Sunpower Parallel string

[Tim D.]

Question for you guys

I'm installing a SBMS120 on an RV with a 12v 300Ah LiFePO4 battery and 3 100 Watt Sunpower flexible solar panels

The SunPower manual specifically says "DANGER!

• SunPower does not recommend connecting these panels in parallel without proper system and safety protection.
• Connecting panels in parallel will double the current output of the panels. DC Currents may be greater than 12 amps for 100 W, 110 W and 170 W, and greater than 6amps for 50 W, in high illumination conditions (>1000 W/m2).
• If shading occurs without additional electronic components, such as a blocking diode, the by-pass diodes may be damaged leading to further panel damage and unsafe conditions including fire.
• If Paralleled panels are attached to a battery for charging, the high current may cause damage to the battery and subsequent safety issues.
• The charging characteristics of any battery should always be checked for compatibility with the current and voltage output of the panels prior to use. "

So I guess my question is: is there a safe way to connect 3 of these panels in Parallel to charge the LiFePO4 battery with the SBMS120?

Would I need to install blocking diodes on each panel? Like in the attached picture? if so would I use 10A diodes since each panel will only make 6 amps?

Appreciate the guidance, I don't want to burn up these panels

[Dacian Todea]

Tim,

You can safely connect 3 of those solar panels in parallel (that will be the max limit for those panels without needing to connect any fuses to the individual panels).

The bypass diodes have nothing to do with parallel panels as shading one of the panels will not result in any current flow from the other parallel panels.

If one of their bypass diodes fails (I expect there will be two of them in a 100W panel but SunPower likes to have non standard panels so you can ask).

In any case they allow 15A max fuse per panel and no matter what happens inside one of the three panels the combined current from the other two panels will not exceed 15A worse case conditions as those panels may output 6 maybe 7A with edge of cloud conditions still less than 15A total that is why this 100W panels can be parallel as group of 3. All the other larger panels that output 10 to 12A peak usually have fuse rating of 20A max and that means only two panels can be paralleled.

Do not add blocking diodes as those will be completely unnecessary and way higher chance to start a fire as 4 to 5W lost as heat on one of those will be fairly difficult to cool.

The SBMS120 has dual PV inputs each with ideal diodes on them so if you prefer and you are not using the other PV input for anything you can connect one of the panels there.

I just looked closer to the spec and they say junction box with by-pass diode implying a single diode probably a 45V rated one but not specified. So it will be much more of a problem with series connected panels no problem with parallel.

Flexible panels will not last long as cells will crack more than likely withing a year or two. There is also the plastic that will fairly fast due to UV thus the 5 years only warranty for 80% of original output power where glass panels have at least 25 years to get to 80%