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Hi. New user here. Ty for any help in advance. I'll try my best to keep this as simple and short as possible.
So I bought 2x used sma sunnyboy 9000tlus-10 off of Ebay like 6 months ago. They were listed as -12 and even came in a -12 box. These were the inverters I planned my entire system around. This is important to my issue bc these inverters basically required a combiner box and one set of conductors ran to the DC side of the inverter....
I have 60 sunpower 340 watt panels on a ground mount like 100ft away from my house. The combiner boxes are at the array and then the 2 sets of conductors go underground into the house to the 2 inverters (or at least where they used to be sigh)
So to the issue. to keep it short we'll just say the original inverters don't work for my application. So I purchased 2x sma sb.xxxxx. 7.7 kw models. The difference between these and the 9000's is the 7.7 have 3x string inputs that can only be like 10 amps @ roughly 580v. So connecting my already combined conductors that are roughly 25amps @425v wont work. Now remind you these lines are underground and 150ft in length.
I've come up with a couple of solutions on my end. Either I can replace the combiner with an inverter and then use the existing lines to bring the ac into the house. The problem with this arrangement is to the grounding. I can get grounding out there but it would either be new rods or I'd have to dig a long trench and run a ground to my existing ground rods. The underground lines I had pulled 2 conductors as grounds initially but I'd need to use those as neutrals in this scenario.
Another issue with this scenario is how do I fuse the strings if they go from the panels to the inverter? The other purpose of the existing combiner is to fuse each conductor coming off the strings.
A different solution I came up with is to leave the original combiner, where the DC comes in I'd have to then UNcombine the string using lusing enclosure a busbar and fuse holders to turn one set of conductors back into 3 sets (2 and 6 total for both). This seems plausible but its highly doubtful I'll be ul compliant bc the available equipment just isn't designed to work in reverse like this. Also an issue is money, this is probably the most expensive solution. Midnite solar sells combiner boxes that are like 150$ a piece plus I'd need to buy the fuse holders and the fuses. This could end up costing 500 or more. I thought about just using power distribution blocks or something but the out going smaller conductors need some kinda protection.
I'm just flabbergasted that they designed 2 different generations in completely opposite ways. I couldnt imagine having a system put in 10 years ago and the inverter dying and needing to replace with a newer model and having to reconfigure this much stuff. Any help would be great. Theres obviously more equipment in my system than I described in this post but I just left that stuff out bc it really has no bearing on what I need to do. If anyone wants more information I'd be more than happy to provide it. Ty.
So I bought 2x used sma sunnyboy 9000tlus-10 off of Ebay like 6 months ago. They were listed as -12 and even came in a -12 box. These were the inverters I planned my entire system around. This is important to my issue bc these inverters basically required a combiner box and one set of conductors ran to the DC side of the inverter....
I have 60 sunpower 340 watt panels on a ground mount like 100ft away from my house. The combiner boxes are at the array and then the 2 sets of conductors go underground into the house to the 2 inverters (or at least where they used to be sigh)
So to the issue. to keep it short we'll just say the original inverters don't work for my application. So I purchased 2x sma sb.xxxxx. 7.7 kw models. The difference between these and the 9000's is the 7.7 have 3x string inputs that can only be like 10 amps @ roughly 580v. So connecting my already combined conductors that are roughly 25amps @425v wont work. Now remind you these lines are underground and 150ft in length.
I've come up with a couple of solutions on my end. Either I can replace the combiner with an inverter and then use the existing lines to bring the ac into the house. The problem with this arrangement is to the grounding. I can get grounding out there but it would either be new rods or I'd have to dig a long trench and run a ground to my existing ground rods. The underground lines I had pulled 2 conductors as grounds initially but I'd need to use those as neutrals in this scenario.
Another issue with this scenario is how do I fuse the strings if they go from the panels to the inverter? The other purpose of the existing combiner is to fuse each conductor coming off the strings.
A different solution I came up with is to leave the original combiner, where the DC comes in I'd have to then UNcombine the string using lusing enclosure a busbar and fuse holders to turn one set of conductors back into 3 sets (2 and 6 total for both). This seems plausible but its highly doubtful I'll be ul compliant bc the available equipment just isn't designed to work in reverse like this. Also an issue is money, this is probably the most expensive solution. Midnite solar sells combiner boxes that are like 150$ a piece plus I'd need to buy the fuse holders and the fuses. This could end up costing 500 or more. I thought about just using power distribution blocks or something but the out going smaller conductors need some kinda protection.
I'm just flabbergasted that they designed 2 different generations in completely opposite ways. I couldnt imagine having a system put in 10 years ago and the inverter dying and needing to replace with a newer model and having to reconfigure this much stuff. Any help would be great. Theres obviously more equipment in my system than I described in this post but I just left that stuff out bc it really has no bearing on what I need to do. If anyone wants more information I'd be more than happy to provide it. Ty.
I haven't used a DC fuse for >2 years. Love the new multi-MPPT inverters 
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