question

spicedreams avatar image

2 strings panels at an angle

Trying to improve power from an existing roof installation.

We have an EasySolar II GX, which has a Multiplus II 48/3000/35-32 inverter plus a SmartSolar MPPT 250/70 solar controller.

We have 6x 320 W Trina Honey panels mounted on the roof of an ISO 20' (6m) shipping container. Because of the space constraints of the container roof, they are oriented about 20 degrees east of the meridian so get morning sun but lose it in the afternoon.

This is not producing enough power, so we have bought another 6x the same panels. We have 2 more 20' shipping containers at about 90 degrees from the original container (close enough that you could consider it one big roof).

Conventional wisdom seems to be that the new panels must be oriented exactly the same imperfect angle (azimuth and elevation) as the existing panels. Is there a better alternative?

I have seen some comment that two strings of panels back to back, facing respectively east and west, will not 'interfere' with each other so you effectively get separate morning and afternoon charge sessions from them.

Is that a better solution? How about having the two strings at 90 degrees, so facing respectively 45 degrees east of the meridian and 45 degrees west? What is the theory around this? What are the EasySolar's constraints?

EasySolar All-in-OneSolar Panel
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2 Answers
michelg avatar image
michelg answered ·

Hi Spicedreams, I had the same issue, and added two arrays of panels with a different orientation, the south ones were providing power in the morning / noon, and the west orientated ones, during the afternoon. My power problems were easily fixed.

Using the same MPPT is possible, I had no issues at all.

Michelimg-20180507-112940.jpg


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Thanks @michelg. What MPPT device are you using? You look like you have double the number of panels facing one way than the other. Do you have 6 parallel strings of 5 panels each? Do you have any way of knowing what the effect of any string is on the overall output?

seb71 avatar image
seb71 answered ·

You have those 6 panels in a single string (all in series)? What is the Voc?


You can also add a second charger for the PV array with the different orientation. Maybe you are not aware about this option.
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thanks @seb71; I believe (will confirm with the installer next 48h) that the 6 panels are currently configured in 2 strings (ie 3s2p). Each panel's Voc is 40.3 V

I know I could add a second MPPT for the new panels, which brings a new level of complexity; I would like to know what my options are with the existing electronics.

@seb71 The panels were in 2 parallel strings, each 3 in series. Just uprated the system this morning, now there are 4 parallel strings each 3 in series. Voc per panel is 40.3 V, so 121 V per string.

You can wire up to 5 of those panels in series in a string for your solar charger.

If you placed all the panels with the same orientation and there are no shading issues, you could/should rewire those 12 panels as 4s3p (4 panels in series in a string; 3 strings in parallel). Higher voltage, lower current. Less potential issues.

With strings in parallel, each string should be protected with gPV fuses. Especially when there are 3 stings or more in parallel.