Virtual Tracker panel arrangement

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Re: Virtual Tracker panel arrangement

Postby Tracker » Tue Aug 12, 2014 9:08 am

..
But there is another possibility..
ADD another inverter. MORE panels... ANY panels and another inverter.. lots available cheap... from folk needing to update their inverter to larger inputs..
.
.
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Re: Virtual Tracker panel arrangement

Postby thechad » Tue Aug 12, 2014 9:37 am

I did consider this but thought it too expensive (cost inline with original install).

Anyone done this? What's the costs compared to buying a bigger inverter?

If i did want to get a larger inverter, say a 3kw, (curr 2kw) where should i look for quality second hand?
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Re: Virtual Tracker panel arrangement

Postby Tracker » Tue Aug 12, 2014 10:58 pm

..
Surely the cost of panels and installation will be the same.. whatever inverter you get..
when you try, you can find PVE inverters for two to three hundred bucks...
..
.
Retired Engineer and keen PV experimenter - Always ready to learn and share.
2 x CMS2000 (fan cooled) GCI and SE 170W panels
1.7kW First Solar/Outback Island circuit - Peak Replacement Power
Governments won't save the world :-) They will just TAX it :-(
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Re: Virtual Tracker panel arrangement

Postby zap » Sun Aug 30, 2015 1:26 pm

Well it has been more than a year since i built my virtual tracker and while there were many people who said it would not work i am satisfied that it does and now i have built another one and the angle has been adjusted to compensate for the setting sun during winter and rising sun during summer. so now the two arrays collect sun seasonally. The east/west collects sun during winter on the east side while the west side is not very effective. and the west north west collects the sun in the after noon during winter then as the season changes the east south east panels collect early morning sun and the west panels collect in the afternoon.

With cheap panels available it makes sense to use them to maximum effect.

I have included the path of the sun for my house. Like the original tracker it seems it will sort it self out as the seasons change My hope is that through out the year i will spread out the power collection rather than getting all my power at once since after all i can't sell more than my contract states. Instead if i can sell the maximum all day all year then i will do better.
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sun Aug 30, 2015 4:25 pm

Good to hear it is working well for you Zap :)

Can you post some pics?
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Re: Virtual Tracker panel arrangement

Postby Quokka2 » Sat Feb 06, 2016 5:56 pm

Okay I've got myself some 190W panels and have decided to give this a go. Am I correct in assuming that each pair of 60 degree inclined east and west-facing panels is wired in series and treated as a single panel for the purpose of voltage and load calcs for my off-grid charge controller and inverter?
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Re: Virtual Tracker panel arrangement

Postby zap » Sat Feb 06, 2016 7:31 pm

yes. wired in line. on each side then parallel down to the inverter. i have two blocks of three on each side to keep the voltage up but the amps down. 106v @ 16 amp + 106v @16 amp but if you have heavier cables you may not need to do that. also consider the amps handled by your regulator. Mine is limited to 60 amps but also limited to 150v so three panels works for me. So 3+3 east + 3+3 west = 106v @16 amps and the sun sorts out tracking.
Hope that makes sense.
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sat Feb 06, 2016 7:39 pm

Just to be clear, all panels in a string must face either east or west. Ideally there will be 120degrees between there they face, but you could use less, depending on your charge controller limits. If they are 120 deg apart, then you could go to almost double the CC rating without danger - note the bulge in output during the middle of the day though. String voltage calcs wont be any different, as the voltage of a string doesn't change much between sun and shade- you have to stay under the Vmax limit for cold temperatures.
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Re: Virtual Tracker panel arrangement

Postby Quokka2 » Sat Feb 06, 2016 11:09 pm

;) Sounds as though what I had assumed was wrong after all; each side wired in series and back to the controller in parallel. That would mean one string peaks in the morning and the other in the afternoon; not one (or two) working all day as I had envisaged.
For the benefit of me and other infidels, perhaps someone could explain why it should be done this way, or for that matter, the relative merits of having panels in long strings vs shorter strings in parallel arrays (apart from simply matching voltage requirements of whatever it is connected to).
Also, to clarify the terminology here, are we using the term "string" just to denote a series of panels wired in series (even though there might be more than one such string connected to the same controller or inverter terminals)?
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sun Feb 07, 2016 8:43 am

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. Current flow in a circuit must be equal all around that circuit, and in this case will be limited by the weakest panel's output- which is why a chimney shadow can wipe out a grid-connected array's output.
As shown earlier in this thread, having a parallel string in shade doesn't limit the output of one in full sun.

Long strings vs short strings into an MPPT charge controller is a trade-off between CC efficiency and cable losses.
The CC's efficiency will be highest at typically 10-20V above Vbatt (for a 48V system), but the losses in the line
decrease with increasing voltage (ie decreasing current), for a given sized array. Losses go up with the square of the current, I^2 X R, so halve the current to get 1/4 the line loss. If you have a long distance between CC and PV array, then it is generally best to go for the highest allowable voltage, as the decrease in CC inefficiency is only small, but the line losses can be quite large, unless you go to large diameter, expensive cables.

A string refers to a group of panels connected in series, and yes parallel strings is the norm for off-grid, and larger grid connected systems.
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