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Forum Index : Solar : Oversize panels

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Davo99
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Joined: 03/06/2019
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Posted: 08:46am 19 Oct 2020
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  Georgen said  Looking through internet I noticed information on solar panel that Voc is for example -0.30%/deg C

What is correct interpretation of this information?


I don't know.
Looking at it I would say the same as you. In practicality, not sure. I have seen panels sitting at over 70oC that makes them roughly 50oC over temp /.3 = a voltage drop of 15 Volts. That would seem to be every panel so in a string could be 150V and I'm damn sure I have never seen my panels fall off by that much.

I have read and was reading today the Americans make a BIG deal about voltage rise in their calculations probably because so much of the country gets snow but, I'll flat out say it, being Americans I find they are very pedantic anyway and I wonder how much is typical internet beat up as is everything on the net.

Might be what the numbers mean but I think there would be more to it as in is that if what we think it is an absolute or a potential that may or may not happen and may be a lot less.

All I know is I have never had any problem with my systems.  I tend to keep strings to a max of 12, Usually they are 8 because of roof area installation considerations and that gives me plenty of head room either way plus when it's going to be cold enough to affect the panels, there is no sun on them anyway so they are probably being dragged down quite low. The rest of the time the losses of them being overheated would be a much bigger concern.

I have tested that many times.  Hose the things down and you can see the power ( can't remember paying attention to the voltage) go up a noticeable amount.  Lasts maybe a minute in the summer sun.  Guess if you had a gravity water source from a creek or something spraying them may yield a higher output. Minute you have to use any power for pumping or fans you are back to square one and have just added cost and failure points.


  Quote  As to cloud effect I read that if Sun comes past cloud edge there are times when Sun rays get reflected on cloud surface and solar panel gets energy from the Sun plus energy reflected.


I understood it to be the water droplets in the clouds Focusing the suns rays and making them more powerful like that. Could be a combination of both. All I know is that IS a real thing and certainly has a marked effect on panels and inverters.  Not sure why But I have seen inverters go screwy enough to know it's a definite effect.

  Quote  Could probably play with mirror or sheet of shiny white plastic to see if this effect could be replicated without cloud.


I gave this a go last summer with the ground mount array. I used some cream coloured sheets of colourbond on the ground in front of the panels.  I did observe a very slight increase in output in the limited observations I made.  I am sure it could be refined over the Rough as guts test I did but I'm also positive my rule of solar inefficiency would come into play and the cost would not justify the result.

My rule says the most cost effective efficiency for solar is inefficiency. In other words, don't try to make what you have more efficient, just add more.
In this case, rather than spend money to set up reflectors, just throw another panel on the ground and you'd probably be a mile ahead than trying to arse around with reflectors.  

Whatever you used would probably cost more than another panel and produce far better output. If you had the room for a reflector or mirror you'd have the room for more panels in the same place  :0)
Anything that would do as a mirror, Probably stainless in this case wouldn't be cheap and would need cleaning as well as some sort of mounting system. for a reflector like a mirror, you'd also need tracking to keep the focus on the panels. My reflector was just diffused but couldn't see any setup really being more cost efficient over just adding more panels and again, reflectors will do nothing in overcast conditions where more panels would be a real benefit.

  Quote  Will try to find if there is U-tube film that addresses this issue.


I did see a post on a forum where a Guy in canada used snow berms to reflect light onto his ground mount panels and got a fair bit over rating due to the cold and the intense  reflectivity off the snow.  He even mounted the panels on the wall of his house and built a rounded berm to help with the reflectivity as the sun moved and the vertical mounting meant the snow didn't cover them. Even vertical, the things made real good power and certainly a world away from what the normal flatter test panel with snow on it was making.
 
Warpspeed
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Posted: 08:53pm 19 Oct 2020
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Have to agree with Dave.

In the old days, solar panels cost big dollars, and trackers and reflectors may have been well worthwhile at the time.  
Today, secondhand panels are so cheap its just not worth the trouble.

Pure white snow is highly reflective.
In the Antarctic, a clear blue sky is quite common and sunburn is a real problem down there, even when its well below freezing. It would be very solar panel friendly place.
Cheers,  Tony.
 
Boppa
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Posted: 11:04am 06 Nov 2020
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Been a while, but I been busy building a shed (temporary house while I build the new house as well)

I picked up 17kw of matched brand secondhand panels off the fbook market place- cost me just under 2 grand for the lot...
I used some of them at the temporary campsite where I had my caravan parked up, and to say I am impressed is putting it mildly- I had two strings of 3x250w in series, each on their own controller to charge the 12v battery bank in the van- one facing west (same as I had at the old place lol), the other was supposed to be facing east, but as I never actually finished its stand- ended up facing to the south the entire time I was at the camp

The south facers were starting their MPPT controller up, and pulsing about 1/4 of an amp at about two second intervals- before the sun was even above the horizon!!!

