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Discuss Maximum number of panels. in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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I'm an experienced sparky, now semi retired, with absolutely no knowledge of solar PV, which I'm trying to do something about.
My questions are quite simple ones, but ones where Google didn't provide a definitive answer.
A typical 2kVA grid tie invertor is a Sunnyboy 2000HF which has a start up voltage of 220V, a minimum of 175V (does this mean that the DC input needs to reach 220V to turn it on, but then it will keep running until the voltage drops below 175?), a maximum input voltage of 700V and a maximum input current of 12A.
If this is connected to 12 x 250W PV panels, is there any possibility of damage caused by excess input, or does the invertor limit its input? Typical panel is 30V and 8A, so I presume series connection would be best, so that they reach the minimum voltage with less irradiance?
12 x 30V = 360V. peak open circuit voltage would be higher at something like 37V, but 12 x 37V = 444V, so comfortably within the max. voltage, and the max. current (series connected) will be 8A, also well within the max. current limit, but 12 x 30V x 8A = 2880W, which is well above the 2kVA rating of the invertor. Am I right in assuming that the invertor self regulates back to 2000kVA?
One more question: I notice in the Sunnyboy manual that in the section for setting the dials in the 'quick module', that dial A to E and dial B to 0 is a setting for "off grid 50Hz". Does this mean that this invertor will operate as a stand alone invertor, with no connection to a 230V AC supply on the output side, the loss of which would normally shut it down?
Thanks in advance for any replies.
 
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I'm an experienced sparky, now semi retired, with absolutely no knowledge of solar PV, which I'm trying to do something about.
My questions are quite simple ones, but ones where Google didn't provide a definitive answer.
A typical 2kVA grid tie invertor is a Sunnyboy 2000HF which has a start up voltage of 220V, a minimum of 175V (does this mean that the DC input needs to reach 220V to turn it on, but then it will keep running until the voltage drops below 175?), a maximum input voltage of 700V and a maximum input current of 12A.
If this is connected to 12 x 250W PV panels, is there any possibility of damage caused by excess input, or does the invertor limit its input? Typical panel is 30V and 8A, so I presume series connection would be best, so that they reach the minimum voltage with less irradiance?
12 x 30V = 360V. peak open circuit voltage would be higher at something like 37V, but 12 x 37V = 444V, so comfortably within the max. voltage, and the max. current (series connected) will be 8A, also well within the max. current limit, but 12 x 30V x 8A = 2880W, which is well above the 2kVA rating of the invertor. Am I right in assuming that the invertor self regulates back to 2000kVA?
One more question: I notice in the Sunnyboy manual that in the section for setting the dials in the 'quick module', that dial A to E and dial B to 0 is a setting for "off grid 50Hz". Does this mean that this invertor will operate as a stand alone invertor, with no connection to a 230V AC supply on the output side, the loss of which would normally shut it down?
Thanks in advance for any replies.
Here's some of the answers:-
Lowest I've seen a bridge tied inverter turn on at is around 80v, SMA's have always been on the high side, and yes 175v is about right to switch one on, I did some experiments once 156v (4 panels) didn't work, needed 5 panels and 184v to switch on. The old ones dropped out at about 125v.
Yes you put the panels in series else your losses will be higher, good old ohms law! Yes the high voltage DC will kill you in an instant so be careful, if its your own system do the panel install on a cloudy day or at night!
Modern inverters with G100 ratings do have a sliding "impedance" to limit the amount of electricity produced, the oldish Sunny Boy you are referring to is 2kw so it can take 2kw of input, not 3 or 4 it doesn't self regulate! However the chance of your panels producing their rated output is fairly low, if they are at the perfect angle to the sun on a sunny summers day then you might get slightly more even but its rare. I'm sure the sunny boy will stand a few hundred watts for a while without falling over as they are extremely well designed bits of kit. Be interested to hear what experienced installers have found with overload margins on different inverter types and makes?
As far as I know you need a Sunny Island to go off grid again i may be corrected on that with the newer Sunny Boy inverters, and before you ask no, no one has found a firmware patch to change one to the other as far as i know, i did look ;-)
Grid tie inverters sense the mains if its not there they will not switch on, if they did the linesmen would all be dead, and that would be bad!
Hope that helps
Cheers
Stuart
 
