Second PV array - installation and trouble
Last Sunday we (Mryia TiBoth, Phelan and me) installed the seconds PV Array I wrote about. Boy, that was fun. First, we attached lashing straps to the array and pulled it onto the small, flat roof. In the next step I secured myself with a belt that was secured by Phelan. After I had moved it (offff, heavy!) the whole array to the main roof we pulled it up inch by inch with another set of straps from the inside. The straps we had slipped though the roof shingles. That went slow but surprisingly well. All that needed to be done after it was in its final postion was to mount and secure it's steel straps on the roof beams on the inner side of the roof. Overall, it took us about four hours. We had to take a break due approaching dark clouds that brought a strong wind and rain with them. After seeing trees bending heavily in about 2km of distance I deemed a wise idea to leave the roof within the next minutes. Indeed, a good idea.
It was about to get dark when the array was secured. What remained was to install the MC4 plugs on the cable I had prepared on the module side and on the ones leading down to the Grid Inverter. It took an hour. Mostly because I had to be careful and because it got pretty dark within minutes. I had a lamp with me up on the roof but the remaining wind and the lack of mobility didn't made it any easier. By the time I was finished with the job I could feel how tired it was. It was one of those moments where you know your done and the body instantly responds with relaxing and comming down from tension and stress. I was glad that I made it from the roof. After spending several hours on the roof, always tensed and alerted, I realised how much stress it was to my body. In fact, I suddenly felt pretty cold and started to shiver. A hot soup and blankets were the perfect match to deal with it.
It was a nice experience. Being on a roof with an angle of about 45° with only a securing rope keeping you from falling is an odd feeling. Logic tells you that everything's fine but your instincts keep annoying you with "what if it rips off due a fault in the material?" and alike. There's something else to learn from it: if you're not sure if you can trust a friend enough to put your life into his hands - literally! - you will know afterwards. Phelan did a great job. I felt completely safe after an hour.
The next days was less fun. After connecting the MC4 Plugs to the second input I waited for the Inverter to switch the second input to MMPT Mode. But it didn't happen. After having a look at the system values I knew why. The array floated between 113 and 118V. But the inverter needs at lest 120V to switch an input online. Arf! A trick made the inverter working on the second input but the array voltage dropped down to 92V. 90V is the lowest value the inverter can work with.
Now I suspect tho things:
1) One half of a module is not working due a faulty Bypass Diode. Calculations told that the missing voltage is exactly about one half of a module. But oddly, when measuring the array on the ground everything was fine. I will test that on the weekend by testing each module by blanking the remaining ones. If all modules read the same values it's case Nr. #2 I supect. If a module turns out to be faulty I've to access it from the backside though the roof. Not the best way but there is no way to access it from the roof - without uninstalling the array completely.
2) Everthing's fine. The modules are old. 10+ years and technology did improve a lot during the last years. Maybe the U/I curve behaves less steep then expected and the low voltage is normal in MPPT mode (Still, it's only 6 Modules). I had a look at the Data Sheet again but it left me without a useful clue. In that case I need to build a workaround. Depending of the final voltage in MPPT mode, I will go with one of the two solutions: Building a circuit that boosts the voltage up to 130V until the inverter is working (and switches itself of afterwards). Or buildung a DC/DC converter that's on all the time, boosting the Voltage from 90 to 130V. I think I will go for the second solution. It will provide a voltage the inverter can work with all the time. Even if I have to deal with losses about 10W with an input power of about 300W.
The situation doesn't make me happy. But well, I'll learn something from it.
Mryia did this nice Time-Lapse Video of us installing the array.
It was about to get dark when the array was secured. What remained was to install the MC4 plugs on the cable I had prepared on the module side and on the ones leading down to the Grid Inverter. It took an hour. Mostly because I had to be careful and because it got pretty dark within minutes. I had a lamp with me up on the roof but the remaining wind and the lack of mobility didn't made it any easier. By the time I was finished with the job I could feel how tired it was. It was one of those moments where you know your done and the body instantly responds with relaxing and comming down from tension and stress. I was glad that I made it from the roof. After spending several hours on the roof, always tensed and alerted, I realised how much stress it was to my body. In fact, I suddenly felt pretty cold and started to shiver. A hot soup and blankets were the perfect match to deal with it.
It was a nice experience. Being on a roof with an angle of about 45° with only a securing rope keeping you from falling is an odd feeling. Logic tells you that everything's fine but your instincts keep annoying you with "what if it rips off due a fault in the material?" and alike. There's something else to learn from it: if you're not sure if you can trust a friend enough to put your life into his hands - literally! - you will know afterwards. Phelan did a great job. I felt completely safe after an hour.
The next days was less fun. After connecting the MC4 Plugs to the second input I waited for the Inverter to switch the second input to MMPT Mode. But it didn't happen. After having a look at the system values I knew why. The array floated between 113 and 118V. But the inverter needs at lest 120V to switch an input online. Arf! A trick made the inverter working on the second input but the array voltage dropped down to 92V. 90V is the lowest value the inverter can work with.
Now I suspect tho things:
1) One half of a module is not working due a faulty Bypass Diode. Calculations told that the missing voltage is exactly about one half of a module. But oddly, when measuring the array on the ground everything was fine. I will test that on the weekend by testing each module by blanking the remaining ones. If all modules read the same values it's case Nr. #2 I supect. If a module turns out to be faulty I've to access it from the backside though the roof. Not the best way but there is no way to access it from the roof - without uninstalling the array completely.
2) Everthing's fine. The modules are old. 10+ years and technology did improve a lot during the last years. Maybe the U/I curve behaves less steep then expected and the low voltage is normal in MPPT mode (Still, it's only 6 Modules). I had a look at the Data Sheet again but it left me without a useful clue. In that case I need to build a workaround. Depending of the final voltage in MPPT mode, I will go with one of the two solutions: Building a circuit that boosts the voltage up to 130V until the inverter is working (and switches itself of afterwards). Or buildung a DC/DC converter that's on all the time, boosting the Voltage from 90 to 130V. I think I will go for the second solution. It will provide a voltage the inverter can work with all the time. Even if I have to deal with losses about 10W with an input power of about 300W.
The situation doesn't make me happy. But well, I'll learn something from it.
Mryia did this nice Time-Lapse Video of us installing the array.
Click to view