New shed is going to get the lot up on the roof when I get the time (I put the temporary ones from the camp up at the shed to give me temporary power)- 5kw east, 7kw north and 5kw west- I can effectively doubt that with the controllers I have, but I seriously doubt I will need to lol

I was just so surprised to get so much power out of these older 250w panels- 1.5kw at the camp kept the batteries at full power every day- and I was using the lappy 24/7, air frier, microwave, fridge etc- even on the cloudiest days when it was raining, I never once even thought about dragging the genny out

I bought 20kwh of Winstons from Trev (16 cells, 48v 400ahr) and a 12kw inverter and 5 solar controllers from Sigineer- total cost was just under $17k- where to get a poxy little 8kw mains connection on (SWER out the front so power limited) was going to cost $42k!!!!- no contest.... (hell I could double the entire offgrid package and it would still cost less than getting the mains on...)

Sure in town the grid may have been an option, but in my driveway, I can hit the state speed limit in a 20 year old Hilux before getting to the front gate from the shed LOL, mains grid just didnt make economic sense...
 
nickskethisniks
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Joined: 17/10/2017
Location: Belgium
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Posted: 12:22pm 06 Nov 2020
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  Boppa said  

I bought 20kwh of Winstons from Trev (16 cells, 48v 400ahr) and a 12kw inverter and 5 solar controllers from Sigineer- total cost was just under $17k- where to get a poxy little 8kw mains connection on (SWER out the front so power limited) was going to cost $42k!!!!- no contest.... (hell I could double the entire offgrid package and it would still cost less than getting the mains on...)

Sure in town the grid may have been an option, but in my driveway, I can hit the state speed limit in a 20 year old Hilux before getting to the front gate from the shed LOL, mains grid just didnt make economic sense...


Oh please, could you post some kind of building log?  It would be nice to follow your build. It will be a serious build for sure, I wish you a lot af Fun building it!
 
nickskethisniks
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Posted: 01:13pm 06 Nov 2020
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  Boppa said  

I bought 20kwh of Winstons from Trev (16 cells, 48v 400ahr) and a 12kw inverter and 5 solar controllers from Sigineer- total cost was just under $17k- where to get a poxy little 8kw mains connection on (SWER out the front so power limited) was going to cost $42k!!!!- no contest.... (hell I could double the entire offgrid package and it would still cost less than getting the mains on...)

Sure in town the grid may have been an option, but in my driveway, I can hit the state speed limit in a 20 year old Hilux before getting to the front gate from the shed LOL, mains grid just didnt make economic sense...


Oh please, could you post some kind of building log?  It would be nice to follow your build. It will be a serious build for sure, I wish you a lot af Fun building it!
 
Boppa
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Posted: 07:19pm 06 Nov 2020
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I'll start a separate thread for the shed, but just quickly...
here's some shots
Just took these...
300mA- not a lot, but still...



The suns not even up yet!!!



Eventually there's 17kw going (points) up there, 5 east, 5 west and 7 north



ETA- thats north we can see, east is to the left, west is to the right...

eta2- yes that 300ma shot was taken just a minute before that shot of the shed- with NO visible sun at all, the panels were putting in 10% of their maximum into the battery bank....
Edited 2020-11-07 05:25 by Boppa
 
Boppa
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Posted: 08:58pm 06 Nov 2020
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An hour or so later- still no direct sunlight on the panels


Well....



MPPT and high voltage series strings- versus PWM and low voltage parallel strings...
No contest....not even on the same continent, let alone the same ballpark....

Later on, with full sunlight, it will hit 30A plus but as it starts putting some charge into the bank before the sun is even up- I'm impressed....
Edited 2020-11-07 07:01 by Boppa
 
Davo99
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Posted: 10:05pm 08 Nov 2020
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  Boppa said  

I picked up 17kw of matched brand secondhand panels off the fbook market place- cost me just under 2 grand for the lot...  


I have been horse trading in panels and getting them much cheaper than most people seem to get them but that was a bargain and a half!
Were they Trina Panels? Seem to be a lot of good size arrays of them going round atm.


