Virtual Tracker panel arrangement

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Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Fri Feb 08, 2013 9:35 am

OK, time to update my Virtual Tracker concept with some data, and it shows that it does work as I expected - 2 parallel arrays in different orientations into a single MPPT charge controller works perfectly well, and is a viable alternative to a tracker, now that PV panel costs have fallen so far. I originally posted about the idea here:
solar-wind-gear/topic1507-40.html#p25960

The idea is to place panels tilted up 60degrees, ie pointing 30 degrees above the horizon, facing east and west, in order to get a fairly constant output throughout the day.
Essentially double the number of panels can be used on a certain rated inverter, ie a 2.5kW inverter with 2.5kW of panels facing north, could accept 5kW of panels in the Virtual Tracker arrangement, with no risk of letting the magic smoke out.
In these days of minimal to zero FiT, at least in NSW, it is desirable to have an even PV output throughout the day, rather than a big peak around solar noon, in order to minimise the giving away of energy to power companies to sell at 50c/kWh or more during peak rate periods. They are making profits at your expense, so it is best avoided if at all possible.

VT-North-facing.comparison.gif
Click to de-fuzz


I prepared this graph from data I collected on the 6th and 7th of January- 2 perfectly clear, hot days. Temperature profile throughout the day was not identical, but was close enough, and both maxima were just over 36C. Solar radiation graphs show identical profiles for both days. Panels used for the test were Indian-Pacific branded 250W monocrystalline panels, on the ground, leaning on an Aluminium adjustable height platform (the latest in high tech mounting systems! ;) ) North facing panels were set to 31deg tilt, equal to my latitude, and in Virtual Tracker arrangement were tiited at 60deg from horizontal, facing east and west.

VT-North-facing.comparison.gif has kW and kWh for both days for north facing and my Virtual Tracker arrangement, plus the Virtual Tracker curve multiplied by 2 to show how it looks in comparison to the north facing array. The slight bulge in the VT profile for a couple of hours either side of solar noon at 13:02 was, I suspect, related to cooler panels- due to them pointing 60 degrees off-sun (@0.5 incident radiation), yet still having the same surface area for radiating heat away. The slight bump at the start of that was also due to panel cooling, when I washed some bird droppings off one panel.
The truncation of the curves before 6pm is due to my location in a valley, I lose the sun about 2 hours before sunset, which in this case handicaps the VT arrangement, so I've marked the difference at solar noon- 0.2kWh less from the VT arrangement than north-facing, which would equate to 0.4kWh down over the day for a location with clear E and W horizons. Clearly there would be minimal gains to be had in locations with restricted views to the east and west, but with clear views there is a real advantage to be had by using more panels in a Virtual Tracker arrangement when looking for flat output curves.
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Re: Virtual Tracker panel arrangement

Postby Tracker » Fri Feb 08, 2013 9:59 am

.
Thanks for the results.. I am surprised at just how FLAT the output really is.

Naturally, if there was a preference for a bias, say to the afternoons, for running that RAC, then you could bias accordingly..

I do assume that the angle of dangle is more important, with the sun being inherently LOWER in the AM/PM sky. ie.. Nth facing, you would have those panels facing UPwards more, for the high-noon sun...

What does all that represent, as a total KwH per day, for the two options of N and E/W..
ie say 2.5Kw North, and 2.5 East and West.. is it 2.75 and 2.25 respectively..
..
.
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Fri Feb 08, 2013 10:21 am

Yes you could lay the north-facing panels flatter to take more advantage of the high summer sun, but with a serious loss to winter output.

Tracker wrote:What does all that represent, as a total KwH per day, for the two options of N and E/W..
ie say 2.5Kw North, and 2.5 East and West.. is it 2.75 and 2.25 respectively..


From the graph you can see the 500W of panels facing North were up to 1.5kWh by solar noon, so 3kWh for the day. 2.5kW of panels would be 15kWh for the day. The Virtual Tracker arrangement gave 1.3kWh by solar noon, so 2.6kWh for the day without a big hill blocking afternoon sun, and 13kWh for the same 2.5kW of panels in the E-W arrangement. But double the panels and your 2.5kW inverter could produce 26kWh for the day, with a much more useful flat output than piling on more N-facing panels to a typical N-facing array.
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Re: Virtual Tracker panel arrangement

Postby Tracker » Fri Feb 08, 2013 3:44 pm

Gordon-Loomberah wrote:From the graph you can see the 500W of panels facing North
were up to 1.5kWh by solar noon, so 3kWh for the day.
2.5kW of panels would be 15kWh for the day.

