diy solar

diy solar

Adding Solar Panels to Existing System

ABarbarian

New Member
Joined
Mar 13, 2022
Messages
30
I am adding panels to an existing inverter+battery system and have planned the panel system as follows:

Existing inverter:
- MPP 4kW PIP-MS4048
- Max PV Input / Output: 3000 W
- Max Charging Current MPPT 60A
- Max PV Input Voc, MPPT Range: 145V, 60~115V

Planned panels:
- BlueTech POLY 345W
- Open Circuit Voltage: 46.2 V
- Voltage at Pmax: 38.2 V
- Max Series Fuse Rating: 15A

Planned panel configuration:
- 3 panels in serial, 2 sets in parallel, total 6 panels
- the combined voltage in serial is about 120 V which is near upper limits for the inverter's input, but is a hot climate and reasonably long cables so I think it will work OK?

Cabling:
- the 2 serial sets will join at basic cable splitter/combiner adapters
- panels to combiner adapters distance ~8m, use 3mm copper wire
- 15A fuse on each serial set's connection to positive adapter (2 fuses)
- combiner adapters to inverter ~20m, use 4mm copper wire
- DC Breaker near inverter 100A/1000V

Anything look wrong or missing?
 
Three panels at an open circuit voltage of 138 volts does not leave much room on a cold day. What is the current rating of panels?
 
I am not sure which spec is the current rating, attached are specification of the panels I am looking at (the 345 watt option)1.jpg2.jpg
 
Max current is 9.5 Amps so you could do 2 panels in series and those sets in parallel for 92 volts and 38 Amps
 
Thanks, so you think the 3 panels in series is too close to the inverters max voltage ... I was concerned about the higher amps and the long cabling to inverter.

If I changed to the configuration you suggest, what sized wire would I need, I guess pretty small 2-3mm for the serial arrays, but after combined I need to travel about 20 meters, would 4 or 6mm be OK?
 
Panel strings is not my primary expertise. It may be worth getting an additional opinion from someone who understands the effects of temperature on panel voltage. The expected minimum temperatures in your area would affect that.

The panel wire can handle 15 Amps but after they are combined you would need wire that can handle 40 Amps and perhaps then some for the distance to get an acceptable voltage drop. I am familiar with US AWG sizes so either consult a mm ire table or perhaps someone who is familiar with that standard. It is a risk management decision about going that close to inverter max and a cost benefit decision about the money you would save using higher voltage and smaller wire.
 
If I were you I would look for panels with a lower Voc.

Your current panel choice:
Voc of 46.2 V x 3 = 138.6 V at 25 °C

With a Voc temp coefficient of -0.32%/°C = 0.443 V/°C, and only 6.4 V of headroom means a temperature at or below 10.5 °C (51 °F) is at risk of exceeding the Voc limit.

If you are confident the array will never experience a low daytime (early morning usually) temperature in that region then 3S is probably OK. Tropical coastal regions would be OK but anywhere inland will have a fair chance of getting that cool.

You might want to consider looking for different panels with a lower Voc.

For example I have an array of 6 x 370 W Longi LR4 panels which have a Voc of 40.7 V.

In that case 3S = 122.1 V at 25 °C which would provide a much greater safety margin (22.6 V) for your MPPT.

My PIP PIP4048HS clone inverter has an input Voc limit of only 105 V, which is why I have a 2S3P array arrangement. But with a Voc limit of 145 V I could definitely change my array to 3S2P. Indeed I am considering an inverter upgrade to one with a higher Voc limit and I would do exactly that.

That said, you can run your array as 2S3P but that will require a combiner box.

That's the arrangement I have with my array, 2S3P to a combiner box then to the inverter.

I have a wire run of about 30 m and use 6 mm² cable from the combiner box to the inverter.
 
Thanks for the replies, I am in Thailand so the temp stays pretty high, but a cold winter morning could get down to about 10°C, I think your advice is good and I will look at adjusting my panels to give a little more safely under the inverter's max
 
Back
Top