  Quote  New shed is going to get the lot up on the roof when I get the time (I put the temporary ones from the camp up at the shed to give me temporary power)- 5kw east, 7kw north and 5kw west- I can effectively doubt that with the controllers I have, but I seriously doubt I will need to lol


I have come to the conclusion that 3 aspect facing arrays will get huge generation out of any inverter/ controller for the reasons you also Found.  They wake up soon as there is any light and are producing till there is virtually none and hold the inverter at max output pretty much the majority of the day. Overclocking the inverter also has many upsides with this. Some see it as wasteful but often producing a max constant output rather than a Max peak output can have it's uses, particularly with battery charging,

  Quote  I was just so surprised to get so much power out of these older 250w panels- 1.5kw at the camp kept the batteries at full power every day- and I was using the lappy 24/7, air frier, microwave, fridge etc- even on the cloudiest days when it was raining, I never once even thought about dragging the genny out


I have had the majority of my system running 250W panels till recently.  When you look at the numbers, there is very little difference between the efficiency of a 250W panel and anything bar the ultra exy ones they are producing now.  It' all comes down to square inches. Sure, there may be a bit of loss through age and a bit through outright efficiency of the panel design but that might add up to 5 % and you'll loose more than that in use through leaves, Dirt, birdsh*t etc. Of course if one was really concerned about getting every last watt you'd have every panel facing north and tilt them 4 times a year.

  Quote  I bought 20kwh of Winstons from Trev (16 cells, 48v 400ahr) and a 12kw inverter and 5 solar controllers from Sigineer- total cost was just under $17k- where to get a poxy little 8kw mains connection on (SWER out the front so power limited) was going to cost $42k!!!!- no contest.... (hell I could double the entire off grid package and it would still cost less than getting the mains on...)


Was talking to my cousin Yesterday at a family get together, He built in the country and only being about 100M from the road, they still wanted him to  pay around $35K ( and said it could have been more) to put the power on at his place. Reckoned they would need to put on another transformer which adjoining properties would also use but wanted him to pay for it.  $30K seems to be the base figure they want now as a matter of Course. I have heard several people quote  that. It's never $10 or 15K, always $30+

He only has 6KW of panels which I raised my severe doubts about. Big house 4 early/ pre teenage kids.... I think a salesman has filled his head with " She'll be right mate" and once they move in they are going to come up very short. He didn't know the battery size but if it's proportional to the panels....
Told him I go up that way to my Dads fairly often so if ( when) he needs to get more panels, let me know and I'll see what I can find for him.

If I were going off grid in his situation, I'd be wanting a LOT more panels than he had and there is certainly no shortage of roof or space for them.


I was reading( and gave up on) a US solar forum. I don't know what it is but the Yanks seem obsessed with pissfarting around with 100W panels like there is nothing else available.  Even on caravans and " RV's"  They want to run every electrical convenience known to man and expect to do it with a few ( if that!) 100W panels.
Suggesting they throw 3 x 250s on there or make  Props to stand them on the ground where they can move them round as well gets reactions like you are telling them to gold plate their van or motorhome.  I don't understand why their mentality is to use so little generation and have such large loads.  I told them what I had on my house and I'm sure many just didn't believe it. Even their home systems are relatively small compared to ours.

They are also battery obsessed even on the grid but again, expect small packs to do 10X the work they can.

Good to read of someone putting in a real system with plenty of capacity that will do the job 99% of the time instead of always falling short.
 
Warpspeed
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Posted: 10:35pm 08 Nov 2020
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With regard to mixing panel sizes, types, directions, and voltages.....

There should be no problem combining strings of different panels facing in various directions, the max power voltage ratings can vary quite a bit too.

But each series string within itself should have identical panels in each string.

The peak power rated voltage is not a sharp peak, but a broad hump and you can allow the voltage to run above or below the actual peak and lose surprisingly little power.

Now take a hypothetical example of some 40 volt rated panels facing north east, and some 45 volt panels facing north west, connected to a single mppt controller through a pair of series diodes.

At dawn the east facing panels will be producing a much higher output power than the western panels, and the mppt controller will quickly find the peak power voltage at around 40 volts. The western facing panels will still probably be producing some useful power at 40 volts.

At mid day, assuming both arrays are of similar power rating, the mppt controller will settle at about 42.5 volts, half way.  Both arrays will work fine and be very close to their peak anyway.

At dusk, the mppt controller will be getting most power from the western panels at 45 volts.  So combining two mismatched arrays is not a problem.  The mppt controller just seeks and settles on the point of maximum combined power under any and all conditions.

The same is true if multiple arrays differ greatly in rated power.  That is going to happen anyway as the sum moves across the sky, and with partial shading.

I have east, west, north, and straight up arrays, feeding a single mppt controller through four diodes and it self adjusts throughout the day and gives excellent results.
Four separate amp meters tell the story, and its all worked happily like that for over three years.  Even the lowest voltage rated panels still contribute their share, so don't worry too much about matching panels, except within in each series string.
Cheers,  Tony.
 
Davo99
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Posted: 09:32am 09 Nov 2020
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I have mixed different panel strings on GTI's and not had any problem either.
I have got the OC voltage close, maybe a bit above on the lesser powered array and combined it with an array of larger panels in separate strings on the same tracker and that works fine.  I end up with off numbers of panels but as you allude to Tony, there is flexibility with the power point and the tracker pulls them down to their happy place and that's it.  

