Mix 150W and 170W solar panels

[melbaylon]

I want to add solar panel that are different from my existing ones. I hope you can give me specific insights about this.

Here is a spreadsheet of my computations. As far as I know the total voltage of the string of PV array in series fits within what my solar charge controller can handle. But I'm not sure if I should consider Imp(current at maximum power) or Isc (short circuit current).

Key specs of the current setup

• 300W solar PV array (2 150W in series)
• ML4860 60A solar charge controller
• 12V 400Ah LiFePO4 battery bank

Specs of my solar charge controller

• Max in put voltage: 150VDC
• Max power: 800W(12V)
• Max charging current: 60A

Specs of current solar panel in use
150W Solarhomes - Mono Crystalline

• Vmp 18.04V
• Imp 8.32A
• Voc 21.65V
• Isc 8.82A

Specs of solar panel to buy
170W Bluesun - Mono Crystalline - Shingled

• Vmp 22.55V
• Imp 7.54A
• Voc 26.65V
• Isc 8.05A

Location and weather

• Cagayan Valley, Philippines
• Temperature: 30±5°C
• Mostly sunny but it rains in the latter parts of the year

Planned configuration
All in one series string (2 150W + 3 170W)

Additional notes

• I’m following this guide on how to mix different solar panels https://solarpanelsvenue.com/mixing-solar-panels/
• I want to go with the 170W Bluesun panels its current rating is close to my existing solar panels
• If my 60A solar charge controller can't handle all 5 panels, I might remove 1 150W panel and save it for when I upgrade to a 48V system.

 

[Short_Shot]

Voltage is a primary concern with total panel current (amps) being secondary. As I understand it, most MPPT controllers are tolerant of "overpaneling" to slightly higher current than their output rating is but this will vary by manufacturer.

However they will not be tolerant of excess voltage.

In series you will have a voc of 123v but you have to watch for increasing voc at lower than rated temps.

I would also watch out for the controller rating. A high quality one shouldn't have issue with running near rated voltage but I know some cheaper ones have complaints of burning out at lower than rated... though this might be a result of high low temp voltages and uninformed users.


You have some headroom here but someone who is more proficient with voc temperature coefficients will need to answer this for you. If you can find the temperature coefficient for Voc rating of all the panels then we can answer for sure.

Regarding that, the Phillipines coldest temp on record that I can find is over 6c so it's probably safe to do the math to that point.

After that you just want to make sure you have bypass diodes installed. Some panels do not come with them.

 

[melbaylon]

You're right. Based on my computations, the Voc of all the panels in series is 123.25V. This is my solar charge controller. I'm not sure what its performance with overpaneling, but it's a well regarded charge controller.

I did the math on temperature coefficients last night and it doesn't change the numbers much to be significant. 25°C is the temp for the STC or standard test condition. The temperature in my town is at 30±5°C most months except for December to February where it can drop to the low 20s. But it doesn't get cold as Baguio. ?

It's my first time hearing about bypass diodes. How do I know if my panels have them or not? And if not, can I add something external?

 

[Short_Shot]

Manufacturer specs might indicate this, otherwise you can look in the little box on the back of each panel.

Alternatively they sell solar connection panels which integrate these bypass diodes.

I'm far from an expert on that subject however so I'd wait for someone else to teach you about diode use.

 

[melbaylon]

Manufacturer specs might indicate this, otherwise you can look in the little box on the back of each panel.

Alternatively they sell solar connection panels which integrate these bypass diodes.

I'm far from an expert on that subject however so I'd wait for someone else to teach you about diode use.

I see. I'll check this for each panel. Thanks for your insights!

 

[melbaylon]

Manufacturer specs might indicate this, otherwise you can look in the little box on the back of each panel.

Alternatively they sell solar connection panels which integrate these bypass diodes.

I'm far from an expert on that subject however so I'd wait for someone else to teach you about diode use.

I can't find anything on the the 150W Solarhome but the 170W Bluesun is listed as having 1 diode.

 

[Short_Shot]

Does it say whether it's a bypass or blocking diode?

The configuration is important.

 

[melbaylon]

Does it say whether it's a bypass or blocking diode?

The configuration is important.

Unfortunately no. I can't find anything like a detailed datasheet. This is the best thing I have: https://www.bluesunpv.com/bluesun-r...lar-cell-mono-all-black-solar-panel_p482.html

By the way, how important is it? Is it critical or a nice to have?

 

[pollenface]

Helps when shading vertical rows of cells, but doesn't help much. No shading is best.

 

[740GLE]

Is there a reason you want one string?

If you add the new PV panels as a whole new string, pointing a slightly different direction your total gain for the day might be higher. I would say it’s prob be better to just add two more panels in a new string instead of 3, if you to go that route.