Would this setup work? More solar added to existing MPPT question

[user3829280]

Connecting the three 100W panels in series and then connecting this to the 455W panel in parallel is the best of the bad options.

Thanks, well yes this is what I had in mind.

The 3 are already in series, so they can stay in series and then I just have to add a Y connector to parallel them to the other larger panel right? Would I require two Y connectors, one for positive and one for negative of just the one for the positive line?

The maximum current of the input wires in this configuration is around 15A, so there is no issue with the current capacity of the existing 10AWG wiring, although voltage drop may further decrease the system’s efficiency depending on the length installed. However, the output wires from the solar controller may need to be thicker than 10AWG with new configuration.

Ok, good. You say from the solar controller, but from the solar controller to where? You mean between the solar controller and the Y connector junction where all the panels meet?

The total there would be 20A or so yes? 15A (around that, don't have the stats handy for the panel) for the large panel, then the 5.2 for the series panels? Is that the right calculation?

Also would I be wanting to add additional fuses anywhere? The existing 3 in series are not fused currently as I was advised on setup is wasn't necessary as they have fuses included or some other built in protection mechanism.

 

[noelex]

Thanks, well yes this is what I had in mind.

The 3 are already in series, so they can stay in series and then I just have to add a Y connector to parallel them to the other larger panel right? Would I require two Y connectors, one for positive and one for negative of just the one for the positive line?

You will need to connect both the positive and negative leads of the 455W panel in parallel with the series output of the three 100W panels. This will require two Y connectors.

Ok, good. You say from the solar controller, but from the solar controller to where? You mean between the solar controller and the Y connector junction where all the panels meet?

The total there would be 20A or so yes? 15A (around that, don't have the stats handy for the panel) for the large panel, then the 5.2 for the series panels? Is that the right calculation?

Also would I be wanting to add additional fuses anywhere? The existing 3 in series are not fused currently as I was advised on setup is wasn't necessary as they have fuses included or some other built in protection mechanism.

We can estimate the maximum current by making a few assumptions. If we consider very bright conditions where the solar panels are capable of their rated output and there are no losses.

Between the solar panel and the controller:
The controller will select an input voltage of around 50V to maximise the total output. The 455W panel will therefore deliver around 9.1A. The output of three 100W panels is more complex to estimate. 50V is a long way from the voltage where these panels will deliver their full output. We can estimate the output as 300x50/70= 214W. With an input voltage of 50V, the maximum current will therefore be 4.3A.

The total of both panels is therefore 9.1+4.3‎ = 13.4A.


Between the solar controller and the batteries:

The 13.4A @50V will be converted to nominal 56A. Assuming no losses and a low charging voltage of 12V.

The above assumes the solar controller is capable of delivering the full 56A. Its capacity may well be less than this, and this will reduce the output and therefore current in both the input and output wires.

 

[PaulRainbow]

Seems like a waste of solar yield to save a few quid on a second controller.

I wonder if the panels are correctly installed, with appropriate fusing for each panel ?

 

[noelex]

Also would I be wanting to add additional fuses anywhere? The existing 3 in series are not fused currently as I was advised on setup is wasn't necessary as they have fuses included or some other built in protection mechanism.

You will need a fuse between the solar controller and the battery, preferably close to the battery. Some solar systems also require separate fusing on the output of each solar panel. There is no danger of the input wire overheating, but there is a risk of the internal wires, particularly in the 100W panels, overheating in a fault condition.

The general rule of thumb is that additional fusing on the input side is required for solar arrays with three or more strings connected in parallel. Your system will be very atypical with the mismatch of solar panel sizes, so these rules of thumb will not work.

We don’t have details of the "Maximium series fuse" specification for the 100W panels, but I would expect the 455W panel to be capable of overheating the internal wires of a 100W panel in a fault condition. I would therefore at least fuse the 100W panels in addition to the fuse on the output side of the controller.

 

[noelex]

Seems like a waste of solar yield to save a few quid on a second controller.

I agree. A second controller would be a much better solution.

 

[SeaCoyote]

MPPT are dummiers - over 3 pcs, they MPPT don't know how to deal with it.
And if they are diffenrent Gen and size it's better to have 2. Also you can go even 12AWG honestly : if you calculate well you will find out 90% of the time 12 AWG cover your solar need. Only if you put over 3 panels in parallels then 10AWG might be recommanded. Here i found some cool wiring diagrams for solar panels.