I have put significantly ( voltage) mismatched strings together and that did not work well at all. The lower voltage array acted like a Load which I did not expect and reduced the output of what the larger array would do on it's own.
The idea with the Diodes is typically brilliant  and would prevent this but with arrays mismatched at over 60V, I don't think the lower voltage array would contribute anything bar in the lowest light conditions.

In my mucking around, Wattage of panels, Voltage and number are all irrelevant if you  get the voltage close to that of the other string you want to parallel them to.

I'm not sure how the fall off is with having panels above VMP. I know the fall off can be Huge when you pull them down too far but I would Imagine there is little if much lost if you are running them at near OC voltage with another string.
That's what I have done when combining a string of weaker panels to more powerful ones, give them  some extra voltage to make up for the pull down under load and in my non scientific observations, this has seemed to work  OK.

I never thought of flat as an orientation of panels but of course it is a very valid one. Seems the ultimate system is not 3 aspects but 4!

When I added to my fathers very non ideal setup last week I crunched the numbers for east west and flat and flat came out on top. I was leaning toward that anyway because of the incalculable of the 150Ft trees all around and the shading. I was keeping an eye on the roof as I was working  though the day and it was clear that even now there is a real distinct window of direct light. I figured best to go for the reflected sky light the rest of the time.

The roof gets virtually no direct sun in winter and only a short window though summer. I was leaning a little to the west aspect because that is when it would be most hot in summer and he'd need his AC but of course the summer months are better with flat panels anyway and the sun disappears behind the trees way down the back paddock fairly early anyhow.  

On his setup, it does not really matter when the power is made, really chasing max KWH generated per day there.  What he looses in winter he'll make up in summer and it's really what he pays per year not per quarter that counts.

Got him enthusiastic again and he was asking about what difference having the trees removed would make? I said if you are planning to live to 150 years old and stay here, fine. If not, the $2500 each of about 50 trees is going to cost to get dropped and the full on year of work getting them disposed of once they hit the ground probably isn't going to be worth it.
 
Warpspeed
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Posted: 11:27pm 09 Nov 2020
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Up orientation is well worth having if you have a convenient flat roof somewhere to do it.

With a horrible grey winter sky, south works just as well as north, but up beats either.
Up also works extra well in mid summer around mid day.

So up can give you the edge both in mid winter (total grey sky) and also in mid summer.
Cheers,  Tony.
 
Davo99
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Posted: 02:40am 10 Nov 2020
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  Warpspeed said  
So up can give you the edge both in mid winter (total grey sky) and also in mid summer.


I said this to someone the other day, " Flat works the most efficiently for the best times, clear Summers days, and the worst times, overcast."

I have read a lot about panels needing tilt to self clean but I have reservations about that.
The panels on the house at 34o keep a lot of dust and dirt on them no matter how much rain there is. I don't see a lot of difference with the 50 panels on the shed.
I also notice when there is a lot of leaves and and crap from tress and bushes,  they are all pretty grubby no matter what the angle.
 
Warpspeed
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Posted: 03:45am 10 Nov 2020
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No roof is ever built dead level, but a five degree slope will drain the roof and also wash the panels clean after a good rain shower.
Cheers,  Tony.
 
Davo99
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Posted: 06:38am 10 Nov 2020
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  Warpspeed said  No roof is ever built dead level, but a five degree slope will drain the roof and also wash the panels clean after a good rain shower.


The shed I built to be temporary but everyone loves which my tractor now lives in has it's roof dead flat. Didn't start out that way But I think something sunk.
Going to have to re do it because the thing leaks like a sieve with the water running between the sheets of tin.

Of course had I WANTED it flat,would have turned out at 15o !!  :0(

I was thinking of going over the top with some panels and tilting and sealing them all together. No idea what I'd do with the power though. Shed is 75M up the back yard.
 
Boppa
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Posted: 01:49pm 02 Dec 2020
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I'm running multiple controllers, simply because it worked out cheaper to go multiple 3kw than fewer larger ones- plus it gives good redundancy lol
I actually unloaded all the panels off the tiltray finally (they have been on it since January :-O )and I dont know how- but there are more panels than I paid for... 72 to be exact... So I actually have 18kw instead of 17 kw...

What a shame....

One thing I found is that the east/west split at my sisters gave great greysky production, so much so thats why I chose to run with it here
(we had two identical systems within a few doors of each other- same company installed them, same time, same guys did it lol) and I found that despite all the neysayers (yes on a US forum lol) that insisted it HAD to be directly south (or north in my case) or they simply wouldn't work- daily output was close enough that random variations would bump one or the the other into first place, when it was cloudy, there was no comparison- the east west split romped it in- 3 to 5kwhrs a day ahead every time
I suspect that it was because the northers could only 'see' about half the sky, where the east/west split could 'see' the whole sky between the two- thats my guess anyway
 
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