jaytee
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I am new to the forum so Hi to everyone out there! I am also a new DIY Solar PV user and I am looking for some technical advice on an unusual string configuration.
So some prelude before the question: I have been looking at Solar on and off bust its always been too expensive and the FIT's keep reducing, 20 year paybacks are not really doing it for me. However I recently found some £15 each panels on ebay and after a bit of messing about I am the proud owner of 20 Canadian Solar 330P panels. All with broken glass of course! Out of the 20 I also have two unbroken ones with slightly damaged frames so I do have a reference for a "good" panel.
Its toughened glass so its like the old car broken windscreens if anyone is old enough to remember them. After a lot of research and some experiments I have used an industial vinyl product to "waterproof" the panels to hopefully stop impacted Riso and current leakage and also prevent frost damage.
On a sunny September day I compared the broken and unbroken panels for open circuit voltage and short circuit current and they were within 5% of each other which tells me the broken glass has not damaged the solar crystals but there is some reflection due to the cracks and shading where the glass is broken into smaller pieces.
I have one string installed consisting of 5 panels at 66' angle West facing. A Power One PVI3.0 (2 string 3kW G83 inverter), DC21 isolators installed locally at the string before the SWA cable and also at the inverter input. The inverter runs through a local CU with dual pole isolator, 16A MCB and 30mA dual pole RCD into the kitchen ring which is connected to the main CU which has a 32A MCB and 30mA dual pole RCD (16th edition installation). Its working a treat!
I was planning to add an East facing string of 5 panels however I can fit 4 panels onto a South facing wall as an option. After running some simulations I am exploring adding 4 panels to the South facing wall, about 80' angle and 4 East facing panels with 60' angle.
As the Sun moves the East panels will become shaded before the South facing panels, and they will also receive direct Sun before the South facing panels. I am aware that one shaded cell will cripple the whole string and to mitigate this the panels have bypass diodes, 3 per panel built in. As each set of cells in the panel see shade the voltage will drop and the bypass diode will pass the string current over the low effort cells. This will operate whenever there is shading on a cell or a panel and the string voltage will be reduced accordingly.
I am thinking that by adding a high current bypass diodes at the appropriate place in the circuit the 4 panels facing South or East can be bypassed and the current from the panels in Sun will be free to flow current to the inverter.
Each panel has a optimum voltage of ~37V so I will get ~148V at the best available current as a minimum once the bypass diode conducts and between 148 and upto ~300V when both sets of panels are in the sun. Nominal current is 8.8A. 20A MC4 mounted bypass diodes are available on ebay as are the various MC4 adaptors to enable correct installation.
Now the question!
Is there any reason this would not work or it would be a problem in terms of safety or fire? I will not installa nother inverter so it will be a choice between South, East or both.
I'm looking forward to comments & opinions, just ask if I've missed out anything important. Cheers.
So some prelude before the question: I have been looking at Solar on and off bust its always been too expensive and the FIT's keep reducing, 20 year paybacks are not really doing it for me. However I recently found some £15 each panels on ebay and after a bit of messing about I am the proud owner of 20 Canadian Solar 330P panels. All with broken glass of course! Out of the 20 I also have two unbroken ones with slightly damaged frames so I do have a reference for a "good" panel.
Its toughened glass so its like the old car broken windscreens if anyone is old enough to remember them. After a lot of research and some experiments I have used an industial vinyl product to "waterproof" the panels to hopefully stop impacted Riso and current leakage and also prevent frost damage.
On a sunny September day I compared the broken and unbroken panels for open circuit voltage and short circuit current and they were within 5% of each other which tells me the broken glass has not damaged the solar crystals but there is some reflection due to the cracks and shading where the glass is broken into smaller pieces.
I have one string installed consisting of 5 panels at 66' angle West facing. A Power One PVI3.0 (2 string 3kW G83 inverter), DC21 isolators installed locally at the string before the SWA cable and also at the inverter input. The inverter runs through a local CU with dual pole isolator, 16A MCB and 30mA dual pole RCD into the kitchen ring which is connected to the main CU which has a 32A MCB and 30mA dual pole RCD (16th edition installation). Its working a treat!
I was planning to add an East facing string of 5 panels however I can fit 4 panels onto a South facing wall as an option. After running some simulations I am exploring adding 4 panels to the South facing wall, about 80' angle and 4 East facing panels with 60' angle.
As the Sun moves the East panels will become shaded before the South facing panels, and they will also receive direct Sun before the South facing panels. I am aware that one shaded cell will cripple the whole string and to mitigate this the panels have bypass diodes, 3 per panel built in. As each set of cells in the panel see shade the voltage will drop and the bypass diode will pass the string current over the low effort cells. This will operate whenever there is shading on a cell or a panel and the string voltage will be reduced accordingly.
I am thinking that by adding a high current bypass diodes at the appropriate place in the circuit the 4 panels facing South or East can be bypassed and the current from the panels in Sun will be free to flow current to the inverter.
Each panel has a optimum voltage of ~37V so I will get ~148V at the best available current as a minimum once the bypass diode conducts and between 148 and upto ~300V when both sets of panels are in the sun. Nominal current is 8.8A. 20A MC4 mounted bypass diodes are available on ebay as are the various MC4 adaptors to enable correct installation.
Now the question!
Is there any reason this would not work or it would be a problem in terms of safety or fire? I will not installa nother inverter so it will be a choice between South, East or both.
I'm looking forward to comments & opinions, just ask if I've missed out anything important. Cheers.