The Virtual Tracker arrangement gave 1.3kWh by solar noon, so 2.6kWh for the day
and 13kWh for the same 2.5kW of panels in the E-W arrangement.
But double the panels and your 2.5kW inverter could produce 26kWh for the day,


Yes - I was unsure exactly what the graphs were saying..

So - Take 2.5kW NORTH and get 15kWh for the day
SPLIT that 2.5kW to E/W and get 13kWh but FLAT response

If you are covering your background use, this is clearly a good idea, and a great answer for those GABLE roof homes, facing NORTH... Something installers should be actively looking for.. 1kW per hour for most of the day.. :D

The remaining interest would be to know how much NORTH paneling , you could add, such that you get minimal clipping.. I was keen to try 1.5kW on E, N, and W, but as you say, you would really need to modify the E/W angle-of-dangle to 60degish..

Would be great if you had that extra 500W pair to set north and compare.. E+N+W

Thanks again, for doing what I wanted to do.. but the bride would have killed me for suggesting..
..
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Fri Feb 08, 2013 4:17 pm

Why would you want to add any N facing panels though? All they will do is increase the midday peak. I think it would be much better to add more E and W facing panels to keep the relatively constant output throughout the day and avoid clipping altogether, but give a higher total energy output than N-facing arrays can, with a given sized inverter. Another advantage is that this arrangement can make the most of any cloud edge effect peaks that don't happen around the middle of the day, something N-facing arrays cant do very effectively, especially when already operating near their input limits, when the inverter is being overdriven to maximise production.

IMHO in NSW at least, the Virtual Tracker is now the best arrangement for businesses that operate during normal business hours with relatively constant loads, and for households with resonably constant loads too, when they don't want to be increasing the profits of the electricity companies.
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Re: Virtual Tracker panel arrangement

Postby Smurf1976 » Fri Feb 08, 2013 9:26 pm

I'm doing something similar but with massive over powering and a bit of voltage mismatch thrown in as well. :D

Facing East (20 degrees N of actual East) are the 8 x 190W panels that have been up for quite a while. Recently added on the Western side (20 degrees to the South of true West) are 9 x 250W panels (which collectively have a marginally lower voltage than the 8 x 190W). And it's all connected to..... a 1.1kW inverter!

Eventually I'll change the inverter I expect, but for the moment it's working quite nicely. The inverter limits its' own output to 1.1kW and spends a lot of time sitting there.

I've done the maths using a few different assumptions and they all point to about 3000 kWh a year being produced in that configuration. There's significant spill of energy due to the inverter limit. But the inverter was already there, and adding the 9 x 250W panels works out as an economically sensible thing to do.

The inverter is running quite nicely but I'm looking into adding forced cooling to it. Eventually there will be a bigger inverter, but that could be quite some time away.
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Re: Virtual Tracker panel arrangement

Postby Clemo » Sat Feb 09, 2013 12:23 pm

Interesting, do you think there would be much to gain by going for a dual MPPT inverter?
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Re: Virtual Tracker panel arrangement

Postby Gordon-Loomberah » Sat Feb 09, 2013 12:39 pm

I don't think there would be much to gain with another MPPT input, but a lot could be gained by using a 2kW inverter with Smurf's current PV array!
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Re: Virtual Tracker panel arrangement

Postby Clemo » Sat Feb 09, 2013 12:52 pm

Have you tried logging a couple of days, one with east disconnected and one with west disconnected for comparison?
I would be interested to see that.
I suspect with a dual tracker you would get a higher peak mid morning and mid afternoon which would fit better with most usage patterns, at least mine anyway.
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Re: Virtual Tracker panel arrangement

Postby Tracker » Sat Feb 09, 2013 1:31 pm

Clemo wrote:I suspect with a dual tracker you would get a higher peak mid morning and mid afternoon which would fit better with most usage patterns, at least mine anyway.

I doubt that the difference would be really discernible, but I was thinking the same..

I would still like to just SEE the combination of E,N,W, so you do get an economical MidDay boost..
It's clear that the E/W does give a practical and flat response.
..
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