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Thanks for the reply - I was beginning to think no one was reading this forum, or I'd asked about some great trade secret.
I've been playing a bit since my post, and strung together eight panels lying against my house wall on a dull day. Saw a peak of about 30W being produced, but as the light got better and faded I was able to observe the start up and shut down voltages.
Further info on what I'm up to: Building roof with eight 250W panels feeding 2.0kW Sunnyboy in adjacent shed with DNO cut out and meters.
Building is now sold, and has it's own electricity supply connected to it, leaving me with the grid tied invertor in the shed, ready to feed into the grid, but no panels connected to it.
I'm intending to set up a ground mounted array on south facing land 30m from the shed, moving the inverter to the array, and connecting the inverter to the shed with SWA, to get back into production. I understand that 1% is the max. voltage drop that should be allowed between inverter and grid connection point, so 6.0mm2 3C SWA should suffice.
I have the space to set up an array of of many panels as I like, but I have obtained 13 x 5 year old 250W panels. The max. voltage of these connected in series should be within the limits of the inverter, but do you think the max. current could cause problems?
Is facing due south at an angle of 30 degrees up from horizontal about right?
As I said in my first post, I'm an experienced electrician in both domestic and commercial work, and am well aware of the dangers of high voltage DC.
 
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ok a few problems, your inverter is G83 not G98 so it cannot be used for a new connection if your going to get it DNO approved! ( You need to look on the MCS approved website for inverters with G98, G99 or G100 approval. I've just got a 5Kw Solis that can take 5.5K of panels but still limit output to 3.68Kw (G100) so has G98 compatiblity) Yes that is toooo many panels, i would think you might get 230Watts out of them? which would be 9 to 10 panels. You can see on a sunny summers day and size accordingly! If you can make a 3 position mounting system, high angle for the winter, medium for the spring and autumn and low for the summer, it will boost your output by a worthwhile amount. If you design it in from the get go it should be fairly simple to do. The 1% is about right its more to do with the inverter sensing the mains than the actual losses in the cable. I have run 6mm DC cable about 30m its better to use 6 than 4 to keep Mr Ohm losses low, or you can run the AC in the SWA swings and roundabouts ;-)
Cheers
Stuart
 
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Thanks for the replies so far - very informative.
So you think I should limit the number of panels to 10, otherwise there's a good chance I'll fry the inverter on a bright summer's day?. I could always mount the extra three as well, I suppose, and switch them out of circuit in the summer months.
As I said in my OP, this is as much an educational project as a financial one. I shall be monitoring the output from the array, so should be able to judge when the output is approaching the limit.
Thanks for the info. about the Gxx classification - I'll bare that in mind if and when the one I have does die.
As regards DNO approval, this is an existing connection that's been switched off for a while, but will now start producing again, albeit with different panels and a relocated invertor. Business as usual, as far as they're concerned.
The reason I asked about the off grid possibilities of this inverter is that it has settings marked "off grid 50Hz" amongst the dial settings in the 'quick module' plugged into the base of the unit. You don't think these work as I'm assuming?
 
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Thanks for the replies so far - very informative.
So you think I should limit the number of panels to 10, otherwise there's a good chance I'll fry the inverter on a bright summer's day?. I could always mount the extra three as well, I suppose, and switch them out of circuit in the summer months.
As I said in my OP, this is as much an educational project as a financial one. I shall be monitoring the output from the array, so should be able to judge when the output is approaching the limit.
Thanks for the info. about the Gxx classification - I'll bare that in mind if and when the one I have does die.
As regards DNO approval, this is an existing connection that's been switched off for a while, but will now start producing again, albeit with different panels and a relocated invertor. Business as usual, as far as they're concerned.
The reason I asked about the off grid possibilities of this inverter is that it has settings marked "off grid 50Hz" amongst the dial settings in the 'quick module' plugged into the base of the unit. You don't think these work as I'm assuming?
I think the off grid is something to do with connecting it to a Sunny Island, you'd have to drop sma technical an email to clarify that. Yes by all means hook up the other panels and maybe use a dc switch to switch them in and out. U will be able to use them all until sometime in April i would guestimate, output shoooots up fast then so be careful! Then switch em back in in September.
 
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I Googled "Sunny Island", thinking all I would get is loads of ads. for exotic holidays, but to my surprise, the main results were for the Sunny Island in question.
It looks like you need one Sunny Island, which will process feeds from a generator, batteries and solar panels, which will then produce an AC output which can be used to turn on as many 'standard' Sunnyboys as you like, connected in parallel to produce an off grid supply.
I would guess that the settings on my inverter that I referred to widen the frequency and voltage limits that the invertor is happy with, to take account of the less accurate generator output, when compared to the grid.
Thanks for all the advice and info. I think I've got enough to go ahead now, and get this grid connection earning again.
The adjustable angle for the panels would be nice, but a little too complicated for this installation on the cheap, so, bearing in mind that I'll have extra panels that can be switched in, would there be an advantage to increasing their angle from the horizontal, to get a better angle to the sun in the winter months?
 
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I'm talking about 40 to 50 degrees up, so that they are more towards the winter sun.
Total output from all the panels would be reduced over the course of the year, but the inverter is the limiting factor in my case.
 

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