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Forum Index : Solar : West & east panels on the same controller
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Hey guys, I have a 80A knock off of the outback flexmax like this Max solar array is 5000w @48v My roof has a reasonable east roof where it can fit 18 panels (4500w)6 strings of 3 in series. Can I fit another 2000w on the west facing roof and not blow it up? @noon in summer they would both be getting sun, but not full sun. Perhaps keep one east string of 3 on a separate breaker feeding the charge controller and monitor it. My gut feeling is it will be fine in Melb winter, but may be too much in summer. I don't know the angle, it's around 20yr old pitched tiled roof, it would be the std pitch you see on most roofs these days. Cheers Caveman Mark Off grid eastern Melb |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Have you got any bottles of electronic smoke and the insertion tool? Build the Regulator with the PCB you got from me and connect the other panels via it will be a much safer route. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I have 1.2Kw east, and 1.2Kw west, both looking 60 degrees above the horizon. Never see more than 1.2Kw at any time of day from those panels. If your roof slope is only twenty degrees, you will get a lot more at mid day, and less at low sun angles. This problem can be solved geometrically with a scale diagram. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yeah, I will be doing that Mad, but I scored 8x 250w panels real cheap that have a 48v max power, they won't go well with the charge controller you designed, but will be fine on the 80A mppt controller. I could always just remove one or two strings from the east roof and hook them up to the mad controller. Then I would have either 3750W East & 2000W West, or really conservative 3000W East & 2000W West On the east roof they are 30v max amps so they are 3 in series for 90V. When the sun comes over to the west roof I was going to wire the 48v max amp panels 2 in series, still well within the controllers 150v max and still pretty close in voltage to the other east side V wise so when they share the sun a bit they won't be too far apart. So basically when the summer sun is directly above and each East/West side collects at the same time, but not at optimum angle just as a rough guide how much do you de rate them? Reckon I'll just try the 3000E and 2000W and monitor it in summer to check max amps. In the mean time just feed excess into the Mad controller as all other panels have a max of 30V power. I'll shut up now, answered my own question. Warp, I've seen your panel angle, they are waaaaay steeper than mine. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Mixing different voltage panels on a MPPT controller does not work well. I have done that before and the charge controller actually made more power when I disconnect the 1500W of different voltage panels. You could do it via a GTI. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
That's interesting, were they facing the same way? Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yes way steeper, but its the optimum angle for getting a very flat power output throughout the whole day. This diagram is a bit Mickey Mouse, but with sixty degree elevated panels, the sun never "sees" less than about 85% of the full area of one panel. Output is pretty constant once the sun is above the horizon.  Twenty degree elevated panels are going to look more like this. There will be a massive mid day power peak, tapering off fairly quickly as the sun angle reduces.  This is all as rough as guts, but a quick and dirty sketch can tell you a lot. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
You forgot to put a smiley face on the sun Tony. Jeez, when you actually put it on paper at look at it side on you can really see the difference. Might be an idea to piss those panels off and get a matching set to my other ones. Cheers fellas, saved me making smoke again. Prob better to run the 4500w (all the same brand etc) on the east roof by themselves via the mppt and the rest via Mad controllers. Could always series those 8 odd ones on an gti like Mad said. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Yes same angle, same direction, the MPPT was trying to find a point in between the ideal for both. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yeah, I wasn't going to try that, kind of figured since mine would be east and west it might be alright and the max amps peak on the panels would be only 6v apart(between east and west sets), but looking at Warps drawing it's pretty clear there is a BIG overlap, which might confuse the controller. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
The angle of the sun on the panels makes little difference to the voltage. Here is the voltages for today from my 2 GTI's, it was cloudy and the regulator has not had any effect on this. The blue and green are identical arrays, the mauve is the same panels and number also but in a different position and the yellow is different panels. The voltage changed very little all day from before dawn to after sunset. It was overcast all day but some periods the cloud was much thinner than others.  This the current, the MPPT keeps the voltage fairly stable and the amps vary.  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Fascinating stuff Mad, looks like doing proper research and checking your system really is critical for peak performance. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
