through a lot further yet.
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sun Feb 07, 2016 11:40 am

My panels are all mounted directly on the painted steel frame.
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Re: Virtual Tracker panel arrangement

Postby Quokka2 » Sun Feb 07, 2016 12:22 pm

Gordon-Loomberah wrote:When a panel is shaded the voltage will be only a little down on one in full sun, but current will be way down, so any panel in a string that is shaded, limits the current flow in that string to the shaded panel's low output current.

Thanks Gordon for making that crystal clear :D I guess it's been explained elsewhere, but this is a long (meandering) thread and a big forum.
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Re: Virtual Tracker panel arrangement

Postby zap » Sun Feb 07, 2016 12:32 pm

Well in plain English the reason we set these up is because usually north facing arrays will peak at midday and so you get all your power between 10 and 2 if you produce 5kw but you are only supposed to out put 2kw then 3 kw is wasted.

If you set up an east/west array you can get full power at sun up and still have full power at sundown. at midday the panels are both active but are both at a disadvantage due to the angle toward the sun the result is you get an even steady flow of power all day. I also have a north facing array but most of my power comes from the virtual tracker (except the midday peak from the north array).

The virtual tracker is active from sun up to sundown producing about 1.5kw all day. on an over cast day when most people are down on power all my panels are active due to light diffusion and reflection. Now i have a second VT facing northwest/southeast to correct for seasonal changes of the sun and again in parallel to the others and it corrects automatically with no loss. All of this is only because with panels as cheap as $100 for 250 watt panel you might as well put them to use but you need to spread the power out over the whole day and over the whole year to get the most out of it.
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Re: Virtual Tracker panel arrangement

Postby jules » Sun Feb 07, 2016 2:16 pm

I've mounted mine almost directly to a steel frame. Out of concern for any potential [groan] galvanic reaction I used fibre washers between the panels and the steel with stainless steel bolts but I doubt there'd be any problem with more direct mounting. I'm expecting that the frames might need some galv. paint before the panels die but if you can get at the frame that isn't too much of a problem.
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Re: Virtual Tracker panel arrangement

Postby evadsiv » Wed Feb 10, 2016 10:59 am

I have noticed that quite a few new installs are going for a system totally on the West Facing roof.
Gordon do you have any data on the power production profile of the West only.
Most of the roofs involved would only have a pitch of 22 degs.
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Wed Feb 10, 2016 11:19 am

I suspect people are probably doing west only to cover air conditioning operation. I dont have any data myself, as my W horizon is well over 20 degrees up, due to living in a valley, so I couldn't get any valid comparitive data.

For an unobstructed horizon, west facing will generally produce slightly less than east facing, due to the higher operating temperatures when the sun is near face-on. Around here, and many inland areas, there tends to be more cloud in the afternoons- cloud formation is loosely correlated with maximum heating, so that could reduce output a bit too. Patchy cloud any time of the day can increase output due to cloud edge effect too, so it is quite complicated to work out for a particular location, without actually collecting data.
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Re: Virtual Tracker panel arrangement

Postby Quokka2 » Wed Feb 10, 2016 12:10 pm

evadsiv wrote:...do you have any data on the power production profile of the West only.

You can model solar production for any roof orientation at any location at pvwatts.nrel.gov. Closest data for you would seem to be Melbourne Airport.
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