Hi there. I want to over panel some my solar build to give me more amperage during cloudy days. Looking to utilize an EG4 6500EX inverter. I know it can handle up to 8kw max across both MPPTs. I want to however have a total of 10KW solar panels and have parallel strings. My question is this- assuming I do not over voltage the MPPTs on the inverter, can I configure my panels in multiple parallel strings to the combiner box and then connect the output of the combiner box to the inverter? As long as I don't over voltage the MPPT, would the MPPT only pull the maximum amount of amperage it needs as opposed to pulling all the amperage from the combiner box? Is this a recommended and safe approach as long as I don't over voltage the MPPT? Thanks in advance.
Over Paneling and Combiner Boxes
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timselectric
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Short answer is, yes it's fine.
Long answer, is that you need to be mindful of the max short circuit current on your SCC.
Long answer, is that you need to be mindful of the max short circuit current on your SCC.
Appreciate your response but I thought it wouldn't matter on the amperage side. So for example, let's say given all my strings that's combined in parallel in the combiner box, let's say that the combiner box can output a maximum of 50A given all the parallel strings. If the MPPT can only take 18A for example as in the case of the EGX 6500EX inverter, wouldn't that MPPT only draw the amount of current that it needs? Assuming of course that the voltage is within working range and I don't have it over-volted.
littleharbor2
Solar Addict
What is the IMP for each string? If there are two MPPT inputs why do you want to combine these strings? The beauty of high voltage dc is that it remains at low amperage and can be ran on small gauge wire.
What I'm looking to do is to over panel slightly on each MPPT. So essentially, 2 parallel strings per MPPT. The reason why I am looking at this is that I want to ensure that I can maximize my solar production even during days when it's cloudy. My understanding is that it doesn't take a tremendous amount of sunlight to produce the voltage but it does take quite a bit of sunlight to produce the amps. As I definitely have to be mindful about how much voltage I send to the MPPTs, the only other variable to influence the power output is to increase potential amperage. So I know I don't absolutely need a combiner box, but I'm thinking that using it can help me maximize power consistently.
With this method, I'm hoping that I can always get close to the maximum power produced even when the days are reasonably cloudy. With the combiner box, that'll allow me to maximize potential amperage without any of the strings negatively impacting the other. Thanks.
With this method, I'm hoping that I can always get close to the maximum power produced even when the days are reasonably cloudy. With the combiner box, that'll allow me to maximize potential amperage without any of the strings negatively impacting the other. Thanks.
timselectric
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Branch connectors and a combiner box do the same thing. Combiner boxes are prettier and cost a lot more. The benefit of a combiner box is local disconnect.(if breakers, not fuse holders) Might be handy for a ground mounted array, very far away. But my panels are on the roof. I turn them of, before I climb up there.
timselectric
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Say, you have 3 strings in parallel. And one string shorted out. The other two strings will provide full short circuit current to that string, until it burns apart. At the moment it burns apart, that short circuit current is sent to the SCC. If it's more than the SCC can handle. The SCC might not be able to get it under control, before damage is done.
I thought the big benefit of combiner boxes is that it eliminates the need for MC4 connectors which typically have a 30A limit and can only accept wire up to a certain size (8AWG?). So the combiner box is useful when your panel array has a current over 30A or when you need larger wire (for longer runs and/or higher currents) than what typically fits in MC4 connectors (such as 6AWG).
Ahhhh, I think I get it. I can see this occurring with branch connectors, but is this risk also applicable to using a combiner box as well with the diodes?
timselectric
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You are correct. I tend to forget that low voltage systems exist. Thanks, for reminding me.
littleharbor2
Solar Addict
Need to know the IMP of each string. If it adds close to or over 18 amps I think you're risking letting the smoke out of your AIO which will require replacing the whole unit. Why dont you get a separate charge controller and run the extra string(s) through it.
timselectric
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Blocking diodes should protect against it. I have MC4 Blocking diodes for my over paneling. Even though 2 of my 3 strings are a combined short circuit current, below the rating of my SCC.
Ok great, thanks. Appreciate the feedback from everyone.