 This is an excellent demonstration of why a very simple constant voltage controller can give almost the same results as a fancy software perturb and observe MPPT controller. Cheers, Tony. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Sometimes if you know what is going on you can make improvements, other times it does not matter. Knowing what is on the graphs has not made any difference to the end result, playing around with the mismatched panels did teach me what does not work. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
With an east/west split, you really need either two separate controllers, or a dual mppt controller We have a east west split, I was very dubious to begin with, but it is surprisingly effecient, in fact I compared it to a neighbours system, which is identical except all north facing, same number of panels, same brand controller, ours starts generating much earlier in the morning than his (thanks to the east facing panels, develops slightly less (about 0.8kw at midday), but develops much later after his has dropped right off. In fact, by switching to the daily generated kwhrs menu on both, as noted same number/brand of panels, same gti inverter, about three houses apart, the east/west split actually develops more kw/hrs a day than the pure north facer, even though its midday peak is slightly less |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Boppa what angle the panels at and what is latitude roughly? With dual MPPT GTI you can use that method and increase the number of panels as each channel usually has a rating greater than 50% of the Inverters total capacity. However I am not talking about doubling the number of panels as was suggested somewhere. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Brisbane, fairly shallow- maybe about 20 deg?- I did have a pic of them on a thread here somewhere... (I'm in nsw atm, so cant take another pic until I get home at the end of the week) |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I think one needs to crunch the numbers if they are looking for max KWH per day than even charge rates. Just reading the above about east/ west panels being the same as north facing I thought that does not add up to what I have seen myself. Last week I was Crunching numbers and found that Tilting my west facing 35o pitch panels even 15o north would make about a 30% gain in winter generation. I ran the numbers for Sydney with my pitch roof, 35o and made a couple of discoveries. East and west facing panels on the calculator all else being the same, do not generate the same outputs ( yearly). West make significantly more power according to the PV watts site. Would have thought is they were true east west they would have been the same or very close to it. Apparently not! East and west facing panels make significantly less than the same amount of north facing panels at the same 35o Pitch on a yearly basis. From the numbers I ran which was 2Kw east, 2KW west worked out at 3926 Kwh. 4 Kw North made 57XX kwh. A significant improvement. Last week I calculated my 5o South facing panels would make next to no improvement facing 5o North if I tilted them back using some brackets I have. Was pretty surprised at that. Looking at the things I can see cutting that tree back beside the shed even more will make a hell of a difference. Between the leaves, bird sh*t and what looks like smeared Mud on them ( Possums?) they are a bloody mess and surprising they haven't fallen off a lot more! Tilting the west facing panels north 15o made a big difference though. Only thing there is, I'd have to space them. Being they would be tilted sideways rather than longways, I figure about 1M spacing should do it to get decent winter returns. The spacing would have to be allowed for on limited area roofs. Given the gains by just slightly tilting the panels, I'm thinking I'll use the significant west facing roof I have now. I wasn't going to as the winter generation which is so much lower on non north facing orientations in winter which is what I really need. That bit of tilt makes them a lot more worth while. I made a bit of a mistake in a way thinking my summer generation would be the most important with AC loads. Realised that to heat the home with the AC, it's the winter Generation I need to pay attention to. Seems no matter which way I put the panels, In summer I'm going to be making way more power than I can use if I optomise for good winter generation. I think before setting up panel orientation where there is a choice, it certainly is a good idea to crunch the numbers for YOUR particular situation and see what works best for your particular needs. The results of different scenarios can be very surprising and unexpected. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Mark is setting up for off-grid so maximum power on the worst days (especially in cold, cloudy, miserable Melbourne) will be the priority. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I would call it a nice balmy climate compared to Scotland, no need for pessimism my sweaty northern friend. Cheers Caveman Mark Off grid eastern Melb |
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