2 serial strings in parallel

[Hendrik Albertus]

This time I am not sure of what is the best way to go.
Here is the dilemma. My roof is two sided. One side looking East (morning sun) and the other side looking West (evening sun). My house is situated in the tropics between the 14th and 15th parallel. So at midday the sun is right above the house. Now I want to install solarpanels on described roof. Two sets of six serial panels in parallel. Question is can I install one serial string on one side of the roof and the other string on the other side. Or should they be arranged in a different manner since the output of the panels wiil not be the same in the early morning or late afternoon.
Please sound advice.

[SunEagle]

I believe it will depend on the inverter you have. Most grid tie inverters have more then one MPPT input so IMO you can wire the East set to one input and the West to the other. Just remember that the total wattage should not exceed the maximum input to the inverter because during Noon time both panel strings may be generating power and inputting the inverter.

[bcroe]

I am going to suggest another variation, that has been working well
here for a decade. A pair of MPPT inputs may each have less capacity
than the inverter total, and my inverters only have one MPPT input.

If you have identical strings facing E and W, no shading issues, it
can be expected they will have near identical MPPT voltages, even
though more current is available from the one with best sun. So they
can simply be individually fused, and then tied directly in parallel, to
the total inverter input. This will also avoid the possibility of one MPPT
input limiting input power to a value less than the total limit, energy lost.

Some may say with only 2 strings no fuses are needed, I would put
them in anyway as a service aid. Bruce Roe

[SunEagle]

I am going to suggest another variation, that has been working well
here for a decade. A pair of MPPT inputs may have less capacity
than the inverter total, and my inverters only have one MPPT input.

If you have identical strings facing E and W, no shading issues, it
can be expected they will have near identical MPPT voltages, even
though more current is available from the one with best sun. So they
can simply be individually fused, and then tied directly in parallel, to
the total inverter input. This will also avoid the possibility of one MPPT
input limiting input power to a value less than the total limit, energy lost.

Some may say with only 2 strings no fuses are needed, I would put
them in anyway as a service aid. Bruce Roe

Yeah, the fusing is due to NEC requirements if you have more then 2 strings but I agree that it does allow you to disconnect a string to perform maintenance.

[Hendrik Albertus]

Thank you both for your reply. That helps a lot but also triggers other questions.

You mentioned an inverter with 2 MPPT inputs, as most grid tied inverters will have. Well maybe in the US of A but certainly not in the SE of A (SouthEast Asia). I have been looking extensively for said inverters and found one (1). That's a 3000W model with V DC rated 380V.; V DC MPPT range 250-500V. To get in that range you need approx. 7 panels in serial. With every panel about 340W is that in total 2380W. That is nearing the maximum of the inverter on one input. Then what to do with the second input? Alternating both inputs? That's not very effectiv, is it. With such input specs you need at least 5000W to my opinion,

Available products in this third world country are mostly limited to inland production, with which I have very bad experiences so are not trusted, or Chinees equipment. Which are better in general. Funny is that in another thread I read that the products from PowMr are considered bad quality. In this part of the world they belong to the top range products.

Originating from the Netherlands I am very familiar with NEN1010 (NEN ten ten) regulations, which are very good. I consider them to be the best from everything I have seen yet. And that is a great part of Europe where i have been working. Honestly I do not know very much about NEC requirements. But do have some concerns there. First of all the power plugs used are the same as here in Thailand and I deem them absolutely worthless. Extremely dangerous and unreliable. The house I have build here is solely installed with equipment from Europe that meets NEN1010 requirements. As of any regulations in this part of the world, I haven't seen or heard anything about it. Non-existing. You want a power attachment to your house? Just pay the fee and they bring the grid to the front of your property with a KWhmeter on a pole. Everything else is your responsibility, your problem. No questions asked, no checking. Thailand is world leader in most death casualties on the roads.Guess what comes second as death cause. Yes, electrocution and always self inflicted.

[Calsun]

Another option is to go with panels that have microinverters on each of them, if a dual MPPT charge controller inverter is not available. If Solis inverters are distributed in your country they would be a good choice.

[Hendrik Albertus]

Thanks for your comment, Meanwhile I have found a few more dual MPPT inverters. They are Sofar brand of which I have no further information but they do have a 5kW modell though. I now have been looking for Solis inverters as you suggested. Haven't been able to find a shop in the country that sells them. But it seems they do have a representative that only has a facebook page. That does't give me much confidence. However I requested a quote and techspecs on their inverters. See what is going to come out of that.

Also I was thinking if it is possible to put diodes in the feedlines so as to prevent the current flowing back in the other string of panels when the conditions aren't equal on both strings. Could anyone with experience or knowledge about this give a comment or advice.
I mean a converter with two PV inputs has to have a circuit to separate them and make them work together. How?

[bcroe]

Also I was thinking if it is possible to put diodes in the feedlines so as to prevent the current flowing back in the other string of panels when the conditions aren't equal on both strings. Could anyone with experience or knowledge about this give a comment or advice.
I mean a converter with two PV inputs has to have a circuit to separate them and make them work together. How?

As I explained, even the panels with poor sun will generate about
the same voltages, be it at less available current. Reduction of
forward current beyond MPPT point will cause the panel voltage
to rise some 20%, toward open circuit. So no reverse current will
flow, no diodes are needed. This has been working here a decade.
Bruce Roe

[Hendrik Albertus]

Aha, now I get the picture. I misinterpreted your message. Thanks for the explanation.
Do you put fuses in both plus and minus lines or just the plus line?

[bcroe]

Aha, now I get the picture. I
misinterpreted your message. Thanks for the explanation. Do you put
fuses in both plus and minus lines or just the plus line?

I use fuses only in each string + line, in this neg ground system. But
the fuses are in a combiner box next to the array. After a 230 foot
underground run, a DC disconnect switch breaks both + and - leads
to the inverter. I found good reason to do this, to remove all power
for inverter work. Panels in sun are always hot, a ground in the
array could make either side hot. Bruce Roe


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